single ionization cluster: Topics by Science.gov

Sample records for single ionization cluster

Single-Photon Ionization Soft-X-Ray Laser Mass Spectrometry of Potential Hydrogen Storage Materials

NASA Astrophysics Data System (ADS)

Dong, F.; Bernstein, E. R.; Rocca, J. J.

A desk-top size capillary discharge 46.9 nm lasear is applied in the gas phase study of nanoclusters. The high photon energy allows for single-photon ionization mass spectrometry with reduced cluster fragmentation. In the present studies, neutral Al m C n and Al m C n H x cluster are investigation for the first time. Single photon ionization through 46.9 nm, 118 nm, 193 nm lasers is used to detect neutral cluster distributions through time of flight mass spectrometry. Al m C n clusters are generated through laser ablation of a mixture of Al and C powders pressed into a disk. An oscillation of the vertical ionization energies (VIEs) of Al m C n clusters is observed in the experiments. The VIEs of Al m C n clusters changes as a function of the numbers of Al and C atoms in the clusters. Al m C n H x clusters are generated through an Al ablation plasma-hydrocarbon reaction, an Al-C ablation plasma reacting with H2 gas, or through cold Al m C n clusters reacting with H2 gas in a fast flow reactor. DFT and ab inito calculations are carried out to explore the structures, IEs, and electronic structures of Al m C n H x clusters. C=C bonds are favored for the lowest energy structures for Al m C n clusters. Be m C n H x are generated through a beryllium ablation plasma-hydrocarbon reaction and detected by single photon ionization of 193 nm laser. Both Al m C n H x and Be m C n H x are considered as potential hydrogen storage materials.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, H.B.; Hu, Y.J.; Bernstein, E.R.

Small methanol clusters are formed by expanding a mixture of methanol vapor seeded in helium and are detected using vacuum UV (vuv) (118 nm) single-photon ionization/linear time-of-flight mass spectrometer (TOFMS). Protonated cluster ions, (CH{sub 3}OH){sub n-1}H{sup +} (n=2-8), formed through intracluster ion-molecule reactions following ionization, essentially correlate to the neutral clusters, (CH{sub 3}OH){sub n}, in the present study using 118 nm light as the ionization source. Both experimental and Born-Haber calculational results clarify that not enough excess energy is released into protonated cluster ions to initiate further fragmentation in the time scale appropriate for linear TOFMS. Size-specific spectra for (CH{submore » 3}OH){sub n} (n=4 to 8) clusters in the OH stretch fundamental region are recorded by IR+vuv (118 nm) nonresonant ion-dip spectroscopy through the detection chain of IR multiphoton predissociation and subsequent vuv single-photon ionization. The general structures and gross features of these cluster spectra are consistent with previous theoretical calculations. The lowest-energy peak contributed to each cluster spectrum is redshifted with increasing cluster size from n=4 to 8, and limits near {approx}3220 cm{sup -1} in the heptamer and octamer. Moreover, IR+vuv nonresonant ionization detected spectroscopy is employed to study the OH stretch first overtone of the methanol monomer. The rotational temperature of the clusters is estimated to be at least 50 K based on the simulation of the monomer rotational envelope under clustering conditions.« less
Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

PubMed

Neustetter, M; Jabbour Al Maalouf, E; Limão-Vieira, P; Denifl, S

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n (+) (0 ≤ n ≤ 6) and W2(CO)n (+) (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n (+) (0 ≤ n ≤ 3) and W2C(CO)n (+) (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.
Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m.

PubMed

Heinbuch, S; Dong, F; Rocca, J J; Bernstein, E R

2006-10-21

Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5 eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5) x 10(4) s(-1) for cluster sizes of 5< or =n< or =16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n+ cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2)(H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed.
Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neustetter, M.; Jabbour Al Maalouf, E.; Denifl, S., E-mail: Stephan.Denifl@uibk.ac.at, E-mail: plimaovieira@fct.unl.pt

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO){sub 6}) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO){sub 6} clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO){sub n}{sup +} (0 ≤ n ≤ 6) and W{sub 2}(CO){sub n}{sup +} (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO){sub n}{sup +} (0 ≤more » n ≤ 3) and W{sub 2}C(CO){sub n}{sup +} (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.« less
Optimizing the ionization and energy absorption of laser-irradiated clusters

NASA Astrophysics Data System (ADS)

Kundu, M.; Bauer, D.

2008-03-01

It is known that rare-gas or metal clusters absorb incident laser energy very efficiently. However, due to the intricate dependencies on all the laser and cluster parameters, it is difficult to predict under which circumstances ionization and energy absorption are optimal. With the help of three-dimensional particle-in-cell simulations of xenon clusters (up to 17256 atoms), it is shown that for a given laser pulse energy and cluster, an optimum wavelength exists that corresponds to the approximate wavelength of the transient, linear Mie-resonance of the ionizing cluster at an early stage of negligible expansion. In a single ultrashort laser pulse, the linear resonance at this optimum wavelength yields much higher absorption efficiency than in the conventional, dual-pulse pump-probe setup of linear resonance during cluster expansion.
Coupled Cluster Studies of Ionization Potentials and Electron Affinities of Single-Walled Carbon Nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Bo; Govind, Niranjan; Aprà, Edoardo

In this paper we apply equation-of-motion coupled cluster (EOMCC) methods in studies of vertical ionization potentials (IP) and electron affinities (EA) for sin- gled walled carbon nanotubes. EOMCC formulations for ionization potentials and electron affinities employing excitation manifolds spanned by single and double ex- citations (IP/EA-EOMCCSD) are used to study IPs and EAs of nanotubes as a function of nanotube length. Several armchair nanotubes corresponding to C20nH20 models with n = 2 - 6 have been used in benchmark calculations. In agreement with previous studies, we demonstrate that the electronegativity of C20nH20 systems remains, to a large extent, independent ofmore » nanotube length. We also compare IP/EA- EOMCCSD results with those obtained with the coupled cluster models with single and double excitations corrected by perturbative triples, CCSD(T), and density func- tional theory (DFT) using global and range-separated hybrid exchange-correlation functionals.« less
Clustered DNA damages induced in isolated DNA and in human cells by low doses of ionizing radiation

NASA Technical Reports Server (NTRS)

Sutherland, B. M.; Bennett, P. V.; Sidorkina, O.; Laval, J.; Lowenstein, D. I. (Principal Investigator)

2000-01-01

Clustered DNA damages-two or more closely spaced damages (strand breaks, abasic sites, or oxidized bases) on opposing strands-are suspects as critical lesions producing lethal and mutagenic effects of ionizing radiation. However, as a result of the lack of methods for measuring damage clusters induced by ionizing radiation in genomic DNA, neither the frequencies of their production by physiological doses of radiation, nor their repairability, nor their biological effects are known. On the basis of methods that we developed for quantitating damages in large DNAs, we have devised and validated a way of measuring ionizing radiation-induced clustered lesions in genomic DNA, including DNA from human cells. DNA is treated with an endonuclease that induces a single-strand cleavage at an oxidized base or abasic site. If there are two closely spaced damages on opposing strands, such cleavage will reduce the size of the DNA on a nondenaturing gel. We show that ionizing radiation does induce clustered DNA damages containing abasic sites, oxidized purines, or oxidized pyrimidines. Further, the frequency of each of these cluster classes is comparable to that of frank double-strand breaks; among all complex damages induced by ionizing radiation, double-strand breaks are only about 20%, with other clustered damage constituting some 80%. We also show that even low doses (0.1-1 Gy) of high linear energy transfer ionizing radiation induce clustered damages in human cells.
Mass Spectroscopy of Neutral Metal Oxide Clusters Using a Desk-Top Soft X-Ray Laser

NASA Astrophysics Data System (ADS)

Dong, F.; Heinbuch, S.; Bernstein, E. R.; Rocca, J. J.

We report the use of a compact 46.9 nm capillary discharge soft x-ray laser in the study of metal-oxide nanoclusters using mass spectroscopy. Transition metal oxides are widely used as heterogeneous catalysts and catalytic supports in industrial processes. There are numerous applications for transition metal oxide catalysts, and although they are widely used, there is a lack of fundamental understanding of the complicated processes that occur on the metal oxide surface during catalysis. Conventional nanocluster spectroscopy techniques have used 193 nm radiation from an ArF excimer laser corresponding to a photon energy of 6.4 eV in order to photoionize a sample. Typical metal oxide nanocluster ionization energies fall into the range of 7-12 eV while some have even higher energies. Therefore a single 6.4 eV photon can not ionize the cluster making multiphoton processes the dominant ionization method. A major problem associated with mass spectroscopy can become evident during the multiphoton ionization of clusters. Specifically, the clusters may fragment during the ionization process and the identification of the neutral parent cluster can become difficult. In the present experiment neutral vanadium, niobium and tantalum oxide clusters are studied by single photon ionization with the 26.5 eV photons produced by a capillary discharge soft x-ray laser.1 During ionization, the metal oxide clusters are observed to be almost free of serious fragmentation. The most stable neutral cluster of vanadium, niobium, and tantalum oxide growth in a saturated oxygen condition are identified as MO2, M2O4/M2O5, M3O7, M4O10, M5O12, M6O15, M7O17, M8O20, and M9O22, which can be represented as a form (MO2)0,1(M2O5)y. M2O5 is identified as a basic unit to build-up the three kinds of metal oxide clusters. In the case of niobium and tantalum oxide clusters, the oxygen-deficient clusters with a structure of (MO2)2(M2O5)y are detected for groups that contain an even number of metal atoms. For vanadium oxide clusters, the oxygen-deficient clusters are detected for every family, indicating a stable structure of (VO2)x(V2O5)y. The stoichiometry of oxygen-rich clusters can be expressed as (MO2)0,1(M2O5)yO1-3 and their structures are consistent with chemically bonded species.
Rare-gas-cluster explosions under irradiation by intense short XUV pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffmann, K.; Murphy, B.; Kandadai, N.

High-intensity, extreme-ultraviolet (XUV) femtosecond interactions with large rare-gas clusters of xenon and argon have been studied at a wavelength of 38 nm. Pulses of XUV radiation with nJ energy are produced by high-order harmonic conversion from a 35-fs, near-infrared, terawatt laser. Mass resolved ion spectra show charge states up to Xe{sup 8+} and Ar{sup 4+}. Kinetic-energy measurements of ions and electrons indicate that a nanoplasma is formed and a hydrodynamic cluster explosion ensues after heating by the short wavelength pulse. It appears that the observed charge states and electron temperatures are consistent with sequential, single-photon ionization and collisional ionization ofmore » ions that have had their ionization potential depressed by plasma continuum lowering in the cluster nanoplasma.« less
Giant plasmon excitation in single and double ionization of C60 by fast highly charged Si and O ions

NASA Astrophysics Data System (ADS)

Kelkar, A. H.; Kadhane, U.; Misra, D.; Tribedi, L. C.

2007-09-01

Se have investigated single and double ionization of C60 molecule in collisions with 2.33 MeV/u Siq+ (q=6-14) and 3.125 MeV/u Oq+ (q=5-8) projectiles. The projectile charge state dependence of the single and double ionization yields of C60 are then compared to those for an ion-atom collision system using Ne gas as a target. A large difference between the gas and the cluster target behaviour was partially explained in terms of a model based on collective excitation namely the giant dipole plasmon resonance (GDPR). The qualitative agreement between the data and GDPR model prediction for single and double ionization signifies the importance of single and double plasmon excitations in the ionization process. A large deviation of the GDPR model for triple and quadruple ionization from the experimental data imply the importance of the other low impact parameter processes such as evaporation, fragmentation and a possible solid-like dynamical screening.
Delayed Ionization in Transition Metal Carbon Clusters

NASA Astrophysics Data System (ADS)

Kooi, S. E.; Castleman, A. W., Jr.

1997-03-01

Mass spectrometric studies of several single and binary transition metal carbon cluster systems, produced in a laser vaporization source, reveal several species that undergo delayed ionization. Pulsed extraction and blocking electric fields, in a time-of-flight mass spectrometer, allow the study of delayed ionization over a time window after excitation with a pulsed laser. In systems where metallocarbohedrenes (Met-Cars) are produced, the Met-Cars are the dominate delayed species. Delayed ionization of binary metal Met-Cars Ti_xM_yC_12 (M=Zr,Nb,Y; x+y=8) is dependent on the ratio of the two metals. Delayed behavior is investigated over a range of photoionization wavelengths and fluences. In order to determine the degree to which the delayed ionization is thermionic in character, the experimental data have been compared to Klots's model for thermionic emission from small particles.
Communication: Strong laser alignment of solvent-solute aggregates in the gas-phase

NASA Astrophysics Data System (ADS)

Trippel, Sebastian; Wiese, Joss; Mullins, Terry; Küpper, Jochen

2018-03-01

Strong quasi-adiabatic laser alignment of the indole-water-dimer clusters, an amino-acid chromophore bound to a single water molecule through a hydrogen bond, was experimentally realized. The alignment was visualized through ion and electron imaging following strong-field ionization. Molecular-frame photoelectron angular distributions showed a clear suppression of the electron yield in the plane of the ionizing laser's polarization, which was analyzed as strong alignment of the molecular cluster with ⟨cos2 θ2D⟩ ≥ 0.9.
Delayed repair of radiation induced clustered DNA damage: Friend or foe?

PubMed Central

Eccles, Laura J.; O’Neill, Peter; Lomax, Martine E.

2011-01-01

A signature of ionizing radiation exposure is the induction of DNA clustered damaged sites, defined as two or more lesions within one to two helical turns of DNA by passage of a single radiation track. Clustered damage is made up of double strand breaks (DSB) with associated base lesions or abasic (AP) sites, and non-DSB clusters comprised of base lesions, AP sites and single strand breaks. This review will concentrate on the experimental findings of the processing of non-DSB clustered damaged sites. It has been shown that non-DSB clustered damaged sites compromise the base excision repair pathway leading to the lifetime extension of the lesions within the cluster, compared to isolated lesions, thus the likelihood that the lesions persist to replication and induce mutation is increased. In addition certain non-DSB clustered damaged sites are processed within the cell to form additional DSB. The use of E. coli to demonstrate that clustering of DNA lesions is the major cause of the detrimental consequences of ionizing radiation is also discussed. The delayed repair of non-DSB clustered damaged sites in humans can be seen as a “friend”, leading to cell killing in tumour cells or as a “foe”, resulting in the formation of mutations and genetic instability in normal tissue. PMID:21130102
Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Anil; Bogdanov, Bogdan

2015-02-14

Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry. Singly as well as multiply charged clusters were formed with the general formulae, (HCOOLi)nLi+, (HCOOLi)nLimm+, (HCOOLi)nHCOO- and (HCOOLi)n(HCOO)mm-. Several magic number cluster ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi)3Li+ being the most abundant and stable cluster ions. Fragmentations of singly charged clusters proceed first by the loss of a dimer unit ((HCOOLi)2) followed by sequential loss of monomer units (HCOOLi). In the case ofmore » positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi)3Li+ at higher collision energies which later fragments to dimer and monomer ions in lower abundance. Quantum mechanical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.« less
Inclusion of orbital relaxation and correlation through the unitary group adapted open shell coupled cluster theory using non-relativistic and scalar relativistic Hamiltonians to study the core ionization potential of molecules containing light to medium-heavy elements

NASA Astrophysics Data System (ADS)

Sen, Sangita; Shee, Avijit; Mukherjee, Debashis

2018-02-01

The orbital relaxation attendant on ionization is particularly important for the core electron ionization potential (core IP) of molecules. The Unitary Group Adapted State Universal Coupled Cluster (UGA-SUMRCC) theory, recently formulated and implemented by Sen et al. [J. Chem. Phys. 137, 074104 (2012)], is very effective in capturing orbital relaxation accompanying ionization or excitation of both the core and the valence electrons [S. Sen et al., Mol. Phys. 111, 2625 (2013); A. Shee et al., J. Chem. Theory Comput. 9, 2573 (2013)] while preserving the spin-symmetry of the target states and using the neutral closed-shell spatial orbitals of the ground state. Our Ansatz invokes a normal-ordered exponential representation of spin-free cluster-operators. The orbital relaxation induced by a specific set of cluster operators in our Ansatz is good enough to eliminate the need for different sets of orbitals for the ground and the core-ionized states. We call the single configuration state function (CSF) limit of this theory the Unitary Group Adapted Open-Shell Coupled Cluster (UGA-OSCC) theory. The aim of this paper is to comprehensively explore the efficacy of our Ansatz to describe orbital relaxation, using both theoretical analysis and numerical performance. Whenever warranted, we also make appropriate comparisons with other coupled-cluster theories. A physically motivated truncation of the chains of spin-free T-operators is also made possible by the normal-ordering, and the operational resemblance to single reference coupled-cluster theory allows easy implementation. Our test case is the prediction of the 1s core IP of molecules containing a single light- to medium-heavy nucleus and thus, in addition to demonstrating the orbital relaxation, we have addressed the scalar relativistic effects on the accuracy of the IPs by using a hierarchy of spin-free Hamiltonians in conjunction with our theory. Additionally, the contribution of the spin-free component of the two-electron Gaunt term, not usually taken into consideration, has been estimated at the Self-Consistent Field (ΔSCF) level and is found to become increasingly important and eventually quite prominent for molecules with third period atoms and below. The accuracies of the IPs computed using UGA-OSCC are found to be of the same order as the Coupled Cluster Singles Doubles (ΔCCSD) values while being free from spin contamination. Since the UGA-OSCC uses a common set of orbitals for the ground state and the ion, it obviates the need of two N5 AO to MO transformation in contrast to the ΔCCSD method.
Inclusion of orbital relaxation and correlation through the unitary group adapted open shell coupled cluster theory using non-relativistic and scalar relativistic Hamiltonians to study the core ionization potential of molecules containing light to medium-heavy elements.

PubMed

Sen, Sangita; Shee, Avijit; Mukherjee, Debashis

2018-02-07

The orbital relaxation attendant on ionization is particularly important for the core electron ionization potential (core IP) of molecules. The Unitary Group Adapted State Universal Coupled Cluster (UGA-SUMRCC) theory, recently formulated and implemented by Sen et al. [J. Chem. Phys. 137, 074104 (2012)], is very effective in capturing orbital relaxation accompanying ionization or excitation of both the core and the valence electrons [S. Sen et al., Mol. Phys. 111, 2625 (2013); A. Shee et al., J. Chem. Theory Comput. 9, 2573 (2013)] while preserving the spin-symmetry of the target states and using the neutral closed-shell spatial orbitals of the ground state. Our Ansatz invokes a normal-ordered exponential representation of spin-free cluster-operators. The orbital relaxation induced by a specific set of cluster operators in our Ansatz is good enough to eliminate the need for different sets of orbitals for the ground and the core-ionized states. We call the single configuration state function (CSF) limit of this theory the Unitary Group Adapted Open-Shell Coupled Cluster (UGA-OSCC) theory. The aim of this paper is to comprehensively explore the efficacy of our Ansatz to describe orbital relaxation, using both theoretical analysis and numerical performance. Whenever warranted, we also make appropriate comparisons with other coupled-cluster theories. A physically motivated truncation of the chains of spin-free T-operators is also made possible by the normal-ordering, and the operational resemblance to single reference coupled-cluster theory allows easy implementation. Our test case is the prediction of the 1s core IP of molecules containing a single light- to medium-heavy nucleus and thus, in addition to demonstrating the orbital relaxation, we have addressed the scalar relativistic effects on the accuracy of the IPs by using a hierarchy of spin-free Hamiltonians in conjunction with our theory. Additionally, the contribution of the spin-free component of the two-electron Gaunt term, not usually taken into consideration, has been estimated at the Self-Consistent Field (ΔSCF) level and is found to become increasingly important and eventually quite prominent for molecules with third period atoms and below. The accuracies of the IPs computed using UGA-OSCC are found to be of the same order as the Coupled Cluster Singles Doubles (ΔCCSD) values while being free from spin contamination. Since the UGA-OSCC uses a common set of orbitals for the ground state and the ion, it obviates the need of two N 5 AO to MO transformation in contrast to the ΔCCSD method.
Mass-Selective Laser Photoionization.

ERIC Educational Resources Information Center

Smalley, R. E.

1982-01-01

Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)
A coupled cluster theory with iterative inclusion of triple excitations and associated equation of motion formulation for excitation energy and ionization potential

NASA Astrophysics Data System (ADS)

Maitra, Rahul; Akinaga, Yoshinobu; Nakajima, Takahito

2017-08-01

A single reference coupled cluster theory that is capable of including the effect of connected triple excitations has been developed and implemented. This is achieved by regrouping the terms appearing in perturbation theory and parametrizing through two different sets of exponential operators: while one of the exponentials, involving general substitution operators, annihilates the ground state but has a non-vanishing effect when it acts on the excited determinant, the other is the regular single and double excitation operator in the sense of conventional coupled cluster theory, which acts on the Hartree-Fock ground state. The two sets of operators are solved as coupled non-linear equations in an iterative manner without significant increase in computational cost than the conventional coupled cluster theory with singles and doubles excitations. A number of physically motivated and computationally advantageous sufficiency conditions are invoked to arrive at the working equations and have been applied to determine the ground state energies of a number of small prototypical systems having weak multi-reference character. With the knowledge of the correlated ground state, we have reconstructed the triple excitation operator and have performed equation of motion with coupled cluster singles, doubles, and triples to obtain the ionization potential and excitation energies of these molecules as well. Our results suggest that this is quite a reasonable scheme to capture the effect of connected triple excitations as long as the ground state remains weakly multi-reference.
Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Anil, E-mail: Anil.Shukla@pnnl.gov; Bogdanov, Bogdan

2015-02-14

Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry (collision-induced dissociation with N{sub 2}). Singly as well as multiply charged clusters were formed in both positive and negative ion modes with the general formulae, (HCOOLi){sub n}Li{sup +}, (HCOOLi){sub n}Li{sub m}{sup m+}, (HCOOLi){sub n}HCOO{sup −}, and (HCOOLi){sub n}(HCOO){sub m}{sup m−}. Several magic number cluster (MNC) ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi){sub 3}Li{sup +} being the most abundant and stable cluster ion. Fragmentations ofmore » singly charged positive clusters proceed first by the loss of a dimer unit ((HCOOLi){sub 2}) followed by the loss of monomer units (HCOOLi) although the former remains the dominant dissociation process. In the case of positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi){sub 3}Li{sup +} as the most abundant fragment ion at higher collision energies which then fragments further to dimer and monomer ions at lower abundances. In the negative ion mode, however, singly charged clusters dissociated via sequential loss of monomer units. Multiply charged clusters in both positive and negative ion modes dissociated mainly via Coulomb repulsion. Quantum chemical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the central lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.« less

Generation of CsI cluster ions for mass calibration in matrix-assisted laser desorption/ionization mass spectrometry.

PubMed

Lou, Xianwen; van Dongen, Joost L J; Meijer, E W

2010-07-01

A simple method was developed for the generation of cesium iodide (CsI) cluster ions up to m/z over 20,000 in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). Calibration ions in both positive and negative ion modes can readily be generated from a single MALDI spot of CsI(3) with 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) matrix. The major cluster ion series observed in the positive ion mode is [(CsI)(n)Cs](+), and in the negative ion mode is [(CsI)(n)I](-). In both cluster series, ions spread evenly every 259.81 units. The easy method described here for the production of CsI cluster ions should be useful for MALDI MS calibrations. Copyright 2010 American Society for Mass Spectrometry. Published by Elsevier Inc. All rights reserved.
Brominated Tyrosine and Polyelectrolyte Multilayer Analysis by Laser Desorption VUV Postionization and Secondary Ion Mass Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

University of Illinois at Chicago; Blaze, Melvin M. T.; Takahashi, Lynelle

2011-03-14

The small molecular analyte 3,5-dibromotyrosine (Br2Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br2Y were analyzed by laser desorption postionization mass spectrometry (LDPI-MS). LDPI-MS using 7.87 eV laser and tunable 8 ? 12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br2Y films allowed detection by≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br2Y to be ~;;8.3?0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at≤8 eV photon energies. However, single photon ionization could only detect Br2Y adsorbed within PEMsmore » when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi3 + secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. The negative ion SIMS depended strongly on the high electron affinity of this specific analyte and the analyte?s condensed phase environment.« less
Dynamics and Fragmentation of Hydrogen Bonded and van der Waal Clusters upon 26.5 eV Soft X-ray Laser Ionization

NASA Astrophysics Data System (ADS)

Dong, Feng; Heinbuch, Scott; Bernstein, Elliot; Rocca, Jorge

2006-05-01

A desk-top soft x-ray laser is applied to the study of water, methanol, ammonia, sulfur dioxide, carbon dioxide, mixed sulfur dioxide-water, and mixed carbon dioxide-water clusters through single photon ionization time of flight mass spectroscopy. Almost all of the energy above the vertical ionization energy is removed by the ejected electron. Protonated water, methanol, and ammonia clusters dominate the mass spectra for the first three systems. The temperatures of the neutral water and methanol clusters can be estimated. In the case of pure SO2 and CO2, the mass spectra are dominated by (SO2)n^+ and (CO2)n^+ cluster series. When a high or low concentration of SO2/CO2 is mixed with water, we observe (SO2/CO2)nH2O^+ or SO2/CO2(H2O)nH^+ in the mass spectra, respectively. The unimolecular dissociation rate constants for reactions involving loss of one neutral molecule are calculated for the protonated water, methanol, and ammonia clusters as well as for SO2 and CO2 clusters. We find that the 26.5 eV soft x-ray laser is a nearly ideal tool for the study of hydrogen bonded and van der Waals cluster systems and we are currently exploring its usefulness for other more strongly bound systems.
Ionization of doped helium nanodroplets: Complexes of C60 with water clusters

NASA Astrophysics Data System (ADS)

Denifl, S.; Zappa, F.; Mähr, I.; Mauracher, A.; Probst, M.; Urban, J.; Mach, P.; Bacher, A.; Bohme, D. K.; Echt, O.; Märk, T. D.; Scheier, P.

2010-06-01

Water clusters are known to undergo an autoprotonation reaction upon ionization by photons or electron impact, resulting in the formation of (H2O)nH3O+. Ejection of OH cannot be quenched by near-threshold ionization; it is only partly quenched when clusters are complexed with inert gas atoms. Mass spectra recorded by electron ionization of water-doped helium droplets show that the helium matrix also fails to quench OH loss. The situation changes drastically when helium droplets are codoped with C60. Charged C60-water complexes are predominantly unprotonated; C60(H2O)4+ and (C60)2(H2O)4+ appear with enhanced abundance. Another intense ion series is due to C60(H2O)nOH+; dehydrogenation is proposed to be initiated by charge transfer between the primary He+ ion and C60. The resulting electronically excited C60+∗ leads to the formation of a doubly charged C60-water complex either via emission of an Auger electron from C60+∗, or internal Penning ionization of the attached water complex, followed by charge separation within {C60(H2O)n}2+. This mechanism would also explain previous observations of dehydrogenation reactions in doped helium droplets. Mass-analyzed ion kinetic energy scans reveal spontaneous (unimolecular) dissociation of C60(H2O)n+. In addition to the loss of single water molecules, a prominent reaction channel yields bare C60+ for sizes n=3, 4, or 6. Ab initio Hartree-Fock calculations for C60-water complexes reveal negligible charge transfer within neutral complexes. Cationic complexes are well described as water clusters weakly bound to C60+. For n=3, 4, or 6, fissionlike desorption of the entire water complex from C60(H2O)n+ energetically competes with the evaporation of a single water molecule.
The Pleiades Using Astronomical Spectroscopic Technique within the Range of H-{alpha} Region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zambri Zainuddin, Mohd; Muhyidin, Meer Ashwinkumar; Ahmad, Nazhatulshima

2011-03-30

The Pleiades is an open star cluster located in the constellation of Taurus, which mainly consists of hot and luminous B-type stars. Observations were conducted over five-day period in December 2009 at Langkawi National Observatory, Malaysia by using 20-inch telescope diameter of Ritchey-Chretien reflector telescope, together with SBIG Self Guided Spectrograph and SBIG ST-7 CCD camera. The spectra of seven main members of the cluster, namely Alcyone; Atlas; Celaeno; Electra; Maia; Merope and Taygeta; and of Alcyone B; a smaller component of Alcyone quadruple system, were obtained in the optical range of approximately 6300 A to 7100 A. This rangemore » was picked due to the vicinity of Balmer H-{alpha} spectral line at 6562.852 A. Alcyone, Electra and Merope were found to have H-{alpha} emissions possibly caused by the presence of equatorial circumstellar disks or envelopes made up of ejected matter. Electra and Merope in particular exhibited peculiar asymmetric double emission peaks, which could be evidence of one-armed density wave in each of their circumstellar disks. Atlas, Celaeno, Merope, Taygeta and Alcyone B showed strong H-{alpha} absorptions with broadening characteristic of high rotational velocities. As deduced from the spectra, the stars were found to have atmospheres with similar chemical content, with spectral lines characteristics of singly ionized silicon, singly ionized iron and singly ionized oxygen. The measured radial velocities of all eight stars also suggest that the cluster could someday disperse.« less
Ionization-induced star formation - IV. Triggering in bound clusters

NASA Astrophysics Data System (ADS)

Dale, J. E.; Ercolano, B.; Bonnell, I. A.

2012-12-01

We present a detailed study of star formation occurring in bound star-forming clouds under the influence of internal ionizing feedback from massive stars across a spectrum of cloud properties. We infer which objects are triggered by comparing our feedback simulations with control simulations in which no feedback was present. We find that feedback always results in a lower star formation efficiency and usually but not always results in a larger number of stars or clusters. Cluster mass functions are not strongly affected by feedback, but stellar mass functions are biased towards lower masses. Ionization also affects the geometrical distribution of stars in ways that are robust against projection effects, but may make the stellar associations more or less subclustered depending on the background cloud environment. We observe a prominent pillar in one simulation which is the remains of an accretion flow feeding the central ionizing cluster of its host cloud and suggest that this may be a general formation mechanism for pillars such as those observed in M16. We find that the association of stars with structures in the gas such as shells or pillars is a good but by no means foolproof indication that those stars have been triggered and we conclude overall that it is very difficult to deduce which objects have been induced to form and which formed spontaneously simply from observing the system at a single time.
Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets.

PubMed

LaForge, A C; Stumpf, V; Gokhberg, K; von Vangerow, J; Stienkemeier, F; Kryzhevoi, N V; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L S; Mudrich, M

2016-05-20

We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets.
Measurement of high-dynamic range x-ray Thomson scattering spectra for the characterization of nano-plasmas at LCLS

DOE PAGES

MacDonald, M. J.; Gorkhover, T.; Bachmann, B.; ...

2016-08-08

Atomic clusters can serve as ideal model systems for exploring ultrafast (~100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano plasmas was limited to coherent x-ray imaging. Here we present the first measurement of spectrally-resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities and ionization. Single shot x-ray Thomson scatterings signals were recorded at 120 Hz using a crystal spectrometer in combination withmore » a single-photon counting and energy-dispersive pnCCD. A precise pump laser collimation scheme enabled recording near background-free scattering spectra from Ar clusters with an unprecedented dynamic range of more than 3 orders of magnitude. As a result, such measurements are important for understanding collective effects in laser-matter interactions on femtosecond timescales, opening new routes for the development of schemes for their ultrafast control.« less
Measurement of high-dynamic range x-ray Thomson scattering spectra for the characterization of nano-plasmas at LCLS

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDonald, M. J., E-mail: macdonm@umich.edu; SLAC National Accelerator Laboratory, Menlo Park, California 94025; Gorkhover, T.

2016-11-15

Atomic clusters can serve as ideal model systems for exploring ultrafast (∼100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano-plasmas was limited to coherent x-ray imaging. Here we present the first measurement of spectrally resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities, and ionization. Single shot x-ray Thomson scattering signals were recorded at 120 Hz using a crystal spectrometer in combination withmore » a single-photon counting and energy-dispersive pnCCD. A precise pump laser collimation scheme enabled recording near background-free scattering spectra from Ar clusters with an unprecedented dynamic range of more than 3 orders of magnitude. Such measurements are important for understanding collective effects in laser-matter interactions on femtosecond time scales, opening new routes for the development of schemes for their ultrafast control.« less
Hartree-Fock calculation of the differential photoionization cross sections of small Li clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galitskiy, S. A.; Artemyev, A. N.; Jänkälä, K.

2015-01-21

Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li{sub 2−8} are systematically computed in a broad interval of the photoelectron kinetic energies for the energetically most stable geometry of each cluster. Calculations of the partial photoelectron continuum waves in clusters are carried out by the single center method within the Hartree-Fock approximation. We study photoionization cross sections per one electron and analyze in some details general trends in the photoionization of inner and outer shells with respect to the size and geometry of a cluster. The present differential cross sections computed for Li{submore » 2} are in a good agreement with the available theoretical data, whereas those computed for Li{sub 3−8} clusters can be considered as theoretical predictions.« less
Gas-phase synthesis of singly and multiply charged polyoxovanadate anions employing electrospray ionization and collision induced dissociation.

PubMed

Al Hasan, Naila M; Johnson, Grant E; Laskin, Julia

2013-09-01

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy(n-) and VxOyCl(n-) ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N(+), tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCl(n-) and VxOyCl(L)((n-1)-) clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl((1-2)-) and VxOy ((1-2)-) anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.
Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

NASA Astrophysics Data System (ADS)

Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

2013-09-01

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n- and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy (1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.
Temperature structure in the Perseus cluster core observed with Hitomi

NASA Astrophysics Data System (ADS)

Hitomi Collaboration; Aharonian, Felix; Akamatsu, Hiroki; Akimoto, Fumie; Allen, Steven W.; Angelini, Lorella; Audard, Marc; Awaki, Hisamitsu; Axelsson, Magnus; Bamba, Aya; Bautz, Marshall W.; Blandford, Roger; Brenneman, Laura W.; Brown, Gregory V.; Bulbul, Esra; Cackett, Edward M.; Chernyakova, Maria; Chiao, Meng P.; Coppi, Paolo S.; Costantini, Elisa; de Plaa, Jelle; de Vries, Cor P.; den Herder, Jan-Willem; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Enoto, Teruaki; Ezoe, Yuichiro; Fabian, Andrew C.; Ferrigno, Carlo; Foster, Adam R.; Fujimoto, Ryuichi; Fukazawa, Yasushi; Furukawa, Maki; Furuzawa, Akihiro; Galeazzi, Massimiliano; Gallo, Luigi C.; Gandhi, Poshak; Giustini, Margherita; Goldwurm, Andrea; Gu, Liyi; Guainazzi, Matteo; Haba, Yoshito; Hagino, Kouichi; Hamaguchi, Kenji; Harrus, Ilana M.; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hayashida, Kiyoshi; Hiraga, Junko S.; Hornschemeier, Ann; Hoshino, Akio; Hughes, John P.; Ichinohe, Yuto; Iizuka, Ryo; Inoue, Hajime; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Iwai, Masachika; Kaastra, Jelle; Kallman, Tim; Kamae, Tsuneyoshi; Kataoka, Jun; Kato, Yuichi; Katsuda, Satoru; Kawai, Nobuyuki; Kelley, Richard L.; Kilbourne, Caroline A.; Kitaguchi, Takao; Kitamoto, Shunji; Kitayama, Tetsu; Kohmura, Takayoshi; Kokubun, Motohide; Koyama, Katsuji; Koyama, Shu; Kretschmar, Peter; Krimm, Hans A.; Kubota, Aya; Kunieda, Hideyo; Laurent, Philippe; Lee, Shiu-Hang; Leutenegger, Maurice A.; Limousin, Olivier; Loewenstein, Michael; Long, Knox S.; Lumb, David; Madejski, Greg; Maeda, Yoshitomo; Maier, Daniel; Makishima, Kazuo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian R.; Mehdipour, Missagh; Miller, Eric D.; Miller, Jon M.; Mineshige, Shin; Mitsuda, Kazuhisa; Mitsuishi, Ikuyuki; Miyazawa, Takuya; Mizuno, Tsunefumi; Mori, Hideyuki; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard F.; Nakagawa, Takao; Nakajima, Hiroshi; Nakamori, Takeshi; Nakashima, Shinya; Nakazawa, Kazuhiro; Nobukawa, Kumiko K.; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ohashi, Takaya; Ohno, Masanori; Okajima, Takashi; Ota, Naomi; Ozaki, Masanobu; Paerels, Frits; Paltani, Stéphane; Petre, Robert; Pinto, Ciro; Porter, Frederick S.; Pottschmidt, Katja; Reynolds, Christopher S.; Safi-Harb, Samar; Saito, Shinya; Sakai, Kazuhiro; Sasaki, Toru; Sato, Goro; Sato, Kosuke; Sato, Rie; Sawada, Makoto; Schartel, Norbert; Serlemtsos, Peter J.; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall K.; Soong, Yang; Stawarz, Łukasz; Sugawara, Yasuharu; Sugita, Satoshi; Szymkowiak, Andrew; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shiníchiro; Takei, Yoh; Tamagawa, Toru; Tamura, Takayuki; Tanaka, Takaaki; Tanaka, Yasuo; Tanaka, Yasuyuki T.; Tashiro, Makoto S.; Tawara, Yuzuru; Terada, Yukikatsu; Terashima, Yuichi; Tombesi, Francesco; Tomida, Hiroshi; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi Go; Uchida, Hiroyuki; Uchiyama, Hideki; Uchiyama, Yasunobu; Ueda, Shutaro; Ueda, Yoshihiro; Uno, Shiníchiro; Urry, C. Megan; Ursino, Eugenio; Watanabe, Shin; Werner, Norbert; Wilkins, Dan R.; Williams, Brian J.; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yatsu, Yoichi; Yonetoku, Daisuke; Zhuravleva, Irina; Zoghbi, Abderahmen

2018-03-01

The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of ˜7΄ in diameter. SXS was operated with an energy resolution of ˜5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8-20 keV energy band.
Zero kinetic energy photoelectron spectroscopy of tryptamine and the dissociation pathway of the singly hydrated cation cluster.

PubMed

Gu, Quanli; Knee, J L

2012-09-14

The relative ionization energies of tryptamine conformations are determined by zero kinetic energy photoelectron spectroscopy and photoionization efficiency measurements. The relative cationic conformational stabilities are compared to the published results for the neutral molecule. In the cation, the interaction strength changes significantly between amino group and either the phenyl or the pyrrole moiety of the indole chromophore where most of the positive charge is located, leading to different conformational structures and relative conformer energies in the cation. In particular, the measured adiabatic ionization potential of isomer B is 60,928 ± 5 cm(-1), at least 400 cm(-1) higher than any of the 6 other tryptamine isomers which all have ionization potentials within 200 cm(-1) of each other. In addition to the monomer, measurements were made on the A conformer of the tryptamine(+)-H(2)O complex including the ionization threshold and cation dissociation energy measured using a threshold photoionization fragmentation method. The water cluster exhibits an unexpectedly high ionization potential of 60,307 ± 100 cm(-1), close to the conformer A monomer of 60 320 ± 100 cm(-1). It also exhibits surprisingly low dissociation energy of 1750 ± 150 cm(-1) compared to other H-bonding involved cation-H(2)O complexes which are typically several thousands of wavenumbers higher. Quantum chemical calculations indicate that upon ionization the structure of the parent molecule in the water complex remains mostly unchanged due to the rigid intermolecular double hydrogen bonded water molecule bridging the monomer backbone and its side chain thus leading to the high ionization potential in the water cluster. The surprisingly low dissociation energy measured in the cationic water complex is attributed to the formation of a much more stable structural isomer H(+) in the exit channel.
A screened independent atom model for the description of ion collisions from atomic and molecular clusters

NASA Astrophysics Data System (ADS)

Lüdde, Hans Jürgen; Horbatsch, Marko; Kirchner, Tom

2018-05-01

We apply a recently introduced model for an independent-atom-like calculation of ion-impact electron transfer and ionization cross sections to proton collisions from water, neon, and carbon clusters. The model is based on a geometrical interpretation of the cluster cross section as an effective area composed of overlapping circular disks that are representative of the atomic contributions. The latter are calculated using a time-dependent density-functional-theory-based single-particle description with accurate exchange-only ground-state potentials. We find that the net capture and ionization cross sections in p-X n collisions are proportional to n α with 2/3 ≤ α ≤ 1. For capture from water clusters at 100 keV impact energy α is close to one, which is substantially different from the value α = 2/3 predicted by a previous theoretical work based on the simplest-level electron nuclear dynamics method. For ionization at 100 keV and for capture at lower energies we find smaller α values than for capture at 100 keV. This can be understood by considering the magnitude of the atomic cross sections and the resulting overlaps of the circular disks that make up the cluster cross section in our model. Results for neon and carbon clusters confirm these trends. Simple parametrizations are found which fit the cross sections remarkably well and suggest that they depend on the relevant bond lengths.
Hundred Thousand Degree Gas in the Virgo Cluster of Galaxies

NASA Astrophysics Data System (ADS)

Sparks, W. B.; Pringle, J. E.; Carswell, R. F.; Donahue, M.; Martin, R.; Voit, M.; Cracraft, M.; Manset, N.; Hough, J. H.

2012-05-01

The physical relationship between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of many galaxy clusters is not understood. It is unclear whether the ~104 K filaments have cooled and condensed from the ambient hot (~107 K) medium or have some other origin such as the infall of cold gas in a merger, or the disturbance of an internal cool reservoir of gas by nuclear activity. Observations of gas at intermediate temperatures (~105-106 K) can potentially reveal whether the central massive galaxies are gaining cool gas through condensation or losing it through conductive evaporation and hence identify plausible scenarios for transport processes in galaxy cluster gas. Here we present spectroscopic detection of ~105 K gas spatially associated with the Hα filaments in a central cluster galaxy, M87, in the Virgo Cluster. The measured emission-line fluxes from triply ionized carbon (C IV 1549 Å) and singly ionized helium (He II 1640 Å) are consistent with a model in which thermal conduction determines the interaction between hot and cold phases.
Chromosome thripsis by DNA double strand break clusters causes enhanced cell lethality, chromosomal translocations and 53BP1-recruitment

PubMed Central

Schipler, Agnes; Mladenova, Veronika; Soni, Aashish; Nikolov, Vladimir; Saha, Janapriya; Mladenov, Emil; Iliakis, George

2016-01-01

Chromosome translocations are hallmark of cancer and of radiation-induced cell killing, reflecting joining of incongruent DNA-ends that alter the genome. Translocation-formation requires DNA end-joining mechanisms and incompletely characterized, permissive chromatin conditions. We show that chromatin destabilization by clusters of DNA double-strand-breaks (DSBs) generated by the I-SceI meganuclease at multiple, appropriately engineered genomic sites, compromises c-NHEJ and markedly increases cell killing and translocation-formation compared to single-DSBs. Translocation-formation from DSB-clusters utilizes Parp1 activity, implicating alt-EJ in their formation. Immunofluorescence experiments show that single-DSBs and DSB-clusters uniformly provoke the formation of single γ-H2AX foci, suggesting similar activation of early DNA damage response (DDR). Live-cell imaging also shows similar single-focus recruitment of the early-response protein MDC1, to single-DSBs and DSB-clusters. Notably, the late DDR protein, 53BP1 shows in live-cell imaging strikingly stronger recruitment to DSB-clusters as compared to single-DSBs. This is the first report that chromatin thripsis, in the form of engineered DSB-clusters, compromises first-line DSB-repair pathways, allowing alt-EJ to function as rescuing-backup. DSB-cluster-formation is indirectly linked to the increased biological effectiveness of high ionization-density radiations, such as the alpha-particles emitted by radon gas or the heavy-ions utilized in cancer therapy. Our observations provide the first direct mechanistic explanation for this long-known effect. PMID:27257076
Truncation of the Binary Distribution Function in Globular Cluster Formation

NASA Astrophysics Data System (ADS)

Vesperini, E.; Chernoff, David F.

1996-02-01

We investigate a population of primordial binaries during the initial stage of evolution of a star cluster. For our calculations we assume that equal-mass stars form rapidly in a tidally truncated gas cloud, that ˜10% of the stars are in binaries, and that the resulting star cluster undergoes an epoch of violent relaxation. We study the collisional interaction of the binaries and single stars, in particular, the ionization of the binaries and the energy exchange between binaries and single stars. We find that for large N systems (N > 1000), even the most violent beginning leaves the binary distribution function largely intact. Hence, the binding energy originally tied up in the cloud's protostellar pairs is preserved during the relaxation process, and the binaries are available to interact at later times within the virialized cluster.
Production of low kinetic energy electrons and energetic ion pairs by Intermolecular Coulombic Decay.

PubMed

Hergenhahn, Uwe

2012-12-01

The paper gives an introduction into Interatomic and Intermolecular Coulombic Decay (ICD). ICD is an autoionization process, which contrary to Auger decay involves neighbouring sites of the initial vacancy as an integral part of the decay transition. As a result of ICD, slow electrons are produced which generally are known to be active in radiation damage. The author summarizes the properties of ICD and reviews a number of important experiments performed in recent years. Intermolecular Coulombic Decay can generally take place in weakly bonded aggregates in the presence of ionizing particles or ionizing radiation. Examples collected here mostly use soft X-rays produced by synchrotron radiation to ionize, and use rare-gas clusters, water clusters or solutes in a liquid jet to observe ICD after irradiation. Intermolecular Coulombic Decay is initiated by single ionization into an excited state. The subsequent relaxation proceeds via an ultra-fast energy transfer to a neighbouring site, where a second ionization occurs. Secondary electrons from ICD have clearly been identified in numerous systems. ICD can take place after primary ionization, as the second step of a decay cascade which also involves Auger decay, or after resonant excitation with an energy which exceeds the ionization potential of the system. ICD is expected to play a role whenever particles or radiation with photon energies above the ionization energies for inner valence electrons are present in weakly bonded matter, e.g., biological tissue. The process produces at the same time a slow electron and two charged atomic or molecular fragments, which will lead to structural changes around the ionized site.
Extreme ionization of Xe clusters driven by ultraintense laser fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heidenreich, Andreas; Last, Isidore; Jortner, Joshua

We applied theoretical models and molecular dynamics simulations to explore extreme multielectron ionization in Xe{sub n} clusters (n=2-2171, initial cluster radius R{sub 0}=2.16-31.0 A ring ) driven by ultraintense infrared Gaussian laser fields (peak intensity I{sub M}=10{sup 15}-10{sup 20} W cm{sup -2}, temporal pulse length {tau}=10-100 fs, and frequency {nu}=0.35 fs{sup -1}). Cluster compound ionization was described by three processes of inner ionization, nanoplasma formation, and outer ionization. Inner ionization gives rise to high ionization levels (with the formation of (Xe{sup q+}){sub n} with q=2-36), which are amenable to experimental observation. The cluster size and laser intensity dependence of themore » inner ionization levels are induced by a superposition of barrier suppression ionization (BSI) and electron impact ionization (EII). The BSI was induced by a composite field involving the laser field and an inner field of the ions and electrons, which manifests ignition enhancement and screening retardation effects. EII was treated using experimental cross sections, with a proper account of sequential impact ionization. At the highest intensities (I{sub M}=10{sup 18}-10{sup 20} W cm{sup -2}) inner ionization is dominated by BSI. At lower intensities (I{sub M}=10{sup 15}-10{sup 16} W cm{sup -2}), where the nanoplasma is persistent, the EII contribution to the inner ionization yield is substantial. It increases with increasing the cluster size, exerts a marked effect on the increase of the (Xe{sup q+}){sub n} ionization level, is most pronounced in the cluster center, and manifests a marked increase with increasing the pulse length (i.e., becoming the dominant ionization channel (56%) for Xe{sub 2171} at {tau}=100 fs). The EII yield and the ionization level enhancement decrease with increasing the laser intensity. The pulse length dependence of the EII yield at I{sub M}=10{sup 15}-10{sup 16} W cm{sup -2} establishes an ultraintense laser pulse length control mechanism of extreme ionization products.« less

Equation of motion coupled cluster methods for electron attachment and ionization potential in polyacenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhaskaran-Nair, Kiran; Kowalski, Karol; Jarrell, Mark

2015-11-05

Polyacenes have attracted considerable attention due to their use in organic based optoelectronic materials. Polyacenes are polycyclic aromatic hydrocarbons composed of fused benzene rings. Key to understanding and design of new functional materials is an understanding of their excited state properties starting with their electron affinity (EA) and ionization potential (IP). We have developed a highly accurate and com- putationally e*fficient EA/IP equation of motion coupled cluster singles and doubles (EA/IP-EOMCCSD) method that is capable of treating large systems and large basis set. In this study we employ the EA/IP-EOMCCSD method to calculate the electron affinity and ionization potential ofmore » naphthalene, anthracene, tetracene, pentacene, hex- acene and heptacene. We have compared our results with other previous theoretical studies and experimental data. Our EA/IP results are in very good agreement with experiment and when compared with the other theoretical investigations our results represent the most accurate calculations as compared to experiment.« less
A universal matter-wave interferometer with optical ionization gratings in the time-domain

PubMed Central

Haslinger, Philipp; Dörre, Nadine; Geyer, Philipp; Rodewald, Jonas; Nimmrichter, Stefan; Arndt, Markus

2015-01-01

Matter-wave interferometry with atoms1 and molecules2 has attracted a rapidly growing interest throughout the last two decades both in demonstrations of fundamental quantum phenomena and in quantum-enhanced precision measurements. Such experiments exploit the non-classical superposition of two or more position and momentum states which are coherently split and rejoined to interfere3-11. Here, we present the experimental realization of a universal near-field interferometer built from three short-pulse single-photon ionization gratings12,13. We observe quantum interference of fast molecular clusters, with a composite de Broglie wavelength as small as 275 fm. Optical ionization gratings are largely independent of the specific internal level structure and are therefore universally applicable to different kinds of nanoparticles, ranging from atoms to clusters, molecules and nanospheres. The interferometer is sensitive to fringe shifts as small as a few nanometers and yet robust against velocity-dependent phase shifts, since the gratings exist only for nanoseconds and form an interferometer in the time-domain. PMID:25983851
CO2 Cluster Ion Beam, an Alternative Projectile for Secondary Ion Mass Spectrometry

NASA Astrophysics Data System (ADS)

Tian, Hua; Maciążek, Dawid; Postawa, Zbigniew; Garrison, Barbara J.; Winograd, Nicholas

2016-09-01

The emergence of argon-based gas cluster ion beams for SIMS experiments opens new possibilities for molecular depth profiling and 3D chemical imaging. These beams generally leave less surface chemical damage and yield mass spectra with reduced fragmentation compared with smaller cluster projectiles. For nanoscale bioimaging applications, however, limited sensitivity due to low ionization probability and technical challenges of beam focusing remain problematic. The use of gas cluster ion beams based upon systems other than argon offer an opportunity to resolve these difficulties. Here we report on the prospects of employing CO2 as a simple alternative to argon. Ionization efficiency, chemical damage, sputter rate, and beam focus are investigated on model compounds using a series of CO2 and Ar cluster projectiles (cluster size 1000-5000) with the same mass. The results show that the two projectiles are very similar in each of these aspects. Computer simulations comparing the impact of Ar2000 and (CO2)2000 on an organic target also confirm that the CO2 molecules in the cluster projectile remain intact, acting as a single particle of m/z 44. The imaging resolution employing CO2 cluster projectiles is improved by more than a factor of two. The advantage of CO2 versus Ar is also related to the increased stability which, in addition, facilitates the operation of the gas cluster ion beams (GCIB) system at lower backing pressure.
Two-Dimensional Animal-Like Fractals in Thin Films

NASA Astrophysics Data System (ADS)

Gao, Hong-jun; Xue, Zeng-quan; Wu, Quan-de; Pang, Shi-jin

1996-02-01

We present a few unique animal-like fractal patterns in ionized-cluster-beam deposited fullerene-tetracyanoquinodimethane thin films. The fractal patterns consisting of animal-like aggregates such as "fishes" and "quasi-seahorses" have been characterized by transmission electron microscopy. The results indicate that the small aggregates of the animal-like body are composed of many single crystals whose crystalline directions are generally different. The formation of the fractal patterns can be attributed to the cluster-diffusion-limited aggregation.
Ion-neutral Clustering of Bile Acids in Electrospray Ionization Across UPLC Flow Regimes

NASA Astrophysics Data System (ADS)

Brophy, Patrick; Broeckling, Corey D.; Murphy, James; Prenni, Jessica E.

2018-02-01

Bile acid authentic standards were used as model compounds to quantitatively evaluate complex in-source phenomenon on a UPLC-ESI-TOF-MS operated in the negative mode. Three different diameter columns and a ceramic-based microfluidic separation device were utilized, allowing for detailed descriptions of bile acid behavior across a wide range of flow regimes and instantaneous concentrations. A custom processing algorithm based on correlation analysis was developed to group together all ion signals arising from a single compound; these grouped signals produce verified compound spectra for each bile acid at each on-column mass loading. Significant adduction was observed for all bile acids investigated under all flow regimes and across a wide range of bile acid concentrations. The distribution of bile acid containing clusters was found to depend on the specific bile acid species, solvent flow rate, and bile acid concentration. Relative abundancies of each cluster changed non-linearly with concentration. It was found that summing all MS level (low collisional energy) ions and ion-neutral adducts arising from a single compound improves linearity across the concentration range (0.125-5 ng on column) and increases the sensitivity of MS level quantification. The behavior of each cluster roughly follows simple equilibrium processes consistent with our understanding of electrospray ionization mechanisms and ion transport processes occurring in atmospheric pressure interfaces. [Figure not available: see fulltext.
Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

2013-07-02

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including V xO y n– and V xO yCl n– ions (x = 1–14, y = 2–36, n = 1–3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V 14O 36Cl(L) 5 (L = Et 4N +, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged V xO yCl n– and V xOmore » yCl(L) (n–1)– clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller V xO yCl (1–2)– and V xO y (1–2)– anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged V xO yCl and V xO y species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of V xO yCl and V xO y anions through low-energy CID. Finally and furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.« less
Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Aryya; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav

2015-07-14

Auger decay is an efficient ultrafast relaxation process of core-shell or inner-shell excited atom or molecule. Generally, it occurs in femto-second or even atto-second time domain. Direct measurement of lifetimes of Auger process of single ionized and double ionized inner-shell state of an atom or molecule is an extremely difficult task. In this paper, we have applied the highly correlated complex absorbing potential-equation-of-motion coupled cluster (CAP-EOMCC) approach which is a combination of CAP and EOMCC approach to calculate the lifetime of the states arising from 2p inner-shell ionization of an Ar atom and 3d inner-shell ionization of Kr atom. Wemore » have also calculated the lifetime of Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}D, Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}S, and Ar{sup 2+}(2p{sup −1}3s{sup −1}) {sup 1}P double ionized states. The predicted results are compared with the other theoretical results as well as experimental results available in the literature.« less
Clustered DNA damages induced in human hematopoietic cells by low doses of ionizing radiation

NASA Technical Reports Server (NTRS)

Sutherland, Betsy M.; Bennett, Paula V.; Cintron-Torres, Nela; Hada, Megumi; Trunk, John; Monteleone, Denise; Sutherland, John C.; Laval, Jacques; Stanislaus, Marisha; Gewirtz, Alan

2002-01-01

Ionizing radiation induces clusters of DNA damages--oxidized bases, abasic sites and strand breaks--on opposing strands within a few helical turns. Such damages have been postulated to be difficult to repair, as are double strand breaks (one type of cluster). We have shown that low doses of low and high linear energy transfer (LET) radiation induce such damage clusters in human cells. In human cells, DSB are about 30% of the total of complex damages, and the levels of DSBs and oxidized pyrimidine clusters are similar. The dose responses for cluster induction in cells can be described by a linear relationship, implying that even low doses of ionizing radiation can produce clustered damages. Studies are in progress to determine whether clusters can be produced by mechanisms other than ionizing radiation, as well as the levels of various cluster types formed by low and high LET radiation.
On the intermolecular Coulombic decay of singly and doubly ionized states of water dimer.

PubMed

Stoychev, Spas D; Kuleff, Alexander I; Cederbaum, Lorenz S

2010-10-21

A semiquantitative study of the intermolecular Coulombic decay (ICD) of singly and doubly ionized water dimer has been carried out with the help of ab initio computed ionization spectra and potential energy curves (PECs). These PECs are particular cuts through the (H(2)O)(2), (H(2)O)(2) (+), and (H(2)O)(2) (++) hypersurfaces along the distance between the two oxygen atoms. A comparison with the recently published experimental data for the ICD in singly ionized water dimers [T. Jahnke, H. Sann, T. Havermeier et al., Nat. Phys. 6, 139 (2010)] and in large water clusters [M. Mucke, M. Braune, S. Barth et al., Nat. Phys. 6, 143 (2010)] shows that such a simplified description in which the internal degrees of freedom of the water molecules are frozen gives surprisingly useful results. Other possible decay channels of the singly ionized water dimer are also investigated and the influence of the H-atom participating in the hydrogen bond on the spectra of the proton-donor and proton-acceptor molecules in the dimer is discussed. Importantly, the decay processes of one-site dicationic states of water dimer are discussed and an estimate of the ICD-electron spectra is made. More than 33% of the dications produced by Auger decay are found to undergo ICD. The qualitative results show that the ICD following Auger decay in water is also expected to be an additional source of low-energy electrons proven to be extremely important for causing damages to living tissues.
Tailoring Ion Charge State Distribution in Tetramethyltin Clusters under Influence of Moderate Intensity Picosecond Laser Pulse: Role of Laser Wavelength and Rate of Energy Deposition

NASA Astrophysics Data System (ADS)

Sharma, Pramod; Das, Soumitra; Vatsa, Rajesh K.

2017-07-01

Systematic manipulation of ionic-outcome in laser-cluster interaction process has been realized for studies carried out on tetramethyltin (TMT) clusters under picosecond laser conditions, determined by choice of laser wavelength and intensity. As a function of laser intensity, TMT clusters exhibit gradual enhancement in overall ionization of its cluster constituents, up to a saturation level of ionization, which was distinct for different wavelengths (266, 355, and 532 nm). Simultaneously, systematic appearance of higher multiply charged atomic ions and shift in relative abundance of multiply charged atomic ions towards higher charge state was observed, using time-of-flight mass spectrometer. At saturation level, multiply charged atomic ions up to (C2+, Sn2+) at 266 nm, (C4+, Sn4+) at 355 nm, and (C4+, Sn6+) at 532 nm were detected. In addition, at 355 nm intra-cluster ion chemistry within the ionized cluster leads to generation of molecular hydrogen ion (H2 +) and triatomic molecular hydrogen ion (H3 +). Generation of multiply charged atomic ions is ascribed to efficient coupling of laser pulse with the cluster media, facilitated by inner-ionized electrons produced within the cluster, at the leading edge of laser pulse. Role of inner-ionized electrons is authenticated by measuring kinetic energy distribution of electrons liberated upon disintegration of excessively ionized cluster, under the influence of picosecond laser pulse.
Electronic and ionization spectra of 1,1-diamino-2,2-dinitroethylene, FOX-7.

PubMed

Borges, Itamar

2014-03-01

Singlet, triplet and ionized states of the energetic molecule 1,1-diamino-2,2-dinitroethylene, known as FOX-7 or DADNE, were investigated using the symmetry-adapted-cluster configuration interaction (SAC-CI) ab initio wave function. The 20 computed singlet transitions, with 2 exceptions, were bright. The most intense singlet transitions were of the n₀→π type-typical of molecules having nitro groups. Fast intersystem crossing (ISC) from the 1¹A, 2¹A and 8¹A bright singlet transitions is possible. Other feasible ISC processes are discussed. The computed singlet and ionization spectra have similar features when compared to nitramide and N,N-dimethylnitramine molecules, which have only a nitro group. The ionization energies of the first 20 states have differences in comparison with Koopmans' energy values that can reach 3 eV. Moreover, the character of the first ionized states, dominated by single ionizations, is not the same when compared with the character resulting from application of Koopmans' theorem.
CO2 Cluster Ion Beam, an Alternative Projectile for Secondary Ion Mass Spectrometry.

PubMed

Tian, Hua; Maciążek, Dawid; Postawa, Zbigniew; Garrison, Barbara J; Winograd, Nicholas

2016-09-01

The emergence of argon-based gas cluster ion beams for SIMS experiments opens new possibilities for molecular depth profiling and 3D chemical imaging. These beams generally leave less surface chemical damage and yield mass spectra with reduced fragmentation compared with smaller cluster projectiles. For nanoscale bioimaging applications, however, limited sensitivity due to low ionization probability and technical challenges of beam focusing remain problematic. The use of gas cluster ion beams based upon systems other than argon offer an opportunity to resolve these difficulties. Here we report on the prospects of employing CO2 as a simple alternative to argon. Ionization efficiency, chemical damage, sputter rate, and beam focus are investigated on model compounds using a series of CO2 and Ar cluster projectiles (cluster size 1000-5000) with the same mass. The results show that the two projectiles are very similar in each of these aspects. Computer simulations comparing the impact of Ar2000 and (CO2)2000 on an organic target also confirm that the CO2 molecules in the cluster projectile remain intact, acting as a single particle of m/z 44. The imaging resolution employing CO2 cluster projectiles is improved by more than a factor of two. The advantage of CO2 versus Ar is also related to the increased stability which, in addition, facilitates the operation of the gas cluster ion beams (GCIB) system at lower backing pressure. Graphical Abstract ᅟ.
A practical theoretical formalism for atomic multielectron processes: direct multiple ionization by a single auger decay or by impact of a single electron or photon

NASA Astrophysics Data System (ADS)

Liu, Pengfei; Zeng, Jiaolong; Yuan, Jianmin

2018-04-01

Multiple electron processes occur widely in atoms, molecules, clusters, and condensed matters when they are interacting with energetic particles or intense laser fields. Direct multielectron processes (DMEP) are the most complicated among the general multiple electron processes and are the most difficult to describe theoretically. In this work, a unified and accurate theoretical formalism is proposed on the DMEP of atoms including the multiple auger decay and multiple ionization by an impact of a single electron or a single photon based on the atomic collision theory described by a correlated many-body Green's function. Such a practical treatment is made possible by taking consideration of the different coherence features of the atoms (matter waves) in the initial and final states. We first explain how the coherence characteristics of the ejected continuum electrons is largely destructed, by taking the electron impact direct double ionization process as an example. The direct double ionization process is completely different from the single ionization where the complete interference can be maintained. The detailed expressions are obtained for the energy correlations among the continuum electrons and energy resolved differential and integral cross sections according to the separation of knock-out (KO) and shake-off (SO) mechanisms for the electron impact direct double ionization, direct double and triple auger decay, and double and triple photoionization (TPI) processes. Extension to higher order DMEP than triple ionization is straight forward by adding contributions of the following KO and SO processes. The approach is applied to investigate the electron impact double ionization processes of C+, N+, and O+, the direct double and triple auger decay of the K-shell excited states of C+ 1s2{s}22{p}2{}2D and {}2P, and the double and TPI of lithium. Comparisons with the experimental and other theoretical investigations wherever available in the literature show that our theoretical formalism is accurate and effective in treating the atomic multielectron processes.
Determination of ionization energies of CnN (n=4-12): Vacuum-ultraviolet (VUV) photoionization experiments and theoretical calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostko, Oleg; Zhou, Jia; Sun, Bian Jian

2010-06-10

Results from single photon vacuum ultraviolet photoionization of astrophysically relevant CnN clusters, n = 4 - 12, in the photon energy range of 8.0 eV to 12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the CnN species. A search through numerous nitrogen-terminated CnN isomers for n=4-9 indicates that the linear isomer has the lowest energy, and therefore should be the most abundant isomer in the molecular beam. Comparison with calculated results also shed light on the energetics of the linear CnN clusters, particularly in the trends of the even-carbonmore » and the odd-carbon series. These results can help guide the search of potential astronomical observations of these neutral molecules together with their cations in highly ionized regions or regions with a high UV/VUV photon flux (ranging from the visible to VUV with flux maxima in the Lyman- region) in the interstellar medium.« less
Determination of ionization energies of CnN (n=4-12): Vacuum-ultraviolet (VUV) photoionization experiments and theoretical calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostko, Oleg; Zhou, Jia; Sun, Bian Jian

2010-03-02

Results from single photon vacuum ultraviolet photoionization of astrophysically relevant CnN clusters, n = 4 - 12, in the photon energy range of 8.0 eV to 12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the CnN species. A search through numerous nitrogen-terminated CnN isomers for n=4-9 indicates that the linear isomer has the lowest energy, and therefore should be the most abundant isomer in the molecular beam. Comparison with calculated results also shed light on the energetics of the linear CnN clusters, particularly in the trends of the even-carbonmore » and the odd-carbon series. These results can help guide the search of potential astronomical observations of these neutral molecules together with their cations in highly ionized regions or regions with a high UV/VUV photon flux (ranging from the visible to VUV with flux maxima in the Lyman-a region) in the interstellar medium.« less
Improvements in Ionized Cluster-Beam Deposition

NASA Technical Reports Server (NTRS)

Fitzgerald, D. J.; Compton, L. E.; Pawlik, E. V.

1986-01-01

Lower temperatures result in higher purity and fewer equipment problems. In cluster-beam deposition, clusters of atoms formed by adiabatic expansion nozzle and with proper nozzle design, expanding vapor cools sufficiently to become supersaturated and form clusters of material deposited. Clusters are ionized and accelerated in electric field and then impacted on substrate where films form. Improved cluster-beam technique useful for deposition of refractory metals.
Non-ideal magnetohydrodynamic simulations of the two-stage fragmentation model for cluster formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Nicole D.; Basu, Shantanu, E-mail: N.Bailey@leeds.ac.uk, E-mail: basu@uwo.ca

2014-01-01

We model molecular cloud fragmentation with thin-disk, non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and partial ionization that transitions from primarily ultraviolet-dominated to cosmic-ray-dominated regimes. These simulations are used to determine the conditions required for star clusters to form through a two-stage fragmentation scenario. Recent linear analyses have shown that the fragmentation length scales and timescales can undergo a dramatic drop across the column density boundary that separates the ultraviolet- and cosmic-ray-dominated ionization regimes. As found in earlier studies, the absence of an ionization drop and regular perturbations leads to a single-stage fragmentation on pc scales in transcritical clouds, somore » that the nonlinear evolution yields the same fragment sizes as predicted by linear theory. However, we find that a combination of initial transcritical mass-to-flux ratio, evolution through a column density regime in which the ionization drop takes place, and regular small perturbations to the mass-to-flux ratio is sufficient to cause a second stage of fragmentation during the nonlinear evolution. Cores of size ∼0.1 pc are formed within an initial fragment of ∼pc size. Regular perturbations to the mass-to-flux ratio also accelerate the onset of runaway collapse.« less
Radiation-induced gene expression in the nematode Caenorhabditis elegans

NASA Technical Reports Server (NTRS)

Nelson, Gregory A.; Jones, Tamako A.; Chesnut, Aaron; Smith, Anna L.

2002-01-01

We used the nematode C. elegans to characterize the genotoxic and cytotoxic effects of ionizing radiation in a simple animal model emphasizing the unique effects of charged particle radiation. Here we demonstrate by RT-PCR differential display and whole genome microarray hybridization experiments that gamma rays, accelerated protons and iron ions at the same physical dose lead to unique transcription profiles. 599 of 17871 genes analyzed (3.4%) showed differential expression 3 hrs after exposure to 3 Gy of radiation. 193 were up-regulated, 406 were down-regulated and 90% were affected only by a single species of radiation. A novel statistical clustering technique identified the regulatory relationships between the radiation-modulated genes and showed that genes affected by each radiation species were associated with unique regulatory clusters. This suggests that independent homeostatic mechanisms are activated in response to radiation exposure as a function of track structure or ionization density.
Density functional study of the structural, electronic, and magnetic properties of Mo n and Mo n S ( n = 1 - 10) clusters

NASA Astrophysics Data System (ADS)

Ziane, M.; Amitouche, F.; Bouarab, S.; Vega, A.

2017-12-01

Structural and electronic properties of pure molybdenum Mo n and molybdenum-sulfide Mo n S ( n = 1 - 10) clusters were investigated in the framework of the density functional theory within the generalized gradient approximation to exchange and correlation with the aim of addressing how doping with a single S atom affects the geometries, magnetic properties, and reactivity of pure molybdenum clusters. These clusters exhibit a less marked tendency to dimerization than their isoelectronic Cr counterparts despite sharing their half-filled valence shell configuration. Doping with a single S impurity is enough to change the structure of the host molybdenum cluster to a large extent, as well as to modify the bonding pattern, the magnetic state and the magnetic moment distribution in the Mo host. Vertical ionization potentials and electron affinities are calculated to determine global reactivity indicators like the electronegativity and the chemical hardness. The results are discussed in terms of the thermodynamical and relative stabilities, charge transfer effects, and spin-polarized densities of electronic states.
Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters

NASA Astrophysics Data System (ADS)

Neustetter, Michael; Mahmoodi-Darian, Masoomeh; Denifl, Stephan

2017-05-01

Mass spectroscopic investigations on tetrahydrofuran (THF, C4H8O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy 70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C4D8O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters.

Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verkhoturov, Stanislav V.; Geng, Sheng; Schweikert, Emile A., E-mail: schweikert@chem.tamu.edu

We present the first data from individual C{sub 60} impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C{sub n}{sup −} clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimentalmore » yields of C{sub n}{sup −} with those of C{sub n}{sup 0} from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C{sub n}{sup −} emission can also explain the emission of electrons. The interaction of C{sub 60} with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.« less
Blue emitting undecaplatinum clusters

NASA Astrophysics Data System (ADS)

Chakraborty, Indranath; Bhuin, Radha Gobinda; Bhat, Shridevi; Pradeep, T.

2014-07-01

A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents. Electronic supplementary information (ESI) available: Details of experimental procedures, instrumentation, chromatogram of the crude cluster; SEM/EDAX, DLS, PXRD, TEM, FT-IR, and XPS of the isolated Pt11 cluster; UV/Vis, MALDI MS and SEM/EDAX of isolated 2 and 3; and 195Pt NMR of the K2PtCl6 standard. See DOI: 10.1039/c4nr02778g
Relaxation times measurement in single and multiply excited xenon clusters

NASA Astrophysics Data System (ADS)

Serdobintsev, P. Yu.; Melnikov, A. S.; Pastor, A. A.; Timofeev, N. A.; Khodorkovskiy, M. A.

2018-05-01

Direct measurement of the rates of nonradiative relaxation processes in electronically excited xenon clusters was carried out. The clusters were created in a pulsed supersonic beam and two-photon excited by femtosecond laser pulses with a wavelength of 263 nm. The measurements were performed using the pump-probe method and electron spectroscopy. It is shown that relaxation of light clusters XeN (N < 15) predominantly occurs by desorption of excited xenon atoms with a characteristic time constant of 3 ps. Heavier electronically excited clusters (N > 10) vibrationally relax to the lowest electronically excited state at a rate of about 0.075 eV/ps. Multiply excited clusters are deactivated via energy exchange between excited centers with the ionization of one of them. The production of electrons in this process occurs with a delay of ˜4 ps from the pump pulse, and the process is completed in 10 ps.
High-resolution electron spectroscopy of lanthanide (Ce, Pr, and Nd) complexes of cyclooctatetraene: the role of 4f electrons.

PubMed

Kumari, Sudesh; Roudjane, Mourad; Hewage, Dilrukshi; Liu, Yang; Yang, Dong-Sheng

2013-04-28

Cerium, praseodymium, and neodymium complexes of 1,3,5,7-cyclooctatetraene (COT) complexes were produced in a laser-vaporization metal cluster source and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and quantum chemical calculations. The computations included the second-order Møller-Plesset perturbation theory, the coupled cluster method with single, double, and perturbative triple excitations, and the state-average complete active space self-consistent field method. The spectrum of each complex exhibits multiple band systems and is assigned to ionization of several low-energy electronic states of the neutral complex. This observation is different from previous studies of M(COT) (M = Sc, Y, La, and Gd), for which a single band system was observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field, and the number of the low-energy states increases rapidly with increasing number of the metal 4f electrons. On the other hand, the 4f electrons have a small effect on the geometries and vibrational frequencies of these lanthanide complexes.
Elimination-Fusion Self-Assembly of a Nanometer-Scale 72-Nucleus Silver Cluster Caging a Pair of [EuW10 O36 ]9- Polyoxometalates.

PubMed

Zhang, Shan-Shan; Su, Hai-Feng; Wang, Zhi; Wang, Xing-Po; Chen, Wen-Xian; Zhao, Quan-Qin; Tung, Chen-Ho; Sun, Di; Zheng, Lan-Sun

2018-02-06

The largest known polyoxometalate (POM)-templated silver-alkynyl cluster, [(EuW 10 O 36 ) 2 @Ag 72 (tBuC≡C) 48 Cl 2 ⋅4 BF 4 ] (SD/Ag20), was isolated under solvothermal conditions and structurally characterized. It was confirmed by single-crystal X-ray diffraction (SCXRD) as a {EuW 10 } 2 -in-{Ag 72 } clusters-in-cluster rod-like compound. The high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) shows that such a double anion-templated cluster is assembled from a crucial single anion-templated Ag 42 intermediate in the solution. The crystallization of Ag 42 species (SD/Ag21), followed by SCXRD, gave an important clue about the assembly route of SD/Ag20 in solution: the Ag 42 cluster eliminates six silver atoms laterally, then fuses together at the vacant face to form the final Ag 72 cluster (elimination-fusion mechanism). The characteristic emission of [EuW 10 O 36 ] 9- is well maintained in SD/Ag20. This work not only provides a new method for the synthesis of larger silver clusters as well as the functional integration of the silver cluster and POMs, but also gives deep insights about the high-nuclear silver cluster assembly mechanism. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Penning ionization electron spectroscopy of CO 2 clusters in collision with metastable rare gas atoms

NASA Astrophysics Data System (ADS)

Maruyama, Ryo; Tanaka, Hideyasu; Yamakita, Yoshihiro; Misaizu, Fuminori; Ohno, Koichi

2000-09-01

Penning ionization electron spectra (PIES) of CO 2 clusters have been observed for the first time. An unusually fast electron band with excess kinetic energies of 1.4-2.9 eV with respect to the monomer band for the ionic X state was observed for CO 2 clusters in collision with He*(2 3S) atoms. While for PIES with Ne*(3 3P), no such unusual band was observed. The unusual band is ascribed to autoionization into stable structures of ionic clusters to which direct ionization processes are almost impossible due to very small Franck-Condon overlaps associated with a very large geometry difference between the ionic and neutral clusters.
Experimental and theoretical study of the microsolvation of sodium atoms in methanol clusters: differences and similarities to sodium-water and sodium-ammonia.

PubMed

Dauster, Ingo; Suhm, Martin A; Buck, Udo; Zeuch, Thomas

2008-01-07

Methanol clusters are generated in a continuous He-seeded supersonic expansion and doped with sodium atoms in a pick-up cell. By this method, clusters of the type Na(CH(3)OH)(n) are formed and subsequently photoionized by applying a tunable dye-laser system. The microsolvation process of the Na 3s electron is studied by determining the ionization potentials (IPs) of these clusters size-selectively for n = 2-40. A decrease is found from n = 2 to 6 and a constant value of 3.19 +/- 0.07 eV for n = 6-40. The experimentally-determined ionization potentials are compared with ionization potentials derived from quantum-chemical calculations, assuming limiting vertical and adiabatic processes. In the first case, energy differences are calculated between the neutral and the ionized cationic clusters of the same geometry. In the second case, the ionized clusters are used in their optimized relaxed geometry. These energy differences and relative stabilities of isomeric clusters vary significantly with the applied quantum-chemical method (B3LYP or MP2). The comparison with the experiment for n = 2-7 reveals strong variations of the ionization potential with the cluster structure indicating that structural diversity and non-vertical pathways give significant signal contributions at the threshold. Based on these findings, a possible explanation for the remarkable difference in IP evolutions of methanol or water and ammonia is presented: for methanol and water a rather localized surface or semi-internal Na 3s electron is excited to either high Rydberg or more localized states below the vertical ionization threshold. This excitation is followed by a local structural relaxation that couples to an autoionization process. For small clusters with n < 6 for methanol and n < 4 for water the addition of solvent molecules leads to larger solvent-metal-ion interaction energies, which consequently lead to lower ionization thresholds. For n = 6 (methanol) and n = 4 (water) this effect comes to a halt, which may be connected with the completion of the first cationic solvation shell limiting the release of local relaxation energy. For Na(NH(3))(n), a largely delocalized and internal electron is excited to autoionizing electronic states, a process that is no longer local and consequently may depend on cluster size up to very large n.
Equation-of-motion coupled-cluster method for doubly ionized states with spin-orbit coupling.

PubMed

Wang, Zhifan; Hu, Shu; Wang, Fan; Guo, Jingwei

2015-04-14

In this work, we report implementation of the equation-of-motion coupled-cluster method for doubly ionized states (EOM-DIP-CC) with spin-orbit coupling (SOC) using a closed-shell reference. Double ionization potentials (DIPs) are calculated in the space spanned by 2h and 3h1p determinants with the EOM-DIP-CC approach at the CC singles and doubles level (CCSD). Time-reversal symmetry together with spatial symmetry is exploited to reduce computational effort. To circumvent the problem of unstable dianion references when diffuse basis functions are included, nuclear charges are scaled. Effect of this stabilization potential on DIPs is estimated based on results from calculations using a small basis set without diffuse basis functions. DIPs and excitation energies of some low-lying states for a series of open-shell atoms and molecules containing heavy elements with two unpaired electrons have been calculated with the EOM-DIP-CCSD approach. Results show that this approach is able to afford a reliable description on SOC splitting. Furthermore, the EOM-DIP-CCSD approach is shown to provide reasonable excitation energies for systems with a dianion reference when diffuse basis functions are not employed.
Equation-of-motion coupled-cluster method for doubly ionized states with spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhifan; Hu, Shu; Guo, Jingwei

2015-04-14

In this work, we report implementation of the equation-of-motion coupled-cluster method for doubly ionized states (EOM-DIP-CC) with spin-orbit coupling (SOC) using a closed-shell reference. Double ionization potentials (DIPs) are calculated in the space spanned by 2h and 3h1p determinants with the EOM-DIP-CC approach at the CC singles and doubles level (CCSD). Time-reversal symmetry together with spatial symmetry is exploited to reduce computational effort. To circumvent the problem of unstable dianion references when diffuse basis functions are included, nuclear charges are scaled. Effect of this stabilization potential on DIPs is estimated based on results from calculations using a small basis setmore » without diffuse basis functions. DIPs and excitation energies of some low-lying states for a series of open-shell atoms and molecules containing heavy elements with two unpaired electrons have been calculated with the EOM-DIP-CCSD approach. Results show that this approach is able to afford a reliable description on SOC splitting. Furthermore, the EOM-DIP-CCSD approach is shown to provide reasonable excitation energies for systems with a dianion reference when diffuse basis functions are not employed.« less
Early stages of styrene-isoprene copolymerization in gas phase clusters probed by resonance enhanced multiphoton ionization.

PubMed

Mahmoud, Hatem; Germanenko, Igor N; El-Shall, M Samy

2006-04-06

We present direct evidence for the formation of the covalent bonded styrene (isoprene)(2) oligomer and the isoprene dimer ions following resonance ionization of the gas phase styrene-isoprene binary clusters. The application of resonance ionization to study polymerization reactions in clusters provides new information on the structure and mechanism of formation of the early stages of polymerization and holds considerable promise for the discovery of new initiation mechanisms and for the development of novel materials with unique properties.
Observation of novel photochemistry in the multiphoton ionization of Mo(CO) sub 6 van der Waals clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peifer, W.R.; Garvey, J.F.

1989-07-27

van der Waals clusters of Mo(CO){sub 6} generated in the free-jet expansion of a pulsed beam of seeded helium are subjected to multiphoton ionization and the product ions analyzed by quadrupole mass spectrometry. Oxomolybdenum and dioxomolybdenum ions are observed to be produced with high efficiency. This behavior is in striking contrast to that of metal carbonyl monomers and covalently bound cluster carbonyls, which under complete ligand loss prior to ionization. The observed photochemistry is ascribed to reactions between a photoproduced molybdenum atom and the ligands of neighboring Mo(CO){sub 6} solvent molecules within the van der Waals cluster.
Secondary ion formation during electronic and nuclear sputtering of germanium

NASA Astrophysics Data System (ADS)

Breuer, L.; Ernst, P.; Herder, M.; Meinerzhagen, F.; Bender, M.; Severin, D.; Wucher, A.

2018-06-01

Using a time-of-flight mass spectrometer attached to the UNILAC beamline located at the GSI Helmholtz Centre for Heavy Ion Research, we investigate the formation of secondary ions sputtered from a germanium surface under irradiation by swift heavy ions (SHI) such as 5 MeV/u Au by simultaneously recording the mass spectra of the ejected secondary ions and their neutral counterparts. In these experiments, the sputtered neutral material is post-ionized via single photon absorption from a pulsed, intensive VUV laser. After post-ionization, the instrument cannot distinguish between secondary ions and post-ionized neutrals, so that both signals can be directly compared in order to investigate the ionization probability of different sputtered species. In order to facilitate an in-situ comparison with typical nuclear sputtering conditions, the system is also equipped with a conventional rare gas ion source delivering a 5 keV argon ion beam. For a dynamically sputter cleaned surface, it is found that the ionization probability of Ge atoms and Gen clusters ejected under electronic sputtering conditions is by more than an order of magnitude higher than that measured for keV sputtered particles. In addition, the mass spectra obtained under SHI irradiation show prominent signals of GenOm clusters, which are predominantly detected as positive or negative secondary ions. From the m-distribution for a given Ge nuclearity n, one can deduce that the sputtered material must originate from a germanium oxide matrix with approximate GeO stoichiometry, probably due to residual native oxide patches even at the dynamically cleaned surface. The results clearly demonstrate a fundamental difference between the ejection and ionization mechanisms in both cases, which is interpreted in terms of corresponding model calculations.
Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

DOE PAGES

Kim, Michelle J.; Zoerb, Matthew C.; Campbell, Nicole R.; ...

2016-04-05

Here, benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt −1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through amore » combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated ( R 2 > 0.95, 10 s averages) over a wide range of sampling conditions.« less
Revealing isomerism in sodium-water clusters: Photoionization spectra of Na(H2O)n (n = 2-90)

NASA Astrophysics Data System (ADS)

Dierking, Christoph W.; Zurheide, Florian; Zeuch, Thomas; Med, Jakub; Parez, Stanislav; Slavíček, Petr

2017-06-01

Soft ionization of sodium tagged polar clusters is increasingly used as a powerful technique for sizing and characterization of small aerosols with possible application, e.g., in atmospheric chemistry or combustion science. Understanding the structure and photoionization of the sodium doped clusters is critical for such applications. In this work, we report on measurements of photoionization spectra for sodium doped water clusters containing 2-90 water molecules. While most of the previous studies focused on the ionization threshold of the Na(H2O)n clusters, we provide for the first time full photoionization spectra, including the high-energy region, which are used as reference for a comparison with theory. As reported in previous work, we have seen an initial drop of the appearance ionization energy with cluster size to values of about 3.2 eV for n <5 . In the size range from n = 5 to n = 15, broad ion yield curves emerge; for larger clusters, a constant range between signal appearance (˜2.8 eV) and signal saturation (˜4.1 eV) has been observed. The measurements are interpreted with ab initio calculations and ab initio molecular dynamics simulations for selected cluster sizes (n ≤ 15). The simulations revealed theory shortfalls when aiming at quantitative agreement but allowed us identifying structural motifs consistent with the observed ionization energy distributions. We found a decrease in the ionization energy with increasing coordination of the Na atom and increasing delocalization of the Na 3s electron cloud. The appearance ionization energy is determined by isomers with fully solvated sodium and a highly delocalized electron cloud, while both fully and incompletely solvated isomers with localized electron clouds can contribute to the high energy part of the photoionization spectrum. Simulations at elevated temperatures show an increased abundance of isomers with low ionization energies, an entropic effect enabling size selective infrared action spectroscopy, based on near threshold photoionization of Na(H2O)n clusters. In addition, simulations of the sodium pick-up process were carried out to study the gradual formation of the hydrated electron which is the basis of the sodium-tagging sizing.
Revealing isomerism in sodium-water clusters: Photoionization spectra of Na(H2O)n (n = 2-90).

PubMed

Dierking, Christoph W; Zurheide, Florian; Zeuch, Thomas; Med, Jakub; Parez, Stanislav; Slavíček, Petr

2017-06-28

Soft ionization of sodium tagged polar clusters is increasingly used as a powerful technique for sizing and characterization of small aerosols with possible application, e.g., in atmospheric chemistry or combustion science. Understanding the structure and photoionization of the sodium doped clusters is critical for such applications. In this work, we report on measurements of photoionization spectra for sodium doped water clusters containing 2-90 water molecules. While most of the previous studies focused on the ionization threshold of the Na(H 2 O) n clusters, we provide for the first time full photoionization spectra, including the high-energy region, which are used as reference for a comparison with theory. As reported in previous work, we have seen an initial drop of the appearance ionization energy with cluster size to values of about 3.2 eV for n<5. In the size range from n = 5 to n = 15, broad ion yield curves emerge; for larger clusters, a constant range between signal appearance (∼2.8 eV) and signal saturation (∼4.1 eV) has been observed. The measurements are interpreted with ab initio calculations and ab initio molecular dynamics simulations for selected cluster sizes (n≤ 15). The simulations revealed theory shortfalls when aiming at quantitative agreement but allowed us identifying structural motifs consistent with the observed ionization energy distributions. We found a decrease in the ionization energy with increasing coordination of the Na atom and increasing delocalization of the Na 3s electron cloud. The appearance ionization energy is determined by isomers with fully solvated sodium and a highly delocalized electron cloud, while both fully and incompletely solvated isomers with localized electron clouds can contribute to the high energy part of the photoionization spectrum. Simulations at elevated temperatures show an increased abundance of isomers with low ionization energies, an entropic effect enabling size selective infrared action spectroscopy, based on near threshold photoionization of Na(H 2 O) n clusters. In addition, simulations of the sodium pick-up process were carried out to study the gradual formation of the hydrated electron which is the basis of the sodium-tagging sizing.
Formation of positive cluster ions Li(n) Br (n = 2-7) and ionization energies studied by thermal ionization mass spectrometry.

PubMed

Veličković, S R; Đustebek, J B; Veljković, F M; Veljković, M V

2012-05-01

Clusters of the type Li(n)X (X = halides) can be considered as potential building blocks of cluster-assembly materials. In this work, Li(n)Br (n = 2-7) clusters were obtained by a thermal ionization source of modified design and selected by a magnetic sector mass spectrometer. Positive ions of the Li(n)Br (n = 4-7) cluster were detected for the first time. The order of ion intensities was Li(2)Br(+) > Li(4)Br(+) > Li(5)Br(+) > Li(6)Br(+) > Li(3)Br(+). The ionization energies (IEs) were measured and found to be 3.95 ± 0.20 eV for Li(2)Br, 3.92 ± 0.20 eV for Li(3)Br, 3.93 ± 0.20 eV for Li(4)Br, 4.08 ± 0.20 eV for Li(5)Br, 4.14 ± 0.20 eV for Li(6)Br and 4.19 ± 0.20 eV for Li(7)Br. All of these clusters have a much lower ionization potential than that of the lithium atom, so they belong to the superalkali class. The IEs of Li(n)Br (n = 2-4) are slightly lower than those in the corresponding small Li(n) or Li(n)H clusters, whereas the IEs of Li(n)Br are very similar to those of Li(n) or Li(n)H for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of Li(n)Br (n = 2-7) clusters (because their ions are hermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications. Copyright © 2012 John Wiley & Sons, Ltd.
Nanosecond laser-cluster interactions at 109-1012 W/cm 2

NASA Astrophysics Data System (ADS)

Singh, Rohtash; Tripathi, V. K.; Vatsa, R. K.; Das, D.

2017-08-01

An analytical model and a numerical code are developed to study the evolution of multiple charge states of ions by irradiating clusters of atoms of a high atomic number (e.g., Xe) by 1.06 μm and 0.53 μm nanosecond laser pulses of an intensity in the range of 109-1012 W/cm 2 . The laser turns clusters into plasma nanoballs. Initially, the momentum randomizing collisions of electrons are with neutrals, but soon these are taken over by collisions with ions. The ionization of an ion to the next higher state of ionization is taken to be caused by an energetic free electron impact, and the rates of impact ionization are suitably modelled by having an inverse exponential dependence of ionizing collision frequency on the ratio of ionization potential to electron temperature. Cluster expansion led adiabatic cooling is a major limiting mechanism on electron temperature. In the intensity range considered, ionization states up to 7 are expected with nanosecond pulses. Another possible mechanism, filamentation of the laser, has also been considered to account for the observation of higher charged states. However, filamentation is seen to be insufficient to cause substantial local enhancement in the intensity to affect electron heating rates.
Matrix Assisted and/or Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of WO3 Clusters Formation in Gas Phase. Nanodiamonds, Fullerene, and Graphene Oxide Matrices

NASA Astrophysics Data System (ADS)

Ausekar, Mayuri Vilas; Mawale, Ravi Madhukar; Pazdera, Pavel; Havel, Josef

2018-03-01

The formation of W x O y +●/-● clusters in the gas phase was studied by laser desorption ionization (LDI) and matrix assisted laser desorption ionization (MALDI) of solid WO3. LDI produced (WO3) n + ●/- ● ( n = 1-7) clusters. In MALDI, when using nano-diamonds (NDs), graphene oxide (GO), or fullerene (C60) matrices, higher mass clusters were generated. In addition to (WO3) n -● clusters, oxygen-rich or -deficient species were found in both LDI and MALDI (with the total number of clusters exceeding one hundred ≈ 137). This is the first time that such matrices have been used for the generation of(WO3) n + ●/-● clusters in the gas phase, while new high mass clusters (WO3) n -● ( n = 12-19) were also detected. [Figure not available: see fulltext.
ULTRAVIOLET ESCAPE FRACTIONS FROM GIANT MOLECULAR CLOUDS DURING EARLY CLUSTER FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, Corey; Pudritz, Ralph; Klessen, Ralf

2017-01-01

The UV photon escape fraction from molecular clouds is a key parameter for understanding the ionization of the interstellar medium and extragalactic processes such as cosmic reionization. We present the ionizing photon flux and the corresponding photon escape fraction ( f {sub esc}) arising as a consequence of star cluster formation in a turbulent, 10{sup 6} M {sub ⊙} giant molecular cloud, simulated using the code FLASH. We make use of sink particles to represent young, star-forming clusters coupled with a radiative transfer scheme to calculate the emergent UV flux. We find that the ionizing photon flux across the cloudmore » boundary is highly variable in time and space due to the turbulent nature of the intervening gas. The escaping photon fraction remains at ∼5% for the first 2.5 Myr, followed by two pronounced peaks at 3.25 and 3.8 Myr with a maximum f {sub esc} of 30% and 37%, respectively. These peaks are due to the formation of large H ii regions that expand into regions of lower density, some of which reaching the cloud surface. However, these phases are short-lived, and f {sub esc} drops sharply as the H ii regions are quenched by the central cluster passing through high-density material due to the turbulent nature of the cloud. We find an average f {sub esc} of 15% with factor of two variations over 1 Myr timescales. Our results suggest that assuming a single value for f {sub esc} from a molecular cloud is in general a poor approximation, and that the dynamical evolution of the system leads to large temporal variation.« less
Influence of the geometrical detail in the description of DNA and the scoring method of ionization clustering on nanodosimetric parameters of track structure: a Monte Carlo study using Geant4-DNA

NASA Astrophysics Data System (ADS)

Bueno, M.; Schulte, R.; Meylan, S.; Villagrasa, C.

2015-11-01

The aim of this study was to evaluate the influence of the geometrical detail of the DNA on nanodosimetric parameters of track structure induced by protons and alpha particles of different energies (LET values ranging from 1 to 162.5~\\text{keV}~μ {{\\text{m}}-1} ) as calculated by Geant4-DNA Monte Carlo simulations. The first geometry considered consisted of a well-structured placement of a realistic description of the DNA double helix wrapped around cylindrical histones (GeomHist) forming a 18 kbp-long chromatin fiber. In the second geometry considered, the DNA was modeled as a total of 1800 ten bp-long homogeneous cylinders (2.3 nm diameter and 3.4 nm height) placed in random positions and orientations (GeomCyl). As for GeomHist, GeomCyl contained a DNA material equivalent to 18 kbp. Geant4-DNA track structure simulations were performed and ionizations were counted in the scoring volumes. For GeomCyl, clusters were defined as the number of ionizations (ν) scored in each 10 bp-long cylinder. For GeomHist, clusters of ionizations scored in the sugar-phosphate groups of the double-helix were revealed by the DBSCAN clustering algorithm according to a proximity criteria among ionizations separated by less than 10 bp. The topology of the ionization clusters formed using GeomHist and GeomCyl geometries were compared in terms of biologically relevant nanodosimetric quantities. The discontinuous modeling of the DNA for GeomCyl led to smaller cluster sizes than for GeomHist. The continuous modeling of the DNA molecule for GeomHist allowed the merging of ionization points by the DBSCAN algorithm giving rise to larger clusters, which were not detectable within the GeomCyl geometry. Mean cluster size (m1) was found to be of the order of 10% higher for GeomHist compared to GeomCyl for LET <15~\\text{keV}~μ {{\\text{m}}-1} . For higher LETs, the difference increased with LET similarly for protons and alpha particles. Both geometries showed the same relationship between m1 and the cumulative relative frequency of clusters with ν ≥slant 3 (f3) within statistical variations, independently of particle type. In order to obtain ionization cluster size distributions relevant for biological DNA lesions, the complex DNA geometry and a scoring method without fixed boundaries should be preferred to the simple cylindrical geometry with a fixed scoring volume.

On the SIMS Ionization Probability of Organic Molecules.

PubMed

Popczun, Nicholas J; Breuer, Lars; Wucher, Andreas; Winograd, Nicholas

2017-06-01

The prospect of improved secondary ion yields for secondary ion mass spectrometry (SIMS) experiments drives innovation of new primary ion sources, instrumentation, and post-ionization techniques. The largest factor affecting secondary ion efficiency is believed to be the poor ionization probability (α + ) of sputtered material, a value rarely measured directly, but estimated to be in some cases as low as 10 -5 . Our lab has developed a method for the direct determination of α + in a SIMS experiment using laser post-ionization (LPI) to detect neutral molecular species in the sputtered plume for an organic compound. Here, we apply this method to coronene (C 24 H 12 ), a polyaromatic hydrocarbon that exhibits strong molecular signal during gas-phase photoionization. A two-dimensional spatial distribution of sputtered neutral molecules is measured and presented. It is shown that the ionization probability of molecular coronene desorbed from a clean film under bombardment with 40 keV C 60 cluster projectiles is of the order of 10 -3 , with some remaining uncertainty arising from laser-induced fragmentation and possible differences in the emission velocity distributions of neutral and ionized molecules. In general, this work establishes a method to estimate the ionization efficiency of molecular species sputtered during a single bombardment event. Graphical Abstract .
An integrated experimental and theoretical reaction path search: analyses of the multistage reaction of an ionized diethylether dimer involving isomerization, proton transfer, and dissociation.

PubMed

Matsuda, Yoshiyuki; Xie, Min; Fujii, Asuka

2018-05-30

An ionization-induced multistage reaction of an ionized diethylether (DEE) dimer involving isomerization, proton transfer, and dissociation is investigated by combining infrared (IR) spectroscopy, tandem mass spectrometry, and a theoretical reaction path search. The vertically-ionized DEE dimer isomerizes to a hydrogen-bonded cluster of protonated DEE and the [DEE-H] radical through barrierless intermolecular proton transfer from the CH bond of the ionized moiety. This isomerization process is confirmed by IR spectroscopy and the theoretical reaction path search. The multiple dissociation pathways following the isomerization are analyzed by tandem mass spectrometry. The isomerized cluster dissociates stepwise into a [protonated DEE-acetaldehyde (AA)] cluster, protonated DEE, and protonated AA. The structure of the fragment ion is also analyzed by IR spectroscopy. The reaction map of the multistage processes is revealed through a harmony of these experimental and theoretical methods.
Angle-Resolved Photoemission of Solvated Electrons in Sodium-Doped Clusters.

PubMed

West, Adam H C; Yoder, Bruce L; Luckhaus, David; Saak, Clara-Magdalena; Doppelbauer, Maximilian; Signorell, Ruth

2015-04-16

Angle-resolved photoelectron spectroscopy of the unpaired electron in sodium-doped water, methanol, ammonia, and dimethyl ether clusters is presented. The experimental observations and the complementary calculations are consistent with surface electrons for the cluster size range studied. Evidence against internally solvated electrons is provided by the photoelectron angular distribution. The trends in the ionization energies seem to be mainly determined by the degree of hydrogen bonding in the solvent and the solvation of the ion core. The onset ionization energies of water and methanol clusters do not level off at small cluster sizes but decrease slightly with increasing cluster size.
Ionization energies and electron affinities from a random-phase-approximation many-body Green's-function method including exchange interactions

NASA Astrophysics Data System (ADS)

Heßelmann, Andreas

2017-06-01

A many-body Green's-function method employing an infinite order summation of ring and exchange-ring contributions to the self-energy is presented. The individual correlation and relaxation contributions to the quasiparticle energies are calculated using an iterative scheme which utilizes density fitting of the particle-hole, particle-particle and hole-hole densities. It is shown that the ionization energies and electron affinities of this approach agree better with highly accurate coupled-cluster singles and doubles with perturbative triples energy difference results than those obtained with second-order Green's-function approaches. An analysis of the correlation and relaxation terms of the self-energy for the direct- and exchange-random-phase-approximation (RPA) Green's-function methods shows that the inclusion of exchange interactions leads to a reduction of the two contributions in magnitude. These differences, however, strongly cancel each other when summing the individual terms to the quasiparticle energies. Due to this, the direct- and exchange-RPA methods perform similarly for the description of ionization energies (IPs) and electron affinities (EAs). The coupled-cluster reference IPs and EAs, if corrected to the adiabatic energy differences between the neutral and charged molecules, were shown to be in very good agreement with experimental measurements.
Multistep Ionization of Argon Clusters in Intense Femtosecond Extreme Ultraviolet Pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bostedt, C.; Thomas, H.; Hoener, M.

The interaction of intense extreme ultraviolet femtosecond laser pulses ({lambda}=32.8 nm) from the FLASH free electron laser (FEL) with clusters has been investigated by means of photoelectron spectroscopy and modeled by Monte Carlo simulations. For laser intensities up to 5x10{sup 13} W/cm{sup 2}, we find that the cluster ionization process is a sequence of direct electron emission events in a developing Coulomb field. A nanoplasma is formed only at the highest investigated power densities where ionization is frustrated due to the deep cluster potential. In contrast with earlier studies in the IR and vacuum ultraviolet spectral regime, we find nomore » evidence for electron emission from plasma heating processes.« less
Photometric properties of stars clusters with young or mixed age stellar populations

NASA Astrophysics Data System (ADS)

Mollá, M.; García-Vargas, M. L.; Martín-Manjón, M. L.

2013-05-01

The main goal of this work is to present and discuss the synthetic photometrical properties of stellar clusters resulting from the PopStar code. Colors in Johnson and SDSS systems, Hα and Hβ luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicities Z = 0.0001, 0.0004, 0.004,0.008,0.02 and 0.05, and ages, from 0.1 Myr to 20 Gyr in Mollá, Garc{í}a-Vargas, & Bressan (2009, MNRAS, 398, 451). Emission lines are shown in Mart{í}n-Manj{ó}n et al. (2010, MNRAS, 403, 2012). Now we calculate colors with the emission lines contribution to the broad band color, so colors include stellar and nebular components, plus the emission lines following the evolution of the cluster and the region geometry in a consistent way. We compare the Single Stellar Populations contaminated and uncontaminated colors (in both Johnson and SDSS systems) and show the importance of emission lines contribution when photometry is used as a tool to characterize stellar populations. With these models we may determine the physical properties of young ionizing clusters when only photometrical observations are available and these correspond to the isolated star forming regions, subtracted the contribution of the underlying population In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometrical properties are the result of the combination of both the young star-forming burst and the host-underlying older population. The second objective of our work is therefore to provide a grid of models for nearby galaxies able to interpret mixed regions where the separation of young and old population is not possible or reliable enough. We obtain a set of PopStar Spectral Energy Distributions (available at PopStar site and also in VO) and derived colors for mixed populations where an underlying host population is combined in different mass ratios with a recent, metal-rich ionizing burst. These colors, together with other photometrical parameters, like Hα radius of the ionized region, and Balmer lines equivalent width and luminosity allow to infer the physical properties of star-forming regions without any spectroscopic information. For details and a complete set of tables and figures see Mollá, García-Vargas, & Martín-Manjón (2012, MNRAS, submitted).
Water cluster fragmentation probed by pickup experiments

NASA Astrophysics Data System (ADS)

Huang, Chuanfu; Kresin, Vitaly V.; Pysanenko, Andriy; Fárník, Michal

2016-09-01

Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ˜3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics.
Radiation-Induced Chemical Dynamics in Ar Clusters Exposed to Strong X-Ray Pulses.

PubMed

Kumagai, Yoshiaki; Jurek, Zoltan; Xu, Weiqing; Fukuzawa, Hironobu; Motomura, Koji; Iablonskyi, Denys; Nagaya, Kiyonobu; Wada, Shin-Ichi; Mondal, Subhendu; Tachibana, Tetsuya; Ito, Yuta; Sakai, Tsukasa; Matsunami, Kenji; Nishiyama, Toshiyuki; Umemoto, Takayuki; Nicolas, Christophe; Miron, Catalin; Togashi, Tadashi; Ogawa, Kanade; Owada, Shigeki; Tono, Kensuke; Yabashi, Makina; Son, Sang-Kil; Ziaja, Beata; Santra, Robin; Ueda, Kiyoshi

2018-06-01

We show that electron and ion spectroscopy reveals the details of the oligomer formation in Ar clusters exposed to an x-ray free electron laser (XFEL) pulse, i.e., chemical dynamics triggered by x rays. With guidance from a dedicated molecular dynamics simulation tool, we find that van der Waals bonding, the oligomer formation mechanism, and charge transfer among the cluster constituents significantly affect ionization dynamics induced by an XFEL pulse of moderate fluence. Our results clearly demonstrate that XFEL pulses can be used not only to "damage and destroy" molecular assemblies but also to modify and transform their molecular structure. The accuracy of the predictions obtained makes it possible to apply the cluster spectroscopy, in connection with the respective simulations, for estimation of the XFEL pulse fluence in the fluence regime below single-atom multiple-photon absorption, which is hardly accessible with other diagnostic tools.
Radiation-Induced Chemical Dynamics in Ar Clusters Exposed to Strong X-Ray Pulses

NASA Astrophysics Data System (ADS)

Kumagai, Yoshiaki; Jurek, Zoltan; Xu, Weiqing; Fukuzawa, Hironobu; Motomura, Koji; Iablonskyi, Denys; Nagaya, Kiyonobu; Wada, Shin-ichi; Mondal, Subhendu; Tachibana, Tetsuya; Ito, Yuta; Sakai, Tsukasa; Matsunami, Kenji; Nishiyama, Toshiyuki; Umemoto, Takayuki; Nicolas, Christophe; Miron, Catalin; Togashi, Tadashi; Ogawa, Kanade; Owada, Shigeki; Tono, Kensuke; Yabashi, Makina; Son, Sang-Kil; Ziaja, Beata; Santra, Robin; Ueda, Kiyoshi

2018-06-01

We show that electron and ion spectroscopy reveals the details of the oligomer formation in Ar clusters exposed to an x-ray free electron laser (XFEL) pulse, i.e., chemical dynamics triggered by x rays. With guidance from a dedicated molecular dynamics simulation tool, we find that van der Waals bonding, the oligomer formation mechanism, and charge transfer among the cluster constituents significantly affect ionization dynamics induced by an XFEL pulse of moderate fluence. Our results clearly demonstrate that XFEL pulses can be used not only to "damage and destroy" molecular assemblies but also to modify and transform their molecular structure. The accuracy of the predictions obtained makes it possible to apply the cluster spectroscopy, in connection with the respective simulations, for estimation of the XFEL pulse fluence in the fluence regime below single-atom multiple-photon absorption, which is hardly accessible with other diagnostic tools.
An all-electron density functional theory study of the structure and properties of the neutral and singly charged M12 and M13 clusters: M = Sc-Zn.

PubMed

Gutsev, G L; Weatherford, C W; Belay, K G; Ramachandran, B R; Jena, P

2013-04-28

The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni13, Cu13, Zn12, and Zn13 are found to be different from the geometries of the corresponding neutral parents. The computed ionization energies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M13 and M13(+) clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 μ(B). Exceptions are found only for Sc12(-), Ti12(+), Mn12(-), Mn12(+), Fe12(-), Fe13(+), and Co12(+).
Dynamic Reactive Ionization with Cluster Secondary Ion Mass Spectrometry

NASA Astrophysics Data System (ADS)

Tian, Hua; Wucher, Andreas; Winograd, Nicholas

2016-02-01

Gas cluster ion beams (GCIB) have been tuned to enhance secondary ion yields by doping small gas molecules such as CH4, CO2, and O2 into an Ar cluster projectile, Arn + ( n = 1000-10,000) to form a mixed cluster. The `tailored beam' has the potential to expand the application of secondary ion mass spectrometry for two- and three-dimensional molecular specific imaging. Here, we examine the possibility of further enhancing the ionization by doping HCl into the Ar cluster. Water deposited on the target surface facilitates the dissociation of HCl. This concerted effect, occurring only at the impact site of the cluster, arises since the HCl is chemically induced to ionize to H+ and Cl- , allowing improved protonation of neutral molecular species. This hypothesis is confirmed by depth profiling through a trehalose thin film exposed to D2O vapor, resulting in ~20-fold increase in protonated molecules. The results show that it is possible to dynamically maintain optimum ionization conditions during depth profiling by proper adjustment of the water vapor pressure. H-D exchange in the trehalose molecule M was monitored upon deposition of D2O on the target surface, leading to the observation of [Mn* + H]+ or [Mn* + D]+ ions, where n = 1-8 hydrogen atoms in the trehalose molecule M have been replaced by deuterium. In general, we discuss the role of surface chemistry and dynamic reactive ionization of organic molecules in increasing the secondary ion yield.
Enhanced one-photon double ionization of atoms and molecules in an environment of different species.

PubMed

Stumpf, V; Kryzhevoi, N V; Gokhberg, K; Cederbaum, L S

2014-05-16

The correlated nature of electronic states in atoms and molecules is manifested in the simultaneous emission of two electrons after absorption of a single photon close to the respective threshold. Numerous observations in atoms and small molecules demonstrate that the double ionization efficiency close to threshold is rather small. In this Letter we show that this efficiency can be dramatically enhanced in the environment. To be specific, we concentrate on the case where the species in question has one or several He atoms as neighbors. The enhancement is achieved by an indirect process, where a He atom of the environment absorbs a photon and the resulting He(+) cation is neutralized fast by a process known as electron transfer mediated decay, producing thereby doubly ionized species. The enhancement of the double ionization is demonstrated in detail for the example of the Mg · He cluster. We show that the double ionization cross section of Mg becomes 3 orders of magnitude larger than the respective cross section of the isolated Mg atom. The impact of more neighbors is discussed and the extension to other species and environments is addressed.
Radiative Feedback of Forming Star Clusters on Their GMC Environments: Theory and Simulation

NASA Astrophysics Data System (ADS)

Howard, C. S.; Pudritz, R. E.; Harris, W. E.

2013-07-01

Star clusters form from dense clumps within a molecular cloud. Radiation from these newly formed clusters feeds back on their natal molecular cloud through heating and ionization which ultimately stops gas accretion into the cluster. Recent studies suggest that radiative feedback effects from a single cluster may be sufficient to disrupt an entire cloud over a short timescale. Simulating cluster formation on a large scale, however, is computationally demanding due to the high number of stars involved. For this reason, we present a model for representing the radiative output of an entire cluster which involves randomly sampling an initial mass function (IMF) as the cluster accretes mass. We show that this model is able to reproduce the star formation histories of observed clusters. To examine the degree to which radiative feedback shapes the evolution of a molecular cloud, we use the FLASH adaptive-mesh refinement hydrodynamics code to simulate cluster formation in a turbulent cloud. Unlike previous studies, sink particles are used to represent a forming cluster rather than individual stars. Our cluster model is then coupled with a raytracing scheme to treat radiative transfer as the clusters grow in mass. This poster will outline the details of our model and present preliminary results from our 3D hydrodynamical simulations.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Michelle J.; Zoerb, Matthew C.; Campbell, Nicole R.

Here, benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt −1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through amore » combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated ( R 2 > 0.95, 10 s averages) over a wide range of sampling conditions.« less
Are clusters important in understanding the mechanisms in atmospheric pressure ionization? Part 1: Reagent ion generation and chemical control of ion populations.

PubMed

Klee, Sonja; Derpmann, Valerie; Wißdorf, Walter; Klopotowski, Sebastian; Kersten, Hendrik; Brockmann, Klaus J; Benter, Thorsten; Albrecht, Sascha; Bruins, Andries P; Dousty, Faezeh; Kauppila, Tiina J; Kostiainen, Risto; O'Brien, Rob; Robb, Damon B; Syage, Jack A

2014-08-01

It is well documented since the early days of the development of atmospheric pressure ionization methods, which operate in the gas phase, that cluster ions are ubiquitous. This holds true for atmospheric pressure chemical ionization, as well as for more recent techniques, such as atmospheric pressure photoionization, direct analysis in real time, and many more. In fact, it is well established that cluster ions are the primary carriers of the net charge generated. Nevertheless, cluster ion chemistry has only been sporadically included in the numerous proposed ionization mechanisms leading to charged target analytes, which are often protonated molecules. This paper series, consisting of two parts, attempts to highlight the role of cluster ion chemistry with regard to the generation of analyte ions. In addition, the impact of the changing reaction matrix and the non-thermal collisions of ions en route from the atmospheric pressure ion source to the high vacuum analyzer region are discussed. This work addresses such issues as extent of protonation versus deuteration, the extent of analyte fragmentation, as well as highly variable ionization efficiencies, among others. In Part 1, the nature of the reagent ion generation is examined, as well as the extent of thermodynamic versus kinetic control of the resulting ion population entering the analyzer region.
Coupled-cluster treatment of molecular strong-field ionization

NASA Astrophysics Data System (ADS)

Jagau, Thomas-C.

2018-05-01

Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules.
Peas in a Pod: Environment and Ionization in Green Pea Galaxies

NASA Astrophysics Data System (ADS)

Kurtz, Heather; Jaskot, Anne; Drew, Patrick; Pare, Dylan; Griffin, Jon; Petersen, Michael

2016-01-01

The Green Peas are extreme, highly ionized, starburst galaxies with strong [OIII] 5007 emission. Using the Sloan Digital Sky Survey, we present statistics on the environment of Green Peas and investigate its effects on their ionized gas properties. Although most dwarf starburst galaxies are in low-density environments, we identify a sample of Green Peas in dense environments. Emission line observations with the WIYN 0.9-meter telescope at Kitt Peak reveal that one cluster Green Pea is more highly ionized in the direction of the cluster center. Ram pressure stripping likely generates this ionization gradient. We explore the role of the environment in enhancing star formation rates and ionization, and we compare the nebular properties of Green Peas in high-density environments to those in low-density environments.
Correlated electronic decay in expanding clusters triggered by intense XUV pulses from a Free-Electron-Laser

PubMed Central

Oelze, Tim; Schütte, Bernd; Müller, Maria; Müller, Jan P.; Wieland, Marek; Frühling, Ulrike; Drescher, Markus; Al-Shemmary, Alaa; Golz, Torsten; Stojanovic, Nikola; Krikunova, Maria

2017-01-01

Irradiation of nanoscale clusters and large molecules with intense laser pulses transforms them into highly-excited non- equilibrium states. The dynamics of intense laser-cluster interaction is encoded in electron kinetic energy spectra, which contain signatures of direct photoelectron emission as well as emission of thermalized nanoplasma electrons. In this work we report on a so far not observed spectrally narrow bound state signature in the electron kinetic energy spectra from mixed Xe core - Ar shell clusters ionized by intense extreme-ultraviolet (XUV) pulses from a free-electron-laser. This signature is attributed to the correlated electronic decay (CED) process, in which an excited atom relaxes and the excess energy is used to ionize the same or another excited atom or a nanoplasma electron. By applying the terahertz field streaking principle we demonstrate that CED-electrons are emitted at least a few picoseconds after the ionizing XUV pulse has ended. Following the recent finding of CED in clusters ionized by intense near-infrared laser pulses, our observation of CED in the XUV range suggests that this process is of general relevance for the relaxation dynamics in laser produced nanoplasmas. PMID:28098175
Probing the early stages of salt nucleation—experimental and theoretical investigations of sodium/potassium thiocyanate cluster anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Shihu; Kong, Xiangyu; Wang, Xue B.

2015-01-14

Due to fast solvent evaporation in electrospray ionization (ESI), the concentration of initially dilute electrolyte solutions rapidly increases to afford formation of supersaturated droplets and generating various pristine anhydrous salt clusters in the gas phase. The size, composition, and charge distributions of these clusters, in principle witness the nucleation evolution in solutions. Herein, we report a microscopic study on the initial stage of nucleation and crystallization of sodium/potassium thiocyanate salt solutions simulated in the ESI process. Singly charged M x(SCN)⁻ x+1, doubly charged M y(SCN)²⁻ y+2 (M = Na, K), and triply charged K z(SCN)³⁻ z+3 anion clusters were producedmore » via electrospray of the corresponding salt solutions, and were characterized by negative ion photoelectron spectroscopy (NIPES). The vertical detachment energies (VDEs) of these sodium/potassium thiocyanate cluster anions were obtained, and theoretical calculations were carried out for sodium thiocyanate clusters in assisting spectral identification. The measured VDEs of singly charged anions M x(SCN)⁻ x+1 (M = Na and K) demonstrate they are superhalogen anions. The existence of doubly charged anions M y (SCN)²⁻ y+2 (y = 2x, x ≥ 4 and 3 for M = Na and K, respectively) and triply charged anions K z(SCN)³⁻ z+3 (z = 3x, x ≥ 6) were initially discovered from the photoelectron spectra for those singly charged anions of Msub>x(SCN)⁻ x+1 with the same mass-to-charge ratio (m/z), and later independently confirmed by observation of their distinct mass spectral distributions and by taking their NIPE spectra for those pure multiply charged anions with their m/z different from the singly charged species. For large clusters, multiply charged clusters are found to become preferred, but at higher temperatures those multiply charged clusters are suppressed. The series of anion clusters investigated here range from molecular-like M₁(SCN)⁻ 2 to nano-sized K₂₂(SCN)³⁻ 25, providing a vivid molecular-level growth pattern reflecting the initial salt nucleation process.« less
Relativistic equation-of-motion coupled-cluster method using open-shell reference wavefunction: Application to ionization potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pathak, Himadri, E-mail: hmdrpthk@gmail.com; Sasmal, Sudip, E-mail: sudipsasmal.chem@gmail.com; Vaval, Nayana

2016-08-21

The open-shell reference relativistic equation-of-motion coupled-cluster method within its four-component description is successfully implemented with the consideration of single- and double- excitation approximations using the Dirac-Coulomb Hamiltonian. At the first attempt, the implemented method is employed to calculate ionization potential value of heavy atomic (Ag, Cs, Au, Fr, and Lr) and molecular (HgH and PbF) systems, where the effect of relativity does really matter to obtain highly accurate results. Not only the relativistic effect but also the effect of electron correlation is crucial in these heavy atomic and molecular systems. To justify the fact, we have taken two further approximationsmore » in the four-component relativistic equation-of-motion framework to quantify how the effect of electron correlation plays a role in the calculated values at different levels of theory. All these calculated results are compared with the available experimental data as well as with other theoretically calculated values to judge the extent of accuracy obtained in our calculations.« less

Combined experimental and theoretical study of the benzocaine/Ar van der Waals system in supersonic expansions.

PubMed

León, Iker; Aguado, Edurne; Lesarri, Alberto; Fernández, José A; Castaño, Fernando

2009-02-12

The electronic spectra of Benzocaine x Ar(n), n = 0-4 were obtained using two-color resonance enhanced multiphoton ionization; the 1:1 and 1:2 clusters were investigated by ultraviolet/ultraviolet hole burning, stimulated emission pumping, and other laser spectroscopies. A single isomer was found for the 1:1 cluster, while two isomers of the 1:2 cluster were found: one with the two Ar atoms on the same side of the chromophore, and the other with the two Ar atoms sitting on opposite sides of the chromophore. The observed shifts point to the existence of a single isomer for the 1:3 and 1:4 species. Dissociation energies for the neutral ground and first excited electronic state and the ion ground electronic state of the complexes have been determined by the fragmentation threshold method and by ab initio calculations conducted at the MP2 level with 6-31++g(2d, p), 6-311++g(2d, p) and AUG-cc-pVTZ basis sets. The results are compared with those obtained for other similar systems.
Calculation on spectrum of direct DNA damage induced by low-energy electrons including dissociative electron attachment.

PubMed

Liu, Wei; Tan, Zhenyu; Zhang, Liming; Champion, Christophe

2017-03-01

In this work, direct DNA damage induced by low-energy electrons (sub-keV) is simulated using a Monte Carlo method. The characteristics of the present simulation are to consider the new mechanism of DNA damage due to dissociative electron attachment (DEA) and to allow determining damage to specific bases (i.e., adenine, thymine, guanine, or cytosine). The electron track structure in liquid water is generated, based on the dielectric response model for describing electron inelastic scattering and on a free-parameter theoretical model and the NIST database for calculating electron elastic scattering. Ionization cross sections of DNA bases are used to generate base radicals, and available DEA cross sections of DNA components are applied for determining DNA-strand breaks and base damage induced by sub-ionization electrons. The electron elastic scattering from DNA components is simulated using cross sections from different theoretical calculations. The resulting yields of various strand breaks and base damage in cellular environment are given. Especially, the contributions of sub-ionization electrons to various strand breaks and base damage are quantitatively presented, and the correlation between complex clustered DNA damage and the corresponding damaged bases is explored. This work shows that the contribution of sub-ionization electrons to strand breaks is substantial, up to about 40-70%, and this contribution is mainly focused on single-strand break. In addition, the base damage induced by sub-ionization electrons contributes to about 20-40% of the total base damage, and there is an evident correlation between single-strand break and damaged base pair A-T.
Assessment of Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) in Radiation Chemistry: Ionized Water Dimer.

PubMed

Chalabala, Jan; Uhlig, Frank; Slavíček, Petr

2018-03-29

Ionization in the condensed phase and molecular clusters leads to a complicated chain of processes with coupled electron-nuclear dynamics. It is difficult to describe such dynamics with conventional nonadiabatic molecular dynamics schemes since the number of states swiftly increases as the molecular system grows. It is therefore attractive to use a direct electron and nuclear propagation such as the real-time time-dependent density functional theory (RT-TDDFT). Here we report a RT-TDDFT benchmark study on simulations of singly and doubly ionized states of a water monomer and dimer as a prototype for more complex processes in a condensed phase. We employed the RT-TDDFT based Ehrenfest molecular dynamics with a generalized gradient approximate (GGA) functional and compared it with wave-function-based surface hopping (SH) simulations. We found that the initial dynamics of a singly HOMO ionized water dimer is similar for both the RT-TDDFT/GGA and the SH simulations but leads to completely different reaction channels on a longer time scale. This failure is attributed to the self-interaction error in the GGA functionals and it can be avoided by using hybrid functionals with large fraction of exact exchange (represented here by the BHandHLYP functional). The simulations of doubly ionized states are reasonably described already at the GGA level. This suggests that the RT-TDDFT/GGA method could describe processes following the autoionization processes such as Auger emission, while its applicability to more complex processes such as intermolecular Coulombic decay remains limited.
Analysis of trace fibers by IR-MALDESI imaging coupled with high resolving power MS

PubMed Central

Cochran, Kristin H.; Barry, Jeremy A.; Robichaud, Guillaume

2016-01-01

Trace evidence is a significant portion of forensic cases. Textile fibers are a common form of trace evidence that are gaining importance in criminal cases. Currently, qualitative techniques that do not yield structural information are primarily used for fiber analysis, but mass spectrometry is gaining an increasing role in this field. Mass spectrometry yields more quantitative structural information about the dye and polymer that can be used for more conclusive comparisons. Matrix-assisted laser desorption electrospray ionization (MALDESI) is a hybrid ambient ionization source being investigated for use in mass spectrometric fiber analysis. In this manuscript, IR-MALDESI was used as a source for mass spectrometry imaging (MSI) of a dyed nylon fiber cluster and single fiber. Information about the fiber polymer as well as the dye were obtained from a single fiber which was on the order of 10 μm in diameter. These experiments were performed directly from the surface of a tape lift of the fiber with a background of extraneous fibers. PMID:25081013
Analysis of trace fibers by IR-MALDESI imaging coupled with high resolving power MS.

PubMed

Cochran, Kristin H; Barry, Jeremy A; Robichaud, Guillaume; Muddiman, David C

2015-01-01

Trace evidence is a significant portion of forensic cases. Textile fibers are a common form of trace evidence that are gaining importance in criminal cases. Currently, qualitative techniques that do not yield structural information are primarily used for fiber analysis, but mass spectrometry is gaining an increasing role in this field. Mass spectrometry yields more quantitative structural information about the dye and polymer that can be used for more conclusive comparisons. Matrix-assisted laser desorption electrospray ionization (MALDESI) is a hybrid ambient ionization source being investigated for use in mass spectrometric fiber analysis. In this manuscript, IR-MALDESI was used as a source for mass spectrometry imaging (MSI) of a dyed nylon fiber cluster and single fiber. Information about the fiber polymer as well as the dye were obtained from a single fiber which was on the order of 10 μm in diameter. These experiments were performed directly from the surface of a tape lift of the fiber with a background of extraneous fibers.
On star formation in stellar systems. I - Photoionization effects in protoglobular clusters

NASA Technical Reports Server (NTRS)

Tenorio-Tagle, G.; Bodenheimer, P.; Lin, D. N. C.; Noriega-Crespo, A.

1986-01-01

The progressive ionization and subsequent dynamical evolution of nonhomogeneously distributed low-metal-abundance diffuse gas after star formation in globular clusters are investigated analytically, taking the gravitational acceleration due to the stars into account. The basic equations are derived; the underlying assumptions, input parameters, and solution methods are explained; and numerical results for three standard cases (ionization during star formation, ionization during expansion, and evolution resulting in a stable H II region at its equilibrium Stromgren radius) are presented in graphs and characterized in detail. The time scale of residual-gas loss in typical clusters is found to be about the same as the lifetime of a massive star on the main sequence.
The TIME-Pilot intensity mapping experiment

NASA Astrophysics Data System (ADS)

Crites, A. T.; Bock, J. J.; Bradford, C. M.; Chang, T. C.; Cooray, A. R.; Duband, L.; Gong, Y.; Hailey-Dunsheath, S.; Hunacek, J.; Koch, P. M.; Li, C. T.; O'Brient, R. C.; Prouve, T.; Shirokoff, E.; Silva, M. B.; Staniszewski, Z.; Uzgil, B.; Zemcov, M.

2014-08-01

TIME-Pilot is designed to make measurements from the Epoch of Reionization (EoR), when the first stars and galaxies formed and ionized the intergalactic medium. This will be done via measurements of the redshifted 157.7 um line of singly ionized carbon ([CII]). In particular, TIME-Pilot will produce the first detection of [CII] clustering fluctuations, a signal proportional to the integrated [CII] intensity, summed over all EoR galaxies. TIME-Pilot is thus sensitive to the emission from dwarf galaxies, thought to be responsible for the balance of ionizing UV photons, that will be difficult to detect individually with JWST and ALMA. A detection of [CII] clustering fluctuations would validate current theoretical estimates of the [CII] line as a new cosmological observable, opening the door for a new generation of instruments with advanced technology spectroscopic array focal planes that will map [CII] fluctuations to probe the EoR history of star formation, bubble size, and ionization state. Additionally, TIME-Pilot will produce high signal-to-noise measurements of CO clustering fluctuations, which trace the role of molecular gas in star-forming galaxies at redshifts 0 < z < 2. With its unique atmospheric noise mitigation, TIME-Pilot also significantly improves sensitivity for measuring the kinetic Sunyaev-Zel'dovich (kSZ) effect in galaxy clusters. TIME-Pilot will employ a linear array of spectrometers, each consisting of a parallel-plate diffraction grating. The spectrometer bandwidth covers 185-323 GHz to both probe the entire redshift range of interest and to include channels at the edges of the band for atmospheric noise mitigation. We illuminate the telescope with f/3 horns, which balances the desire to both couple to the sky with the best efficiency per beam, and to pack a large number of horns into the fixed field of view. Feedhorns couple radiation to the waveguide spectrometer gratings. Each spectrometer grating has 190 facets and provides resolving power above 100. At this resolution, the longest dimension of the grating is 31 cm, which allows us to stack gratings in two blocks (one for each polarization) of 16 within a single cryostat, providing a 1x16 array of beams in a 14 arcminute field of view. Direct absorber TES sensors sit at the output of the grating on six linear facets over the output arc, allowing us to package and read out the detectors as arrays in a modular manner. The 1840 detectors will be read out with the NIST time-domain-multiplexing (TDM) scheme and cooled to a base temperature of 250 mK with a 3He sorption refrigerator. We present preliminary designs for the TIME-Pilot cryogenics, spectrometers, bolometers, and optics.
Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters

NASA Astrophysics Data System (ADS)

Hans, Andreas; Stumpf, Vasili; Holzapfel, Xaver; Wiegandt, Florian; Schmidt, Philipp; Ozga, Christian; Reiß, Philipp; Ben Ltaief, Ltaief; Küstner-Wetekam, Catmarna; Jahnke, Till; Ehresmann, Arno; Demekhin, Philipp V.; Gokhberg, Kirill; Knie, André

2018-01-01

We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne2+-{{{N}}{{e}}}n-1 initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with < n> ≈ 2800. These states relax further producing Ne+-Ne+-{{{N}}{{e}}}n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the{}{{{N}}{{e}}}2+(2{{{p}}}-2{[}1{{D}}]){--}{{{N}}{{e}}}n-1 initial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.
Investigating the synthesis of ligated metal clusters in solution using a flow reactor and electrospray ionization mass spectrometry.

PubMed

Olivares, Astrid; Laskin, Julia; Johnson, Grant E

2014-09-18

The scalable synthesis of ligated subnanometer metal clusters containing an exact number of atoms is of interest due to the highly size-dependent catalytic, electronic, and optical properties of these species. While significant research has been conducted on the batch preparation of clusters through reduction synthesis in solution, the processes of metal complex reduction as well as cluster nucleation, growth, and postreduction etching are still not well understood. Herein, we demonstrate a prototype temperature-controlled flow reactor for qualitatively studying cluster formation in solution at steady-state conditions. Employing this technique, methanol solutions of a chloro(triphenylphosphine)gold precursor, 1,4-bis(diphenylphosphino)butane capping ligand, and borane-tert-butylamine reducing agent were combined in a mixing tee and introduced into a heated capillary with a known length. In this manner, the temperature dependence of the relative abundance of different ionic reactants, intermediates, and products synthesized in real time was characterized qualitatively using online mass spectrometry. A wide distribution of doubly and triply charged cationic gold clusters was observed as well as smaller singly charged organometallic complexes. The results demonstrate that temperature plays a crucial role in determining the relative population of cationic gold clusters and, in general, that higher temperature promotes the formation of doubly charged clusters and singly charged organometallic complexes while reducing the abundance of triply charged species. Moreover, the distribution of clusters observed at elevated temperatures is found to be consistent with that obtained at longer reaction times at room temperature, thereby demonstrating that heating may be used to access cluster distributions characteristic of different stages of batch reduction synthesis in solution.
Energy and charge transfer in ionized argon coated water clusters.

PubMed

Kočišek, J; Lengyel, J; Fárník, M; Slavíček, P

2013-12-07

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar(+) and water occurs above the threshold; at higher electron energies above ~28 eV, an excitonic transfer process between Ar(+)* and water opens leading to new products Ar(n)H(+) and (H2O)(n)H(+). On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)(n)H2(2+) and (H2O)(n)(2+) ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.
Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. III. Coulomb explosion of deuterium clusters.

PubMed

Last, Isidore; Jortner, Joshua

2004-08-15

In this paper we present a theoretical and computational study of the energetics and temporal dynamics of Coulomb explosion of molecular clusters of deuterium (D2)n/2 (n = 480 - 7.6 x 10(4), cluster radius R0 = 13.1 - 70 A) in ultraintense laser fields (laser peak intensity I = 10(15) - 10(20)W cm(-2)). The energetics of Coulomb explosion was inferred from the dependence of the maximal energy EM and the average energy Eav of the product D+ ions on the laser intensity, the laser pulse shape, the cluster radius, and the laser frequency. Electron dynamics of outer cluster ionization and nuclear dynamics of Coulomb explosion were investigated by molecular dynamics simulations. Several distinct laser pulse shape envelopes, involving a rectangular field, a Gaussian field, and a truncated Gaussian field, were employed to determine the validity range of the cluster vertical ionization (CVI) approximation. The CVI predicts that Eav, EM proportional to R0(2) and that the energy distribution is P(E) proportional to E1/2. For a rectangular laser pulse the CVI conditions are satisfied when complete outer ionization is obtained, with the outer ionization time toi being shorter than both the pulse width and the cluster radius doubling time tau2. By increasing toi, due to the increase of R0 or the decrease of I, we have shown that the deviation of Eav from the corresponding CVI value (Eav(CVI)) is (Eav(CVI) - Eav)/Eav(CVI) approximately (toi/2.91tau2)2. The Gaussian pulses trigger outer ionization induced by adiabatic following of the laser field and of the cluster size, providing a pseudo-CVI behavior at sufficiently large laser fields. The energetics manifest the existence of a finite range of CVI size dependence, with the validity range for the applicability of the CVI being R0 < or = (R0)I, with (R0)I representing an intensity dependent boundary radius. Relating electron dynamics of outer ionization to nuclear dynamics for Coulomb explosion induced by a Gaussian pulse, the boundary radius (R0)I and the corresponding ion average energy (Eav)I were inferred from simulations and described in terms of an electrostatic model. Two independent estimates of (R0)I, which involve the cluster size where the CVI relation breaks down and the cluster size for the attainment of complete outer ionization, are in good agreement with each other, as well as with the electrostatic model for cluster barrier suppression. The relation (Eav)I proportional to (R0)I(2) provides the validity range of the pseudo-CVI domain for the cluster sizes and laser intensities, where the energetics of D+ ions produced by Coulomb explosion of (D)n clusters is optimized. The currently available experimental data [Madison et al., Phys. Plasmas 11, 1 (2004)] for the energetics of Coulomb explosion of (D)n clusters (Eav = 5 - 7 keV at I = 2 x 10(18) W cm(-2)), together with our simulation data, lead to the estimates of R0 = 51 - 60 A, which exceed the experimental estimate of R0 = 45 A. The predicted anisotropy of the D+ ion energies in the Coulomb explosion at I = 10(18) W cm(-2) is in accord with experiment. We also explored the laser frequency dependence of the energetics of Coulomb explosion in the range nu = 0.1 - 2.1 fs(-1) (lambda = 3000 - 140 nm), which can be rationalized in terms of the electrostatic model. (c) 2004 American Institute of Physics.
Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (Cmore » 2H 2) n +, just like ionized acetylene clusters. The fragmentation products result from reactive ion- molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4H 4 + and C 6H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts ( > 2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2H 2) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6H 6 + isomers. Lastly, these results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.« less
Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

PubMed Central

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; Fang, Yigang; Kostko, Oleg

2017-01-01

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion–molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion–molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM. PMID:28484019
Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

PubMed

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P; Fang, Yigang; Kostko, Oleg; Ahmed, Musahid; Head-Gordon, Martin

2017-05-23

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C 2 H 2 ) n + , just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4 H 4 + and C 6 H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2 H 2 ) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6 H 6 + isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.
Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation

DOE PAGES

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; ...

2017-05-08

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (Cmore » 2H 2) n +, just like ionized acetylene clusters. The fragmentation products result from reactive ion- molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4H 4 + and C 6H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts ( > 2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2H 2) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6H 6 + isomers. Lastly, these results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.« less
Direct Standard-Free Quantitation of Tamiflu® and Other Pharmaceutical Tablets using Clustering Agents with Electrospray Ionization Mass Spectrometry

PubMed Central

Flick, Tawnya G.; Leib, Ryan D.; Williams, Evan R.

2010-01-01

Accurate and rapid quantitation is advantageous to identify counterfeit and substandard pharmaceutical drugs. A standard-free electrospray ionization mass spectrometry method is used to directly determine the dosage in the prescription and over-the-counter drugs, Tamiflu®, Sudafed®, and Dramamine®. A tablet of each drug was dissolved in aqueous solution, filtered, and introduced into solutions containing a known concentration of either L-tryptophan, L-phenylalanine or prednisone as clustering agents. The active ingredient(s) incorporates statistically into large clusters of the clustering agent where effects of differential ionization/detection are substantially reduced. From the abundances of large clusters, the dosages of the active ingredients in each of the tablets were determined to typically better than 20% accuracy even when the ionization/detection efficiency of the individual components differed by over 100×. Although this unorthodox method for quantitation is not as accurate as using conventional standards, it has the advantages that it is fast, it can be applied to mixtures where the identities of the analytes are unknown, and it can be used when suitable standards may not be readily available, such as schedule I or II controlled substances or new designer drugs that have not previously been identified. PMID:20092258
Core-core and core-valence correlation energy atomic and molecular benchmarks for Li through Ar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ranasinghe, Duminda S.; Frisch, Michael J.; Petersson, George A., E-mail: gpetersson@wesleyan.edu

2015-12-07

We have established benchmark core-core, core-valence, and valence-valence absolute coupled-cluster single double (triple) correlation energies (±0.1%) for 210 species covering the first- and second-rows of the periodic table. These species provide 194 energy differences (±0.03 mE{sub h}) including ionization potentials, electron affinities, and total atomization energies. These results can be used for calibration of less expensive methodologies for practical routine determination of core-core and core-valence correlation energies.
On the calculation of the energies of dissociation, cohesion, vacancy formation, electron attachment, and the ionization potential of small metallic clusters containing a monovacancy

NASA Astrophysics Data System (ADS)

Pogosov, V. V.; Reva, V. I.

2017-09-01

In terms of the model of stable jellium, self-consistent calculations of spatial distributions of electrons and potentials, as well as of energies of dissociation, cohesion, vacancy formation, electron attachment, and ionization potentials of solid clusters of Mg N , Li N (with N ≤ 254 ) and of clusters containing a vacancy ( N ≥ 12) have been performed. The contribution of a monovacancy to the energy of the cluster and size dependences of its characteristics and of asymptotics have been discussed. Calculations have been performed using a SKIT-3 cluster at Glushkov Institute of Cybernetics, National Academy of Sciences, Ukraine (Rpeak = 7.4 Tflops).
Mercury-induced fragmentation of n-decane and n-undecane in positive mode ion mobility spectrometry.

PubMed

Gunzer, F

2015-09-21

Ion mobility spectrometry is a well-known technique for trace gas analysis. Using soft ionization techniques, fragmentation of analytes is normally not observed, with the consequence that analyte spectra of single substances are quite simple, i.e. showing in general only one peak. If the concentration is high enough, an extra cluster peak involving two analyte molecules can often be observed. When investigating n-alkanes, different results regarding the number of peaks in the spectra have been obtained in the past using this spectrometric technique. Here we present results obtained when analyzing n-alkanes (n-hexane to n-undecane) with a pulsed electron source, which show no fragmentation or clustering at all. However, when investigating a mixture of mercury and an n-alkane, a situation quite typical in the oil and gas industry, a strong fragmentation and cluster formation involving these fragments has been observed exclusively for n-decane and n-undecane.
Probing the early stages of salt nucleation—Experimental and theoretical investigations of sodium/potassium thiocyanate cluster anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, S. H. M.; Kong, Xiang-Yu; Wang, Xue-Bin, E-mail: xuebin.wang@pnnl.gov

2015-01-14

Due to the fast solvent evaporation in electrospray ionization (ESI), the concentration of initially dilute electrolyte solutions rapidly increases to afford the formation of supersaturated droplets and generation of various pristine anhydrous salt clusters in the gas phase. The size, composition, and charge distributions of these clusters, in principle, witness the nucleation evolution in solutions. Herein, we report a microscopic study on the initial stage of nucleation and crystallization of sodium/potassium thiocyanate salt solutions simulated in the ESI process. Singly charged M{sub x}(SCN){sub x+1}{sup −}, doubly charged M{sub y}(SCN){sub y+2}{sup 2−} (M = Na, K), and triply charged K{sub z}(SCN){submore » z+3}{sup 3−} anion clusters (x, y, and z stand for the number of alkali atoms in the singly, doubly, and triply charged clusters, respectively) were produced via electrospray of the corresponding salt solutions and were characterized by negative ion photoelectron spectroscopy (NIPES). The vertical detachment energies (VDEs) of these sodium/potassium thiocyanate cluster anions were obtained, and theoretical calculations were carried out for the sodium thiocyanate clusters in assisting spectral identification. The measured VDEs of singly charged anions M{sub x}(SCN){sub x+1}{sup −} (M = Na and K) demonstrate that they are superhalogen anions. The existence of doubly charged anions M{sub y}(SCN){sub y+2}{sup 2−} (y = 2x, x ≥ 4 and 3 for M = Na and K, respectively) and triply charged anions K{sub z}(SCN){sub z+3}{sup 3−} (z = 3x, x ≥ 6) was initially discovered from the photoelectron spectra for those singly charged anions of M{sub x}(SCN){sub x+1}{sup −} with the same mass-to-charge ratio (m/z), and later independently confirmed by the observation of their distinct mass spectral distributions and by taking their NIPE spectra for those pure multiply charged anions with their m/z different from the singly charged species. For large clusters, multiply charged clusters were found to become preferred, but at higher temperatures, those multiply charged clusters were suppressed. The series of anion clusters investigated here range from molecular-like M{sub 1}(SCN){sub 2}{sup −} to nano-sized K{sub 22}(SCN){sub 25}{sup 3−}, providing a vivid molecular-level growth pattern reflecting the initial salt nucleation process.« less

Color gradients in cooling flow cluster central galaxies and the ionization of cluster emission line systems

NASA Technical Reports Server (NTRS)

Romanishin, W.

1988-01-01

Preliminary results are given for a program to measure color gradients in the central galaxies in clusters with a variety of cooling flow rates. The objectives are to search for extended blue continuum regions indicative of star formation, to study the spatial distribution of star formation, and to make a quantitative measure of the amount of light from young stars, which can lead to a measure of the star formation rate (for an assumed initial mass function). Four clusters with large masses and large cluster H-alpha emission fluxes are found to have an excess of blue light concentrated to the centers of the cluster central galaxy. Assumption of a disk IMF leads to the conclusion that the starlight might play a major role in ionizing the emission line gas in these clusters.
Collision-Induced Dissociation of Electrosprayed NaCl Clusters: Using Molecular Dynamics Simulations to Visualize Reaction Cascades in the Gas Phase

NASA Astrophysics Data System (ADS)

Schachel, Tilo D.; Metwally, Haidy; Popa, Vlad; Konermann, Lars

2016-11-01

Infusion of NaCl solutions into an electrospray ionization (ESI) source produces [Na( n+1)Cl n ]+ and other gaseous clusters. The n = 4, 13, 22 magic number species have cuboid ground state structures and exhibit elevated abundance in ESI mass spectra. Relatively few details are known regarding the mechanisms whereby these clusters undergo collision-induced dissociation (CID). The current study examines to what extent molecular dynamics (MD) simulations can be used to garner insights into the sequence of events taking place during CID. Experiments on singly charged clusters reveal that the loss of small neutrals is the dominant fragmentation pathway. MD simulations indicate that the clusters undergo extensive structural fluctuations prior to decomposition. Consistent with the experimentally observed behavior, most of the simulated dissociation events culminate in ejection of small neutrals ([NaCl] i , with i = 1, 2, 3). The MD data reveal that the prevalence of these dissociation channels is linked to the presence of short-lived intermediates where a relatively compact core structure carries a small [NaCl] i protrusion. The latter can separate from the parent cluster via cleavage of a single Na-Cl contact. Fragmentation events of this type are kinetically favored over other dissociation channels that would require the quasi-simultaneous rupture of multiple electrostatic contacts. The CID behavior of NaCl cluster ions bears interesting analogies to that of collisionally activated protein complexes. Overall, it appears that MD simulations represent a valuable tool for deciphering the dissociation of noncovalently bound systems in the gas phase.
Generation and collision-induced dissociation of ammonium tetrafluoroborate cluster ions.

PubMed

Dain, Ryan P; Van Stipdonk, Michael J

2008-07-01

Singly and doubly charged cluster ions of ammonium tetrafluoroborate (NH4BF4) with general formula [(NH4BF4)nNH4]+ and [(NH4BF4)m(NH4)2]2+, respectively, were generated by electrospray ionization (ESI) and their fragmentation examined using collision-induced dissociation (CID) and ion-trap tandem mass spectrometry. CID of [(NH4BF4)nNH4]+ caused the loss of one or more neutral NH4BF4 units. The n = 2 cluster, [(NH4BF4)2NH4]+, was unique in that it also exhibited a dissociation pathway in which HBF4 was eliminated to create [(NH4BF4)(NH3)NH4]+. Dissociation of [(NH4BF4)m(NH4)2]2+ occurred through two general pathways: (a) 'fission' to produce singly charged cluster ions and (b) elimination of one or more neutral NH4BF4 units to leave doubly charged product ions. CID profiles, and measurements of changing precursor and product ion signal intensity as a function of applied collision voltage, were collected for [(NH4BF4)nNH4]+ and compared with those for analogous [(NaBF4)nNa]+ and [(KBF4)nK]+ ions to determine the influence of the cation on the relative stability of cluster ions. In general, the [(NH4BF4)nNH4]+ clusters were found to be easier to dissociate than both the sodium and potassium clusters of comparable size, with [(KBF4)nK]+ ions the most difficult to dissociate.
ON THE IONIZATION OF LUMINOUS WMAP SOURCES IN THE GALAXY: CONSTRAINTS FROM He RECOMBINATION LINE OBSERVATIONS WITH THE GBT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roshi, D. Anish; Plunkett, Adele; Rosero, Viviana

2012-04-10

Murray and Raham used the Wilkinson Microwave Anisotropy Probe (WMAP) free-free foreground emission map to identify diffuse ionized regions (DIRs) in the Galaxy. It has been found that the 18 most luminous WMAP sources produce more than half of the total ionizing luminosity of the Galaxy. We observed radio recombination lines (RRLs) toward the luminous WMAP source G49.75-0.45 with the Green Bank Telescope near 1.4 GHz. Hydrogen RRL is detected toward the source but no helium line is detected, implying that n{sub He{sup +}}/n{sub H{sup +}}< 0.024. This limit puts severe constraint on the ionizing spectrum. The total ionizing luminositymore » of G49 (3.05 Multiplication-Sign 10{sup 51} s{sup -1}) is {approx}2.8 times the luminosity of all radio H II regions within this DIR and this is generally the case for other WMAP sources. Murray and Rahman propose that the additional ionization is due to massive clusters ({approx}7.5 Multiplication-Sign 10{sup 3} M{sub Sun} for G49) embedded in the WMAP sources. Such clusters should produce enough photons with energy {>=}24.6 eV to fully ionize helium in the DIR. Our observations rule out a simple model with G49 ionized by a massive cluster. We also considered 'leaky' H II region models for the ionization of the DIR, suggested by Lockman and Anantharamaiah, but these models also cannot explain our observations. We estimate that the helium ionizing photons need to be attenuated by {approx}>10 times to explain the observations. If selective absorption of He ionizing photons by dust is causing this additional attenuation, then the ratio of dust absorption cross sections for He and H ionizing photons should be {approx}>6.« less
Geometric and electronic structures of silicon-sodium binary clusters. I. Ionization energy of SinNam

NASA Astrophysics Data System (ADS)

Kishi, Reiko; Iwata, Suehiro; Nakajima, Atsushi; Kaya, Koji

1997-08-01

Sodium doped silicon clusters (SinNam; 1⩽n⩽14, 1⩽m⩽5) produced by two types of laser vaporization were studied. The adsorption of Na atoms on the Sin clusters leads the substantial lowering of the ionization energy, Ei, of SinNam clusters. Their reactivity toward NO molecules was measured with a fast flow reactor, and the anticorrelation between the Eis and the reactivity was clearly observed; species having low Ei exhibit high reactivity and vice versa. Moreover, the clear parallelism between the Eis of SinNa and the EAs of Sin is found. This is consistent with the fact that the structure of SinNa clusters keeps the frame of the corresponding Sin cluster unchanged and that the electronic structure of SinNa is similar to that of the corresponding negative ion Sin-. In addition to the experimental studies, the geometries, adsorption energies, and vertical ionization energies of SinNa (n=1-7) were investigated with ab initio MO calculations including electron correlation; The Møller-Plesset perturbation theory was used and the configuration interaction (CI) calculation was carried out, particularly for a diatomic molecule, SiNa.
Classical plasma dynamics of Mie-oscillations in atomic clusters

NASA Astrophysics Data System (ADS)

Kull, H.-J.; El-Khawaldeh, A.

2018-04-01

Mie plasmons are of basic importance for the absorption of laser light by atomic clusters. In this work we first review the classical Rayleigh-theory of a dielectric sphere in an external electric field and Thomson’s plum-pudding model applied to atomic clusters. Both approaches allow for elementary discussions of Mie oscillations, however, they also indicate deficiencies in describing the damping mechanisms by electrons crossing the cluster surface. Nonlinear oscillator models have been widely studied to gain an understanding of damping and absorption by outer ionization of the cluster. In the present work, we attempt to address the issue of plasmon relaxation in atomic clusters in more detail based on classical particle simulations. In particular, we wish to study the role of thermal motion on plasmon relaxation, thereby extending nonlinear models of collective single-electron motion. Our simulations are particularly adopted to the regime of classical kinetics in weakly coupled plasmas and to cluster sizes extending the Debye-screening length. It will be illustrated how surface scattering leads to the relaxation of Mie oscillations in the presence of thermal motion and of electron spill-out at the cluster surface. This work is intended to give, from a classical perspective, further insight into recent work on plasmon relaxation in quantum plasmas [1].
HOW TO FIND YOUNG MASSIVE CLUSTER PROGENITORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bressert, E.; Longmore, S.; Testi, L.

2012-10-20

We propose that bound, young massive stellar clusters form from dense clouds that have escape speeds greater than the sound speed in photo-ionized gas. In these clumps, radiative feedback in the form of gas ionization is bottled up, enabling star formation to proceed to sufficiently high efficiency so that the resulting star cluster remains bound even after gas removal. We estimate the observable properties of the massive proto-clusters (MPCs) for existing Galactic plane surveys and suggest how they may be sought in recent and upcoming extragalactic observations. These surveys will potentially provide a significant sample of MPC candidates that willmore » allow us to better understand extreme star-formation and massive cluster formation in the Local Universe.« less
STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matzner, Christopher D.; Jumper, Peter H., E-mail: matzner@astro.utoronto.ca

2015-12-10

During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when itsmore » column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive.« less
Clusters of primordial black holes and reionization problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belotsky, K. M., E-mail: k-belotsky@yandex.ru; Kirillov, A. A., E-mail: kirillov-aa@yandex.ru; Rubin, S. G., E-mail: sergeirubin@list.ru

2015-05-15

Clusters of primordial black holes may cause the formation of quasars in the early Universe. In turn, radiation from these quasars may lead to the reionization of the Universe. However, the evaporation of primordial black holes via Hawking’s mechanism may also contribute to the ionization of matter. The possibility of matter ionization via the evaporation of primordial black holes with allowance for existing constraints on their density is discussed. The contribution to ionization from the evaporation of primordial black holes characterized by their preset mass spectrum can roughly be estimated at about 10{sup −3}.
Clustered DNA damages induced by high and low LET radiation, including heavy ions

NASA Technical Reports Server (NTRS)

Sutherland, B. M.; Bennett, P. V.; Schenk, H.; Sidorkina, O.; Laval, J.; Trunk, J.; Monteleone, D.; Sutherland, J.; Lowenstein, D. I. (Principal Investigator)

2001-01-01

Clustered DNA damages--here defined as two or more lesions (strand breaks, oxidized purines, oxidized pyrimidines or abasic sites) within a few helical turns--have been postulated as difficult to repair accurately, and thus highly significant biological lesions. Further, attempted repair of clusters may produce double strand breaks (DSBs). However, until recently, there was no way to measure ionizing radiation-induced clustered damages, except DSB. We recently described an approach for measuring classes of clustered damages (oxidized purine clusters, oxidized pyrimidine clusters, abasic clusters, along with DSB). We showed that ionizing radiation (gamma rays and Fe ions, 1 GeV/amu) does induce such clusters in genomic DNA in solution and in human cells. These studies also showed that each damage cluster results from one radiation hit (and its track), thus indicating that they can be induced by very low doses of radiation, i.e. two independent hits are not required for cluster induction. Further, among all complex damages, double strand breaks comprise--at most-- 20%, with the other clustered damages being at least 80%.
Measuring masses of single bacterial whole cells with a quadrupole ion trap.

PubMed

Peng, Wen-Ping; Yang, Yi-Chang; Kang, Ming-Wei; Lee, Yuan T; Chang, Huan-Cheng

2004-09-29

A novel method has been developed to precisely measure the masses of single bacterial whole cells using a quadrupole ion trap as an electrodynamic balance. The bacterial cells were introduced into the ion trap by matrix-assisted laser desorption/ionization, confined in space by audio frequency ac fields, and detected by elastic light scattering. Mass measurement accuracy approaching 0.1% was achieved for Escherichia coli K-12 with a mass distribution of +/-3% from 60 repetitive measurements of the particles and their clusters. This is the first high-precision mass measurement reported for any intact microorganisms with masses greater than 1 x 1010 Da. The method opens new avenues for high-precision mass measurement of single microbial particles and offers an alternative approach for rapid identification of microorganisms by mass spectrometry.
Magnetic switching in Crx (x = 2-8) and its oxide cluster series

NASA Astrophysics Data System (ADS)

Shah, Esha V.; Roy, Debesh R.

2018-04-01

First principle studies on the magnetic ground state structure, noncollinearity, binding energy and various electronic properties of a series of Crx (x = 2-8) clusters are performed. In order to investigate the effect of ionization and oxidation on the clusters, the anionic (Crx-) and oxidized (CrxO2) analogues of those clusters are also studied in detail. To calculate adiabatic electron affinity of CrxO2 clusters, additionally CrxO2- analogues are also included in the present work. An interesting even (non-magnetic) - odd (magnetic) feature in the considered cluster series has been noticed. The similar behavior is also reflected from their electronic properties as even (less reactive) - odd (more reactive). The most of the neutral and ionized chromium clusters, viz., Crx and Crx- are found to be noncollinear in their ground states, whereas oxidation stabilized those clusters into the collinear spin alignments. The bond distances of Cr clusters are found to be close with available experimental studies.
Novel size-dependent chemistry within ionized van der Waals clusters of 1,1-difluoroethane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coolbaugh, M.T.; Peifer, W.R.; Garvey, J.F.

1990-02-22

The authors present in this paper evidence for size-dependent cluster chemistry occurring in van der Waals clusters of 1,1-difluoroethane. Clusters of C{sub 2}H{sub 4}F{sub 2} are produced from a neat adiabatic expansion and are ionized via electron impact. In addition to the anticipated fragment ions, we observe ions with the general empirical formula of M{sub n}H{sup +} (where n {ge} 4). The reactive process that generates this species cannot be rationalized in terms of intramolecular analogues of known gas-phase bimolecular ion-molecular reactions. Hence, we fell the production of this product cluster ion represents an additional example of a brand newmore » class of ion-molecule reactions that can only occur within the unique solvated environment of the cluster.« less
Real-time analysis of self-assembled nucleobases by Venturi easy ambient sonic-spray ionization mass spectrometry.

PubMed

Na, Na; Shi, Ruixia; Long, Zi; Lu, Xin; Jiang, Fubin; Ouyang, Jin

2014-10-01

In this study, the real-time analysis of self-assembled nucleobases was employed by Venturi easy ambient sonic-spray ionization mass spectrometry (V-EASI-MS). With the analysis of three nucleobases including 6-methyluracil (6MU), uracil (U) and thymine (T) as examples, different orders of clusters centered with different metal ions were recorded in both positive and negative modes. Compared with the results obtained by traditional electrospray ionization mass spectrometry (ESI-MS) under the same condition, more clusters with high orders, such as [6MU7+Na](+), [6MU15+2NH4](2+), [6MU10+Na](+), [T7+Na](+), and [T15+2NH4](2+) were detected by V-EASI-MS, which demonstrated the soft ionization ability of V-EASI for studying the non-covalent interaction in a self-assembly process. Furthermore, with the injection of K(+) to the system by a syringe pumping, the real-time monitoring of the formation of nucleobases clusters was achieved by the direct extraction of samples from the system under the Venturi effect. Therefore, the effect of cations on the formation of clusters during self-assembly of nucleobases was demonstrated, which was in accordance with the reports. Free of high voltage, heating or radiation during the ionization, this technique is much soft and suitable for obtaining the real-time information of the self-assembly system, which also makes it quite convenient for extraction samples from the reaction system. This "easy and soft" ionization technique has provided a potential pathway for monitoring and controlling the self-assembly processes. Copyright © 2014 Elsevier B.V. All rights reserved.
Effect of multiple plasmon excitation on single, double and multiple ionizations of C60 in collisions with fast highly charged Si ions

NASA Astrophysics Data System (ADS)

Kelkar, A. H.; Kadhane, U.; Misra, D.; Kumar, A.; Tribedi, L. C.

2007-06-01

We have investigated the single and multiple ionizations of the C60 molecule in collisions with fast Siq+ projectiles for various projectile charge states (q) between q = 6 and 14. The q-dependence of the ionization cross sections and their ratios is compared with the giant dipole plasmon resonance (GDPR) model. The excellent qualitative agreement with the model in case of single and double ionizations and also a reasonable agreement with the triple (and to some extent with quadruple) ionization (without evaporation) yields signify dominant contributions of the single-, double- and triple-plasmon excitations on the single- and multiple-ionization process.
Track structure in radiation biology: theory and applications.

PubMed

Nikjoo, H; Uehara, S; Wilson, W E; Hoshi, M; Goodhead, D T

1998-04-01

A brief review is presented of the basic concepts in track structure and the relative merit of various theoretical approaches adopted in Monte-Carlo track-structure codes are examined. In the second part of the paper, a formal cluster analysis is introduced to calculate cluster-distance distributions. Total experimental ionization cross-sections were least-square fitted and compared with the calculation by various theoretical methods. Monte-Carlo track-structure code Kurbuc was used to examine and compare the spectrum of the secondary electrons generated by using functions given by Born-Bethe, Jain-Khare, Gryzinsky, Kim-Rudd, Mott and Vriens' theories. The cluster analysis in track structure was carried out using the k-means method and Hartigan algorithm. Data are presented on experimental and calculated total ionization cross-sections: inverse mean free path (IMFP) as a function of electron energy used in Monte-Carlo track-structure codes; the spectrum of secondary electrons generated by different functions for 500 eV primary electrons; cluster analysis for 4 MeV and 20 MeV alpha-particles in terms of the frequency of total cluster energy to the root-mean-square (rms) radius of the cluster and differential distance distributions for a pair of clusters; and finally relative frequency distribution for energy deposited in DNA, single-strand break and double-strand breaks for 10MeV/u protons, alpha-particles and carbon ions. There are a number of Monte-Carlo track-structure codes that have been developed independently and the bench-marking presented in this paper allows a better choice of the theoretical method adopted in a track-structure code to be made. A systematic bench-marking of cross-sections and spectra of the secondary electrons shows differences between the codes at atomic level, but such differences are not significant in biophysical modelling at the macromolecular level. Clustered-damage evaluation shows: that a substantial proportion of dose ( 30%) is deposited by low-energy electrons; the majority of DNA damage lesions are of simple type; the complexity of damage increases with increased LET, while the total yield of strand breaks remains constant; and at high LET values nearly 70% of all double-strand breaks are of complex type.
Electron molecular ion recombination: product excitation and fragmentation.

PubMed

Adams, Nigel G; Poterya, Viktoriya; Babcock, Lucia M

2006-01-01

Electron-ion dissociative recombination is an important ionization loss process in any ionized gas containing molecular ions. This includes the interstellar medium, circumstellar shells, cometary comae, planetary ionospheres, fusion plasma boundaries, combustion flames, laser plasmas and chemical deposition and etching plasmas. In addition to controlling the ionization density, the process generates many radical species, which can contribute to a parallel neutral chemistry. Techniques used to obtain rate data and product information (flowing afterglows and storage rings) are discussed and recent data are reviewed including diatomic to polyatomic ions and cluster ions. The data are divided into rate coefficients and cross sections, including their temperature/energy dependencies, and quantitative identification of neutral reaction products. The latter involve both ground and electronically excited states and including vibrational excitation. The data from the different techniques are compared and trends in the data are examined. The reactions are considered in terms of the basic mechanisms (direct and indirect processes including tunneling) and recent theoretical developments are discussed. Finally, new techniques are mentioned (for product identification; electrostatic storage rings, including single and double rings; Coulomb explosion) and new ways forward are suggested.
Clusters of DNA damage induced by ionizing radiation: formation of short DNA fragments. II. Experimental detection

NASA Technical Reports Server (NTRS)

Rydberg, B.; Chatterjee, A. (Principal Investigator)

1996-01-01

The basic 30-nm chromatin fiber in the mammalian cell consists of an unknown (possibly helical) arrangement of nucleosomes, with about 1.2 kb of DNA per 10-nm length of fiber. Track-structure considerations suggest that interactions of single delta rays or high-LET particles with the chromatin fiber might result in the formation of multiple lesions spread over a few kilobases of DNA (see the accompanying paper: W.R. Holley and A. Chatterjee, Radiat. Res. 145, 188-199, 1996). In particular, multiple DNA double-strand breaks and single-strand breaks may form. To test this experimentally, primary human fibroblasts were labeled with [3H]thymidine and exposed at 0 degrees C to X rays or accelerated nitrogen or iron ions in the LET range of 97-440 keV/microns. DNA was isolated inside agarose plugs and subjected to agarose gel electrophoresis under conditions that allowed good separation of 0.1-2 kb size DNA. The bulk of DNA remained in the well or migrated only a small distance into the gel. It was found that DNA fragments in the expected size range were formed linearly with dose with an efficiency that increased with LET. A comparison of the yield of such fragments with the yield of total DNA double-strand breaks suggests that for the high-LET ions a substantial proportion (20-90%) of DNA double-strand breaks are accompanied within 0.1-2 kb by at least one additional DNA double-strand break. It is shown that these results are in good agreement with theoretical calculations based on treating the 30-nm chromatin fiber as the target for ionizing particles. Theoretical considerations also predict that the clusters will contain numerous single-strand breaks and base damages. It is proposed that such clusters be designated "regionally multiply damaged sites." Postirradiation incubation at 37 degrees C resulted in a decline in the number of short DNA fragments, suggesting a repair activity. The biological significance of regionally multiply damaged sites is presently unknown.
Valence ionized states of iron pentacarbonyl and eta5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy.

PubMed

Fukuda, Ryoichi; Ehara, Masahiro; Nakatsuji, Hiroshi; Kishimoto, Naoki; Ohno, Koichi

2010-02-28

Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS.
Probing electronic wave functions of sodium-doped clusters: Dyson orbitals, anisotropy parameters, and ionization cross-sections

DOE PAGES

Gunina, Anastasia O.; Krylov, Anna I.

2016-11-14

We apply high-level ab initio methods to describe the electronic structure of small clusters of ammonia and dimethylether (DME) doped with sodium, which provide a model for solvated electrons. We investigate the effect of the solvent and cluster size on the electronic states. We consider both energies and properties, with a focus on the shape of the electronic wave function and the related experimental observables such as photoelectron angular distributions. The central quantity in modeling photoionization experiments is the Dyson orbital, which describes the difference between the initial N-electron and final (N-1)-electron states of a system. Dyson orbitals enter themore » expression of the photoelectron matrix element, which determines total and partial photoionization cross-sections. We compute Dyson orbitals for the Na(NH3)n and Na(DME)m clusters using correlated wave functions (obtained with equation-of-motion coupled-cluster model for electron attachment with single and double substitutions) and compare them with more approximate Hartree-Fock and Kohn-Sham orbitals. As a result, we also analyze the effect of correlation and basis sets on the shapes of Dyson orbitals and the experimental observables.« less

Structure and Electronic Properties of Ionized PAH Clusters

NASA Astrophysics Data System (ADS)

Joblin, Christine; Kokkin, Damian L.; Sabbah, Hassan; Bonnamy, Anthony; Dontot, Leo; Rapacioli, Mathias; Simon, Aude; Spiegelman, Fernand; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Falvo, Cyril; Gamboa, Antonio; Brechignac, Philippe; Garcia, Gustavo A.; Nahon, Laurent

2014-06-01

Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This suggestion is a motivation for further characterization of the properties of these clusters in particular when they are ionized. We have used a molecular beam coupled to the photoelectron-photoion coincidence spectrometer DELICIOUS II/ III at the VUV beamline DESIRS of the synchrotron SOLEIL to characterize the electronic properties of cationic coronene (C24H12) and pyrene (C16H10) clusters up to the pentamer and heptamer, respectively. These experimental results are analysed in the light of electronic structure calculations. Simulations of the properties of ionized PAH clusters are faced with the difficulty of describing charge delocalization in these large systems. We will show that recent developments combining a Density Functional Tight Binding method with Configuration Interaction scheme is successful in simulating the ionization potential, which gives strong confidence into the predicted structures for these PAH clusters. We will also present current effort to study charge transfer states by performing complementary measurements with the PIRENEA ion trap set-up. Joint ANR project GASPARIM, ANR-10-BLAN-501 M. Rapacioli, C. Joblin and P. Boissel Astron. & Astrophys., 429 (2005), 193-204. G. Garcia, H. Soldi-Lose and L. Nahon Rev. Sci. Instrum., 80 (2009), 023102; G. Garcia, B. Cunha de Miranda, M. Tia, S. Daly, L. Nahon, Rev. Sci. Instrum., 84 (2013), 053112 M. Rapacioli, A. Simon, L. Dontot and F. Spiegelman Phys. Status Solidi B, 249 (2) (2012), 245-258; L. Dontot, M. Rapacioli and F. Spiegelman (2014) submitted
Using reflection time-of-flight mass spectrometer techniques to investigate cluster dynamics and bonding

NASA Astrophysics Data System (ADS)

Wei, Shiqing; Castleman, A. W., Jr.

1994-02-01

Lase based time-of-flight mass spectrometer systems affixed with reflectrons are valuable tools for investigating cluster dynamics and reactions, spectroscopy and structures. Utilizing the reflectron time-of-flight mass spectrometer techniques, both decay fractions and kinetic energy releases of metastable cluster ions can be measured with high precision. By applying related theoretical models, the desired thermochemical values of metastable species can be deduced, which are otherwise very difficult to obtain. Several examples are discussed with attention focused on ammonia as a test case for hydrogen bond systems, and xenon for weaker van der Waals clusters. A brief overview of applications to investigating solvation effects on reactions and structures, delayed electron transfer and ionization through intracluster Penning ionization is also given.
Formation of iron complexs from trifluoroacetic acid based liquid chromatography mobile phases as interference ions in liquid chromatography/electrospray ionization mass spectrometric analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Anil K.; Zhang, Rui; Orton, Daniel J.

Two unexpected singly charged ions at m/z 1103 and 944 have been observed in mass spectra obtained from electrospray ionization-mass spectrometric analysis of liquid chromatography effluents with mobile phases containing trifluoroacetic acid. Accurate mass measurement and tandem mass spectrometry studies revealed that these two ions are not due to any contamination from solvents and chemicals used for mobile and stationary phases or from the laboratory atmospheric environment. Instead these ions are clusters of trifluoroacetic acid formed in association with acetonitrile, water and iron from the stainless steel union used to connect the column with the electrospray tip and to applymore » high voltage; the molecular formulae are Fe+((OH)(H2O)2)9(CF3COOH)5 and Fe+((OH)(H2O)2)6 (CF3COOH)5.« less
Ultraviolet gas absorption and dust extinction toward M8

NASA Technical Reports Server (NTRS)

Boggs, Don; Bohm-Vitense, Erika

1990-01-01

Interstellar absorption lines are analyzed using high-resolution IUE spectra of 11 stars in the young cluster NGC 6530 located in the M8 region. High-velocity clouds at -35 km/s and -60 km/s are seen toward all cluster stars. The components arise in gases that are part of large interstellar bubbles centered on the cluster and driven by stellar winds of the most luminous members. Absorption lines of species of different ionization states are separated in velocity. The velocity stratification is best explained as a 'champagne' flow of ionized gas away from the cluster. The C IV/Si IV ratios toward the hotter cluster members are consistent with simple photoionization models if the gas-phase C/Si ratio is increased by preferential accretion onto dust grains. High ion column densities in the central cluster decline with distance from W93, suggesting that radiation from a hot source near W93 has photoionized gas in the central cluster.
A new scheme for perturbative triples correction to (0,1) sector of Fock space multi-reference coupled cluster method: theory, implementation, and examples.

PubMed

Dutta, Achintya Kumar; Vaval, Nayana; Pal, Sourav

2015-01-28

We propose a new elegant strategy to implement third order triples correction in the light of many-body perturbation theory to the Fock space multi-reference coupled cluster method for the ionization problem. The computational scaling as well as the storage requirement is of key concerns in any many-body calculations. Our proposed approach scales as N(6) does not require the storage of triples amplitudes and gives superior agreement over all the previous attempts made. This approach is capable of calculating multiple roots in a single calculation in contrast to the inclusion of perturbative triples in the equation of motion variant of the coupled cluster theory, where each root needs to be computed in a state-specific way and requires both the left and right state vectors together. The performance of the newly implemented scheme is tested by applying to methylene, boron nitride (B2N) anion, nitrogen, water, carbon monoxide, acetylene, formaldehyde, and thymine monomer, a DNA base.
Energetics of charged metal clusters containing vacancies

NASA Astrophysics Data System (ADS)

Pogosov, Valentin V.; Reva, Vitalii I.

2018-01-01

We study theoretically large metal clusters containing vacancies. We propose an approach, which combines the Kohn-Sham results for monovacancy in a bulk of metal and analytical expansions in small parameters cv (relative concentration of vacancies) and RN,v -1, RN ,v being cluster radii. We obtain expressions of the ionization potential and electron affinity in the form of corrections to electron work function, which require only the characteristics of 3D defect-free metal. The Kohn-Sham method is used to calculate the electron profiles, ionization potential, electron affinity, electrical capacitance; dissociation, cohesion, and monovacancy-formation energies of the small perfect clusters NaN, MgN, AlN (N ≤ 270) and the clusters containing a monovacancy (N ≥ 12) in the stabilized-jellium model. The quantum-sized dependences for monovacancy-formation energies are calculated for the Schottky scenario and the "bubble blowing" scenario, and their asymptotic behavior is also determined. It is shown that the asymptotical behaviors of size dependences for these two mechanisms differ from each other and weakly depend on the number of atoms in the cluster. The contribution of monovacancy to energetics of charged clusters and the size dependences of their characteristics and asymptotics are discussed. It is shown that the difference between the characteristics for the neutral and charged clusters is entirely determined by size dependences of ionization potential and electron affinity. Obtained analytical dependences may be useful for the analysis of the results of photoionization experiments and for the estimation of the size dependences of the vacancy concentration including the vicinity of the melting point.
Clusters of Point Defects Near Dislocations as a Tool to Control CdZnTe Electrical Parameters by Ultrasound

NASA Astrophysics Data System (ADS)

Olikh, Ya. M.; Tymochko, M. D.; Olikh, O. Ya.; Shenderovsky, V. A.

2018-05-01

We studied the temperature dependence (77-300 K) of the electron concentration and mobility using the Hall method under ultrasound (the acoustic Hall method) to determine the mechanisms by which ultrasound influences the electrical activity of near-dislocation clusters in n-type low-ohmic Cd1-x Zn x Te single crystals (N Cl ≈ 1024 m-3; x = 0; 0.04) with different dislocation density (0.4-5.1) × 1010 m-2. Changes in electrophysical parameters were found to occur as a function of temperature and ultrasound intensity. To evaluate the relative contribution of different charge carrier scattering mechanisms (lattice scattering, ionized impurity scattering, neutral impurity scattering, and dislocation scattering) and their change under ultrasound, a differential evolution method was used. This method made it possible to analyze experimental mobility μ H(T) by its nonlinear approximation with characteristic temperature dependence for each mechanism. An increase in neutral impurity scattering and a decrease in ionized impurity and dislocation scattering components were observed under ultrasound. The character and the amount of these acoustically induced changes correlate with particular sample dislocation characteristics. It was concluded that the observed effects are related to the acoustically induced transformation of the point-defect structure, mainly in the near dislocation crystal regions.
NON-LOCAL THERMODYNAMICAL EQUILIBRIUM EFFECTS ON THE IRON ABUNDANCE OF ASYMPTOTIC GIANT BRANCH STARS IN 47 TUCANAE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lapenna, E.; Mucciarelli, A.; Lanzoni, B.

2014-12-20

We present the iron abundance of 24 asymptotic giant branch (AGB) stars, members of the globular cluster 47 Tucanae, obtained with high-resolution spectra collected with the FEROS spectrograph at the MPG/ESO 2.2 m Telescope. We find that the iron abundances derived from neutral lines (with a mean value [Fe I/H] =–0.94 ± 0.01, σ = 0.08 dex) are systematically lower than those derived from single ionized lines ([Fe II/H] =–0.83 ± 0.01, σ = 0.05 dex). Only the latter are in agreement with those obtained for a sample of red giant branch (RGB) cluster stars, for which the Fe I andmore » Fe II lines provide the same iron abundance. This finding suggests that non-local thermodynamical equilibrium (NLTE) effects driven by overionization mechanisms are present in the atmosphere of AGB stars and significantly affect the Fe I lines while leaving Fe II features unaltered. On the other hand, the very good ionization equilibrium found for RGB stars indicates that these NLTE effects may depend on the evolutionary stage. We discuss the impact of this finding on both the chemical analysis of AGB stars and on the search for evolved blue stragglers.« less
Optimal control of the strong-field ionization of silver clusters in helium droplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Truong, N. X.; Goede, S.; Przystawik, A.

Optimal control techniques combined with femtosecond laser pulse shaping are applied to steer and enhance the strong-field induced emission of highly charged atomic ions from silver clusters embedded in helium nanodroplets. With light fields shaped in amplitude and phase we observe a substantial increase of the Ag{sup q+} yield for q>10 when compared to bandwidth-limited and optimally stretched pulses. A remarkably simple double-pulse structure, containing a low-intensity prepulse and a stronger main pulse, turns out to produce the highest atomic charge states up to Ag{sup 20+}. A negative chirp during the main pulse hints at dynamic frequency locking to themore » cluster plasmon. A numerical optimal control study on pure silver clusters with a nanoplasma model converges to a similar pulse structure and corroborates that the optimal light field adapts to the resonant excitation of cluster surface plasmons for efficient ionization.« less
Generation of strongly coupled Xe cluster nanoplasmas by low intensive soft x-ray laser irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Namba, S.; Hasegawa, N.; Kishimoto, M.

A seeding gas jet including Xe clusters was irradiated with a laser-driven plasma soft x-ray laser pulse ({lambda}=13.9 nm, {approx}7 ps, {<=}5 Multiplication-Sign 10{sup 9} W/cm{sup 2}), where the laser photon energy is high enough to ionize 4d core electrons. In order to clarify how the innershell ionization followed by the Auger electron emission is affected under the intense laser irradiation, the electron energy distribution was measured. Photoelectron spectra showed that the peak position attributed to 4d hole shifted to lower energy and the spectral width was broadened with increasing cluster size. Moreover, the energy distribution exhibited that a stronglymore » coupled cluster nanoplasma with several eV was generated.« less
Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency

NASA Astrophysics Data System (ADS)

Zeegers, Guido P.; Günthardt, Barbara F.; Zenobi, Renato

2016-04-01

Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0-3.53 Jcm-2) and the ion extraction delay time (0-950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements.
A simple way to model nebulae with distributed ionizing stars

NASA Astrophysics Data System (ADS)

Jamet, L.; Morisset, C.

2008-04-01

Aims: This work is a follow-up of a recent article by Ercolano et al. that shows that, in some cases, the spatial dispersion of the ionizing stars in a given nebula may significantly affect its emission spectrum. The authors found that the dispersion of the ionizing stars is accompanied by a decrease in the ionization parameter, which at least partly explains the variations in the nebular spectrum. However, they did not research how other effects associated to the dispersion of the stars may contribute to those variations. Furthermore, they made use of a unique and simplified set of stellar populations. The scope of the present article is to assess whether the variation in the ionization parameter is the dominant effect in the dependence of the nebular spectrum on the distribution of its ionizing stars. We examined this possibility for various regimes of metallicity and age. We also investigated a way to model the distribution of the ionizing sources so as to bypass expensive calculations. Methods: We wrote a code able to generate random stellar populations and to compute the emission spectra of their associated nebulae through the widespread photoionization code cloudy. This code can process two kinds of spatial distributions of the stars: one where all the stars are concentrated at one point, and one where their separation is such that their Strömgren spheres do not overlap. Results: We found that, in most regimes of stellar population ages and gas metallicities, the dependence of the ionization parameter on the distribution of the stars is the dominant factor in the variation of the main nebular diagnostics with this distribution. We derived a method to mimic those effects with a single calculation that makes use of the common assumptions of a central source and a spherical nebula, in the case of constant density objects. This represents a computation time saving by a factor of at least several dozen in the case of H ii regions ionized by massive clusters.
Generation of gas-phase ions from charged clusters: an important ionization step causing suppression of matrix and analyte ions in matrix-assisted laser desorption/ionization mass spectrometry.

PubMed

Lou, Xianwen; van Dongen, Joost L J; Milroy, Lech-Gustav; Meijer, E W

2016-12-30

Ionization in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a very complicated process. It has been reported that quaternary ammonium salts show extremely strong matrix and analyte suppression effects which cannot satisfactorily be explained by charge transfer reactions. Further investigation of the reasons causing these effects can be useful to improve our understanding of the MALDI process. The dried-droplet and modified thin-layer methods were used as sample preparation methods. In the dried-droplet method, analytes were co-crystallized with matrix, whereas in the modified thin-layer method analytes were deposited on the surface of matrix crystals. Model compounds, tetrabutylammonium iodide ([N(Bu) 4 ]I), cesium iodide (CsI), trihexylamine (THA) and polyethylene glycol 600 (PEG 600), were selected as the test analytes given their ability to generate exclusively pre-formed ions, protonated ions and metal ion adducts respectively in MALDI. The strong matrix suppression effect (MSE) observed using the dried-droplet method might disappear using the modified thin-layer method, which suggests that the incorporation of analytes in matrix crystals contributes to the MSE. By depositing analytes on the matrix surface instead of incorporating in the matrix crystals, the competition for evaporation/ionization from charged matrix/analyte clusters could be weakened resulting in reduced MSE. Further supporting evidence for this inference was found by studying the analyte suppression effect using the same two sample deposition methods. By comparing differences between the mass spectra obtained via the two sample preparation methods, we present evidence suggesting that the generation of gas-phase ions from charged matrix/analyte clusters may induce significant suppression of matrix and analyte ions. The results suggest that the generation of gas-phase ions from charged matrix/analyte clusters is an important ionization step in MALDI-MS. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Ratios of double to single ionization of He and Ne by strong 400-nm laser pulses using the quantitative rescattering theory

NASA Astrophysics Data System (ADS)

Chen, Zhangjin; Li, Xiaojin; Zatsarinny, Oleg; Bartschat, Klaus; Lin, C. D.

2018-01-01

We present numerical simulations of the ratio between double and single ionization of He and Ne by intense laser pulses at wavelengths of 390 and 400 nm, respectively. The yields of doubly charged ions due to nonsequential double ionization (NSDI) are obtained by employing the quantitative rescattering (QRS) model. In this model, the NSDI ionization probability is expressed as a product of the returning electron wave packet (RWP) and the total scattering cross sections for laser-free electron impact excitation and electron impact ionization of the parent ion. According to the QRS theory, the same RWP is also responsible for the emission of high-energy above-threshold ionization photoelectrons. To obtain absolute double-ionization yields, the RWP is generated by solving the time-dependent Schrödinger equation (TDSE) within a one-electron model. The same TDSE results can also be taken to obtain single-ionization yields. By using the TDSE results to calibrate single ionization and the RWP obtained from the strong-field approximation, we further simplify the calculation such that the nonuniform laser intensity distribution in the focused laser beam can be accounted for. In addition, laser-free electron impact excitation and ionization cross sections are calculated using the state-of-the-art many-electron R -matrix theory. The simulation results for double-to-single-ionization ratios are found to compare well with experimental data and support the validity of the nonsequential double-ionization mechanism for the covered intensity region.
Size dependent fragmentation of argon clusters in the soft x-ray ionization regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gisselbrecht, Mathieu; Lindgren, Andreas; Burmeister, Florian

Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters ({>=}100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slowermore » processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ('heat') dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.« less
Dynamics and fragmentation of van der Waals and hydrogen bonded cluster cations: (NH{sub 3}){sub n} and (NH{sub 3}BH{sub 3}){sub n} ionized at 10.51 eV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Bing; Bernstein, Elliot R., E-mail: erb@Colostate.edu; Shin, Joong-Won

A 118 nm laser is employed as a high energy, single photon (10.51 eV/photon) source for study of the dynamics and fragmentation of the ammonia borane (NH{sub 3}BH{sub 3}) cation and its cluster ions through time of flight mass spectrometry. The behavior of ammonia ion and its cluster ions is also investigated under identical conditions in order to explicate the ammonia borane results. Charge distributions, molecular orbitals, and spin densities for (NH{sub 3}BH{sub 3}){sub n} and its cations are explored at both the second-order perturbation theory (MP2) and complete active space self-consistent field (CASSCF) theory levels. Initial dissociation mechanisms andmore » potential energy surfaces for ionized NH{sub 3}BH{sub 3}, NH{sub 3}, and their clusters are calculated at the MP2/6-311++G(d,p) level. Protonated clusters (NH{sub 3}){sub x}H{sup +} dominate ammonia cluster mass spectra: our calculations show that formation of (NH{sub 3}){sub n−1}H{sup +} and NH{sub 2} from the nascent (NH{sub 3}){sub n}{sup +} has the lowest energy barrier for the system. The only common features for the (NH{sub 3}){sub n}{sup +} and (NH{sub 3}BH{sub 3}){sub n}{sup +} mass spectra under these conditions are found to be NH{sub y}{sup +} (y = 0,…,4) at m/z = 14–18. Molecular ions with both {sup 11}B and {sup 10}B isotopes are observed, and therefore, product ions observed for the (NH{sub 3}BH{sub 3}){sub n} cluster system derive from (NH{sub 3}BH{sub 3}){sub n} clusters themselves, not from the NH{sub 3} moiety of NH{sub 3}BH{sub 3} alone. NH{sub 3}BH{sub 2}{sup +} is the most abundant ionization product in the (NH{sub 3}BH{sub 3}){sub n}{sup +} cluster spectra: calculations support that for NH{sub 3}BH{sub 3}{sup +}, an H atom is lost from the BH{sub 3} moiety with an energy barrier of 0.67 eV. For (NH{sub 3}BH{sub 3}){sub 2}{sup +} and (NH{sub 3}BH{sub 3}){sub 3}{sup +} clusters, a B{sup δ+}⋯H{sup δ−}⋯{sup δ−}H⋯{sup δ+}B bond can form in the respective cluster ions, generating a lower energy, more stable ion structure. The first step in the (NH{sub 3}BH{sub 3}){sub n}{sup +} (n = 2, 3) dissociation is the breaking of the B{sup δ+}⋯H{sup δ−}⋯{sup δ−}H⋯{sup δ+}B moiety, leading to the subsequent release of H{sub 2} from the latter cluster ion. The overall reaction mechanisms calculated are best represented and understood employing a CASSCF natural bond orbital description of the valence electron distribution for the various clusters and monomers. Comparison of the present results with those found for solid NH{sub 3}BH{sub 3} suggests that NH{sub 3}BH{sub 3} can be a good hydrogen storage material.« less
Observation of correlated electronic decay in expanding clusters triggered by near-infrared fields

PubMed Central

Schütte, B.; Arbeiter, M.; Fennel, T.; Jabbari, G.; Kuleff, A.I.; Vrakking, M.J.J.; Rouzée, A.

2015-01-01

When an excited atom is embedded into an environment, novel relaxation pathways can emerge that are absent for isolated atoms. A well-known example is interatomic Coulombic decay, where an excited atom relaxes by transferring its excess energy to another atom in the environment, leading to its ionization. Such processes have been observed in clusters ionized by extreme-ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay process that occurs following nanoplasma formation and Rydberg atom generation in the ionization of clusters by intense, non-resonant infrared laser fields. Relaxation of the Rydberg states and transfer of the available electronic energy to adjacent electrons in Rydberg states or quasifree electrons in the expanding nanoplasma leaves a distinct signature in the electron kinetic energy spectrum. These so far unobserved electron-correlation-driven energy transfer processes may play a significant role in the response of any nano-scale system to intense laser light. PMID:26469997
Hierarchical Velocity Structure in the Core of Abell 2597

NASA Technical Reports Server (NTRS)

Still, Martin; Mushotzky, Richard

2004-01-01

We present XMM-Newton RGS and EPIC data of the putative cooling flow cluster Abell 2597. Velocities of the low-ionization emission lines in the spectrum are blue shifted with respect to the high-ionization lines by 1320 (sup +660) (sub -210) kilometers per second, which is consistent with the difference in the two peaks of the galaxy velocity distribution and may be the signature of bulk turbulence, infall, rotation or damped oscillation in the cluster. A hierarchical velocity structure such as this could be the direct result of galaxy mergers in the cluster core, or the injection of power into the cluster gas from a central engine. The uniform X-ray morphology of the cluster, the absence of fine scale temperature structure and the random distribution of the the galaxy positions, independent of velocity, suggests that our line of sight is close to the direction of motion. These results have strong implications for cooling flow models of the cluster Abell 2597. They give impetus to those models which account for the observed temperature structure of some clusters using mergers instead of cooling flows.
Vibrational spectra and structures of neutral Si(m)C(n) clusters (m + n = 6): sequential doping of silicon clusters with carbon atoms.

PubMed

Savoca, Marco; Lagutschenkov, Anita; Langer, Judith; Harding, Dan J; Fielicke, André; Dopfer, Otto

2013-02-14

Vibrational spectra of mixed silicon carbide clusters Si(m)C(n) with m + n = 6 in the gas phase are obtained by resonant infrared-vacuum-ultraviolet two-color ionization (IR-UV2CI for n ≤ 2) and density functional theory (DFT) calculations. Si(m)C(n) clusters are produced in a laser vaporization source, in which the silicon plasma reacts with methane. Subsequently, they are irradiated with tunable IR light from an IR free electron laser before they are ionized with UV photons from an F(2) laser. Resonant absorption of one or more IR photons leads to an enhanced ionization efficiency for Si(m)C(n) and provides the size-specific IR spectra. IR spectra measured for Si(6), Si(5)C, and Si(4)C(2) are assigned to their most stable isomers by comparison with calculated linear absorption spectra. The preferred Si(m)C(n) structures with m + n = 6 illustrate the systematic transition from chain-like geometries for bare C(6) to three-dimensional structures for bare Si(6). In contrast to bulk SiC, carbon atom segregation is observed already for the smallest n (n = 2).
Analytical Energy Gradients for Excited-State Coupled-Cluster Methods

NASA Astrophysics Data System (ADS)

Wladyslawski, Mark; Nooijen, Marcel

The equation-of-motion coupled-cluster (EOM-CC) and similarity transformed equation-of-motion coupled-cluster (STEOM-CC) methods have been firmly established as accurate and routinely applicable extensions of single-reference coupled-cluster theory to describe electronically excited states. An overview of these methods is provided, with emphasis on the many-body similarity transform concept that is the key to a rationalization of their accuracy. The main topic of the paper is the derivation of analytical energy gradients for such non-variational electronic structure approaches, with an ultimate focus on obtaining their detailed algebraic working equations. A general theoretical framework using Lagrange's method of undetermined multipliers is presented, and the method is applied to formulate the EOM-CC and STEOM-CC gradients in abstract operator terms, following the previous work in [P.G. Szalay, Int. J. Quantum Chem. 55 (1995) 151] and [S.R. Gwaltney, R.J. Bartlett, M. Nooijen, J. Chem. Phys. 111 (1999) 58]. Moreover, the systematics of the Lagrange multiplier approach is suitable for automation by computer, enabling the derivation of the detailed derivative equations through a standardized and direct procedure. To this end, we have developed the SMART (Symbolic Manipulation and Regrouping of Tensors) package of automated symbolic algebra routines, written in the Mathematica programming language. The SMART toolkit provides the means to expand, differentiate, and simplify equations by manipulation of the detailed algebraic tensor expressions directly. The Lagrangian multiplier formulation establishes a uniform strategy to perform the automated derivation in a standardized manner: A Lagrange multiplier functional is constructed from the explicit algebraic equations that define the energy in the electronic method; the energy functional is then made fully variational with respect to all of its parameters, and the symbolic differentiations directly yield the explicit equations for the wavefunction amplitudes, the Lagrange multipliers, and the analytical gradient via the perturbation-independent generalized Hellmann-Feynman effective density matrix. This systematic automated derivation procedure is applied to obtain the detailed gradient equations for the excitation energy (EE-), double ionization potential (DIP-), and double electron affinity (DEA-) similarity transformed equation-of-motion coupled-cluster singles-and-doubles (STEOM-CCSD) methods. In addition, the derivatives of the closed-shell-reference excitation energy (EE-), ionization potential (IP-), and electron affinity (EA-) equation-of-motion coupled-cluster singles-and-doubles (EOM-CCSD) methods are derived. Furthermore, the perturbative EOM-PT and STEOM-PT gradients are obtained. The algebraic derivative expressions for these dozen methods are all derived here uniformly through the automated Lagrange multiplier process and are expressed compactly in a chain-rule/intermediate-density formulation, which facilitates a unified modular implementation of analytic energy gradients for CCSD/PT-based electronic methods. The working equations for these analytical gradients are presented in full detail, and their factorization and implementation into an efficient computer code are discussed.

Effects of molecular weight and cationization agent on the sensitivity of Bi cluster secondary ion mass spectrometry.

PubMed

Fujii, Makiko; Shishido, Rie; Satoh, Takaya; Suzuki, Shigeru; Matsuo, Jiro

2016-07-30

Bi cluster secondary ion mass spectrometry (SIMS) is one of the most promising tools for precise analysis of synthetic polymers. However, the sensitivity in the high-mass region is still insufficient compared with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Accordingly, the effects of metal assistance (cationization agents) were investigated in this study. To investigate the effects caused by varying the ionization agent, three different polyethylene glycol (PEG) samples were prepared, one with an Ag-deposited film, and two others mixed with Ag and Na, respectively. The measurements were performed by using a commercial Bi cluster SIMS and MALDI-TOFMS systems. The mass spectrum obtained with MALDI-TOFMS was used as a reference molecular weight distribution to evaluate the effects of molecular weight and primary ion species (Bi + , Bi 3 + , Bi 3 2 + ) on the sensitivity of Bi cluster SIMS. The intensity of each secondary ion was the highest in Bi 3 2 + irradiation, and the lowest in Bi + irradiation. Regarding the cationization agents, the secondary ion yield was the highest for the sample mixed with Ag, while the degree of decay of sensitivity along with the increase in molecular weight was the smallest for the sample mixed with Na. It was suggested that the cationization mechanism consists of pre-formed ionization and gas-phase ionization processes. The sensitivity of Bi cluster SIMS decreases to approximately one-fiftieth in every 1000 u. These results might help in understanding the mechanism of cationization and further enhancement of secondary ion yields of polymers. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-07-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014 h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated with its brightest cluster galaxy, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing a meaningful role. We have argued that old stars, often invoked to explain low-ionization nuclear emission-line region emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power laws with slopes in the range expected from shock models. These models also show, however, that only ˜10 per cent of H α luminosity can be explained by shocks. We conclude that shocks probably associated with the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but cannot be the major source of ionizing photons.
Comprehensive Biothreat Cluster Identification by PCR/Electrospray-Ionization Mass Spectrometry

PubMed Central

Sampath, Rangarajan; Mulholland, Niveen; Blyn, Lawrence B.; Massire, Christian; Whitehouse, Chris A.; Waybright, Nicole; Harter, Courtney; Bogan, Joseph; Miranda, Mary Sue; Smith, David; Baldwin, Carson; Wolcott, Mark; Norwood, David; Kreft, Rachael; Frinder, Mark; Lovari, Robert; Yasuda, Irene; Matthews, Heather; Toleno, Donna; Housley, Roberta; Duncan, David; Li, Feng; Warren, Robin; Eshoo, Mark W.; Hall, Thomas A.; Hofstadler, Steven A.; Ecker, David J.

2012-01-01

Technology for comprehensive identification of biothreats in environmental and clinical specimens is needed to protect citizens in the case of a biological attack. This is a challenge because there are dozens of bacterial and viral species that might be used in a biological attack and many have closely related near-neighbor organisms that are harmless. The biothreat agent, along with its near neighbors, can be thought of as a biothreat cluster or a biocluster for short. The ability to comprehensively detect the important biothreat clusters with resolution sufficient to distinguish the near neighbors with an extremely low false positive rate is required. A technological solution to this problem can be achieved by coupling biothreat group-specific PCR with electrospray ionization mass spectrometry (PCR/ESI-MS). The biothreat assay described here detects ten bacterial and four viral biothreat clusters on the NIAID priority pathogen and HHS/USDA select agent lists. Detection of each of the biothreat clusters was validated by analysis of a broad collection of biothreat organisms and near neighbors prepared by spiking biothreat nucleic acids into nucleic acids extracted from filtered environmental air. Analytical experiments were carried out to determine breadth of coverage, limits of detection, linearity, sensitivity, and specificity. Further, the assay breadth was demonstrated by testing a diverse collection of organisms from each biothreat cluster. The biothreat assay as configured was able to detect all the target organism clusters and did not misidentify any of the near-neighbor organisms as threats. Coupling biothreat cluster-specific PCR to electrospray ionization mass spectrometry simultaneously provides the breadth of coverage, discrimination of near neighbors, and an extremely low false positive rate due to the requirement that an amplicon with a precise base composition of a biothreat agent be detected by mass spectrometry. PMID:22768032
Charge Retention by Monodisperse Gold Clusters on Surfaces Prepared Using Soft Landing of Mass Selected Ions

NASA Astrophysics Data System (ADS)

Johnson, Grant; Priest, Thomas; Laskin, Julia

2012-02-01

Monodisperse gold clusters have been prepared on surfaces in different charge states through soft landing of mass-selected ions. Gold clusters were synthesized in methanol solution by reduction of a gold precursor with a weak reducing agent in the presence of a diphosphine capping ligand. Electrospray ionization was used to introduce the clusters into the gas-phase and mass-selection was employed to isolate a single ionic cluster species which was delivered to surfaces at well controlled kinetic energies. Using in-situ time of flight secondary ion mass spectrometry (SIMS) it is demonstrated that the cluster retains its 3+ charge state when soft landed onto the surface of a fluorinated self assembled monolayer on gold. In contrast, when deposited onto carboxylic acid terminated and conventional alkyl thiol surfaces on gold the clusters exhibit larger relative abundances of the 2+ and 1+ charge states, respectively. The kinetics of charge reduction on the surface have been investigated using in-situ Fourier Transform Ion Cyclotron Resonance SIMS. It is shown that an extremely slow interfacial charge reduction occurs on the fluorinated monolayer surface while an almost instantaneous neutralization takes place on the surface of the alkyl thiol monolayer. Our results demonstrate that the size and charge state of small gold clusters on surfaces, both of which exert a dramatic influence on their chemical and physical properties, may be tuned through soft landing of mass-selected ions onto selected substrates.
Multiple ionization of C 60 in collisions with 2.33 MeV/u O-ions and giant plasmon excitation

NASA Astrophysics Data System (ADS)

Kelkar, A. H.; Kadhane, U.; Misra, D.; Kumar, Ajay; Tribedi, L. C.

2007-03-01

Single and multiple ionization of C60 in collisions with fast (v = 9.7 a.u.) Oq+ ions have been studied. Relative cross sections for production of C 601+ to C 604+ have been measured. The intensity ratios of double-to-single ionization agree very well with a model based on giant dipole plasmon resonance (GDPR). Almost linear increasing trend of the yields of single and double ionizations with projectile charge state is well reproduced by the single and double plasmon excitation mechanisms. The observed charge state independence of triple and quadruple ionization is in sharp contrast to the GDPR model.
Metal-cluster ionization energy: A profile-insensitive exact expression for the size effect

NASA Astrophysics Data System (ADS)

Seidl, Michael; Perdew, John P.; Brajczewska, Marta; Fiolhais, Carlos

1997-05-01

The ionization energy of a large spherical metal cluster of radius R is I(R)=W+(+c)/R, where W is the bulk work function and c~-0.1 is a material-dependent quantum correction to the electrostatic size effect. We present 'Koopmans' and 'displaced-profile change-in-self-consistent-field' expressions for W and c within the ordinary and stabilized-jellium models. These expressions are shown to be exact and equivalent when the exact density profile of a large neutral cluster is employed; these equivalences generalize the Budd-Vannimenus theorem. With an approximate profile obtained from a restricted variational calculation, the 'displaced-profile' expressions are the more accurate ones. This profile insensitivity is important, because it is not practical to extract c from solutions of the Kohn-Sham equations for small metal clusters.
Insight into acid-base nucleation experiments by comparison of the chemical composition of positive, negative, and neutral clusters.

PubMed

Bianchi, Federico; Praplan, Arnaud P; Sarnela, Nina; Dommen, Josef; Kürten, Andreas; Ortega, Ismael K; Schobesberger, Siegfried; Junninen, Heikki; Simon, Mario; Tröstl, Jasmin; Jokinen, Tuija; Sipilä, Mikko; Adamov, Alexey; Amorim, Antonio; Almeida, Joao; Breitenlechner, Martin; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Kangasluoma, Juha; Keskinen, Helmi; Kim, Jaeseok; Kirkby, Jasper; Laaksonen, Ari; Lawler, Michael J; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Tomé, António; Virtanen, Annele; Viisanen, Yrjö; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M; Ye, Penglin; Curtius, Joachim; Kulmala, Markku; Worsnop, Douglas R; Donahue, Neil M; Baltensperger, Urs

2014-12-02

We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid-base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster-cluster collision.
Infrared absorption of methanethiol clusters (CH3SH)n, n = 2-5, recorded with a time-of-flight mass spectrometer using IR depletion and VUV ionization

NASA Astrophysics Data System (ADS)

Fu, Lung; Han, Hui-Ling; Lee, Yuan-Pern

2012-12-01

We investigated IR spectra in the CH- and SH-stretching regions of size-selected methanethiol clusters, (CH3SH)n with n = 2-5, in a pulsed supersonic jet using infrared (IR)-vacuum ultraviolet (VUV) ionization. VUV emission at 132.50 nm served as the source of ionization in a time-of-flight mass spectrometer. Clusters were dissociated with light from a tunable IR laser before ionization. The variations in intensity of methanethiol cluster ions (CH3SH)n+ were monitored as the IR laser light was tuned across the range 2470-3100 cm-1. In the SH-stretching region, the spectrum of (CH3SH)2 shows a weak band near 2601 cm-1, red-shifted only 7 cm-1 from that of the monomer. In contrast, all spectra of (CH3SH)n, n = 3-5, show a broad band near 2567 cm-1 with much greater intensity. In the CH-stretching region, absorption bands of (CH3SH)2 are located near 2865, 2890, 2944, and 3010 cm-1, red-shifted by 3-5 cm-1 from those of CH3SH. These red shifts increase slightly for larger clusters and bands near 2856, 2884, 2938, and 3005 cm-1 were observed for (CH3SH)5. These spectral results indicate that the S-H...S hydrogen bond plays an important role in clusters with n = 3-5, but not in (CH3SH)2, in agreement with theoretical predictions. The absence of a band near 2608 cm-1 that corresponds to absorption of the non-hydrogen-bonded SH moiety and the large width of observed feature near 2567 cm-1 indicate that the dominant stable structures of (CH3SH)n, n = 3-5, have a cyclic hydrogen-bonded framework.
APOBEC3 cytidine deaminases in double-strand DNA break repair and cancer promotion.

PubMed

Nowarski, Roni; Kotler, Moshe

2013-06-15

High frequency of cytidine to thymidine conversions was identified in the genome of several types of cancer cells. In breast cancer cells, these mutations are clustered in long DNA regions associated with single-strand DNA (ssDNA), double-strand DNA breaks (DSB), and genomic rearrangements. The observed mutational pattern resembles the deamination signature of cytidine to uridine carried out by members of the APOBEC3 family of cellular deaminases. Consistently, APOBEC3B (A3B) was recently identified as the mutational source in breast cancer cells. A3G is another member of the cytidine deaminases family predominantly expressed in lymphoma cells, where it is involved in mutational DSB repair following ionizing radiation treatments. This activity provides us with a new paradigm for cancer cell survival and tumor promotion and a mechanistic link between ssDNA, DSBs, and clustered mutations. Cancer Res; 73(12); 3494-8. ©2013 AACR. ©2013 AACR.
Ligand induced structural isomerism in phosphine coordinated gold clusters revealed by ion mobility mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ligare, Marshall R.; Baker, Erin S.; Laskin, Julia

Structural isomerism in ligated gold clusters is revealed using electrospray ionization ion mobility spectrometry mass spectrometry. Phosphine ligated Au8 clusters are shown to adopt more “extended” type structures with increasing exchange of methyldiphenylphosphine (MePPh2) for triphenylphosphine (PPh3). These ligand-dependant structure-property relationships are critical to applications of clusters in catalysis.
Catalog of open clusters and associated interstellar matter

NASA Technical Reports Server (NTRS)

Leisawitz, David

1988-01-01

The Catalog of Open Clusters and Associated Interstellar Matter summarizes observations of 128 open clusters and their associated ionized, atomic, and molecular iinterstellar matter. Cluster sizes, distances, radial velocities, ages, and masses, and the radial velocities and masses of associated interstellar medium components, are given. The database contains information from approximately 400 references published in the scientific literature before 1988.
Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency.

PubMed

Zeegers, Guido P; Günthardt, Barbara F; Zenobi, Renato

2016-04-01

Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0-3.53 Jcm(-2)) and the ion extraction delay time (0-950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements. Graphical Abstract ᅟ.
Study of BenW (n = 1-12) clusters: An electron collision perspective

NASA Astrophysics Data System (ADS)

Modak, Paresh; Kaur, Jaspreet; Antony, Bobby

2017-08-01

This article explores electron scattering cross sections by Beryllium-Tungsten clusters (BenW). Beryllium and tungsten are important elements for plasma facing wall components, especially for the deuterium/tritium phase of ITER and in the recently installed JET. The present study focuses on different electron impact interactions in terms of elastic cross section (Qel), inelastic cross section (Qinel), ionization cross section (Qion), and momentum transfer cross section (Qmtcs) for the first twelve clusters belonging to the BenW family. It also predicts the evolution of the cross section with the size of the cluster. These cross sections are used as an input to model processes in plasma. The ionization cross section presented here is compared with the available reported data. This is the first comprehensive report on cross section data for all the above-mentioned scattering channels, to the best of our knowledge. Such broad analysis of cross section data gives vital insight into the study of local chemistry of electron interactions with BenW (n = 1-12) clusters in plasma.
Far-infrared image restoration analysis of the protostellar cluster in S140

NASA Technical Reports Server (NTRS)

Lester, D. F.; Harvey, P. M.; Joy, M.; Ellis, H. B., Jr.

1986-01-01

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.
Formation of multiply charged ions from large molecules using massive-cluster impact.

PubMed

Mahoney, J F; Cornett, D S; Lee, T D

1994-05-01

Massive-cluster impact is demonstrated to be an effective ionization technique for the mass analysis of proteins as large as 17 kDa. The design of the cluster source permits coupling to both magnetic-sector and quadrupole mass spectrometers. Mass spectra are characterized by the almost total absence of chemical background and a predominance of multiply charged ions formed from 100% glycerol matrix. The number of charge states produced by the technique is observed to range from +3 to +9 for chicken egg lysozyme (14,310 Da). The lower m/z values provided by higher charge states increase the effective mass range of analyses performed with conventional ionization by fast-atom bombardment or liquid secondary ion mass spectrometry.
Clustering Effects on Dynamics in Ionomer Solutions: A Neutron Spin Echo Insight

NASA Astrophysics Data System (ADS)

Perahia, Dvora; Wijesinghe, Sidath; Senanayake, Manjula; Wickramasinghe, Anuradhi; Mohottalalage, Supun S.; Ohl, Michael

Ionizable blocks in ionomers associate into aggregates serving as physical cross-links and concurrently form transport pathways. The dynamics of ionomers underline their functionality. Incorporating small numbers of ionic groups into polymers significantly constraint their dynamics. Recent computational studies demonstrated a direct correlation between ionic cluster morphology and polymer dynamics. Here using neutron spin echo, we probe the segmental dynamics of polystyrene sulfonate (PSS) as the degree of sulfonation of the PSS and the solution dielectrics are varied. Specifically, 20Wt% PSS of 11,000 g/mol with polydispersity of 1.02 with 3% and 9% sulfonation were studies in toluene (dielectric constant ɛ = 2.8), a good solvent for polystyrene, and with 5Wt% of ethanol (ɛ = 24.3l) added. The dynamic structure factor S(q,t) was analyzed with a single exponential except for a limited q range where two time constants associated with constraint and mobile segments were detected. S(q,t) exhibits several distinctive time and length scales for the dynamics with a crossover appearing at the length scale of the ionic clusters. NSF DMR 1611136.
Polymerization in the gas phase, in clusters, and on nanoparticle surfaces.

PubMed

El-Shall, M Samy

2008-07-01

Gas phase and cluster experiments provide unique opportunities to quantitatively study the effects of initiators, solvents, chain transfer agents, and inhibitors on the mechanisms of polymerization. Furthermore, a number of important phenomena, unique structures, and novel properties may exist during gas-phase and cluster polymerization. In this regime, the structure of the growing polymer may change dramatically and the rate coefficient may vary significantly upon the addition of a single molecule of the monomer. These changes would be reflected in the properties of the oligomers deposited from the gas phase. At low pressures, cationic and radical cationic polymerizations may proceed in the gas phase through elimination reactions. In the same systems at high pressure, however, the ionic intermediates may be stabilized, and addition without elimination may occur. In isolated van der Waals clusters of monomer molecules, sequential polymerization with several condensation steps can occur on a time scale of a few microseconds following the ionization of the gas-phase cluster. The cluster reactions, which bridge gas-phase and condensed-phase chemistry, allow examination of the effects of controlled states of aggregation. This Account describes several examples of gas-phase and cluster polymerization studies where the most significant results can be summarized as follows: (1) The carbocation polymerization of isobutene shows slower rates with increasing polymerization steps resulting from entropy barriers, which could explain the need for low temperatures for the efficient propagation of high molecular weight polymers. (2) Radical cation polymerization of propene can be initiated by partial charge transfer from an ionized aromatic molecule such as benzene coupled with covalent condensation of the associated propene molecules. This novel mechanism leads exclusively to the formation of propene oligomer ions and avoids other competitive products. (3) Structural information on the oligomers formed by gas-phase polymerization can be obtained using the mass-selected ion mobility technique where the measured collision cross-sections of the selected oligomer ions and collision-induced dissociation can provide fairly accurate structural identifications. The identification of the structures of the dimers and trimers formed in the gas-phase thermal polymerization of styrene confirms that the polymerization proceeds according to the Mayo mechanism. Similarly, the ion mobility technique has been utilized to confirm the formation of benzene cations by intracluster polymerization following the ionization of acetylene clusters. Finally, it has been shown that polymerization of styrene vapor on the surface of activated nanoparticles can lead to the incorporation of a variety of metal and metal oxide nanoparticles within polystyrene films. The ability to probe the reactivity and structure of the small growing oligomers in the gas phase can provide fundamental insight into mechanisms of polymerization that are difficult to obtain from condensed-phase studies. These experiments are also important for understanding the growth mechanisms of complex organics in flames, combustion processes, interstellar clouds, and solar nebula where gas-phase reactions, cluster polymerization, and surface catalysis on dust nanoparticles represent the major synthetic pathways. This research can lead to the discovery of novel initiation mechanisms and reaction pathways with applications in the synthesis of oligomers and nanocomposites with unique and improved properties.
Volume shift and charge instability of simple-metal clusters

NASA Astrophysics Data System (ADS)

Brajczewska, M.; Vieira, A.; Fiolhais, C.; Perdew, J. P.

1996-12-01

Experiment indicates that small clusters show changes (mostly contractions) of the bond lengths with respect to bulk values. We use the stabilized jellium model to study the self-expansion and self-compression of spherical clusters (neutral or ionized) of simple metals. Results from Kohn - Sham density functional theory are presented for small clusters of Al and Na, including negatively-charged ones. We also examine the stability of clusters with respect to charging.
Hydrogen bonding in water clusters and their ionized counterparts.

PubMed

Neela, Y Indra; Mahadevi, A Subha; Sastry, G Narahari

2010-12-30

Ab initio and DFT computations were carried out on four distinct hydrogen-bonded arrangements of water clusters (H(2)O)(n), n = 2-20, represented as W1D, W2D, W2DH, and W3D. The variation in the strength of hydrogen bond as a function of the chain length is studied. In all the four cases, there is a substantial cooperative interaction, albeit in different degrees. The effect of basis set superposition error (BSSE) on the complexation energy of water clusters has been analyzed. Atoms in molecules (AIM) analysis performed to evaluate the nature of the hydrogen bonding shows a high correlation between hydrogen bond strength and the trends in complexation energy. Solvated water clusters exhibit lower complexation energies compared to corresponding gas-phase geometries on PCM (polarized continuum model) optimization. The feasibility of stripping an electron or addition of an electron increases dramatically as the cluster size increases. Although W3D caged structures are stable for neutral clusters, the helical W2DH arrangement appeared to be an optimal choice for its ionized counterparts.
Electron-induced chemistry in imidazole clusters embedded in helium nanodroplets

NASA Astrophysics Data System (ADS)

Kuhn, Martin; Raggl, Stefan; Martini, Paul; Gitzl, Norbert; Darian, Masoomeh Mahmoodi; Goulart, Marcelo; Postler, Johannes; Feketeová, Linda; Scheier, Paul

2018-02-01

Electron-induced chemistry in imidazole (IMI) clusters embedded in helium nanodroplets (with an average size of 2 × 105 He atoms) has been investigated with high-resolution time-of-flight mass spectrometry. The formation of both, negative and positive, ions was monitored as a function of the cluster size n. In both ion spectra a clear series of peaks with IMI cluster sizes up to at least 25 are observed. While the anions are formed by collisions of IMI n with He*-, the cations are formed through ionization of IMI n by He+ as the measured onset for the cation formation is observed at 24.6 eV (ionization energy of He). The most abundant series of anions are dehydrogenated anions IMI n-1(IMI-H)-, while other anion series are IMI clusters involving CN and C2H4 moieties. The formation of cations is dominated by the protonated cluster ions IMI n H+, while the intensity of parent cluster cations IMI n + is also observed preferentially for the small cluster size n. The observation of series of cluster cations [IMI n CH3]+ suggests either CH3+ cation to be solvated by n neutral IMI molecules, or the electron-induced chemistry has led to the formation of protonated methyl-imidazole solvated by ( n - 1) neutral IMI molecules.

HST/WFPC2 and VLT/ISAAC Observations of Proplyds in the Giant H II Region NGC 3603

NASA Astrophysics Data System (ADS)

Brandner, Wolfgang; Grebel, Eva K.; Chu, You-Hua; Dottori, Horacio; Brandl, Bernhard; Richling, Sabine; Yorke, Harold W.; Points, Sean D.; Zinnecker, Hans

2000-01-01

We report the discovery of three proplyd-like structures in the giant H II region NGC 3603. The emission nebulae are clearly resolved in narrowband and broadband HST/WFPC2 observations in the optical and broadband VLT/ISAAC observations in the near-infrared. All three nebulae are tadpole shaped, with the bright ionization front at the head facing the central cluster and a fainter ionization front around the tail pointing away from the cluster. Typical sizes are 6000 AUx20,000 AU The nebulae share the overall morphology of the proplyds (PROto PLanetarY DiskS) in Orion, but are 20 to 30 times larger in size. Additional faint filaments located between the nebulae and the central ionizing cluster can be interpreted as bow shocks resulting from the interaction of the fast winds from the high-mass stars in the cluster with the evaporation flow from the proplyds. Low-resolution spectra of the brightest nebula, which is at a projected separation of 1.3 pc from the cluster, reveal that it has the spectral excitation characteristics of an ultra compact H II region with electron densities well in excess of 104 cm-3. The near-infrared data reveal a point source superposed on the ionization front. The striking similarity of the tadpole-shaped emission nebulae in NGC 3603 to the proplyds in Orion suggests that the physical structure of both types of objects might be the same. We present two-dimensional radiation hydrodynamical simulations of an externally illuminated star-disk-envelope system, which was still in its main accretion phase when first exposed to ionizing radiation from the central cluster. The simulations reproduce the overall morphology of the proplyds in NGC 3603 very well, but also indicate that mass-loss rates of up to 10-5 Msolar yr-1 are required in order to explain the size of the proplyds. Due to these high mass-loss rates, the proplyds in NGC 3603 should only survive ~105 yr. Despite this short survival time, we detect three proplyds. This indicates that circumstellar disks must be common around young stars in NGC 3603 and that these particular proplyds have only recently been exposed to their present harsh UV environment.
Different mechanisms of cluster explosion within a unified smooth particle hydrodynamics Thomas-Fermi approach: Optical and short-wavelength regimes compared

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rusek, Marian; Orlowski, Arkadiusz

2005-04-01

The dynamics of small ({<=}55 atoms) argon clusters ionized by an intense femtosecond laser pulse is studied using a time-dependent Thomas-Fermi model. The resulting Bloch-like hydrodynamic equations are solved numerically using the smooth particle hydrodynamics method without the necessity of grid simulations. As follows from recent experiments, absorption of radiation and subsequent ionization of clusters observed in the short-wavelength laser frequency regime (98 nm) differs considerably from that in the optical spectral range (800 nm). Our theoretical approach provides a unified framework for treating these very different frequency regimes and allows for a deeper understanding of the underlying cluster explosionmore » mechanisms. The results of our analysis following from extensive numerical simulations presented in this paper are compared both with experimental findings and with predictions of other theoretical models.« less
Communication: Protonation process of formic acid from the ionization and fragmentation of dimers induced by synchrotron radiation in the valence region

NASA Astrophysics Data System (ADS)

Arruda, Manuela S.; Medina, Aline; Sousa, Josenilton N.; Mendes, Luiz A. V.; Marinho, Ricardo R. T.; Prudente, Frederico V.

2016-04-01

The ionization and fragmentation of monomers of organic molecules have been extensively studied in the gas phase using mass spectroscopy. In the spectra of these molecules it is possible to identify the presence of protonated cations, which have a mass-to-charge ratio one unit larger than the parent ion. In this work, we investigate this protonation process as a result of dimers photofragmentation. Experimental photoionization and photofragmentation results of doubly deuterated formic acid (DCOOD) in the gas phase by photons in the vacuum ultraviolet region are presented. The experiment was performed by using a time-of-flight mass spectrometer installed at the Brazilian Synchrotron Light Laboratory and spectra for different pressure values in the experimental chamber were obtained. The coupled cluster approach with single and double substitutions was employed to assist the experimental analysis. Results indicate that protonated formic acid ions are originated from dimer dissociation, and the threshold photoionization of (DCOOD)ṡD+ is also determined.
Down syndrome and ionizing radiation.

PubMed

Verger, P

1997-12-01

This review examines the epidemiologic and experimental studies into the possible role ionizing radiation might play in Down Syndrome (trisomy 21). It is prompted by a report of a temporal cluster of cases of this chromosomal disorder observed in West Berlin exactly 9 mo after the radioactive cloud from Chernobyl passed. In approximately 90% of cases, Down Syndrome is due to the nondisjunction of chromosome 21, most often in the oocyte, which may be exposed to ionizing radiation during two separate periods: before the completion of the first meiosis or around the time of ovulation. Most epidemiologic studies into trisomies and exposure to ionizing radiation examine only the first period; the Chernobyl cluster is related to the second. Analysis of these epidemiologic results indicates that the possibility that ionizing radiation might be a risk factor in Down Syndrome cannot be excluded. The experimental results, although sometimes contradictory, demonstrate that irradiation may induce nondisjunction in oogenesis and spermatogenesis; they cannot, however, be easily extrapolated to humans. The weaknesses of epidemiologic studies into the risk factors for Down Syndrome at birth (especially the failure to take into account the trisomy cases leading to spontaneous abortion) are discussed. We envisage the utility and feasibility of new studies, in particular among women exposed to prolonged or repeated artificially-produced ionizing radiation.
Electron impact ionization cross sections of beryllium-tungsten clusters*

NASA Astrophysics Data System (ADS)

Sukuba, Ivan; Kaiser, Alexander; Huber, Stefan E.; Urban, Jan; Probst, Michael

2016-01-01

We report calculated electron impact ionization cross sections (EICSs) of beryllium-tungsten clusters, BenW with n = 1,...,12, from the ionization threshold to 10 keV using the Deutsch-Märk (DM) and the binary-encounter-Bethe (BEB) formalisms. The positions of the maxima of DM and BEB cross sections are mostly close to each other. The DM cross sections are more sensitive with respect to the cluster size. For the clusters smaller than Be4W they yield smaller cross sections than BEB and vice versa larger cross sections than BEB for clusters larger than Be6W. The maximum cross section values for the singlet-spin groundstate clusters range from 7.0 × 10-16 cm2 at 28 eV (BeW) to 54.2 × 10-16 cm2 at 43 eV (Be12W) for the DM cross sections and from 13.5 × 10-16 cm2 at 43 eV (BeW) to 38.9 × 10-16 cm2 at 43 eV (Be12W) for the BEB cross sections. Differences of the EICSs in different isomers and between singlet and triplet states are also explored. Both the DM and BEB cross sections could be fitted perfectly to a simple expression used in modeling and simulation codes in the framework of nuclear fusion research. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2015-60583-7
Electron impact ionization of size selected hydrogen clusters (H2)N: ion fragment and neutral size distributions.

PubMed

Kornilov, Oleg; Toennies, J Peter

2008-05-21

Clusters consisting of normal H2 molecules, produced in a free jet expansion, are size selected by diffraction from a transmission nanograting prior to electron impact ionization. For each neutral cluster (H2)(N) (N=2-40), the relative intensities of the ion fragments Hn+ are measured with a mass spectrometer. H3+ is found to be the most abundant fragment up to N=17. With a further increase in N, the abundances of H3+, H5+, H7+, and H9+ first increase and, after passing through a maximum, approach each other. At N=40, they are about the same and more than a factor of 2 and 3 larger than for H11+ and H13+, respectively. For a given neutral cluster size, the intensities of the ion fragments follow a Poisson distribution. The fragmentation probabilities are used to determine the neutral cluster size distribution produced in the expansion at a source temperature of 30.1 K and a source pressure of 1.50 bar. The distribution shows no clear evidence of a magic number N=13 as predicted by theory and found in experiments with pure para-H2 clusters. The ion fragment distributions are also used to extract information on the internal energy distribution of the H3+ ions produced in the reaction H2+ + H2-->H3+ +H, which is initiated upon ionization of the cluster. The internal energy is assumed to be rapidly equilibrated and to determine the number of molecules subsequently evaporated. The internal energy distribution found in this way is in good agreement with data obtained in an earlier independent merged beam scattering experiment.
Structural evolution study of 1-2 nm gold clusters

NASA Astrophysics Data System (ADS)

Beltrán, M. R.; Suárez Raspopov, R.; González, G.

2011-12-01

We have explored lowest energy minima structures of gold atom clusters both, charged and neutral (Aun^{ν}νn with n = 20, 28, 34, 38, 55, 75, 101, 146, 147, 192, 212 atoms and ν = 0, ±1). The structures have been obtained from first principles generalized gradient approximation, density functional theory (DFT) calculations based on norm-conserving pseudopotentials and numerical atomic basis sets. We have found two new disordered or defective isomers lower in energy than their ordered counterparts for n = 101, 147. The purpose of this work is to systematically study the difference between the electronic properties of the two lowest ordered and disordered isomers for each size. Our results agree with previous first principle calculations and with some recent experimental results (Au20 and Au101). For each case we report total energies, binding energies, ionization potentials, electron affinities, density of states, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, Housdorff chirality measure index and their simulated image in a high resolution transmission electron microscopy (HRTEM). The calculated properties of the two low lying (ordered and disordered) isomers show clear differences as to be singled out in a suitable experimental setting. An extensive discussion on the evolution with size of the cohesive energy, the ionization potentials, the electron affinities, the HOMO-LUMO gaps and their index of chirality to determine the crossover between them is given.
STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 13+} AND SINGLE IONIZATION OF Fe{sup 16+} AND Fe{sup 17+}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hahn, M.; Novotny, O.; Savin, D. W.

2013-04-10

We report measurements of electron impact ionization for Fe{sup 13+}, Fe{sup 16+}, and Fe{sup 17+} over collision energies from below threshold to above 3000 eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state. For single ionization of Fe{sup 13+}, we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud and Raymond is more than 30% larger, while that of Dere is about 20%more » greater. Much of the discrepancy with Dere is due to the theory overestimating the contribution of excitation-autoionization via n = 2 excitations. Double ionization of Fe{sup 13+} is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe{sup 16+} and Fe{sup 17+} agree with theoretical calculations to within the experimental uncertainties.« less
The Measurement of Sulfur Oxidation Products and Their Role in Homogeneous Nucleation

NASA Technical Reports Server (NTRS)

Eisele, F. L.

1999-01-01

An improved version of a transverse ion source was developed which uses selected ion chemical ionization mass spectrometry techniques inside of a particle nucleation flow tube. These new techniques are very unique, in that the chemical ionization is done inside of the flow tube rather than by having to remove the compounds and clusters of interest which are lost on first contact,with any surfaces. The transverse source is also unique because it allows the ion reaction time to be varied over more than an order of magnitude, which in turn makes possible the separation of ion induced cluster growth from the charging of preexisting molecular clusters. As a result of combining these unique capabilities, the first ever measurements of prenucleation molecular clusters were performed. These clusters are the intermediate stage of growth in the gas-to-particle conversion process. This new technique provides a means of observing clusters containing 2, 3, 4, ... and up to about 8 sulfuric acid molecules, where the critical cluster size under these measurement conditions was about 4 or 5. Thus, the nucleation process can now be directly observed and even growth beyond the critical cluster size can be investigated. The details of this investigation are discussed in a recently submitted paper, which is included as Appendix A. Measurements of the diffusion coefficient of sulfuric acid and sulfuric acid clustered with a water molecule have also been performed. The measurements are also discussed in more detail in another recently submitted paper which is included as Appendix B. The empirical results discussed in both of these papers provide a critical test of present nucleation theories. They also provide new hope for resolving many of the huge discrepancies between field observation and model prediction of particle nucleation. The second part of the research conducted under this project was directed towards the development of new chemical ionization techniques for measuring sulfur oxidation products.
Clusters of Monoisotopic Elements for Calibration in (TOF) Mass Spectrometry

NASA Astrophysics Data System (ADS)

Kolářová, Lenka; Prokeš, Lubomír; Kučera, Lukáš; Hampl, Aleš; Peňa-Méndez, Eladia; Vaňhara, Petr; Havel, Josef

2017-03-01

Precise calibration in TOF MS requires suitable and reliable standards, which are not always available for high masses. We evaluated inorganic clusters of the monoisotopic elements gold and phosphorus (Au n +/Au n - and P n +/P n -) as an alternative to peptides or proteins for the external and internal calibration of mass spectra in various experimental and instrumental scenarios. Monoisotopic gold or phosphorus clusters can be easily generated in situ from suitable precursors by laser desorption/ionization (LDI) or matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Their use offers numerous advantages, including simplicity of preparation, biological inertness, and exact mass determination even at lower mass resolution. We used citrate-stabilized gold nanoparticles to generate gold calibration clusters, and red phosphorus powder to generate phosphorus clusters. Both elements can be added to samples to perform internal calibration up to mass-to-charge ( m/z) 10-15,000 without significantly interfering with the analyte. We demonstrated the use of the gold and phosphorous clusters in the MS analysis of complex biological samples, including microbial standards and total extracts of mouse embryonic fibroblasts. We believe that clusters of monoisotopic elements could be used as generally applicable calibrants for complex biological samples.
IONIZED GAS KINEMATICS AT HIGH RESOLUTION. V. [Ne ii], MULTIPLE CLUSTERS, HIGH EFFICIENCY STAR FORMATION, AND BLUE FLOWS IN HE 2–10

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, Sara; Turner, Jean; Lacy, John

2015-11-20

We measured the 12.8 μm [Ne ii] line in the dwarf starburst galaxy He 2–10 with the high-resolution spectrometer TEXES on the NASA IRTF. The data cube has a diffraction-limited spatial resolution of ∼1″ and a total velocity resolution, including thermal broadening, of ∼5 km s{sup −1}. This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the M/R of the clusters and themore » ≃30%–40% star formation efficiencies, the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature, which we identify with the interface of the H ii region and a cold dense clump. These data offer an unprecedented view of the interaction of embedded H ii regions with their environment.« less
Ionization of elements in medium power capacitively coupled argon plasma torch with single and double ring electrodes.

PubMed

Ponta, Michaela; Frentiu, Maria; Frentiu, Tiberiu

2012-06-01

A medium power, low Ar consumption capacitively coupled plasma torch (275 W, 0.4 L min-1) with molybdenum tubular electrode and single or two ring electrodes in non-local thermodynamic equilibrium (LTE) was characterized with respect to its ability to achieve element ionization. Ionization degrees of Ca, Mg, Mn and Cd were determined from ionic-to-atomic emission ratio and ionization equilibrium according to Saha's equation. The ionization degrees resulted from the Saha equation were higher by 9-32% than those obtained from spectral lines intensity in LTE regime and closer to reality. A linear decrease of ionization with increase of ionization energy of elements was observed. Plasma torch with two ring electrodes provided higher ionization degrees (85 ± 7% Ca, 79 ± 7% Mn, 80 ± 7% Mg and 73 ± 8% Cd) than those in single ring arrangement (70 ± 6% Ca, 57 ± 7% Mn, 57 ± 8% Mg and 42 ± 9% Cd). The Ca ionization decreased linearly by up to 79 ± 4% and 53 ± 6% in plasma with two ring electrodes and single ring respectively in the presence of up to 400 µg mL-1 Na as interferent. The studied plasma was effective in element ionization and could be a potential ion source in mass spectrometry.
High resolution far-infrared observations of the evolved H II region M16

DOE Office of Scientific and Technical Information (OSTI.GOV)

McBreen, B.; Fazio, G.G.; Jaffe, D.T.

1982-03-01

M16 is an evolved, extremely density bounded H II region, which now consists only of a series of ionization fronts at molecular cloud boundaries. The source of ionization is the OB star cluster (NGC 6611) which is about 5 x 10/sup 6/ years old. We used the CFA/UA 102 cm balloon-borne telescope to map this region and detected three far-infrared (far-IR) sources embedded in an extended ridge of emission. Source I is an unresolved far-IR source embedded in a molecular cloud near a sharp ionization front. An H/sub 2/O maser is associated with this source, but no radio continuum emissionmore » has been observed. The other two far-IR sources (II and III) are associated with ionized gas-molecular cloud interfaces, with the far-IR radiation arising from dust at the boundary heated by the OB cluster. Source II is located at the southern prominent neutral intrusion with its associated bright rims and dark ''elephant trunk'' globules that delineate the current progress of the ionization front into the neutral material, and Source III arises at the interface of the northern molecular cloud fragment.« less
DNA damage and repair after high LET radiation

NASA Astrophysics Data System (ADS)

O'Neill, Peter; Cucinotta, Francis; Anderson, Jennifer

Predictions from biophysical models of interactions of radiation tracks with cellular DNA indicate that clustered DNA damage sites, defined as two or more lesions formed within one or two helical turns of the DNA by passage of a single radiation track, are formed in mammalian cells. These complex DNA damage sites are regarded as a signature of ionizing radiation exposure particularly as the likelihood of clustered damage sites arising endogenously is low. For instance, it was predicted from biophysical modelling that 30-40% of low LET-induced double strand breaks (DSB), a form of clustered damage, are complex with the yield increasing to >90% for high LET radiation, consistent with the reduced reparability of DSB with increasing ionization density of the radiation. The question arises whether the increased biological effects such as mutagenesis, carcinogenesis and lethality is in part related to DNA damage complexity and/or spatial distribution of the damage sites, which may lead to small DNA fragments. With particle radiation it is also important to consider not only delta-rays which may cause clustered damaged sites and may be highly mutagenic but the non-random spatial distribution of DSB which may lead to deletions. In this overview I will concentrate on the molecular aspects of the variation of the complexity of DNA damage on radiation quality and the challenges this complexity presents the DNA damage repair pathways. I will draw on data from micro-irradiations which indicate that the repair of DSBs by non-homologous end joining is highly regulated with pathway choice and kinetics of repair dependent on the chemical complexity of the DSB. In summary the aim is to emphasis the link between the spatial distribution of energy deposition events related to the track, the molecular products formed and the consequence of damage complexity contributing to biological effects and to present some of the outstanding molecular challenges with particle radiation.
Interaction of intense ultrashort pulse lasers with clusters.

NASA Astrophysics Data System (ADS)

Petrov, George

2007-11-01

The last ten years have witnessed an explosion of activity involving the interaction of clusters with intense ultrashort pulse lasers. Atomic or molecular clusters are targets with unique properties, as they are halfway between solid and gases. The intense laser radiation creates hot dense plasma, which can provide a compact source of x-rays and energetic particles. The focus of this investigation is to understand the salient features of energy absorption and Coulomb explosion by clusters. The evolution of clusters is modeled with a relativistic time-dependent 3D Molecular Dynamics (MD) model [1]. The Coulomb interaction between particles is handled by a fast tree algorithm, which allows large number of particles to be used in simulations [2]. The time histories of all particles in a cluster are followed in time and space. The model accounts for ionization-ignition effects (enhancement of the laser field in the vicinity of ions) and a variety of elementary processes for free electrons and charged ions, such as optical field and collisional ionization, outer ionization and electron recapture. The MD model was applied to study small clusters (1-20 nm) irradiated by a high-intensity (10^16-10^20 W/cm^2) sub-picosecond laser pulse. We studied fundamental cluster features such as energy absorption, x-ray emission, particle distribution, average charge per atom, and cluster explosion as a function of initial cluster radius, laser peak intensity and wavelength. Simulations of novel applications, such as table-top nuclear fusion from exploding deuterium clusters [3] and high power synchrotron radiation for biological applications and imaging [4] have been performed. The application for nuclear fusion was motivated by the efficient absorption of laser energy (˜100%) and its high conversion efficiency into ion kinetic energy (˜50%), resulting in neutron yield of 10^6 neutrons/Joule laser energy. Contributors: J. Davis and A. L. Velikovich. [1] G. M. Petrov, et al Phys. Plasmas 12 063103 (2005); 13 033106 (2006) [2] G. M. Petrov, J. Davis, European Phys. J. D 41 629 (2007) [3] G. M. Petrov, J. Davis, A. L. Velikovich, Plasma Phys. Contr. Fusion 48 1721 (2006) [4] G. M. Petrov, J. Davis, A. L. Velikovich, J. Phys. B 39 4617 (2006)
Understanding the evolution of luminescent gold quantum clusters in protein templates.

PubMed

Chaudhari, Kamalesh; Xavier, Paulrajpillai Lourdu; Pradeep, Thalappil

2011-11-22

We show that the time-dependent biomineralization of Au(3+) by native lactoferrin (NLf) and bovine serum albumin (BSA) resulting in near-infrared (NIR) luminescent gold quantum clusters (QCs) occurs through a protein-bound Au(1+) intermediate and subsequent emergence of free protein. The evolution was probed by diverse tools, principally, using matrix-assisted laser desorption ionization mass spectrometry (MALDI MS), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The importance of alkaline pH in the formation of clusters was probed. At neutral pH, a Au(1+)-protein complex was formed (starting from Au(3+)) with the binding of 13-14 gold atoms per protein. When the pH was increased above 12, these bound gold ions were further reduced to Au(0) and nucleation and growth of cluster commenced, which was corroborated by the beginning of emission; at this point, the number of gold atoms per protein was ~25, suggesting the formation of Au(25). During the cluster evolution, at certain time intervals, for specific molar ratios of gold and protein, occurrence of free protein was noticed in the mass spectra, suggesting a mixture of products and gold ion redistribution. By providing gold ions at specific time of the reaction, monodispersed clusters with enhanced luminescence could be obtained, and the available quantity of free protein could be utilized efficiently. Monodispersed clusters would be useful in obtaining single crystals of protein-protected noble metal quantum clusters where homogeneity of the system is of primary concern. © 2011 American Chemical Society
Typing of Ochrobactrum anthropi clinical isolates using automated repetitive extragenic palindromic-polymerase chain reaction DNA fingerprinting and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry.

PubMed

Quirino, Angela; Pulcrano, Giovanna; Rametti, Linda; Puccio, Rossana; Marascio, Nadia; Catania, Maria Rosaria; Matera, Giovanni; Liberto, Maria Carla; Focà, Alfredo

2014-03-22

Ochrobactrum anthropi (O. anthropi), is a non-fermenting gram-negative bacillus usually found in the environment. Nevertheless, during the past decade it has been identified as pathogenic to immunocompromised patients. In this study, we assessed the usefulness of the automated repetitive extragenic palindromic-polymerase chain reaction (rep-PCR-based DiversiLab™ system, bioMèrieux, France) and of matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF MS) for typing of twentythree O. anthropi clinical isolates that we found over a four-months period (from April 2011 to August 2011) in bacteriemic patients admitted in the same operative unit of our hospital. Pulsed-field gel electrophoresis (PFGE), commonly accepted as the gold standard technique for typing, was also used. Analysis was carried out using the Pearson correlation coefficient to determine the distance matrice and the unweighted pair group method with arithmetic mean (UPGMA) to generate dendogram. Rep-PCR analysis identified four different patterns: three that clustered together with 97% or more pattern similarity, and one whose members showed < 95% pattern similarity. Interestingly, strains isolated later (from 11/06/2011 to 24/08/2011) displayed a pattern with 99% similarity. MALDI-TOF MS evaluation clustered the twentythree strains of O. anthropi into a single group containing four distinct subgroups, each comprising the majority of strains clustering below 5 distance levels, indicating a high similarity between the isolates. Our results indicate that these isolates are clonally-related and the methods used afforded a valuable contribution to the epidemiology, prevention and control of the infections caused by this pathogen.
Advanced carbon-based material C{sub 60} modification using partially ionized cluster and energetic beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du Yuancheng; Ren Zhongmin; Ning Zhifeng

1997-06-20

Two processes have been undertaken using Partially ionized cluster deposition (PICBD) and energetic ion bombardment beams deposition (IBD) respectively. C{sub 60} films deposited by PICBD at V=0 and 65 V, which result in highly textured close-packed structure in orientation (110) and being more polycrystalline respectively, the resistance of C{sub 60} films to oxygen diffusion contamination will be improved. In the case of PICBD, the ionized C{sub 60} soccer-balls molecules in the evaporation beams will be fragmented in collision with the substrate under the elevated accelerating fields Va. As a new synthetic IBD processing, two low energy (400 and 1000 eV)more » nitrogen ion beams have been used to bombard C{sub 60} films to synthesize the carbon nitride films.« less
The Effect of Clustering on Estimations of the UV Ionizing Background from the Proximity Effect

NASA Astrophysics Data System (ADS)

Pascarelle, S. M.; Lanzetta, K. M.; Chen, H. W.

1999-09-01

There have been several determinations of the ionizing background using the proximity effect observed in the distibution of Lyman-alpha absorption lines in the spectra of QSOs at high redshift. It is usually assumed that the distribution of lines should be the same at very small impact parameters to the QSO as it is at large impact parameters, and any decrease in line density at small impact parameters is due to ionizing radiation from the QSO. However, if these Lyman-alpha absorption lines arise in galaxies (Lanzetta et al. 1995, Chen et al. 1998), then the strength of the proximity effect may have been underestimated in previous work, since galaxies are known to cluster around QSOs. Therefore, the UV background estimations have likely been overestimated by the same factor.
Track structure of protons and other light ions in liquid water: applications of the LIonTrack code at the nanometer scale.

PubMed

Bäckström, G; Galassi, M E; Tilly, N; Ahnesjö, A; Fernández-Varea, J M

2013-06-01

The LIonTrack (Light Ion Track) Monte Carlo (MC) code for the simulation of H(+), He(2+), and other light ions in liquid water is presented together with the results of a novel investigation of energy-deposition site properties from single ion tracks. The continuum distorted-wave formalism with the eikonal initial state approximation (CDW-EIS) is employed to generate the initial energy and angle of the electrons emitted in ionizing collisions of the ions with H2O molecules. The model of Dingfelder et al. ["Electron inelastic-scattering cross sections in liquid water," Radiat. Phys. Chem. 53, 1-18 (1998); "Comparisons of calculations with PARTRAC and NOREC: Transport of electrons in liquid water," Radiat. Res. 169, 584-594 (2008)] is linked to the general-purpose MC code PENELOPE/penEasy to simulate the inelastic interactions of the secondary electrons in liquid water. In this way, the extended PENELOPE/penEasy code may provide an improved description of the 3D distribution of energy deposits (EDs), making it suitable for applications at the micrometer and nanometer scales. Single-ionization cross sections calculated with the ab initio CDW-EIS formalism are compared to available experimental values, some of them reported very recently, and the theoretical electronic stopping powers are benchmarked against those recommended by the ICRU. The authors also analyze distinct aspects of the spatial patterns of EDs, such as the frequency of nearest-neighbor distances for various radiation qualities, and the variation of the mean specific energy imparted in nanoscopic targets located around the track. For 1 MeV/u particles, the C(6+) ions generate about 15 times more clusters of six EDs within an ED distance of 3 nm than H(+). On average clusters of two to three EDs for 1 MeV/u H(+) and clusters of four to five EDs for 1 MeV/u C(6+) could be expected for a modeling double strand break distance of 3.4 nm.

The State of the Warm and Cold Gas in the Extreme Starburst at the Core of the Phoenix Galaxy Cluster (SPT-CLJ2344-4243)

NASA Astrophysics Data System (ADS)

McDonald, Michael; Swinbank, Mark; Edge, Alastair C.; Wilner, David J.; Veilleux, Sylvain; Benson, Bradford A.; Hogan, Michael T.; Marrone, Daniel P.; McNamara, Brian R.; Wei, Lisa H.; Bayliss, Matthew B.; Bautz, Marshall W.

2014-03-01

We present new optical integral field spectroscopy (Gemini South) and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to have a massive starburst (~800 M ⊙ yr-1) in the central, brightest cluster galaxy, most likely fueled by the rapidly cooling intracluster medium. These new data reveal a complex emission-line nebula, extending for >30 kpc from the central galaxy, detected at [O II]λλ3726, 3729, [O III]λλ4959, 5007, Hβ, Hγ, Hδ, [Ne III]λ3869, and He II λ4686. The total Hα luminosity, assuming Hα/Hβ = 2.85, is L Hα = 7.6 ± 0.4 ×1043 erg s-1, making this the most luminous emission-line nebula detected in the center of a cool core cluster. Overall, the relative fluxes of the low-ionization lines (e.g., [O II], Hβ) to the UV continuum are consistent with photoionization by young stars. In both the center of the galaxy and in a newly discovered highly ionized plume to the north of the galaxy, the ionization ratios are consistent with both shocks and active galactic nucleus (AGN) photoionization. We speculate that this extended plume may be a galactic wind, driven and partially photoionized by both the starburst and central AGN. Throughout the cluster we measure elevated high-ionization line ratios (e.g., He II/Hβ, [O III]/Hβ), coupled with an overall high-velocity width (FWHM gsim 500 km s-1), suggesting that shocks are likely important throughout the interstellar medium of the central galaxy. These shocks are most likely driven by a combination of stellar winds from massive young stars, core-collapse supernovae, and the central AGN. In addition to the warm, ionized gas, we detect a substantial amount of cold, molecular gas via the CO(3-2) transition, coincident in position with the galaxy center. We infer a molecular gas mass of M_{H_2} = 2.2 ± 0.6 × 1010 M ⊙, which implies that the starburst will consume its fuel in ~30 Myr if it is not replenished. The L IR/M_{H_2} that we measure for this cluster is consistent with the starburst limit of 500 L ⊙/M ⊙, above which radiation pressure is able to disperse the cold reservoir. The combination of the high level of turbulence in the warm phase and the high L IR/M_{H_2} ratio suggests that this violent starburst may be in the process of quenching itself. We propose that phases of rapid star formation may be common in the cores of galaxy clusters, but so short-lived that their signatures are quickly erased and appear only in a subsample of the most strongly cooling clusters.
Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

NASA Astrophysics Data System (ADS)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n = 2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.
The Pillars of Creation revisited with MUSE: gas kinematics and high-mass stellar feedback traced by optical spectroscopy

NASA Astrophysics Data System (ADS)

McLeod, A. F.; Dale, J. E.; Ginsburg, A.; Ercolano, B.; Gritschneder, M.; Ramsay, S.; Testi, L.

2015-06-01

Integral field unit (IFU) data of the iconic Pillars of Creation in M16 are presented. The ionization structure of the pillars was studied in great detail over almost the entire visible wavelength range, and maps of the relevant physical parameters, e.g. extinction, electron density, electron temperature, line-of-sight velocity of the ionized and neutral gas are shown. In agreement with previous authors, we find that the pillar tips are being ionized and photoevaporated by the massive members of the nearby cluster NGC 6611. They display a stratified ionization structure where the emission lines peak in a descending order according to their ionization energies. The IFU data allowed us to analyse the kinematics of the photoevaporative flow in terms of the stratified ionization structure, and we find that, in agreement with simulations, the photoevaporative flow is traced by a blueshift in the position-velocity profile. The gas kinematics and ionization structure have allowed us to produce a sketch of the 3D geometry of the Pillars, positioning the pillars with respect to the ionizing cluster stars. We use a novel method to detect a previously unknown bipolar outflow at the tip of the middle pillar and suggest that it has an embedded protostar as its driving source. Furthermore we identify a candidate outflow in the leftmost pillar. With the derived physical parameters and ionic abundances, we estimate a mass-loss rate due to the photoevaporative flow of 70 M⊙ Myr-1 which yields an expected lifetime of approximately 3 Myr.
Dissociative-ionization cross sections for 12-keV-electron impact on CO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhatt, Pragya; Singh, Raj; Yadav, Namita

The dissociative ionization of a CO{sub 2} molecule is studied at an electron energy of 12 keV using the multiple ion coincidence imaging technique. The absolute partial ionization cross sections and the precursor-specific absolute partial ionization cross sections of resulting fragment ions are obtained and reported. It is found that {approx}75% of single ionization, 22% of double ionization, and {approx}2% of triple ionization of the parent molecule contribute to the total fragment ion yield; quadruple ionization of CO{sub 2} is found to make a negligibly small contribution. Furthermore, the absolute partial ionization cross sections for ion-pair and ion-triple formation aremore » measured for nine dissociative ionization channels of up to a quadruply ionized CO{sub 2} molecule. In addition, the branching ratios for single-ion, ion-pair, and ion-triple formation are also determined.« less
Infrared Absorption of Methanol-Water Clusters Mn(H2O), n = 1-4, Recorded with the Vuv-Ionization Techniques

NASA Astrophysics Data System (ADS)

Lee, Yu-Fang; Lee, Yuan-Pern

2016-06-01

We investigated IR spectra in the CH- and OH-stretching regions of size-selected methanol-water clusters, Mn(H_2O) with M representing CH_3OH and n = 1-4, in a pulsed supersonic jet by using the VUV (vacuum-ultraviolet)-ionization/IR-depletion technique. The VUV light at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser served as a source of dissociation for clusters before ionization. Spectra of methanol-water clusters in the OH region show significant variations as the number of methanol molecules increase, whereas spectra in the CH region are similar. For M(H_2O), absorption of a structure with H_2O as a proton donor was observed at 3570, 3682, and 3722 wn, whereas that of methanol as a proton donor was observed at 3611 and 3753 wn. For M2(H_2O), the OH-stretching band of the dangling OH of H_2O was observed at 3721 wn, whereas overlapped bands near 3425, 3472, and 3536 wn correspond to the OH-stretching modes of three hydrogen-bonded OH in a cyclic structure. For M3(H_2O), the dangling OH shifts to 3715 wn, and the hydrogen-bonded OH-stretching bands become much broader, with a band near 3179 wn having the smallest wavenumber. Scaled harmonic vibrational wavenumbers and relative IR intensities predicted for the methanol-water clusters with the M06-2X/aug-cc-pVTZ method are consistent with our experimental results. For M4(H_2O), observed spectrum agree less with theoretical predictions, indicating the presence of isomers other than the most stable cyclic one. Spectra of Mn(H_2O) and Mn+1 are compared and the cooperative hydrogen-bonding is discussed.
Revealing Thermal Instabilities in the Core of the Phoenix Cluster

NASA Astrophysics Data System (ADS)

McDonald, Michael

2017-08-01

The Phoenix cluster is the most relaxed cluster known, and hosts the strongest cool core of any cluster yet discovered. At the center of this cluster is a massive starburst galaxy, with a SFR of 500-1000 Msun/yr, seemingly satisfying the early cooling flow predictions, despite the presence of strong AGN feedback from the central supermassive black hole. Here we propose deep narrow-band imaging of the central 120 kpc of the cluster, to map the warm (10^4K) ionized gas via the [O II] emission line. In low-z clusters, such as Perseus and Abell 1795, the warm, ionized phase is of critical importance to map out thermal instabilities in the hot gas, and maps of Halpha and [O II] have been used for decades to understand how (and how not) cooling proceeds in the intracluster medium. The data proposed for here, combined with deep ALMA data, a recently-approved Large Chandra Program, and recently-approved multi-frequency JVLA data, will allow us to probe the cooling ICM, the cool, filamentary gas, the cold molecular gas, the star-forming population, and the AGN jets all on scales of <10 kpc. This multi-observatory campaign, focusing on the most extreme cooling cluster, will lead to a more complete understanding of how and why thermal instabilities develop in the hot ICM of cool core clusters.
First principles study of structural, electronic and magnetic properties of SnGe n (0, ±1) ( n = 1–17) clusters

NASA Astrophysics Data System (ADS)

Djaadi, Soumaia; Eddine Aiadi, Kamal; Mahtout, Sofiane

2018-04-01

The structures, relative stability and magnetic properties of pure Ge n +1, neutral cationic and anionic SnGe n (n = 1–17) clusters have been investigated by using the first principles density functional theory implemented in SIESTA packages. We find that with the increasing of cluster size, the Ge n +1 and SnGe n (0, ±1) clusters tend to adopt compact structures. It has been also found that the Sn atom occupied a peripheral position for SnGe n clusters when n < 12 and occupied a core position for n > 12. The structural and electronic properties such as optimized geometries, fragmentation energy, binding energy per atom, HOMO–LUMO gaps and second-order differences in energy of the pure Ge n +1 and SnGe n clusters in their ground state are calculated and analyzed. All isomers of neutral SnGe n clusters are generally nonmagnetic except for n = 1 and 4, where the total spin magnetic moments is 2μ b. The total (DOS) and partial density of states of these clusters have been calculated to understand the origin of peculiar magnetic properties. The cluster size dependence of vertical ionization potentials, vertical electronic affinities, chemical hardness, adiabatic electron affinities and adiabatic ionization potentials have been calculated and discussed.
The interaction of an ionizing ligand with enzymes having a single ionizing group. Implications for the reaction of folate analogues with dihydrofolate reductase.

PubMed

Stone, S R; Morrison, J F

1983-06-29

Binding theory has been developed for the reaction of an ionizing enzyme with an ionizing ligand. Consideration has been given to the most general scheme in which all possible reactions and interconversions occur as well as to schemes in which certain interactions do not take place. Equations have been derived in terms of the variation of the apparent dissociation constant (Kiapp) as a function of pH. These equations indicate that plots of pKiapp against pH can be wave-, half-bell- or bell-shaped according to the reactions involved. A wave is obtained whenever there is formation of the enzyme-ligand complexes, ionized enzyme . ionized ligand and protonated enzyme . protonated ligand. The additional formation of singly protonated enzyme-ligand complexes does not affect the wave form of the plot, but can influence the shape of the overall curve. The formation of either ionized enzyme . ionized ligand or protonated enzyme . protonated ligand, with or without singly protonated enzyme-ligand species, gives rise to a half-bell-shaped plot. If only singly protonated enzyme-ligand complexes are formed the plots are bell-shaped, but it is not possible to deduce the ionic forms of the reactants that participate in complex formation. Depending on the reaction pathways, true values for the ionization and dissociation constants may or may not be determined.
Infrared absorption of methanol clusters (CH3OH)n with n = 2-6 recorded with a time-of-flight mass spectrometer using infrared depletion and vacuum-ultraviolet ionization.

PubMed

Han, Hui-Ling; Camacho, Cristopher; Witek, Henryk A; Lee, Yuan-Pern

2011-04-14

We investigated IR spectra in the CH- and OH-stretching regions of size-selected methanol clusters, (CH(3)OH)(n) with n = 2-6, in a pulsed supersonic jet by using the IR-VUV (vacuum-ultraviolet) ionization technique. VUV emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser emission served as a source of predissociation or excitation before ionization. The variations of intensity of protonated methanol cluster ions (CH(3)OH)(n)H(+) and CH(3)OH(+) and (CH(3)OH)(2)(+) were monitored as the IR laser light was tuned across the range 2650-3750 cm(-1). Careful processing of these action spectra based on photoionization efficiencies and the production and loss of each cluster due to photodissociation yielded IR spectra of the size-selected clusters. Spectra of methanol clusters in the OH region have been extensively investigated; our results are consistent with previous reports, except that the band near 3675 cm(-1) is identified as being associated with the proton acceptor of (CH(3)OH)(2). Spectra in the CH region are new. In the region 2800-3050 cm(-1), bands near 2845, 2956, and 3007 cm(-1) for CH(3)OH split into 2823, 2849, 2934, 2955, 2984, and 3006 cm(-1) for (CH(3)OH)(2) that correspond to proton donor and proton acceptor, indicating that the methanol dimer has a preferred open-chain structure. In contrast, for (CH(3)OH)(3), the splitting diminishes and the bands near 2837, 2954, and 2987 cm(-1) become narrower, indicating a preferred cyclic structure. Anharmonic vibrational wavenumbers predicted for the methanol open-chain dimer and the cyclic trimer with the B3LYP∕VPT2∕ANO1 level of theory are consistent with experimental results. For the tetramer and pentamer, the spectral pattern similar to that of the trimer but with greater widths was observed, indicating that the most stable structures are also cyclic.
Autoionization following nanoplasma formation in atomic and molecular clusters

NASA Astrophysics Data System (ADS)

Schütte, Bernd; Lahl, Jan; Oelze, Tim; Krikunova, Maria; Vrakking, Marc J. J.; Rouzée, Arnaud

2016-05-01

Nanoplasmas resulting from the ionization of nano-scale particles by intense laser pulses are typically described by quasiclassical models, where electron emission is understood to take place via thermal processes. Recently, we discovered that, following the interaction of intense near-infrared (NIR) laser pulses with molecular oxygen clusters, electron emission from nanoplasmas can also occur from atomic bound states via autoionization [Schütte et al., Phys. Rev. Lett. 114, 123002 (2015)]. Here we extend these studies and demonstrate that the formation and decay of doubly-excited atoms and ions is a very common phenomenon in nanoplasmas. We report on the observation of autoionization involving spin-orbit excited states in molecular oxygen and carbon dioxide clusters as well as in atomic krypton and xenon clusters ionized by intense NIR pulses, for which we find clear bound-state signatures in the electron kinetic energy spectra. By applying terahertz (THz) streaking, we show that the observed autoionization processes take place on a picosecond to nanosecond timescale after the interaction of the NIR laser pulse with the clusters. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.
OPTICAL PHOTOMETRIC AND POLARIMETRIC INVESTIGATION OF NGC 1931

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, A. K.; Eswaraiah, C.; Sharma, Saurabh

We present optical photometric and polarimetric observations of stars toward NGC 1931 with the aim of deriving cluster parameters such as distance, reddening, age, and luminosity/mass function as well as understanding dust properties and star formation in the region. The distance to the cluster is found to be 2.3 {+-} 0.3 kpc and the reddening E(B - V) in the region is found to be variable. The stellar density contours reveal two clusters in the region. The observations suggest a differing reddening law within the cluster region. Polarization efficiency of the dust grains toward the direction of the cluster ismore » found to be less than that for the general diffuse interstellar medium (ISM). The slope of the mass function (-0.98 {+-} 0.22) in the southern region in the mass range of 0.8 < M/M {sub Sun} < 9.8 is found to be shallower in comparison to that in the northern region (-1.26 {+-} 0.23), which is comparable to the Salpeter value (-1.35). The K-band luminosity function (KLF) of the region is found to be comparable to the average value of the slope ({approx}0.4) for young clusters obtained by Lada and Lada; however, the slope of the KLF is steeper in the northern region as compared to the southern region. The region is probably ionized by two B2 main-sequence-type stars. The mean age of the young stellar objects (YSOs) is found to be 2 {+-} 1 Myr, which suggests that the identified YSOs could be younger than the ionizing sources of the region. The morphology of the region, the distribution and ages of the YSOs, and ionizing sources indicate a triggered star formation in the region.« less
Circular dichroism in photo-single-ionization of unoriented atoms.

PubMed

Feagin, James M

2002-01-28

We predict circular dichroism in photo-single-ionization angular distributions from spherically symmetric atomic states if the ionized electron is detected using two-slit interferometry. We demonstrate that the resulting electron interference pattern captures phase information on quadrupole corrections to the photoionization amplitude lost in conventional angular distributions.
Al7CX (X=Li-Cs) clusters: Stability and the prospect for cluster materials

NASA Astrophysics Data System (ADS)

Ashman, C.; Khanna, S. N.; Pederson, M. R.; Kortus, J.

2000-12-01

Al7C clusters, recently found to have a high-electron affinity and exceptional stability, are shown to form ionic molecules when combined with alkali-metal atoms. Our studies, based on an ab initio gradient-corrected density-functional scheme, show that Al7CX (X=Li-Cs) clusters have a very low-electron affinity and a high-ionization potential. When combined, the two- and four-atom composite clusters of Al7CLi units leave the Al7C clusters almost intact. Preliminary studies indicate that Al7CLi may be suitable to form cluster-based materials.
Ionization-induced solvent migration in acetanilide-methanol clusters inferred from isomer-selective infrared spectroscopy.

PubMed

Weiler, Martin; Nakamura, Takashi; Sekiya, Hiroshi; Dopfer, Otto; Miyazaki, Mitsuhiko; Fujii, Masaaki

2012-12-07

We present the resonance-enhanced multiphoton ionization, infrared-ultraviolet hole burning (IR-UV HB), and IR dip spectra of the trans-acetanilide-methanol (AA-MeOH) cluster in the S(0), S(1), and cationic ground state (D(0)) in a supersonic jet. The IR-UV HB spectra demonstrate the co-existence of two isomers in S(0,1), in which MeOH binds either to the NH or the CO site of the peptide linkage in AA, denoted as AA(NH)-MeOH and AA(CO)-MeOH. When AA(CO)-MeOH is selectively ionized, its IR spectrum in D(0) is the same as that measured for AA(+) (NH)-MeOH. Thus, photoionization of AA(CO)-MeOH induces migration of MeOH from the CO to the NH site with 100% yield. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Computation of Electron Impact Ionization Cross sections of Iron Hydrogen Clusters - Relevance in Fusion Plasmas

NASA Astrophysics Data System (ADS)

Patel, Umang; Joshipura, K. N.

2017-04-01

Plasma-wall interaction (PWI) is one of the key issues in nuclear fusion research. In nuclear fusion devices, such as the JET tokamak or the ITER, first-wall materials will be directly exposed to plasma components. Erosion of first-wall materials is a consequence of the impact of hydrogen and its isotopes as main constituents of the hot plasma. Besides the formation of gas-phase atomic species in various charge states, di- and polyatomic molecular species are expected to be formed via PWI processes. These compounds may profoundly disturb the fusion plasma, may lead to unfavorable re-deposition of materials and composites in other areas of the vessel. Interaction between atoms, molecules as well transport of impurities are of interest for modelling of fusion plasma. Qion by electron impact are such process also important in low temperature plasma processing, astrophysics etc. We reported electron impact Qionfor iron hydrogen clusters, FeHn (n = 1 to 10) from ionization threshold to 2000 eV. A semi empirical approach called Complex Scattering Potential - Ionization Contribution (CSP-ic) has been employed for the reported calculation. In context of fusion relevant species Qion were reported for beryllium and its hydrides, tungsten and its oxides and cluster of beryllium-tungsten by Huber et al.. Iron hydrogen clusters are another such species whose Qion were calculated through DM and BEB formalisms, same has been compared with present calculations.
Spectrum of complex DNA damages depends on the incident radiation

NASA Astrophysics Data System (ADS)

Hada, M.; Sutherland, B.

Ionizing radiation induces clustered DNA damages in DNA-two or more abasic sites oxidized bases and strand breaks on opposite DNA strands within a few helical turns Clustered damages are considered to be difficult to repair and therefore potentially lethal and mutagenic damages Although induction of single strand breaks and isolated lesions has been studied extensively little is known of factors affecting induction of clusters other than double strand breaks DSB The aim of the present study was to determine whether the type of incident radiation could affect yield or spectra of specific clusters Genomic T7 DNA a simple 40 kbp linear blunt-ended molecule was irradiated in non-scavenging buffer conditions with Fe 970 MeV n Ti 980 MeV n C 293 MeV n Si 586 MeV n ions or protons 1 GeV n at the NASA Space Radiation Laboratory or with 100 kVp X-rays Irradiated DNA was treated with homogeneous Fpg or Nfo proteins or without enzyme treatment for DSB quantitation then electrophoresed in neutral agarose gels DSB Fpg-OxyPurine clusters and Nfo-Abasic clusters were quantified by number average length analysis The results show that the yields of all these complex damages depend on the incident radiation Although LETs are similar protons induced twice as many DSBs than did X-rays Further the spectrum of damage also depends on the radiation The yield damage Mbp Gy of all damages decreased with increasing linear energy transfer LET of the radiation The relative frequencies of DSBs to Abasic- and OxyBase clusters were higher
Electron interaction with nitromethane embedded in helium droplets: attachment and ionization measurements.

PubMed

Ferreira da Silva, F; Ptasińska, S; Denifl, S; Gschliesser, D; Postler, J; Matias, C; Märk, T D; Limão-Vieira, P; Scheier, P

2011-11-07

Results of a detailed study on electron interactions with nitromethane (CH(3)NO(2)) embedded in helium nanodroplets are reported. Anionic and cationic products formed are analysed by mass spectrometry. When the doped helium droplets are irradiated with low-energy electrons of about 2 eV kinetic energy, exclusively parent cluster anions (CH(3)NO(2))(n)(-) are formed. At 8.5 eV, three anion cluster series are observed, i.e., (CH(3)NO(2))(n)(-), [(CH(3)NO(2))(n)-H](-), and (CH(3)NO(2))(n)NO(2)(-), the latter being the most abundant. The results obtained for anions are compared with previous electron attachment studies with bare nitromethane and nitromethane condensed on a surface. The cation chemistry (induced by electron ionization of the helium matrix at 70 eV and subsequent charge transfer from He(+) to the dopant cluster) is dominated by production of methylated and protonated nitromethane clusters, (CH(3)NO(2))(n)CH(3)(+) and (CH(3)NO(2))(n)H(+).
Cluster dynamics transcending chemical dynamics toward nuclear fusion

PubMed Central

Heidenreich, Andreas; Jortner, Joshua; Last, Isidore

2006-01-01

Ultrafast cluster dynamics encompasses femtosecond nuclear dynamics, attosecond electron dynamics, and electron-nuclear dynamics in ultraintense laser fields (peak intensities 1015–1020 W·cm−2). Extreme cluster multielectron ionization produces highly charged cluster ions, e.g., (C4+(D+)4)n and (D+I22+)n at IM = 1018 W·cm−2, that undergo Coulomb explosion (CE) with the production of high-energy (5 keV to 1 MeV) ions, which can trigger nuclear reactions in an assembly of exploding clusters. The laser intensity and the cluster size dependence of the dynamics and energetics of CE of (D2)n, (HT)n, (CD4)n, (DI)n, (CD3I)n, and (CH3I)n clusters were explored by electrostatic models and molecular dynamics simulations, quantifying energetic driving effects, and kinematic run-over effects. The optimization of table-top dd nuclear fusion driven by CE of deuterium containing heteroclusters is realized for light-heavy heteroclusters of the largest size, which allows for the prevalence of cluster vertical ionization at the highest intensity of the laser field. We demonstrate a 7-orders-of-magnitude enhancement of the yield of dd nuclear fusion driven by CE of light-heavy heteroclusters as compared with (D2)n clusters of the same size. Prospective applications for the attainment of table-top nucleosynthesis reactions, e.g., 12C(P,γ)13N driven by CE of (CH3I)n clusters, were explored. PMID:16740666
Cluster dynamics transcending chemical dynamics toward nuclear fusion.

PubMed

Heidenreich, Andreas; Jortner, Joshua; Last, Isidore

2006-07-11

Ultrafast cluster dynamics encompasses femtosecond nuclear dynamics, attosecond electron dynamics, and electron-nuclear dynamics in ultraintense laser fields (peak intensities 10(15)-10(20) W.cm(-2)). Extreme cluster multielectron ionization produces highly charged cluster ions, e.g., (C(4+)(D(+))(4))(n) and (D(+)I(22+))(n) at I(M) = 10(18) W.cm(-2), that undergo Coulomb explosion (CE) with the production of high-energy (5 keV to 1 MeV) ions, which can trigger nuclear reactions in an assembly of exploding clusters. The laser intensity and the cluster size dependence of the dynamics and energetics of CE of (D(2))(n), (HT)(n), (CD(4))(n), (DI)(n), (CD(3)I)(n), and (CH(3)I)(n) clusters were explored by electrostatic models and molecular dynamics simulations, quantifying energetic driving effects, and kinematic run-over effects. The optimization of table-top dd nuclear fusion driven by CE of deuterium containing heteroclusters is realized for light-heavy heteroclusters of the largest size, which allows for the prevalence of cluster vertical ionization at the highest intensity of the laser field. We demonstrate a 7-orders-of-magnitude enhancement of the yield of dd nuclear fusion driven by CE of light-heavy heteroclusters as compared with (D(2))(n) clusters of the same size. Prospective applications for the attainment of table-top nucleosynthesis reactions, e.g., (12)C(P,gamma)(13)N driven by CE of (CH(3)I)(n) clusters, were explored.
Monte Carlo event generators in atomic collisions: A new tool to tackle the few-body dynamics

NASA Astrophysics Data System (ADS)

Ciappina, M. F.; Kirchner, T.; Schulz, M.

2010-04-01

We present a set of routines to produce theoretical event files, for both single and double ionization of atoms by ion impact, based on a Monte Carlo event generator (MCEG) scheme. Such event files are the theoretical counterpart of the data obtained from a kinematically complete experiment; i.e. they contain the momentum components of all collision fragments for a large number of ionization events. Among the advantages of working with theoretical event files is the possibility to incorporate the conditions present in a real experiment, such as the uncertainties in the measured quantities. Additionally, by manipulating them it is possible to generate any type of cross sections, specially those that are usually too complicated to compute with conventional methods due to a lack of symmetry. Consequently, the numerical effort of such calculations is dramatically reduced. We show examples for both single and double ionization, with special emphasis on a new data analysis tool, called four-body Dalitz plots, developed very recently. Program summaryProgram title: MCEG Catalogue identifier: AEFV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 2695 No. of bytes in distributed program, including test data, etc.: 18 501 Distribution format: tar.gz Programming language: FORTRAN 77 with parallelization directives using scripting Computer: Single machines using Linux and Linux servers/clusters (with cores with any clock speed, cache memory and bits in a word) Operating system: Linux (any version and flavor) and FORTRAN 77 compilers Has the code been vectorised or parallelized?: Yes RAM: 64-128 kBytes (the codes are very cpu intensive) Classification: 2.6 Nature of problem: The code deals with single and double ionization of atoms by ion impact. Conventional theoretical approaches aim at a direct calculation of the corresponding cross sections. This has the important shortcoming that it is difficult to account for the experimental conditions when comparing results to measured data. In contrast, the present code generates theoretical event files of the same type as are obtained in a real experiment. From these event files any type of cross sections can be easily extracted. The theoretical schemes are based on distorted wave formalisms for both processes of interest. Solution method: The codes employ a Monte Carlo Event Generator based on theoretical formalisms to generate event files for both single and double ionization. One of the main advantages of having access to theoretical event files is the possibility of adding the conditions present in real experiments (parameter uncertainties, environmental conditions, etc.) and to incorporate additional physics in the resulting event files (e.g. elastic scattering or other interactions absent in the underlying calculations). Additional comments: The computational time can be dramatically reduced if a large number of processors is used. Since the codes has no communication between processes it is possible to achieve an efficiency of a 100% (this number certainly will be penalized by the queuing waiting time). Running time: Times vary according to the process, single or double ionization, to be simulated, the number of processors and the type of theoretical model. The typical running time is between several hours and up to a few weeks.

PROPERTIES OF QSO METAL-LINE ABSORPTION SYSTEMS AT HIGH REDSHIFTS: NATURE AND EVOLUTION OF THE ABSORBERS AND NEW EVIDENCE ON ESCAPE OF IONIZING RADIATION FROM GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boksenberg, Alec; Sargent, Wallace L. W., E-mail: boksy@ast.cam.ac.uk

2015-05-15

Using Voigt-profile-fitting procedures on Keck High Resolution Spectrograph spectra of nine QSOs, we identify 1099 C IV absorber components clumped in 201 systems outside the Lyman forest over 1.6 ≲ z ≲ 4.4. With associated Si IV, C II, Si II and N V where available, we investigate the bulk statistical and ionization properties of the components and systems and find no significant change in redshift for C IV and Si IV while C II, Si II and N V change substantially. The C IV components exhibit strong clustering, but no clustering is detected for systems on scales from 150 kmmore » s{sup –1} out to 50,000 km s{sup –1}. We conclude that the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios, we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find that the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence, and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample, the collective escape of radiation is sufficient to maintain the intergalactic medium ionized over the full range 1.9 < z ≲ 4.4.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Michael; Bautz, Marshall W.; Swinbank, Mark

We present new optical integral field spectroscopy (Gemini South) and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to have a massive starburst (∼800 M {sub ☉} yr{sup –1}) in the central, brightest cluster galaxy, most likely fueled by the rapidly cooling intracluster medium. These new data reveal a complex emission-line nebula, extending for >30 kpc from the central galaxy, detected at [O II]λλ3726, 3729, [O III]λλ4959, 5007, Hβ, Hγ, Hδ, [Ne III]λ3869, and He II λ4686. The total Hα luminosity, assuming Hα/Hβ = 2.85, is L {sub Hα} =more » 7.6 ± 0.4 ×10{sup 43} erg s{sup –1}, making this the most luminous emission-line nebula detected in the center of a cool core cluster. Overall, the relative fluxes of the low-ionization lines (e.g., [O II], Hβ) to the UV continuum are consistent with photoionization by young stars. In both the center of the galaxy and in a newly discovered highly ionized plume to the north of the galaxy, the ionization ratios are consistent with both shocks and active galactic nucleus (AGN) photoionization. We speculate that this extended plume may be a galactic wind, driven and partially photoionized by both the starburst and central AGN. Throughout the cluster we measure elevated high-ionization line ratios (e.g., He II/Hβ, [O III]/Hβ), coupled with an overall high-velocity width (FWHM ≳ 500 km s{sup –1}), suggesting that shocks are likely important throughout the interstellar medium of the central galaxy. These shocks are most likely driven by a combination of stellar winds from massive young stars, core-collapse supernovae, and the central AGN. In addition to the warm, ionized gas, we detect a substantial amount of cold, molecular gas via the CO(3-2) transition, coincident in position with the galaxy center. We infer a molecular gas mass of M{sub H{sub 2}} = 2.2 ± 0.6 × 10{sup 10} M {sub ☉}, which implies that the starburst will consume its fuel in ∼30 Myr if it is not replenished. The L {sub IR}/M{sub H{sub 2}} that we measure for this cluster is consistent with the starburst limit of 500 L {sub ☉}/M {sub ☉}, above which radiation pressure is able to disperse the cold reservoir. The combination of the high level of turbulence in the warm phase and the high L {sub IR}/M{sub H{sub 2}} ratio suggests that this violent starburst may be in the process of quenching itself. We propose that phases of rapid star formation may be common in the cores of galaxy clusters, but so short-lived that their signatures are quickly erased and appear only in a subsample of the most strongly cooling clusters.« less
Relaxation channels of multi-photon excited xenon clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serdobintsev, P. Yu.; Melnikov, A. S.; Department of Physics, St. Petersburg State University, Saint Petersburg 198904

2015-09-21

The relaxation processes of the xenon clusters subjected to multi-photon excitation by laser radiation with quantum energies significantly lower than the thresholds of excitation of atoms and ionization of clusters were studied. Results obtained by means of the photoelectron spectroscopy method showed that desorption processes of excited atoms play a significant role in the decay of two-photon excited xenon clusters. A number of excited states of xenon atoms formed during this process were discovered and identified.
Examining the structural evolution of bicarbonate–water clusters: insights from photoelectron spectroscopy, basin-hopping structural search, and comparison with available IR spectral studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Hui; Hou, Gao-Lei; Liu, Yi-Rong

2016-05-31

Bicarbonate serves a crucial biochemical role in the physiological pH buffering system and also has important atmospheric implications. In the current study, HCO 3 $-$(H 2O) n (n = 0-13) clusters were successfully produced via electrospray ionization of corresponding bulk salt solution, and were characterized by combining negative ion photoelectron spectroscopy and theoretical calculations. The photoelectron spectra reveal that the electron binding energy monotonically increases with the cluster size up to n = 10 and remains largely the same after n > 10. The photo-detaching feature of the solute HCO3$-$itself, which dominates in the small clusters, diminishes with increase ofmore » water coverage. Based on the charge distribution and molecular orbital analyses, the universal high electron binding energy tail that dominates in the larger clusters can be attributed to ionization of water. Thus, the transition of ionization from solute to solvent at the size larger than n=10 has been observed. Extensive theoretical structural search based on the Basin-Hopping unbiased method was carried out, and a plethora of low energy isomers have been obtained for each medium and large size. By comparing the simulated photoelectron spectra and calculated electron binding energies with the experiments, as well as by comparing the simulated infrared spectra with previously reported IR spectra, the probable global minima and the structural evolutionary routes are presented. The nature of bicarbonate-water interactions are mainly electrostatic as implied by the electron localization function (ELF) analysis.« less
Probing the Dragonfish star-forming complex: the ionizing population of the young massive cluster Mercer 30

NASA Astrophysics Data System (ADS)

de la Fuente, D.; Najarro, F.; Borissova, J.; Ramírez Alegría, S.; Hanson, M. M.; Trombley, C.; Figer, D. F.; Davies, B.; Garcia, M.; Kurtev, R.; Urbaneja, M. A.; Smith, L. C.; Lucas, P. W.; Herrero, A.

2016-05-01

It has recently been claimed that the nebula, Dragonfish, is powered by a superluminous but elusive OB association. However, systematic searches in near-infrared photometric surveys have found many other cluster candidates in this region of the sky. Among these, the first confirmed young massive cluster was Mercer 30, where Wolf-Rayet stars were found.We perform a new characterization of Mercer 30 with unprecedented accuracy, combining NICMOS/HST and VVV photometric data with multi-epoch ISAAC/VLT H- and K-band spectra. Stellar parameters for most of spectroscopically observed cluster members are found through precise non-LTE atmosphere modeling with the CMFGEN code. Our spectrophotometric study for this cluster yields a new, revised distance of d = (12.4 ± 1.7) kpc and a total of QHMc30 ≈ 6.70 × 1050 s-1 Lyman ionizing photons. A cluster age of (4.0 ± 0.8) Myr is found through isochrone fitting, and a total mass of (1.6 ± 0.6) × 104M⊙ is estimated, thanks to our extensive knowledge of the post-main-sequence population. As a consequence, membership of Mercer 30 to the Dragonfish star-forming complex is confirmed, allowing us to use this cluster as a probe for the whole complex, which turns out to be extremely large (~400 pc across) and located at the outer edge of the Sagittarius-Carina spiral arm (~11 kpc from the Galactic center). The Dragonfish complex hosts 19 young clusters or cluster candidates (including Mercer 30 and a new candidate presented in this work) and an estimated minimum of nine field Wolf-Rayet stars. All these contributions account for, at least 73% of the ionization of the Dragonfish nebula and leaves little or no room for the alleged superluminous OB association; alternative explanations are discussed. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs IDs 179.B-2002, 081.D-0471, 083.D-0765, 087.D-0957, and 089.D-0989.
Atomic Cluster Ionization and Attosecond Generation at Long Wavelengths

DTIC Science & Technology

2015-10-31

fellowships for further studies in science, mathematics, engineering or technology fields: Student Metrics This section only applies to graduating...order to investigate this we use a modified Lewenstein quantum model in which the cluster is represented by a 1D Coulomb potential for the parent ion
ORIGIN: Metal Creation and Evolution From The Cosmic Dawn

NASA Astrophysics Data System (ADS)

Piro, L.; den Herder, J. W.; Ohashi, T.; Hartmann, D. H.; Kouveliotou, C.

2011-08-01

ORIGIN is a mission designed to use Gamma-Ray Bursts as a unique probe to study the cosmic history of baryons and the metal enrichment from the first stars up to the present Universe. Reconstructing the cosmic history of metals, from the first population of stars to the processes involved in the formation of galaxies and clusters of galaxies, is a key observational challenge. Observing any single star in the early Universe is in fact beyond the reach of presently planned mission. By measuring GRB redshifts and abundances in the circumburst medium deep into the era of re-ionization (z>6), ORIGIN will discover when star formation started and how it evolved into the present day structures. ORIGIN will collect 400 GRBs per year covering the full redshift distribution. About twice per month a GRB from the re-ionization era will trigger the instruments. The resulting multi-element abundance patterns derived from high resolution X-ray and IR observations will map the evolving chemical composition of the early Universe, ``fingerprint'' the elusive PopIII stars, and constrain the shape of the Initial Mass Function (IMF) of the first stars. While not observing GRB afterglows, ORIGIN will map element abundances in local structures (z<2) by determining the properties of the hot IGM in clusters and groups of galaxies and the Warm-Hot Intergalactic Medium (WHIM). In this paper we focus on the use of GRB to track the earliest star populations.
Localization Microscopy Analyses of MRE11 Clusters in 3D-Conserved Cell Nuclei of Different Cell Lines.

PubMed

Eryilmaz, Marion; Schmitt, Eberhard; Krufczik, Matthias; Theda, Franziska; Lee, Jin-Ho; Cremer, Christoph; Bestvater, Felix; Schaufler, Wladimir; Hausmann, Michael; Hildenbrand, Georg

2018-01-22

In radiation biophysics, it is a subject of nowadays research to investigate DNA strand break repair in detail after damage induction by ionizing radiation. It is a subject of debate as to what makes up the cell's decision to use a certain repair pathway and how the repair machinery recruited in repair foci is spatially and temporarily organized. Single-molecule localization microscopy (SMLM) allows super-resolution analysis by precise localization of single fluorescent molecule tags, resulting in nuclear structure analysis with a spatial resolution in the 10 nm regime. Here, we used SMLM to study MRE11 foci. MRE11 is one of three proteins involved in the MRN-complex (MRE11-RAD50-NBS1 complex), a prominent DNA strand resection and broken end bridging component involved in homologous recombination repair (HRR) and alternative non-homologous end joining (a-NHEJ). We analyzed the spatial arrangements of antibody-labelled MRE11 proteins in the nuclei of a breast cancer and a skin fibroblast cell line along a time-course of repair (up to 48 h) after irradiation with a dose of 2 Gy. Different kinetics for cluster formation and relaxation were determined. Changes in the internal nano-scaled structure of the clusters were quantified and compared between the two cell types. The results indicate a cell type-dependent DNA damage response concerning MRE11 recruitment and cluster formation. The MRE11 data were compared to H2AX phosphorylation detected by γH2AX molecule distribution. These data suggested modulations of MRE11 signal frequencies that were not directly correlated to DNA damage induction. The application of SMLM in radiation biophysics offers new possibilities to investigate spatial foci organization after DNA damaging and during subsequent repair.
Localization Microscopy Analyses of MRE11 Clusters in 3D-Conserved Cell Nuclei of Different Cell Lines

PubMed Central

Eryilmaz, Marion; Schmitt, Eberhard; Krufczik, Matthias; Theda, Franziska; Lee, Jin-Ho; Cremer, Christoph; Bestvater, Felix; Schaufler, Wladimir; Hildenbrand, Georg

2018-01-01

In radiation biophysics, it is a subject of nowadays research to investigate DNA strand break repair in detail after damage induction by ionizing radiation. It is a subject of debate as to what makes up the cell’s decision to use a certain repair pathway and how the repair machinery recruited in repair foci is spatially and temporarily organized. Single-molecule localization microscopy (SMLM) allows super-resolution analysis by precise localization of single fluorescent molecule tags, resulting in nuclear structure analysis with a spatial resolution in the 10 nm regime. Here, we used SMLM to study MRE11 foci. MRE11 is one of three proteins involved in the MRN-complex (MRE11-RAD50-NBS1 complex), a prominent DNA strand resection and broken end bridging component involved in homologous recombination repair (HRR) and alternative non-homologous end joining (a-NHEJ). We analyzed the spatial arrangements of antibody-labelled MRE11 proteins in the nuclei of a breast cancer and a skin fibroblast cell line along a time-course of repair (up to 48 h) after irradiation with a dose of 2 Gy. Different kinetics for cluster formation and relaxation were determined. Changes in the internal nano-scaled structure of the clusters were quantified and compared between the two cell types. The results indicate a cell type-dependent DNA damage response concerning MRE11 recruitment and cluster formation. The MRE11 data were compared to H2AX phosphorylation detected by γH2AX molecule distribution. These data suggested modulations of MRE11 signal frequencies that were not directly correlated to DNA damage induction. The application of SMLM in radiation biophysics offers new possibilities to investigate spatial foci organization after DNA damaging and during subsequent repair. PMID:29361783
Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster

NASA Astrophysics Data System (ADS)

Nguyen-Luong, Q.; Anderson, L. D.; Motte, F.; Kim, Kee-Tae; Schilke, P.; Carlhoff, P.; Beuther, H.; Schneider, N.; Didelon, P.; Kramer, C.; Louvet, F.; Nony, T.; Bihr, S.; Rugel, M.; Soler, J.; Wang, Y.; Bronfman, L.; Simon, R.; Menten, K. M.; Wyrowski, F.; Walmsley, C. M.

2017-08-01

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO+ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density ˜70-1500 cm-3 driven by the WR/OB cluster, which produces a total Lyα photon flux of 1.5× {10}50 s-1. This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 {km} {{{s}}}-1) near the YMC and by dynamical broadening (8-36 {km} {{{s}}}-1) near the shell’s edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.
Illustrating the Concepts of Isotopes and Mass Spectrometry in Introductory Courses: A MALDI-TOF Mass Spectrometry Laboratory Experiment

ERIC Educational Resources Information Center

Dopke, Nancy Carter; Lovett, Timothy Neal

2007-01-01

Mass spectrometry is a widely used and versatile tool for scientists in many different fields. Soft ionization techniques such as matrix-assisted laser desorption/ionization (MALDI) allow for the analysis of biomolecules, polymers, and clusters. This article describes a MALDI mass spectrometry experiment designed for students in introductory…
Supramolecular clusters between carbohydrates and concave pyridines. Detection in the gas phase by resonance-enhanced multi-photon ionization reflectron time-of-flight mass spectrometer.

PubMed

Liebig, Timo; Lüning, Ulrich; Grotemeyer, Jürgen

2006-01-01

For the first time the formation of supramolecular clusters between concave pyridines and different carbohydrates could be observed in the gas phase. The different clusters have been investigated by means of laser desorption into a supersonic beam followed by resonant multi photon excitation yielding mass spectra with high intensity of the different cluster. These preliminary results open a way for the investigations of the hydrogen bonds in these compounds.
Displacement damage and predicted non-ionizing energy loss in GaAs

NASA Astrophysics Data System (ADS)

Gao, Fei; Chen, Nanjun; Hernandez-Rivera, Efrain; Huang, Danhong; LeVan, Paul D.

2017-03-01

Large-scale molecular dynamics (MD) simulations, along with bond-order interatomic potentials, have been applied to study the defect production for lattice atom recoil energies from 500 eV to 20 keV in gallium arsenide (GaAs). At low energies, the most surviving defects are single interstitials and vacancies, and only 20% of the interstitial population is contained in clusters. However, a direct-impact amorphization in GaAs occurs with a high degree of probability during the cascade lifetime for Ga PKAs (primary knock-on atoms) with energies larger than 2 keV. The results reveal a non-linear defect production that increases with the PKA energy. The damage density within a cascade core is evaluated, and used to develop a model that describes a new energy partition function. Based on the MD results, we have developed a model to determine the non-ionizing energy loss (NIEL) in GaAs, which can be used to predict the displacement damage degradation induced by space radiation on electronic components. The calculated NIEL predictions are compared with the available data, thus validating the NIEL model developed in this study.
On the Ionization and Ion Transmission Efficiencies of Different ESI-MS Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cox, Jonathan T.; Marginean, Ioan; Smith, Richard D.

2014-09-30

It is well known that the achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. In this report we systematically study the ion transmission and ionization efficiencies in different ESI-MS interface configurations. The configurations under investigation include a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interfaces with a single emitter and an emitter array, respectively. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuringmore » the total gas phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Our experimental results suggest that the overall ion utilization efficiency in the SPIN-MS interface configurations is better than that in the inlet capillary based ESI-MS interface configurations.« less
Low-energy electron-impact single ionization of helium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colgan, J.; Pindzola, M. S.; Childers, G.

2006-04-15

A study is made of low-energy electron-impact single ionization of ground-state helium. The time-dependent close-coupling method is used to calculate total integral, single differential, double differential, and triple differential ionization cross sections for impact electron energies ranging from 32 to 45 eV. For all quantities, the calculated cross sections are found to be in very good agreement with experiment, and for the triple differential cross sections, good agreement is also found with calculations made using the convergent close-coupling technique.
Target electron ionization in Li2+-Li collisions: A multi-electron perspective

NASA Astrophysics Data System (ADS)

Śpiewanowski, M. D.; Gulyás, L.; Horbatsch, M.; Kirchner, T.

2015-05-01

The recent development of the magneto-optical trap reaction-microscope has opened a new chapter for detailed investigations of charged-particle collisions from alkali atoms. It was shown that energy-differential cross sections for ionization from the outer-shell in O8+-Li collisions at 1500 keV/amu can be readily explained with the single-active-electron approximation. Understanding of K-shell ionization, however, requires incorporating many-electron effects. An ionization-excitation process was found to play an important role. We present a theoretical study of target electron removal in Li2+-Li collisions at 2290 keV/amu. The results indicate that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. On one hand, we find only weak contributions from multi-electron processes. On the other hand, a large discrepancy between experimental and single-particle theoretical results indicate that multi-electron processes involving ionization from the outer shell may be important for a complete understanding of the process. Work supported by NSERC, Canada and the Hungarian Scientific Research Fund.
Method for Continuous Monitoring of Electrospray Ion Formation

NASA Astrophysics Data System (ADS)

Metzler, Guille; Crathern, Susan; Bachmann, Lorin; Fernández-Metzler, Carmen; King, Richard

2017-10-01

A method for continuously monitoring the performance of electrospray ionization without the addition of hardware or chemistry to the system is demonstrated. In the method, which we refer to as SprayDx, cluster ions with solvent vapor natively formed by electrospray are followed throughout the collection of liquid chromatography-selected reaction monitoring data. The cluster ion extracted ion chromatograms report on the consistency of the ion formation and detection system. The data collected by the SprayDx method resemble the data collected for postcolumn infusion of analyte. The response of the cluster ions monitored reports on changes in the physical parameters of the ion source such as voltage and gas flow. SprayDx is also observed to report on ion suppression in a fashion very similar to a postcolumn infusion of analyte. We anticipate the method finding utility as a continuous readout on the performance of electrospray and other atmospheric pressure ionization processes. [Figure not available: see fulltext.
Desorption electrospray ionization mass spectrometry of DNA nucleobases: implications for a liquid film model.

PubMed

Qiu, Bo; Luo, Hai

2009-05-01

Desorption electrospray ionization (DESI) mass spectrometry has been implemented on a commercial ion-trap mass spectrometer and used to optimize mass spectrometric conditions for DNA nucleobases: adenine, cytosine, thymine, and guanine. Experimental parameters including spray voltage, distance between mass spectrometer inlet and the sampled spot, and nebulizing gas inlet pressure were optimized. Cluster ions including some magic number clusters of nucleobases were observed for the first time using DESI mass spectrometry. The formation of the cluster species was found to vary with the nucleobases, acidification of the spray solvent, and the deposited sample amount. All the experimental results can be explained well using a liquid film model based on the two-step droplet pick-up mechanism. It is further suggested that solubility of the analytes in the spray solvent is an important factor to consider for their studies by using DESI. 2009 John Wiley & Sons, Ltd.
Soft-landing ion mobility of silver clusters for small-molecule matrix-assisted laser desorption ionization mass spectrometry and imaging of latent fingerprints.

PubMed

Walton, Barbara L; Verbeck, Guido F

2014-08-19

Matrix-assisted laser desorption ionization (MALDI) imaging is gaining popularity, but matrix effects such as mass spectral interference and damage to the sample limit its applications. Replacing traditional matrices with silver particles capable of equivalent or increased photon energy absorption from the incoming laser has proven to be beneficial for low mass analysis. Not only can silver clusters be advantageous for low mass compound detection, but they can be used for imaging as well. Conventional matrix application methods can obstruct samples, such as fingerprints, rendering them useless after mass analysis. The ability to image latent fingerprints without causing damage to the ridge pattern is important as it allows for further characterization of the print. The application of silver clusters by soft-landing ion mobility allows for enhanced MALDI and preservation of fingerprint integrity.
1997 Technical Digest Series. Volume 7: Applications of High Field and Short Wavelength Sources VII

DTIC Science & Technology

1997-03-01

clusters irradiated with ultrashort , high intensity laser pulses can exhibit "ionization ig- nition" which leads...8, 9]. 25-atom Ne clusters and 25-atom Ar clusters are modelled as irradiated by a 800 nm, 15 fs (fwhm) laser pulse with peak intensities ranging...Measurements of the spatial and spectral properties of ultrashort , intense laser pulses propagating in underdense plasmas demonstrate

IONIZED GAS IN THE FIRST 10 kpc OF THE INTERSTELLAR GALACTIC HALO: METAL ION FRACTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howk, J. Christopher; Consiglio, S. Michelle, E-mail: jhowk@nd.edu, E-mail: smconsiglio@ucla.edu

2012-11-10

We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high-resolution ultraviolet absorption-line spectroscopy of post-asymptotic giant branch stars in the globular clusters Messier 3 [(l, b) = (42.{sup 0}2, +78.{sup 0}7), d = 10.2 kpc, and z = 10.0 kpc] and Messier 5 [(l, b) = (3.{sup 0}9, +46.{sup 0}8), d = 7.5 kpc, and z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, Smore » VI, and H I. These clusters also house millisecond pulsars, whose dispersion measures give an electron column density from which we infer the H II column in these directions. We find fractions of S{sup +2} in the WIM for the M 3 and M 5 sight lines x(S{sup +2}) {identical_to} N(S{sup +2})/N(S) = 0.33 {+-} 0.07 and 0.47 {+-} 0.09, respectively, with variations perhaps related to location. With negligible quantities of the higher ionization states, we conclude that S{sup +} and S{sup +2} account for all of the S in the WIM. We extend the methodology to study the ion fractions in the warm and hot ionized gas of the Milky Way, including the high ions Si{sup +3}, C{sup +3}, N{sup +4}, and O{sup +5}. The vast majority of the Galactic ionized gas is warm (T {approx} 10{sup 4} K) and photoionized (the WIM) or very hot (T > 4 Multiplication-Sign 10{sup 5} K) and collisionally ionized. The common tracer of ionized gas beyond the Milky Way, O{sup +5}, traces <1% of the total ionized gas mass of the Milky Way.« less
Ab initio investigation of structure, stability, thermal behavior, bonding, and infrared spectra of ionized water cluster (H2O)6+

NASA Astrophysics Data System (ADS)

Liu, Lei; Hu, Cui-E.; Tang, Mei; Chen, Xiang-Rong; Cai, Ling-Cang

2016-10-01

The low-lying isomers of cationic water cluster (H2O)6+ have been globally explored by using particle swarm optimization algorithm in conjunction with quantum chemical calculations. Compared with previous results, our searching method covers a wide range of structural isomers of (H2O)6+ and therefore turns out to be more effective. With these local minima, geometry optimization and vibrational analysis are performed for the most interesting clusters at second-order Møller-Plesset (MP2)/aug-cc-pVDZ level, and their energies are further refined at MP2/aug-cc-pVTZ and coupled-cluster theory with single, double, and perturbative triple excitations/aug-cc-pVDZ level. The interaction energies using the complete basis set limits at MP2 level are also reported. The relationships between their structure arrangement and their energies are discussed. Based on the results of thermal simulation, structural change from a four-numbered ring to a tree-like structure occurs at T ≈ 45 K, and the relative population of six lowest-free-energy isomers is found to exceed 4% at some point within the studied temperature range. Studies reveal that, among these six isomers, two new-found isomers constitute 10% of isomer population at 180 K, and the experimental spectra can be better explained with inclusions of the two isomers. The molecular orbitals for six representative cationic water clusters are also studied. Through topological and reduced density gradient analysis, we investigated the structural characteristics and the bonding strengths of these water cluster radical cations.
Galaxy Protoclusters as Drivers of Cosmic Star Formation History in the First 2 Gyr

NASA Astrophysics Data System (ADS)

Chiang, Yi-Kuan; Overzier, Roderik A.; Gebhardt, Karl; Henriques, Bruno

2017-08-01

Present-day clusters are massive halos containing mostly quiescent galaxies, while distant protoclusters are extended structures containing numerous star-forming galaxies. We investigate the implications of this fundamental change in a cosmological context using a set of N-body simulations and semi-analytic models. We find that the fraction of the cosmic volume occupied by all (proto)clusters increases by nearly three orders of magnitude from z = 0 to z = 7. We show that (proto)cluster galaxies are an important and even dominant population at high redshift, as their expected contribution to the cosmic star formation rate density rises (from 1% at z = 0) to 20% at z = 2 and 50% at z = 10. Protoclusters thus provide a significant fraction of the cosmic ionizing photons, and may have been crucial in driving the timing and topology of cosmic reionization. Internally, the average history of cluster formation can be described by three distinct phases: at z ˜ 10-5, galaxy growth in protoclusters proceeded in an inside-out manner, with centrally dominant halos that are among the most active regions in the universe; at z ˜ 5-1.5, rapid star formation occurred within the entire 10-20 Mpc structures, forming most of their present-day stellar mass; at z ≲ 1.5, violent gravitational collapse drove these stellar contents into single cluster halos, largely erasing the details of cluster galaxy formation due to relaxation and virialization. Our results motivate observations of distant protoclusters in order to understand the rapid, extended stellar growth during cosmic noon, and their connection to reionization during cosmic dawn.
Identification of multiply charged proteins and amino acid clusters by liquid nitrogen assisted spray ionization mass spectrometry.

PubMed

Kumar Kailasa, Suresh; Hasan, Nazim; Wu, Hui-Fen

2012-08-15

The development of liquid nitrogen assisted spray ionization mass spectrometry (LNASI MS) for the analysis of multiply charged proteins (insulin, ubiquitin, cytochrome c, α-lactalbumin, myoglobin and BSA), peptides (glutathione, HW6, angiotensin-II and valinomycin) and amino acid (arginine) clusters is described. The charged droplets are formed by liquid nitrogen assisted sample spray through a stainless steel nebulizer and transported into mass analyzer for the identification of multiply charged protein ions. The effects of acids and modifier volumes for the efficient ionization of the above analytes in LNASI MS were carefully investigated. Multiply charged proteins and amino acid clusters were effectively identified by LNASI MS. The present approach can effectively detect the multiply charged states of cytochrome c at 400 nM. A comparison between LNASI and ESI, CSI, SSI and V-EASI methods on instrumental conditions, applied temperature and observed charge states for the multiply charged proteins, shows that the LNASI method produces the good quality spectra of amino acid clusters at ambient conditions without applied any electric field and heat. To date, we believe that the LNASI method is the most simple, low cost and provided an alternative paradigm for production of multiply charged ions by LNASI MS, just as ESI-like ions yet no need for applying any electrical field and it could be operated at low temperature for generation of highly charged protein/peptide ions. Copyright © 2012 Elsevier B.V. All rights reserved.
Microhydration and the Enhanced Acidity of Free Radicals.

PubMed

Walton, John C

2018-02-14

Recent theoretical research employing a continuum solvent model predicted that radical centers would enhance the acidity (RED-shift) of certain proton-donor molecules. Microhydration studies employing a DFT method are reported here with the aim of establishing the effect of the solvent micro-structure on the acidity of radicals with and without RED-shifts. Microhydration cluster structures were obtained for carboxyl, carboxy-ethynyl, carboxy-methyl, and hydroperoxyl radicals. The numbers of water molecules needed to induce spontaneous ionization were determined. The hydration clusters formed primarily round the CO₂ units of the carboxylate-containing radicals. Only 4 or 5 water molecules were needed to induce ionization of carboxyl and carboxy-ethynyl radicals, thus corroborating their large RED-shifts.
Far-infrared observations of the evolved H II region M16

NASA Technical Reports Server (NTRS)

Mcbreen, B.; Fazio, G. G.; Jaffe, D. T.

1982-01-01

The results of far infrared (FIR) observations of the larger H II region M16, associated with the young open star cluster NGC 6611, are discussed. Three FIR sources detected on an extended ridge of FIR emission within the scanned region are described. The observations confirm that M16 is an H II region in a late stage of evolution. The H II region has expanded and is now extremely density bounded, consisting of an extended region of ionized gas and a series of ionization fronts located at the surrounding molecular cloud boundaries nearest to the exciting OB star cluster. The FIR radiation arises from heated dust at these boundaries.
The sensitivity of benzene cluster cation chemical ionization mass spectrometry to select biogenic terpenes

NASA Astrophysics Data System (ADS)

Lavi, Avi; Vermeuel, Michael P.; Novak, Gordon A.; Bertram, Timothy H.

2018-06-01

Benzene cluster cations are a sensitive and selective reagent ion for chemical ionization of select biogenic volatile organic compounds. We have previously reported the sensitivity of a field deployable chemical ionization time-of-flight mass spectrometer (CI-ToFMS), using benzene cluster cation ion chemistry, for detection of dimethyl sulfide, isoprene and α-pinene. Here, we present laboratory measurements of the sensitivity of the same instrument to a series of terpenes, including isoprene, α-pinene, β-pinene, D-limonene, ocimene, β-myrcene, farnesene, α-humulene, β-caryophyllene, and isolongifolene at atmospherically relevant mixing ratios (< 100 pptv). In addition, we determine the dependence of CI-ToFMS sensitivity on the reagent ion neutral delivery concentration and water vapor concentration. We show that isoprene is primarily detected as an adduct (C5H8 ṡ C6H6+) with a sensitivity ranging between 4 and 10 ncps ppt-1, which depends strongly on the reagent ion precursor concentration, de-clustering voltages, and specific humidity (SH). Monoterpenes are detected primarily as the molecular ion (C10H16+) with an average sensitivity, across the five measured compounds, of 14 ± 3 ncps ppt-1 for SH between 7 and 14 g kg-1, typical of the boreal forest during summer. Sesquiterpenes are detected primarily as the molecular ion (C15H24+) with an average sensitivity, across the four measured compounds, of 9.6 ± 2.3 ncps ppt-1, that is also independent of specific humidity. Comparable sensitivities across broad classes of terpenes (e.g., monoterpenes and sesquiterpenes), coupled to the limited dependence on specific humidity, suggest that benzene cluster cation CI-ToFMS is suitable for field studies of biosphere-atmosphere interactions.
Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y−(HF)n (Y=F, O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator

PubMed Central

Sakamoto, Kenya; Sekimoto, Kanako; Takayama, Mitsuo

2017-01-01

Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF)n. The HF molecules were ionized in the form of complex ions associated with the negative core ions Y− produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y−(HF)n (Y=F, O2), where larger clusters with n≥4 were not detected. The mechanisms for the formation of the HF, F−(HF)n, and O2−(HF)n species were discussed from the standpoints of the HF generator and APCDI MS. By performing energy-resolved collision-induced dissociation (CID) experiments on the cluster ions F−(HF)n (n=1–3), the energies for the loss of HF from F−(HF)3, F−(HF)2, and F−(HF) were evaluated to be 1 eV or lower, 1 eV or higher, and 2 eV, respectively, on the basis of their center-of-mass energy (ECM). These ECM values were consistent with the values of 0.995, 1.308, and 2.048 eV, respectively, obtained by ab initio calculations. The stability of [O2(HF)n]− (n=1–4) was discussed on the basis of the bond lengths of O2H–F−(HF)n and O2−H–F(HF)n obtained by ab initio calculations. The calculations indicated that [O2(HF)4]− separated into O2H and F−(HF)3. PMID:28966900
Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y-(HF) n (Y=F, O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator.

PubMed

Sakamoto, Kenya; Sekimoto, Kanako; Takayama, Mitsuo

2017-01-01

Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF) n . The HF molecules were ionized in the form of complex ions associated with the negative core ions Y - produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y - (HF) n (Y=F, O 2 ), where larger clusters with n ≥4 were not detected. The mechanisms for the formation of the HF, F - (HF) n , and O 2 - (HF) n species were discussed from the standpoints of the HF generator and APCDI MS. By performing energy-resolved collision-induced dissociation (CID) experiments on the cluster ions F - (HF) n ( n =1-3), the energies for the loss of HF from F - (HF) 3 , F - (HF) 2 , and F - (HF) were evaluated to be 1 eV or lower, 1 eV or higher, and 2 eV, respectively, on the basis of their center-of-mass energy ( E CM ). These E CM values were consistent with the values of 0.995, 1.308, and 2.048 eV, respectively, obtained by ab initio calculations. The stability of [O 2 (HF) n ] - ( n =1-4) was discussed on the basis of the bond lengths of O 2 H-F - (HF) n and O 2 - H-F(HF) n obtained by ab initio calculations. The calculations indicated that [O 2 (HF) 4 ] - separated into O 2 H and F - (HF) 3 .
Ion collision-induced chemistry in pure and mixed loosely bound clusters of coronene and C60 molecules.

PubMed

Domaracka, Alicja; Delaunay, Rudy; Mika, Arkadiusz; Gatchell, Michael; Zettergren, Henning; Cederquist, Henrik; Rousseau, Patrick; Huber, Bernd A

2018-05-23

Ionization, fragmentation and molecular growth have been studied in collisions of 22.5 keV He2+- or 3 keV Ar+-projectiles with pure loosely bound clusters of coronene (C24H12) molecules or with loosely bound mixed C60-C24H12 clusters by using mass spectrometry. The heavier and slower Ar+ projectiles induce prompt knockout-fragmentation - C- and/or H-losses - from individual molecules and highly efficient secondary molecular growth reactions before the clusters disintegrate on picosecond timescales. The lighter and faster He2+ projectiles have a higher charge and the main reactions are then ionization by ions that are not penetrating the clusters. This leads mostly to cluster fragmentation without molecular growth. However, here penetrating collisions may also lead to molecular growth but to a much smaller extent than with 3 keV Ar+. Here we present fragmentation and molecular growth mass distributions with 1 mass unit resolution, which reveals that the same numbers of C- and H-atoms often participate in the formation and breaking of covalent bonds inside the clusters. We find that masses close to those with integer numbers of intact coronene molecules, or with integer numbers of both intact coronene and C60 molecules, are formed where often one or several H-atoms are missing or have been added on. We also find that super-hydrogenated coronene is formed inside the clusters.
GW and Bethe-Salpeter study of small water clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blase, Xavier, E-mail: xavier.blase@neel.cnrs.fr; Boulanger, Paul; Bruneval, Fabien

We study within the GW and Bethe-Salpeter many-body perturbation theories the electronic and optical properties of small (H{sub 2}O){sub n} water clusters (n = 1-6). Comparison with high-level CCSD(T) Coupled-Cluster at the Single Double (Triple) levels and ADC(3) Green’s function third order algebraic diagrammatic construction calculations indicates that the standard non-self-consistent G{sub 0}W{sub 0}@PBE or G{sub 0}W{sub 0}@PBE0 approaches significantly underestimate the ionization energy by about 1.1 eV and 0.5 eV, respectively. Consequently, the related Bethe-Salpeter lowest optical excitations are found to be located much too low in energy when building transitions from a non-self-consistent G{sub 0}W{sub 0} description ofmore » the quasiparticle spectrum. Simple self-consistent schemes, with update of the eigenvalues only, are shown to provide a weak dependence on the Kohn-Sham starting point and a much better agreement with reference calculations. The present findings rationalize the theory to experiment possible discrepancies observed in previous G{sub 0}W{sub 0} and Bethe-Salpeter studies of bulk water. The increase of the optical gap with increasing cluster size is consistent with the evolution from gas to dense ice or water phases and results from an enhanced screening of the electron-hole interaction.« less
Cluster model studies of anion and molecular specificities via electrospray ionization photoelectron spectroscopy

DOE PAGES

Wang, Xue -Bin

2017-01-06

Ion specificity, a widely observed macroscopic phenomenon in condensed phases and at interfaces, is essentially a fundamental chemical physical issue. We have been investigating such effects using cluster models in an “atom-by-atom” and “molecule-by-molecule” fashion not possible with condensed-phase methods. We use electrospray ionization (ESI) to generate molecular and ionic clusters to simulate key molecular entities involved in local binding regions, and characterize them employing negative ion photoelectron spectroscopy (NIPES). Inter- and intramolecular interactions and binding configurations are directly obtained as functions of cluster size and composition, providing insightful molecular-level description and characterization over the local active sites that playmore » crucial roles in determining solution chemistry and condensed phase phenomena. Finally, the topics covered in this article are relevant to a wide scope of research fields ranging from ion specific effects in electrolyte solutions, ion selectivity/recognition in normal functioning of life, to molecular specificity in aerosol particle formation, as well as in rational material design and synthesis.« less
Energy Characteristics of Small Metal Clusters Containing Vacancies

NASA Astrophysics Data System (ADS)

Reva, V. I.; Pogosov, V. V.

2018-02-01

Self-consistent calculations of spatial distributions of electrons, potentials, and energies of dissociation, cohesion, vacancy formation, and electron attachment, as well as the ionization potential of solid Al N , Na N clusters ( N ≥ 254), and clusters containing a vacancy ( N ≥ 12) have been performed using a model of stable jellium. The contribution of a monovacancy to the energy of the cluster, the size dependences of the characteristics, and their asymptotic forms have been considered. The calculations have been performed on the SKIT-3 cluster at the Glushkov Institute of Cybernetics, National Academy of Sciences of Ukraine (Rpeak = 7.4 Tflops).
Nuclear Fusion induced by Coulomb Explosion of Heteronuclear Clusters

NASA Astrophysics Data System (ADS)

Last, Isidore; Jortner, Joshua

2001-07-01

We propose a new mechanism for the production of high-energy ( E>3 keV) deuterons, suitable to induce dd nuclear fusion, based on multielectron ionization and Coulomb explosion of heteronuclear deuterium containing molecular clusters, e.g., (D2O)n, in intense ( 1016-2×1018 W/cm2) laser fields. Cluster size equations for E, in conjunction with molecular dynamics simulations, reveal important advantages of Coulomb explosion of (D2O)n heteronuclear clusters, as compared with (D)n clusters. These involve the considerably increased D+ kinetic energy and a narrow, high-energy distribution of deuterons.
Compendium of Single Event Effects, Total Ionizing Dose, and Displacement Damage for Candidate Spacecraft Electronics for NASA

NASA Technical Reports Server (NTRS)

LaBel, Kenneth A.; OBryan, Martha V.; Chen, Dakai; Campola, Michael J.; Casey, Megan C.; Pellish, Jonathan A.; Lauenstein, Jean-Marie; Wilcox, Edward P.; Topper, Alyson D.; Ladbury, Raymond L.;

2014-01-01

We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to proton and heavy ion induced single event effects (SEE), proton-induced displacement damage (DD), and total ionizing dose (TID). Introduction: This paper is a summary of test results.NASA spacecraft are subjected to a harsh space environment that includes exposure to various types of ionizing radiation. The performance of electronic devices in a space radiation environment is often limited by its susceptibility to single event effects (SEE), total ionizing dose (TID), and displacement damage (DD). Ground-based testing is used to evaluate candidate spacecraft electronics to determine risk to spaceflight applications. Interpreting the results of radiation testing of complex devices is quite difficult. Given the rapidly changing nature of technology, radiation test data are most often application-specific and adequate understanding of the test conditions is critical. Studies discussed herein were undertaken to establish the application-specific sensitivities of candidate spacecraft and emerging electronic devices to single-event upset (SEU), single-event latchup (SEL), single-event gate rupture (SEGR), single-event burnout (SEB), single-event transient (SET), TID, enhanced low dose rate sensitivity (ELDRS), and DD effects.

Formaldehyde and methanol formation from reaction of carbon monoxide and hydrogen on neutral Fe2S2 clusters in the gas phase.

PubMed

Yin, Shi; Wang, Zhechen; Bernstein, Elliot R

2013-04-07

Reaction of CO with H2 on neutral FemSn clusters in a fast flow reactor is investigated both experimentally and theoretically. Single photon ionization at 118 nm is used to detect neutral cluster distributions through time of flight mass spectrometry. FemSn clusters are generated through laser ablation of a mixed iron-sulfur target in the presence of a pure helium carrier gas. A strong size dependent reactivity of (FeS)m clusters toward CO is characterized. The reaction FeS + CO → Fe + OCS is found for the FeS cluster, and the association product Fe2S2CO is observed for the Fe2S2 cluster. Products Fe2S2(13)COH2 and Fe2S2(13)COH4 are identified for reactions of (13)CO and H2 on Fe2S2 clusters: this suggests that the Fe2S2 cluster has a high catalytic activity for hydrogenation reactions of CO to form formaldehyde and methanol. Density functional theory (DFT) calculations are performed to explore the potential energy surfaces for the two reactions: Fe2S2 + CO + 2H2 → Fe2S2 + CH3OH; and Fe2S2 + CO + H2 → Fe2S2 + CH2O. A barrierless, thermodynamically favorable pathway is obtained for both catalytic processes. Catalytic cycles for formaldehyde and methanol formation from CO and H2 on a Fe2S2 cluster are proposed based on our experimental and theoretical investigations. The various reaction mechanisms explored by DFT are in good agreement with the experimental results. Condensed phase iron sulfide, which contains exposed Fe2S2 units on its surface, is suggested to be a good catalyst for low temperature formaldehyde/methanol synthesis.
Ionization heating in rare-gas clusters under intense XUV laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arbeiter, Mathias; Fennel, Thomas

The interaction of intense extreme ultraviolet (XUV) laser pulses ({lambda}=32 nm, I=10{sup 11}-10{sup 14} W/cm{sup 2}) with small rare-gas clusters (Ar{sub 147}) is studied by quasiclassical molecular dynamics simulations. Our analysis supports a very general picture of the charging and heating dynamics in finite samples under short-wavelength radiation that is of relevance for several applications of free-electron lasers. First, up to a certain photon flux, ionization proceeds as a series of direct photoemission events producing a jellium-like cluster potential and a characteristic plateau in the photoelectron spectrum as observed in Bostedt et al. [Phys. Rev. Lett. 100, 133401 (2008)]. Second,more » beyond the onset of photoelectron trapping, nanoplasma formation leads to evaporative electron emission with a characteristic thermal tail in the electron spectrum. A detailed analysis of this transition is presented. Third, in contrast to the behavior in the infrared or low vacuum ultraviolet range, the nanoplasma energy capture proceeds via ionization heating, i.e., inner photoionization of localized electrons, whereas collisional heating of conduction electrons is negligible up to high laser intensities. A direct consequence of the latter is a surprising evolution of the mean energy of emitted electrons as function of laser intensity.« less
On the Ionization and Ion Transmission Efficiencies of Different ESI-MS Interfaces

PubMed Central

Cox, Jonathan T.; Marginean, Ioan; Smith, Richard D.; Tang, Keqi

2014-01-01

The achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. These performance characteristics are difficult to evaluate and compare across multiple platforms as it is difficult to correlate electrical current measurements to actual analyte ions reaching the detector of a mass spectrometer. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuring the total gas phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Using this method we systematically studied the ion transmission and ionization efficiencies of different ESI-MS interface configurations, including a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interface with a single emitter and an emitter array, respectively. Our experimental results indicate that the overall ion utilization efficiency of SPIN-MS interface configurations exceeds that of the inlet capillary-based ESI-MS interface configurations. PMID:25267087
On the ionization and ion transmission efficiencies of different ESI-MS interfaces.

PubMed

Cox, Jonathan T; Marginean, Ioan; Smith, Richard D; Tang, Keqi

2015-01-01

The achievable sensitivity of electrospray ionization mass spectrometry (ESI-MS) is largely determined by the ionization efficiency in the ESI source and ion transmission efficiency through the ESI-MS interface. These performance characteristics are difficult to evaluate and compare across multiple platforms as it is difficult to correlate electrical current measurements to actual analyte ions reaching the detector of a mass spectrometer. We present an effective method to evaluate the overall ion utilization efficiency of an ESI-MS interface by measuring the total gas-phase ion current transmitted through the interface and correlating it to the observed ion abundance measured in the corresponding mass spectrum. Using this method, we systematically studied the ion transmission and ionization efficiencies of different ESI-MS interface configurations, including a single emitter/single inlet capillary, single emitter/multi-inlet capillary, and a subambient pressure ionization with nanoelectrospray (SPIN) MS interface with a single emitter and an emitter array, respectively. Our experimental results indicate that the overall ion utilization efficiency of SPIN-MS interface configurations exceeds that of the inlet capillary-based ESI-MS interface configurations.
Multiconfiguration Pair-Density Functional Theory Is Free From Delocalization Error.

PubMed

Bao, Junwei Lucas; Wang, Ying; He, Xiao; Gagliardi, Laura; Truhlar, Donald G

2017-11-16

Delocalization error has been singled out by Yang and co-workers as the dominant error in Kohn-Sham density functional theory (KS-DFT) with conventional approximate functionals. In this Letter, by computing the vertical first ionization energy for well separated He clusters, we show that multiconfiguration pair-density functional theory (MC-PDFT) is free from delocalization error. To put MC-PDFT in perspective, we also compare it with some Kohn-Sham density functionals, including both traditional and modern functionals. Whereas large delocalization errors are almost universal in KS-DFT (the only exception being the very recent corrected functionals of Yang and co-workers), delocalization error is removed by MC-PDFT, which bodes well for its future as a step forward from KS-DFT.

A singly charged ion source for radioactive {sup 11}C ion acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katagiri, K.; Noda, A.; Nagatsu, K.

2016-02-15

A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive {sup 11}C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source wasmore » found to have favorable performance as a singly charged ion source.« less
Ionized-Cluster Beam/Partially Ionized Beam Deposition of Electro- Optical and Nonlinear Optical Organic Materials and Device Development

DTIC Science & Technology

1993-08-29

4’- CH3 O--\\\\4 4N -2 nitrostilbene NO 2J (MMONS) 4’-dimethylamfino OCH3 -N-4-stylbazolium j, o3 - 200 3125 1000 tosylate (DAST)or 0 3 (CH3)2N CH3 Styrylpyridinium PH cyanine dye 400 1490 470 ( SPCD ) SO4 (CH3 ½2N lh3 20
Electron emission from transfer ionization reaction in 30 keV amu‑1 He 2+ on Ar collision

NASA Astrophysics Data System (ADS)

Amaya-Tapia, A.; Antillón, A.; Estrada, C. D.

2018-06-01

A model is presented that describes the transfer ionization process in H{e}2++Ar collision at a projectile energy of 30 keV amu‑1. It is based on a semiclassical independent-particle close-coupling method that yields a reasonable agreement between calculated and experimental values of the total single-ionization and single-capture cross sections. It is found that the transfer ionization reaction is predominantly carried out through simultaneous capture and ionization, rather than by sequential processes. The transfer-ionization differential cross section in energy that is obtained satisfactorily reproduces the global behavior of the experimental data. Additionally, the probabilities of capture and ionization as function of the impact parameter for H{e}2++A{r}+ and H{e}++A{r}+ collisions are calculated, as far as we know, for the first time. The results suggest that the model captures essential elements that describe the two-electron transfer ionization process and could be applied to systems and processes of two electrons.
Measurement of track structure parameters of low and medium energy helium and carbon ions in nanometric volumes

NASA Astrophysics Data System (ADS)

Hilgers, G.; Bug, M. U.; Rabus, H.

2017-10-01

Ionization cluster size distributions produced in the sensitive volume of an ion-counting wall-less nanodosimeter by monoenergetic carbon ions with energies between 45 MeV and 150 MeV were measured at the TANDEM-ALPI ion accelerator facility complex of the LNL-INFN in Legnaro. Those produced by monoenergetic helium ions with energies between 2 MeV and 20 MeV were measured at the accelerator facilities of PTB and with a 241Am alpha particle source. C3H8 was used as the target gas. The ionization cluster size distributions were measured in narrow beam geometry with the primary beam passing the target volume at specified distances from its centre, and in broad beam geometry with a fan-like primary beam. By applying a suitable drift time window, the effective size of the target volume was adjusted to match the size of a DNA segment. The measured data were compared with the results of simulations obtained with the PTB Monte Carlo code PTra. Before the comparison, the simulated cluster size distributions were corrected with respect to the background of additional ionizations produced in the transport system of the ionized target gas molecules. Measured and simulated characteristics of the particle track structure are in good agreement for both types of primary particles and for both types of the irradiation geometry. As the range in tissue of the ions investigated is within the typical extension of a spread-out Bragg peak, these data are useful for benchmarking not only ‘general purpose’ track structure simulation codes, but also treatment planning codes used in hadron therapy. Additionally, these data sets may serve as a data base for codes modelling the induction of radiation damages at the DNA-level as they almost completely characterize the ionization component of the nanometric track structure.
On the ultrafast charge migration and subsequent charge directed reactivity in Cl⋯N halogen-bonded clusters following vertical ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandra, Sankhabrata; Bhattacharya, Atanu, E-mail: atanub@ipc.iisc.ernet.in; Periyasamy, Ganga

2015-06-28

In this article, we have presented ultrafast charge transfer dynamics through halogen bonds following vertical ionization of representative halogen bonded clusters. Subsequent hole directed reactivity of the radical cations of halogen bonded clusters is also discussed. Furthermore, we have examined effect of the halogen bond strength on the electron-electron correlation- and relaxation-driven charge migration in halogen bonded complexes. For this study, we have selected A-Cl (A represents F, OH, CN, NH{sub 2}, CF{sub 3}, and COOH substituents) molecules paired with NH{sub 3} (referred as ACl:NH{sub 3} complex): these complexes exhibit halogen bonds. To the best of our knowledge, this ismore » the first report on purely electron correlation- and relaxation-driven ultrafast (attosecond) charge migration dynamics through halogen bonds. Both density functional theory and complete active space self-consistent field theory with 6-31 + G(d, p) basis set are employed for this work. Upon vertical ionization of NCCl⋯NH{sub 3} complex, the hole is predicted to migrate from the NH{sub 3}-end to the ClCN-end of the NCCl⋯NH{sub 3} complex in approximately 0.5 fs on the D{sub 0} cationic surface. This hole migration leads to structural rearrangement of the halogen bonded complex, yielding hydrogen bonding interaction stronger than the halogen bonding interaction on the same cationic surface. Other halogen bonded complexes, such as H{sub 2}NCl:NH{sub 3}, F{sub 3}CCl:NH{sub 3}, and HOOCCl:NH{sub 3}, exhibit similar charge migration following vertical ionization. On the contrary, FCl:NH{sub 3} and HOCl:NH{sub 3} complexes do not exhibit any charge migration following vertical ionization to the D{sub 0} cation state, pointing to interesting halogen bond strength-dependent charge migration.« less
Optical signatures of molecular particles via mass-selected cluster spectroscopy

NASA Technical Reports Server (NTRS)

Duncan, Michael A.

1990-01-01

A new molecular beam apparatus was developed to study optical absorption in cold (less than 100 K) atomic clusters and complexes produced by their condensation with simple molecular gases. In this instrument, ionized clusters produced in a laser vaporization nozzle source are mass selected and studied with photodissociation spectroscopy at visible and ultraviolet wavelengths. This new approach can be applied to synthesize and characterize numerous particulates and weakly bound complexes expected in planetary atmospheres and in comets.
Reprint of: Negative carbon cluster ion beams: New evidence for the special nature of C60

NASA Astrophysics Data System (ADS)

Liu, Y.; O'brien, S. C.; Zhang, Q.; Heath, J. R.; Tittel, F. K.; Curl, R. F.; Kroto, H. W.; Smalley, R. E.

2013-12-01

Cold carbon cluster negative ions are formed by supersonic expansion of a plasma created at the nozzle of a supersonic cluster beam source by an excimer laser pulse. The observed distribution of mass peaks for the Cn- ions for n > 40 demonstrates that the evidence previously given for the special stability of neutral C60 and the existence of spheroidal carbon shells cannot be an artifact of the ionization conditions.
Bright Young Star Clusters in NGC5253 with LEGUS

NASA Astrophysics Data System (ADS)

Calzetti, Daniela; Johnson, Kelsey E.; Adamo, Angela; Gallagher, John S.; Andrews, Jennifer E.; Smith, Linda J.; Clayton, Geoffrey C.; Lee, Janice C.; Sabbi, Elena; Ubeda, Leonardo; Kim, Hwihyun; Ryon, Jenna E.; Thilker, David A.; Bright, Stacey N.; Zackrisson, Erik; Kennicutt, Robert; de Mink, Selma E.; Whitmore, Bradley C.; Aloisi, Alessandra; Chandar, Rupali; Cignoni, Michele; Cook, David; Dale, Daniel A.; Elmegreen, Bruce; Elmegreen, Debra M.; Evans, Aaron S.; Fumagalli, Michele; Gouliermis, Dimitrios; Grasha, Kathryn; Grebel, Eva; Krumholz, Mark R.; Walterbos, Rene A. M.; Wofford, Aida; Brown, Thomas M.; Christian, Carol A.; Dobbs, Claire; Herrero-Davo`, Artemio; Kahre, Lauren; Messa, Matteo; Nair, Preethi; Nota, Antonella; Östlin, Göran; Pellerin, Anne; Sacchi, Elena; Schaerer, Daniel; Tosi, Monica

2016-01-01

Using UV-to-H broad and narrow-band HST imaging, we derive the ages and masses of the 11 brightest star clusters in the dwarf galaxy NGC5253. This galaxy, located at ~3 Mpc, hosts an intense starburst, which includes a centrally-concentrated dusty region with strong thermal radio emission (the `radio nebula'). The HST imaging includes data from the Cycle 21 Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), in addition to narrow--band H-alpha (6563 A), P-beta (12820 A), and P-alpha (18756 A). The bright clusters have ages ~1-15 Myr and masses ~1E4 - 2.5E5 Msun. Two of the 11 star clusters are located within the radio nebula, and suffer from significant dust attenuation. Both are extremely young, with a best-fit age around 1 Myr, and masses ~7.5E4 and ~2.5E5 Msun, respectively. The most massive of the two `radio nebula' clusters is 2-4 times less massive than previously estimated and is embedded within a cloud of dust with A_V~50 mag. The two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.
Ionized cluster beam deposition

NASA Technical Reports Server (NTRS)

Kirkpatrick, A. R.

1983-01-01

Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.
Scattering Response of Sucrose Clusters with Intense XFEL Pulses in Water Window

NASA Astrophysics Data System (ADS)

Ho, Phay; Benedikt Daurer, Benedikt; Bielecki, Johan; Hantke, Max; Maia, Filipe; Knight, Chris; Hajdu, Janos; Young, Linda; Bostedt, Christoph

2017-04-01

We present a combined experimental and theoretical study about the effects of non-linear x-ray ionization dynamics on the scattering response of molecular clusters in the soft x-ray regime that includes and goes beyond the water window. Nanosized sucrose clusters were irradiated with intense XFEL pulses (photon energy from 500 to 1500 eV and pulse duration of 180 fs). Surprisingly, the measured scattering signals near the oxygen K-edge in the water window are found to be substantially smaller than those at higher photon energies. We employ Monte-Carlo/Molecular Dynamics calculations to investigate the x-ray processes as a function of pulse parameters (photon energy, bandwidth and pulse duration) and cluster size. We demonstrate the important role of resonant excitation (RE) in the molecular scattering response in the water window. In particular, 1s ->2p RE cycling enabled in the oxygen atom/ion provide additional ionization pathways which, combined with the long pulse duration, lead to substantial reduction in scattering power of sugar clusters for photon energies just below the oxygen K-edge. Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Dept of Energy, Contract DE-AC02-06CH11357.
Reduced repair capacity of a DNA clustered damage site comprised of 8-oxo-7,8-dihydro-2'-deoxyguanosine and 2-deoxyribonolactone results in an increased mutagenic potential of these lesions

DOE PAGES

Cunniffe, Siobhan; O’Neill, Peter; Greenberg, Marc M.; ...

2014-04-01

A signature of ionizing radiation is the induction of DNA clustered damaged sites. Non-double strand break (DSB) clustered damage has been shown to compromise the base excision repair pathway, extending the lifetimes of the lesions within the cluster, compared to isolated lesions. This increases the likelihood the lesions persist to replication and thus increasing the mutagenic potential of the lesions within the cluster. Lesions formed by ionizing radiation include 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and 2-deoxyribonolactone (dL). dL poses an additional challenge to the cell as it is not repaired by the short-patch base excision repair pathway. Here we show recalcitrant dL repairmore » is reflected in mutations observed when DNA containing it and a proximal 8-oxodGuo is replicated in Escherichia coli. 8-oxodGuo in close proximity to dL on the opposing DNA strand results in an enhanced frequency of mutation of the lesions within the cluster and a 20 base sequence flanking the clustered damage site in an E. coli based plasmid assay. In vitro repair of a dL lesion is reduced when compared to the repair of an abasic (AP) site and a tetrahydrofuran (THF), and this is due mainly to a reduction in the activity of polymerase β, leading to retarded FEN1 and ligase 1 activities. This study has given insights in to the biological effects of clusters containing dL.« less
Clustering effects in ionic polymers: Molecular dynamics simulations.

PubMed

Agrawal, Anupriya; Perahia, Dvora; Grest, Gary S

2015-08-01

Ionic clusters control the structure, dynamics, and transport in soft matter. Incorporating a small fraction of ionizable groups in polymers substantially reduces the mobility of the macromolecules in melts. These ionic groups often associate into random clusters in melts, where the distribution and morphology of the clusters impact the transport in these materials. Here, using molecular dynamic simulations we demonstrate a clear correlation between cluster size and morphology with the polymer mobility in melts of sulfonated polystyrene. We show that in low dielectric media ladderlike clusters that are lower in energy compared with spherical assemblies are formed. Reducing the electrostatic interactions by enhancing the dielectric constant leads to morphological transformation from ladderlike clusters to globular assemblies. Decrease in electrostatic interaction significantly enhances the mobility of the polymer.
II Zw 40 - 30 Doradus on Steroids

NASA Astrophysics Data System (ADS)

Leitherer, Claus; Lee, Janice C.; Levesque, Emily M.

2017-11-01

We obtained HST COS G140L spectra of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster embedded in a radio-bright nebula, similar to those observed in the related blue compact dwarfs NGC 5253 and Henize 2-10. The ultraviolet spectrum of II Zw 40 is exceptional in terms of the strength of He II 1640, O III] 1666 and C III] 1909. We determined reddening, age, and the cluster mass from the ultraviolet data. The super nebula and the ionizing cluster exceed the ionizing luminosity and stellar mass of the local benchmark 30 Doradus by an order of magnitude. Comparison with stellar evolution models accounting for rotation reveals serious short-comings: these models do not account for the presence of Wolf-Rayet-like stars at young ages observed in II Zw 40. Photoionization modeling is used to probe the origin of the nebular lines and determine gas phase abundances. C/O is solar, in agreement with the result of the stellar-wind modeling.
Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tench, R. J.; Balooch, M.; Bernardez, L.; Allen, Mike J.; Siekhaus, W. J.; Olander, D. R.; Wang, W.

1990-04-01

Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4 to 100 microns diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO 2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10(exp -5) Torr by 1 to 3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10(exp -8) Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with angstrom resolution. Clusters up to 30 A in diameter were observed.
Electron scattering in large water clusters from photoelectron imaging with high harmonic radiation.

PubMed

Gartmann, Thomas E; Hartweg, Sebastian; Ban, Loren; Chasovskikh, Egor; Yoder, Bruce L; Signorell, Ruth

2018-06-06

Low-energy electron scattering in water clusters (H2O)n with average cluster sizes of n < 700 is investigated by angle-resolved photoelectron spectroscopy using high harmonic radiation at photon energies of 14.0, 20.3, and 26.5 eV for ionization from the three outermost valence orbitals. The measurements probe the evolution of the photoelectron anisotropy parameter β as a function of cluster size. A remarkably steep decrease of β with increasing cluster size is observed, which for the largest clusters reaches liquid bulk values. Detailed electron scattering calculations reveal that neither gas nor condensed phase scattering can explain the cluster data. Qualitative agreement between experiment and simulations is obtained with scattering calculations that treat cluster scattering as an intermediate case between gas and condensed phase scattering.
On the accuracy of density functional theory and wave function methods for calculating vertical ionization energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKechnie, Scott; Booth, George H.; Cohen, Aron J.

The best practice in computational methods for determining vertical ionization energies (VIEs) is assessed, via reference to experimentally determined VIEs that are corroborated by highly accurate coupled-cluster calculations. These reference values are used to benchmark the performance of density-functional theory (DFT) and wave function methods: Hartree-Fock theory (HF), second-order Møller-Plesset perturbation theory (MP2) and Electron Propagator Theory (EPT). The core test set consists of 147 small molecules. An extended set of six larger molecules, from benzene to hexacene, is also considered to investigate the dependence of the results on molecule size. The closest agreement with experiment is found for ionizationmore » energies obtained from total energy diff calculations. In particular, DFT calculations using exchange-correlation functionals with either a large amount of exact exchange or long-range correction perform best. The results from these functionals are also the least sensitive to an increase in molecule size. In general, ionization energies calculated directly from the orbital energies of the neutral species are less accurate and more sensitive to an increase in molecule size. For the single-calculation approach, the EPT calculations are in closest agreement for both sets of molecules. For the orbital energies from DFT functionals, only those with long-range correction give quantitative agreement with dramatic failing for all other functionals considered. The results offer a practical hierarchy of approximations for the calculation of vertical ionization energies. In addition, the experimental and computational reference values can be used as a standardized set of benchmarks, against which other approximate methods can be compared.« less
Galaxy Protoclusters as Drivers of Cosmic Star Formation History in the First 2 Gyr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiang, Yi-Kuan; Overzier, Roderik A.; Gebhardt, Karl

Present-day clusters are massive halos containing mostly quiescent galaxies, while distant protoclusters are extended structures containing numerous star-forming galaxies. We investigate the implications of this fundamental change in a cosmological context using a set of N -body simulations and semi-analytic models. We find that the fraction of the cosmic volume occupied by all (proto)clusters increases by nearly three orders of magnitude from z = 0 to z = 7. We show that (proto)cluster galaxies are an important and even dominant population at high redshift, as their expected contribution to the cosmic star formation rate density rises (from 1% at zmore » = 0) to 20% at z = 2 and 50% at z = 10. Protoclusters thus provide a significant fraction of the cosmic ionizing photons, and may have been crucial in driving the timing and topology of cosmic reionization. Internally, the average history of cluster formation can be described by three distinct phases: at z ∼ 10–5, galaxy growth in protoclusters proceeded in an inside-out manner, with centrally dominant halos that are among the most active regions in the universe; at z ∼ 5–1.5, rapid star formation occurred within the entire 10–20 Mpc structures, forming most of their present-day stellar mass; at z ≲ 1.5, violent gravitational collapse drove these stellar contents into single cluster halos, largely erasing the details of cluster galaxy formation due to relaxation and virialization. Our results motivate observations of distant protoclusters in order to understand the rapid, extended stellar growth during cosmic noon, and their connection to reionization during cosmic dawn.« less
Phylogenomic and MALDI-TOF MS Analysis of Streptococcus sinensis HKU4T Reveals a Distinct Phylogenetic Clade in the Genus Streptococcus

PubMed Central

Tse, Herman; Chen, Jonathan H.K.; Tang, Ying; Lau, Susanna K.P.; Woo, Patrick C.Y.

2014-01-01

Streptococcus sinensis is a recently discovered human pathogen isolated from blood cultures of patients with infective endocarditis. Its phylogenetic position, as well as those of its closely related species, remains inconclusive when single genes were used for phylogenetic analysis. For example, S. sinensis branched out from members of the anginosus, mitis, and sanguinis groups in the 16S ribosomal RNA gene phylogenetic tree, but it was clustered with members of the anginosus and sanguinis groups when groEL gene sequences used for analysis. In this study, we sequenced the draft genome of S. sinensis and used a polyphasic approach, including concatenated genes, whole genomes, and matrix-assisted laser desorption ionization-time of flight mass spectrometry to analyze the phylogeny of S. sinensis. The size of the S. sinensis draft genome is 2.06 Mb, with GC content of 42.2%. Phylogenetic analysis using 50 concatenated genes or whole genomes revealed that S. sinensis formed a distinct cluster with Streptococcus oligofermentans and Streptococcus cristatus, and these three streptococci were clustered with the “sanguinis group.” As for phylogenetic analysis using hierarchical cluster analysis of the mass spectra of streptococci, S. sinensis also formed a distinct cluster with S. oligofermentans and S. cristatus, but these three streptococci were clustered with the “mitis group.” On the basis of the findings, we propose a novel group, named “sinensis group,” to include S. sinensis, S. oligofermentans, and S. cristatus, in the Streptococcus genus. Our study also illustrates the power of phylogenomic analyses for resolving ambiguities in bacterial taxonomy. PMID:25331233
Phylogenomic and MALDI-TOF MS analysis of Streptococcus sinensis HKU4T reveals a distinct phylogenetic clade in the genus Streptococcus.

PubMed

Teng, Jade L L; Huang, Yi; Tse, Herman; Chen, Jonathan H K; Tang, Ying; Lau, Susanna K P; Woo, Patrick C Y

2014-10-20

Streptococcus sinensis is a recently discovered human pathogen isolated from blood cultures of patients with infective endocarditis. Its phylogenetic position, as well as those of its closely related species, remains inconclusive when single genes were used for phylogenetic analysis. For example, S. sinensis branched out from members of the anginosus, mitis, and sanguinis groups in the 16S ribosomal RNA gene phylogenetic tree, but it was clustered with members of the anginosus and sanguinis groups when groEL gene sequences used for analysis. In this study, we sequenced the draft genome of S. sinensis and used a polyphasic approach, including concatenated genes, whole genomes, and matrix-assisted laser desorption ionization-time of flight mass spectrometry to analyze the phylogeny of S. sinensis. The size of the S. sinensis draft genome is 2.06 Mb, with GC content of 42.2%. Phylogenetic analysis using 50 concatenated genes or whole genomes revealed that S. sinensis formed a distinct cluster with Streptococcus oligofermentans and Streptococcus cristatus, and these three streptococci were clustered with the "sanguinis group." As for phylogenetic analysis using hierarchical cluster analysis of the mass spectra of streptococci, S. sinensis also formed a distinct cluster with S. oligofermentans and S. cristatus, but these three streptococci were clustered with the "mitis group." On the basis of the findings, we propose a novel group, named "sinensis group," to include S. sinensis, S. oligofermentans, and S. cristatus, in the Streptococcus genus. Our study also illustrates the power of phylogenomic analyses for resolving ambiguities in bacterial taxonomy. © The Author(s) 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
The lowest ionization potentials of Al2

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Barnes, Leslie A.; Taylor, Peter R.

1988-01-01

Potential curves for the lowest two electronic states (X 2 sigma g + and A 2 pi u) of Al2(+) were computed using complete active space SCF/multireference CI wave functions and large Gaussian basis sets. The lowest observable vertical ionization potential (to Al2(+) X 2 sigma g +) of the Al2 X 3 pi u ground state is calculated to occur around 6.1 eV, in excellent agreement with the experimental range of 6.0 to 6.42 eV obtained in recent cluster ionization studies by Cox and co-workers. The second vertical ionization potential (to Al2(+) A 2 pi u) occurs near 6.4 eV, also within the experimental range. The adiabatic IP of 5.90 eV is in good agreement with the value of 5.8 to 6.1 eV deduced by Hanley and co-workers from the difference in thresholds between collision induced dissociation processes of Al3(+). The computed IP values are somewhat larger than those deduced from branching ratios in cluster fragmentation experiments by Jarrold and co-workers. The observation of an ionization threshold below 6.42 eV is shown to be incompatible with an Al2 ground electronic state assignment of 3 sigma g -, but the separation between the two lowest states of Al2 is so small that it is likely that both are populated in the experiments, so that this does not provide unambiguous support for the recent theoretical assignment of the ground state as 3 pi u.

SPECTROSCOPIC ABUNDANCES AND MEMBERSHIP IN THE WOLF 630 MOVING GROUP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bubar, Eric J.; King, Jeremy R., E-mail: ebubar@gmail.co, E-mail: jking2@ces.clemson.ed

The concept of kinematic assemblages evolving from dispersed stellar clusters has remained contentious since Eggen's initial formulation of moving groups in the 1960s. With high-quality parallaxes from the Hipparcos space astrometry mission, distance measurements for thousands of nearby, seemingly isolated stars are currently available. With these distances, a high-resolution spectroscopic abundance analysis can be brought to bear on the alleged members of these moving groups. If a structure is a relic of an open cluster, the members can be expected to be monolithic in age and abundance in as much as homogeneity is observed in young open clusters. In thismore » work, we have examined 34 putative members of the proposed Wolf 630 moving group using high-resolution stellar spectroscopy. The stars of the sample have been chemically tagged to determine abundance homogeneity and confirm the existence of a homogeneous subsample of 19 stars. Fitting the homogeneous subsample with Yale-Yonsei isochrones yields a single evolutionary sequence of {approx}2.7 {+-} 0.5 Gyr. It is concluded that this 19 star subsample of the Wolf 630 moving group sample of 34 stars could represent a dispersed cluster with an ([Fe/H]) = -0.01 {+-} 0.02 and an age of 2.7 {+-} 0.5 Gyr. In addition, chemical abundances of Na and Al in giants are examined for indications of enhancements as observed in field giants of old open clusters; overexcitation/ionization effects are explored in the cooler dwarfs of the sample; and oxygen is derived from the infrared triplet and the forbidden line at {lambda}6300.« less
Coupled-cluster based approach for core-level states in condensed phase: Theory and application to different protonated forms of aqueous glycine

DOE PAGES

Sadybekov, Arman; Krylov, Anna I.

2017-07-07

A theoretical approach for calculating core-level states in condensed phase is presented. The approach is based on equation-of-motion coupled-cluster theory (EOMCC) and effective fragment potential (EFP) method. By introducing an approximate treatment of double excitations in the EOM-CCSD (EOM-CC with single and double substitutions) ansatz, we address poor convergence issues that are encountered for the core-level states and significantly reduce computational costs. While the approximations introduce relatively large errors in the absolute values of transition energies, the errors are systematic. Consequently, chemical shifts, changes in ionization energies relative to reference systems, are reproduced reasonably well. By using different protonation formsmore » of solvated glycine as a benchmark system, we show that our protocol is capable of reproducing the experimental chemical shifts with a quantitative accuracy. The results demonstrate that chemical shifts are very sensitive to the solvent interactions and that explicit treatment of solvent, such as EFP, is essential for achieving quantitative accuracy.« less
Coupled-cluster based approach for core-level states in condensed phase: Theory and application to different protonated forms of aqueous glycine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadybekov, Arman; Krylov, Anna I.

A theoretical approach for calculating core-level states in condensed phase is presented. The approach is based on equation-of-motion coupled-cluster theory (EOMCC) and effective fragment potential (EFP) method. By introducing an approximate treatment of double excitations in the EOM-CCSD (EOM-CC with single and double substitutions) ansatz, we address poor convergence issues that are encountered for the core-level states and significantly reduce computational costs. While the approximations introduce relatively large errors in the absolute values of transition energies, the errors are systematic. Consequently, chemical shifts, changes in ionization energies relative to reference systems, are reproduced reasonably well. By using different protonation formsmore » of solvated glycine as a benchmark system, we show that our protocol is capable of reproducing the experimental chemical shifts with a quantitative accuracy. The results demonstrate that chemical shifts are very sensitive to the solvent interactions and that explicit treatment of solvent, such as EFP, is essential for achieving quantitative accuracy.« less
Trace detection of organic compounds in complex sample matrixes by single photon ionization ion trap mass spectrometry: real-time detection of security-relevant compounds and online analysis of the coffee-roasting process.

PubMed

Schramm, Elisabeth; Kürten, Andreas; Hölzer, Jasper; Mitschke, Stefan; Mühlberger, Fabian; Sklorz, Martin; Wieser, Jochen; Ulrich, Andreas; Pütz, Michael; Schulte-Ladbeck, Rasmus; Schultze, Rainer; Curtius, Joachim; Borrmann, Stephan; Zimmermann, Ralf

2009-06-01

An in-house-built ion trap mass spectrometer combined with a soft ionization source has been set up and tested. As ionization source, an electron beam pumped vacuum UV (VUV) excimer lamp (EBEL) was used for single-photon ionization. It was shown that soft ionization allows the reduction of fragmentation of the target analytes and the suppression of most matrix components. Therefore, the combination of photon ionization with the tandem mass spectrometry (MS/MS) capability of an ion trap yields a powerful tool for molecular ion peak detection and identification of organic trace compounds in complex matrixes. This setup was successfully tested for two different applications. The first one is the detection of security-relevant substances like explosives, narcotics, and chemical warfare agents. One test substance from each of these groups was chosen and detected successfully with single photon ionization ion trap mass spectrometry (SPI-ITMS) MS/MS measurements. Additionally, first tests were performed, demonstrating that this method is not influenced by matrix compounds. The second field of application is the detection of process gases. Here, exhaust gas from coffee roasting was analyzed in real time, and some of its compounds were identified using MS/MS studies.
Bruker biotyper matrix-assisted laser desorption ionization-time of flight mass spectrometry system for identification of Nocardia, Rhodococcus, Kocuria, Gordonia, Tsukamurella, and Listeria species.

PubMed

Hsueh, Po-Ren; Lee, Tai-Fen; Du, Shin-Hei; Teng, Shih-Hua; Liao, Chun-Hsing; Sheng, Wang-Hui; Teng, Lee-Jene

2014-07-01

We evaluated whether the Bruker Biotyper matrix-associated laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) system provides accurate species-level identifications of 147 isolates of aerobically growing Gram-positive rods (GPRs). The bacterial isolates included Nocardia (n = 74), Listeria (n = 39), Kocuria (n = 15), Rhodococcus (n = 10), Gordonia (n = 7), and Tsukamurella (n = 2) species, which had all been identified by conventional methods, molecular methods, or both. In total, 89.7% of Listeria monocytogenes, 80% of Rhodococcus species, 26.7% of Kocuria species, and 14.9% of Nocardia species (n = 11, all N. nova and N. otitidiscaviarum) were correctly identified to the species level (score values, ≥ 2.0). A clustering analysis of spectra generated by the Bruker Biotyper identified six clusters of Nocardia species, i.e., cluster 1 (N. cyriacigeorgica), cluster 2 (N. brasiliensis), cluster 3 (N. farcinica), cluster 4 (N. puris), cluster 5 (N. asiatica), and cluster 6 (N. beijingensis), based on the six peaks generated by ClinProTools with the genetic algorithm, i.e., m/z 2,774.477 (cluster 1), m/z 5,389.792 (cluster 2), m/z 6,505.720 (cluster 3), m/z 5,428.795 (cluster 4), m/z 6,525.326 (cluster 5), and m/z 16,085.216 (cluster 6). Two clusters of L. monocytogenes spectra were also found according to the five peaks, i.e., m/z 5,594.85, m/z 6,184.39, and m/z 11,187.31, for cluster 1 (serotype 1/2a) and m/z 5,601.21 and m/z 11,199.33 for cluster 2 (serotypes 1/2b and 4b). The Bruker Biotyper system was unable to accurately identify Nocardia (except for N. nova and N. otitidiscaviarum), Tsukamurella, or Gordonia species. Continuous expansion of the MALDI-TOF MS databases to include more GPRs is necessary. Copyright © 2014, American Society for Microbiology. All Rights Reserved.
Ionization of pyridine: Interplay of orbital relaxation and electron correlation.

PubMed

Trofimov, A B; Holland, D M P; Powis, I; Menzies, R C; Potts, A W; Karlsson, L; Gromov, E V; Badsyuk, I L; Schirmer, J

2017-06-28

The valence shell ionization spectrum of pyridine was studied using the third-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function and the outer-valence Green's function method. The results were used to interpret angle resolved photoelectron spectra recorded with synchrotron radiation in the photon energy range of 17-120 eV. The lowest four states of the pyridine radical cation, namely, 2 A 2 (1a 2 -1 ), 2 A 1 (7a 1 -1 ), 2 B 1 (2b 1 -1 ), and 2 B 2 (5b 2 -1 ), were studied in detail using various high-level electronic structure calculation methods. The vertical ionization energies were established using the equation-of-motion coupled-cluster approach with single, double, and triple excitations (EOM-IP-CCSDT) and the complete basis set extrapolation technique. Further interpretation of the electronic structure results was accomplished using Dyson orbitals, electron density difference plots, and a second-order perturbation theory treatment for the relaxation energy. Strong orbital relaxation and electron correlation effects were shown to accompany ionization of the 7a 1 orbital, which formally represents the nonbonding σ-type nitrogen lone-pair (nσ) orbital. The theoretical work establishes the important roles of the π-system (π-π* excitations) in the screening of the nσ-hole and of the relaxation of the molecular orbitals in the formation of the 7a 1 (nσ) -1 state. Equilibrium geometric parameters were computed using the MP2 (second-order Møller-Plesset perturbation theory) and CCSD methods, and the harmonic vibrational frequencies were obtained at the MP2 level of theory for the lowest three cation states. The results were used to estimate the adiabatic 0-0 ionization energies, which were then compared to the available experimental and theoretical data. Photoelectron anisotropy parameters and photoionization partial cross sections, derived from the experimental spectra, were compared to predictions obtained with the continuum multiple scattering approach.
INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P., E-mail: jcortes@alma.cl, E-mail: ehardy@nrao.cl, E-mail: jeff.kenney@yale.edu

2015-01-01

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between themore » optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.« less
Damage pattern as a function of radiation quality and other factors.

PubMed

Burkart, W; Jung, T; Frasch, G

1999-01-01

An understanding of damage pattern in critical cellular structures such as DNA is an important prerequisite for a mechanistic assessment of primary radiation damage, its possible repair, and the propagation of residual changes in somatic and germ cells as potential contributors to disease or ageing. Important quantitative insights have been made recently on the distribution in time and space of critical lesions from direct and indirect action of ionizing radiation on mammalian cells. When compared to damage from chemicals or from spontaneous degradation, e.g. depurination or base deamination in DNA, the potential of even low-LET radiation to create local hot spots of damage from single particle tracks is of utmost importance. This has important repercussions on inferences from critical biological effects at high dose and dose rate exposure situations to health risks at chronic, low-level exposures as experienced in environmental and controlled occupational settings. About 10,000 DNA lesions per human cell nucleus and day from spontaneous degradation and chemical attack cause no apparent effect, but a dose of 4 Gy translating into a similar number of direct and indirect DNA breaks induces acute lethality. Therefore, single lesions cannot explain the high efficiency of ionizing radiation in the induction of mutation, transformation and loss of proliferative capacity. Clustered damage leading to poorly repairable double-strand breaks or even more complex local DNA degradation, correlates better with fixed damage and critical biological endpoints. A comparison with other physical, chemical and biological agents indicates that ionizing radiation is indeed set apart from these by its unique micro- and nano-dosimetric traits. Only a few other agents such as bleomycin have a similar potential to cause complex damage from single events. However, in view of the multi-stage mechanism of carcinogenesis, it is still an open question whether dose-effect linearity for complex primary DNA damage and resulting fixed critical cellular lesions translate into linearity for radiation-induced cancer. To solve this enigma, a quantitative assessment of all genotoxic and harmful non-genotoxic agents affecting the human body would be needed.
Differentiation of Lactobacillus brevis strains using Matrix-Assisted-Laser-Desorption-Ionization-Time-of-Flight Mass Spectrometry with respect to their beer spoilage potential.

PubMed

Kern, Carola C; Vogel, Rudi F; Behr, Jürgen

2014-06-01

Lactobacillus (L.) brevis is one of the most frequently encountered bacteria in beer-spoilage incidents. As the species Lactobacillus brevis comprises strains showing varying ability to grow in beer, ranging from growth in low hopped wheat to highly hopped pilsner beer, differentiation and classification of L. brevis with regard to their beer-spoiling ability is of vital interest for the brewing industry. Matrix-Assisted-Laser-Desorption-Ionization-Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) has been shown as a powerful tool for species and sub-species differentiation of bacterial isolates and is increasingly used for strain-level differentiation. Seventeen L. brevis strains, representative of different spoilage types, were characterized according to their tolerance to iso-alpha-acids and their growth in wheat-, lager- and pilsner beer. MALDI-TOF MS spectra were acquired to perform strain-level identification, cluster analysis and biomarker detection. Strain-level identification was achieved in 90% out of 204 spectra. Misidentification occurred nearly exclusively among strains belonging to the same spoilage type. Though spectra of strongly beer-spoiling strains showed remarkable similarity, no decisive single markers were detected to be present in all strains of one group. However, MALDI-TOF MS spectra can be reliably assigned to the corresponding strain and thus allow to track single strains and connect them to their physiological properties. Copyright © 2013 Elsevier Ltd. All rights reserved.
Stabilization of sulfuric acid dimers by ammonia, methylamine, dimethylamine, and trimethylamine

NASA Astrophysics Data System (ADS)

Jen, Coty N.; McMurry, Peter H.; Hanson, David R.

2014-06-01

This study experimentally explores how ammonia (NH3), methylamine (MA), dimethylamine (DMA), and trimethylamine (TMA) affect the chemical formation mechanisms of electrically neutral clusters that contain two sulfuric acid molecules (dimers). Dimers may also contain undetectable compounds, such as water or bases, that evaporate upon ionization and sampling. Measurements were conducted using a glass flow reactor which contained a steady flow of humidified nitrogen with sulfuric acid concentrations of 107 to 109 cm-3. A known molar flow rate of a basic gas was injected into the flow reactor. The University of Minnesota Cluster Chemical Ionization Mass Spectrometer was used to measure the resulting sulfuric acid vapor and cluster concentrations. It was found that, for a given concentration of sulfuric acid vapor, the dimer concentration increases with increasing concentration of the basic gas, eventually reaching a plateau. The base concentrations at which the dimer concentrations saturate suggest NH3 < MA < TMA ≲ DMA in forming stabilized sulfuric acid dimers. Two heuristic models for cluster formation by acid-base reactions are developed to interpret the data. The models provide ranges of evaporation rate constants that are consistent with observations and leads to an analytic expression for nucleation rates that is consistent with atmospheric observations.
All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry.

PubMed

Yuan, Chengqian; Liu, Xianhu; Zeng, Chenghui; Zhang, Hanyu; Jia, Meiye; Wu, Yishi; Luo, Zhixun; Fu, Hongbing; Yao, Jiannian

2016-02-01

We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.
Population structure of pigs determined by single nucleotide polymorphisms observed in assembled expressed sequence tags.

PubMed

Matsumoto, Toshimi; Okumura, Naohiko; Uenishi, Hirohide; Hayashi, Takeshi; Hamasima, Noriyuki; Awata, Takashi

2012-01-01

We have collected more than 190000 porcine expressed sequence tags (ESTs) from full-length complementary DNA (cDNA) libraries and identified more than 2800 single nucleotide polymorphisms (SNPs). In this study, we tentatively chose 222 SNPs observed in assembled ESTs to study pigs of different breeds; 104 were selected by comparing the cDNA sequences of a Meishan pig and samples of three-way cross pigs (Landrace, Large White, and Duroc: LWD), and 118 were selected from LWD samples. To evaluate the genetic variation between the chosen SNPs from pig breeds, we determined the genotypes for 192 pig samples (11 pig groups) from our DNA reference panel with matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Of the 222 reference SNPs, 186 were successfully genotyped. A neighbor-joining tree showed that the pig groups were classified into two large clusters, namely, Euro-American and East Asian pig populations. F-statistics and the analysis of molecular variance of Euro-American pig groups revealed that approximately 25% of the genetic variations occurred because of intergroup differences. As the F(IS) values were less than the F(ST) values(,) the clustering, based on the Bayesian inference, implied that there was strong genetic differentiation among pig groups and less divergence within the groups in our samples. © 2011 The Authors. Animal Science Journal © 2011 Japanese Society of Animal Science.
Single and multiple ionization of C60 fullerenes and collective effects in collisions with highly charged C, F, and Si ions with energy 3 MeV/u

NASA Astrophysics Data System (ADS)

Kelkar, A. H.; Kadhane, U.; Misra, D.; Gulyas, L.; Tribedi, L. C.

2010-10-01

We have measured absolute cross sections for single, double, triple, and quadruple ionization of C60 in collisions with 3 MeV/u C, F, and Si projectile ions at various projectile charge states. The experiment was performed using the recoil-ion time-of-flight technique. Projectile charge state dependence of the ionization yields was compared mainly with a model based on the giant dipole plasmon resonance (GDPR). In some cases, the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) model which is normally applied for ion-atom collisions was also used as a reference. An excellent qualitative agreement between the experimental data for single and double ionization and the GDPR model predictions was found for all projectile charge states.
Evaluation of the quality of herbal teas by DART/TOF-MS.

PubMed

Prchalová, J; Kovařík, F; Rajchl, A

2017-02-01

The paper focuses on the optimization, settings and validation of direct analysis in real time coupled with time-of-flight detector when used for the evaluation of the quality of selected herbal teas (fennel, chamomile, nettle, linden, peppermint, thyme, lemon balm, marigold, sage, rose hip and St. John's wort). The ionization mode, the optimal ionization temperature and the type of solvent for sample extraction were optimized. The characteristic compounds of the analysed herbal teas (glycosides, flavonoids and phenolic and terpenic substances, such as chamazulene, anethole, menthol, thymol, salviol and hypericin) were detected. The obtained mass spectra were evaluated by multidimensional chemometric methods, such as cluster analysis, linear discriminate analysis and principal component analysis. The chemometric methods showed that the single variety herbal teas were grouped according to their taxonomic affiliation. The developed method is suitable for quick identification of herbs and can be potentially used for assessing the quality and authenticity of herbal teas. Direct analysis in real time/time-of-flight-MS is also suitable for the evaluation of selected substances contained in the mentioned herbs and herbal products. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.
A Compendium of Recent Optocoupler Radiation Test Data

NASA Technical Reports Server (NTRS)

Label, K. A.; Kniffin, S. D.; Reed, R. A.; Kim, H. S.; Wert, J. L.; Oberg, D. L.; Normand, E.; Johnston, A. H.; Lum, G. K.; Koga, R.;

2000-01-01

We present a compendium of optocoupler radiation test data including neutron, proton and heavy ion Displacement Damage (DD), Single Event Transients (SET) and Total Ionizing Dose (TID). Proton data includes ionizing and non-ionizing damage mechanisms.

The formation of molecules in interstellar clouds from singly and multiply ionized atoms

NASA Technical Reports Server (NTRS)

Langer, W. D.

1978-01-01

The suggestion is considered that multiply ionized atoms produced by K- and L-shell X-ray ionization and cosmic-ray ionization can undergo ion-molecule reactions and also initiate molecule production. The role of X-rays in molecule production in general is discussed, and the contribution to molecule production of the C(+) radiative association with hydrogen is examined. Such gas-phase reactions of singly and multiply ionized atoms are used to calculate molecular abundances of carbon-, nitrogen-, and oxygen-bearing species. The column densities of the molecules are evaluated on the basis of a modified version of previously developed isobaric cloud models. It is found that reactions of multiply ionized carbon with H2 can contribute a significant fraction of the observed CH in diffuse interstellar clouds in the presence of diffuse X-ray structures or discrete X-ray sources and that substantial amounts of CH(+) can be produced under certain conditions.
Kinetic energy distribution of multiply charged ions in Coulomb explosion of Xe clusters.

PubMed

Heidenreich, Andreas; Jortner, Joshua

2011-02-21

We report on the calculations of kinetic energy distribution (KED) functions of multiply charged, high-energy ions in Coulomb explosion (CE) of an assembly of elemental Xe(n) clusters (average size (n) = 200-2171) driven by ultra-intense, near-infrared, Gaussian laser fields (peak intensities 10(15) - 4 × 10(16) W cm(-2), pulse lengths 65-230 fs). In this cluster size and pulse parameter domain, outer ionization is incomplete∕vertical, incomplete∕nonvertical, or complete∕nonvertical, with CE occurring in the presence of nanoplasma electrons. The KEDs were obtained from double averaging of single-trajectory molecular dynamics simulation ion kinetic energies. The KEDs were doubly averaged over a log-normal cluster size distribution and over the laser intensity distribution of a spatial Gaussian beam, which constitutes either a two-dimensional (2D) or a three-dimensional (3D) profile, with the 3D profile (when the cluster beam radius is larger than the Rayleigh length) usually being experimentally realized. The general features of the doubly averaged KEDs manifest the smearing out of the structure corresponding to the distribution of ion charges, a marked increase of the KEDs at very low energies due to the contribution from the persistent nanoplasma, a distortion of the KEDs and of the average energies toward lower energy values, and the appearance of long low-intensity high-energy tails caused by the admixture of contributions from large clusters by size averaging. The doubly averaged simulation results account reasonably well (within 30%) for the experimental data for the cluster-size dependence of the CE energetics and for its dependence on the laser pulse parameters, as well as for the anisotropy in the angular distribution of the energies of the Xe(q+) ions. Possible applications of this computational study include a control of the ion kinetic energies by the choice of the laser intensity profile (2D∕3D) in the laser-cluster interaction volume.
A theoretical study of the adiabatic and vertical ionization potentials of water.

PubMed

Feller, David; Davidson, Ernest R

2018-06-21

Theoretical predictions of the three lowest adiabatic and vertical ionization potentials of water were obtained from the Feller-Peterson-Dixon approach. This approach combines multiple levels of coupled cluster theory with basis sets as large as aug-cc-pV8Z in some cases and various corrections up to and including full configuration interaction theory. While agreement with experiment for the adiabatic ionization potential of the lowest energy 2 B 1 state was excellent, differences for other states were much larger, sometimes exceeding 10 kcal/mol (0.43 eV). Errors of this magnitude are inconsistent with previous benchmark work on 52 adiabatic ionization potentials, where a root mean square of 0.20 kcal/mol (0.009 eV) was found. Difficulties in direct comparisons between theory and experiment for vertical ionization potentials are discussed. With regard to the differences found for the 2 A 1 / 2 Π u and 2 B 2 adiabatic ionization potentials, a reinterpretation of the experimental spectrum appears justified.
Theoretical prediction of the ionization energies of the C4H7 radicals: 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals.

PubMed

Lau, Kai-Chung; Zheng, Wenxu; Wong, Ning-Bew; Li, Wai-Kee

2007-10-21

The ionization energies (IEs) for the 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals have been calculated by the wave function based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasiperturbative triple excitation [CCSD(T)]. The zero-point vibrational energy correction, the core-valence electronic correction, and the scalar relativistic effect correction are included in these calculations. The present CCSD(T)/CBS results are then compared with the IEs determined in the photoelectron experiment by Schultz et al. [J. Am. Chem. Soc. 106, 7336 (1984)] The predicted IE value (7.881 eV) of 2-methylallyl radical is found to compare very favorably with the experimental value of 7.90+/-0.02 eV. Two ionization transitions for cis-1-methylallyl and trans-1-methylallyl radicals have been considered here. The comparison between the predicted IE values and the previous measurements shows that the photoelectron peak observed by Schultz et al. likely corresponds to the adiabatic ionization transition for the trans-1-methylallyl radical to form trans-1-methylallyl cation. Although a precise IE value for the cyclopropylmethyl radical has not been directly determined, the experimental value deduced indirectly using other known energetic data is found to be in good accord with the present CCSD(T)/CBS prediction. We expect that the Franck-Condon factor for ionization transition of c-C4H7-->bicyclobutonium is much less favorable than that for ionization transition of c-C4H7-->planar-C4H7+, and the observed IE in the previous photoelectron experiment is likely due to the ionization transition for c-C4H7-->planar-C4H7+. Based on our CCSD(T)/CBS prediction, the ionization transition of c-C4H7-->bicyclobutonium with an IE value around 6.92 eV should be taken as the adiabatic ionization transition for the cyclobutyl radical. The present study provides support for the conclusion that the CCSD(T)/CBS approach with high-level energetic corrections can be used to provide reliable IE predictions for C4 hydrocarbon radicals with an uncertainty of +/-22 meV. The CCSD(T)/CBS predictions to the heats of formation for the aforementioned radicals and cations are also presented.
Computational studies of atmospherically-relevant chemical reactions in water clusters and on liquid water and ice surfaces.

PubMed

Gerber, R Benny; Varner, Mychel E; Hammerich, Audrey D; Riikonen, Sampsa; Murdachaew, Garold; Shemesh, Dorit; Finlayson-Pitts, Barbara J

2015-02-17

CONSPECTUS: Reactions on water and ice surfaces and in other aqueous media are ubiquitous in the atmosphere, but the microscopic mechanisms of most of these processes are as yet unknown. This Account examines recent progress in atomistic simulations of such reactions and the insights provided into mechanisms and interpretation of experiments. Illustrative examples are discussed. The main computational approaches employed are classical trajectory simulations using interaction potentials derived from quantum chemical methods. This comprises both ab initio molecular dynamics (AIMD) and semiempirical molecular dynamics (SEMD), the latter referring to semiempirical quantum chemical methods. Presented examples are as follows: (i) Reaction of the (NO(+))(NO3(-)) ion pair with a water cluster to produce the atmospherically important HONO and HNO3. The simulations show that a cluster with four water molecules describes the reaction. This provides a hydrogen-bonding network supporting the transition state. The reaction is triggered by thermal structural fluctuations, and ultrafast changes in atomic partial charges play a key role. This is an example where a reaction in a small cluster can provide a model for a corresponding bulk process. The results support the proposed mechanism for production of HONO by hydrolysis of NO2 (N2O4). (ii) The reactions of gaseous HCl with N2O4 and N2O5 on liquid water surfaces. Ionization of HCl at the water/air interface is followed by nucleophilic attack of Cl(-) on N2O4 or N2O5. Both reactions proceed by an SN2 mechanism. The products are ClNO and ClNO2, precursors of atmospheric atomic chlorine. Because this mechanism cannot result from a cluster too small for HCl ionization, an extended water film model was simulated. The results explain ClNO formation experiments. Predicted ClNO2 formation is less efficient. (iii) Ionization of acids at ice surfaces. No ionization is found on ideal crystalline surfaces, but the process is efficient on isolated defects where it involves formation of H3O(+)-acid anion contact ion pairs. This behavior is found in simulations of a model of the ice quasi-liquid layer corresponding to large defect concentrations in crystalline ice. The results are in accord with experiments. (iv) Ionization of acids on wet quartz. A monolayer of water on hydroxylated silica is ordered even at room temperature, but the surface lattice constant differs significantly from that of crystalline ice. The ionization processes of HCl and H2SO4 are of high yield and occur in a few picoseconds. The results are in accord with experimental spectroscopy. (v) Photochemical reactions on water and ice. These simulations require excited state quantum chemical methods. The electronic absorption spectrum of methyl hydroperoxide adsorbed on a large ice cluster is strongly blue-shifted relative to the isolated molecule. The measured and calculated adsorption band low-frequency tails are in agreement. A simple model of photodynamics assumes prompt electronic relaxation of the excited peroxide due to the ice surface. SEMD simulations support this, with the important finding that the photochemistry takes place mainly on the ground state. In conclusion, dynamics simulations using quantum chemical potentials are a useful tool in atmospheric chemistry of water media, capable of comparison with experiment.

LASER DESORPTION/IONIZATION OF SINGLE ULTRAFINE MULTICOMPONENT AEROSOLS. (R823980)

EPA Science Inventory

Laser desorption/ionization characteristics of single
ultrafine multicomponent aerosols have been investigated.
The results confirm earlier findings that (a) the negative
ion spectra are dominated by free electrons and (b) the ion
yield-to-mass ratio is higher for ...
Neutron-Impact Ionization of H and He

NASA Astrophysics Data System (ADS)

Lee, T.-G.; Ciappina, M. F.; Robicheaux, F.; Pindzola, M. S.

2014-05-01

Perturbative distorted-wave and non-perturbative close-coupling methods are used to study neutron-impact ionization of H and He. For single ionization of H, we find excellent agreement between the distorted-wave and close-coupling results at all incident energies. For double ionization of He, we find poor agreement between the distorted-wave and close-coupling results, except at the highest incident energies. We present the ratio of double to single ionization for He as a guide to experimental checks of theory at low energies and experimental confirmation of the rapid rise of the ratio at high energies. This work was supported in part by grants from NSF and US DoE. Computational work was carried out at NERSC in Oakland, California, NICS in Knoxville, Tennessee, and OLCF in Oak Ridge, Tennessee.
A Miniaturized Linear Wire Ion Trap with Electron Ionization and Single Photon Ionization Sources

NASA Astrophysics Data System (ADS)

Wu, Qinghao; Tian, Yuan; Li, Ailin; Andrews, Derek; Hawkins, Aaron R.; Austin, Daniel E.

2017-05-01

A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline.
Clustering effects in ionic polymers: Molecular dynamics simulations

DOE PAGES

Agrawal, Anupriya; Perahia, Dvora; Grest, Gary S.

2015-08-18

Ionic clusters control the structure, dynamics, and transport in soft matter. Incorporating a small fraction of ionizable groups in polymers substantially reduces the mobility of the macromolecules in melts. Furthermore, these ionic groups often associate into random clusters in melts, where the distribution and morphology of the clusters impact the transport in these materials. Here, using molecular dynamic simulations we demonstrate a clear correlation between cluster size and morphology with the polymer mobility in melts of sulfonated polystyrene. We show that in low dielectric media ladderlike clusters that are lower in energy compared with spherical assemblies are formed. Reducing themore » electrostatic interactions by enhancing the dielectric constant leads to morphological transformation from ladderlike clusters to globular assemblies. Finally, decrease in electrostatic interaction significantly enhances the mobility of the polymer.« less
Non-DSB clustered DNA lesions. Does theory colocalize with the experiment?

NASA Astrophysics Data System (ADS)

Nikitaki, Zacharenia; Nikolov, Vladimir; Mavragani, Ifigeneia V.; Plante, Ianik; Emfietzoglou, Dimitris; Iliakis, George; Georgakilas, Alexandros G.

2016-11-01

Ionizing radiation results in various kinds of DNA lesions such as double strand breaks (DSBs) and other non-DSB base lesions. These lesions may be formed in close proximity (i.e., within a few nanometers) resulting in clustered types of DNA lesions. These damage clusters are considered the fingerprint of ionizing radiation, notably charged particles of high linear energy transfer (LET). Accumulating theoretical and experimental evidence suggests that the induction of these clustered lesions appears under various irradiation conditions but also as a result of high levels of oxidative stress. The biological significance of these clustered DNA lesions pertains to the inability of cells to process them efficiently compared to isolated DNA lesions. The results in the case of unsuccessful or erroneous repair can vary from mutations up to chromosomal instability. In this mini review, we discuss of several Monte Carlo simulations codes and experimental evidence regarding the induction and repair of radiation-induced non-DSB complex DNA lesions. We also critically present the most widely used methodologies (i.e., gel electrophoresis and fluorescence microscopy [in situ colocalization assays]). Based on the comparison of different approaches, we provide examples and suggestions for the improved detection of these lesions in situ. Based on the current status of knowledge, we conclude that there is a great need for improvement of the detection techniques at the cellular or tissue level, which will provide valuable information for understanding the mechanisms used by the cell to process clustered DNA lesions.
Massive Stars and the Ionization of the Diffuse Medium

NASA Astrophysics Data System (ADS)

Kahre, Lauren E.; Walterbos, Rene A. M.

2015-08-01

Diffuse ionized Gas (DIG, sometimes called the warm ionized medium or WIM) has been recognized as a major component of the interstellar medium (ISM) in disk galaxies. A general understanding of the characteristics of the DIG is emerging, but several questions remain unanswered. One of these is the ionization mechanism for this gas, believed to be connected to OB stars and HII regions. Using 5-band (NUV (2750 A), U, V, B, and I) photometric imaging data from the Hubble Space Telescope (HST) Legacy Extragalactic Ultraviolet Survey (LEGUS) and ground-based Halpha data from the Local Volume Legacy (LVL) survey and HST Halpha data from LEGUS, we will investigate the photoionization of HII regions and DIG in nearly 50 galaxies. The 5-band photometry will enable us to determine properties of the most massive stars and reddening corrections for specific regions within a galaxy. Luminosities and ages for groups and clusters will be obtained from SED-fitting of photometric data. For individual stars ages will be determined from isochrone-fitting using reddening-corrected color-magnitude diagrams. We can then obtain estimates of the ionizing luminosities by matching these photometric properties for massive stars and clusters to various stellar atmosphere models. We will compare these predictions to the inferred Lyman continuum production rates from reddening-corrected ground- and HST-based Halpha data for HII regions and DIG. This particular presentation will demonstrate the above process for a set of selected regions in galaxies within the LEGUS sample. It will subsequently be expanded to cover the full LEGUS sample, with the overall goals of obtaining a better understanding of the radiative energy feedback from massive stars on the ISM, particularly their ability to ionize the surrounding ISM over a wide range of spatial scales and SFR surface densities, and to connect the ionization of the ISM to HII region morphologies.
Correlated proton-electron hole dynamics in protonated water clusters upon extreme ultraviolet photoionization

PubMed Central

Li, Zheng; Vendrell, Oriol

2016-01-01

The ultrafast nuclear and electronic dynamics of protonated water clusters H+(H2O)n after extreme ultraviolet photoionization is investigated. In particular, we focus on cluster cations with n = 3, 6, and 21. Upon ionization, two positive charges are present in the cluster related to the excess proton and the missing electron, respectively. A correlation is found between the cluster's geometrical conformation and initial electronic energy with the size of the final fragments produced. For situations in which the electron hole and proton are initially spatially close, the two entities become correlated and separate in a time-scale of 20 to 40 fs driven by strong non-adiabatic effects. PMID:26798842
The Technical and Biological Reproducibility of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) Based Typing: Employment of Bioinformatics in a Multicenter Study.

PubMed

Oberle, Michael; Wohlwend, Nadia; Jonas, Daniel; Maurer, Florian P; Jost, Geraldine; Tschudin-Sutter, Sarah; Vranckx, Katleen; Egli, Adrian

2016-01-01

The technical, biological, and inter-center reproducibility of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI TOF MS) typing data has not yet been explored. The aim of this study is to compare typing data from multiple centers employing bioinformatics using bacterial strains from two past outbreaks and non-related strains. Participants received twelve extended spectrum betalactamase-producing E. coli isolates and followed the same standard operating procedure (SOP) including a full-protein extraction protocol. All laboratories provided visually read spectra via flexAnalysis (Bruker, Germany). Raw data from each laboratory allowed calculating the technical and biological reproducibility between centers using BioNumerics (Applied Maths NV, Belgium). Technical and biological reproducibility ranged between 96.8-99.4% and 47.6-94.4%, respectively. The inter-center reproducibility showed a comparable clustering among identical isolates. Principal component analysis indicated a higher tendency to cluster within the same center. Therefore, we used a discriminant analysis, which completely separated the clusters. Next, we defined a reference center and performed a statistical analysis to identify specific peaks to identify the outbreak clusters. Finally, we used a classifier algorithm and a linear support vector machine on the determined peaks as classifier. A validation showed that within the set of the reference center, the identification of the cluster was 100% correct with a large contrast between the score with the correct cluster and the next best scoring cluster. Based on the sufficient technical and biological reproducibility of MALDI-TOF MS based spectra, detection of specific clusters is possible from spectra obtained from different centers. However, we believe that a shared SOP and a bioinformatics approach are required to make the analysis robust and reliable.
THE VERY MASSIVE STAR CONTENT OF THE NUCLEAR STAR CLUSTERS IN NGC 5253

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, L. J.; Crowther, P. A.; Calzetti, D.

2016-05-20

The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H α emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy ofmore » #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M {sub ⊙}, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope . We emphasize that population synthesis models with upper mass cutoffs greater than 100 M {sub ⊙} are crucial for future studies of young massive star clusters at all redshifts.« less
Role of isolated and clustered DNA damage and the post-irradiating repair process in the effects of heavy ion beam irradiation.

PubMed

Tokuyama, Yuka; Furusawa, Yoshiya; Ide, Hiroshi; Yasui, Akira; Terato, Hiroaki

2015-05-01

Clustered DNA damage is a specific type of DNA damage induced by ionizing radiation. Any type of ionizing radiation traverses the target DNA molecule as a beam, inducing damage along its track. Our previous study showed that clustered DNA damage yields decreased with increased linear energy transfer (LET), leading us to investigate the importance of clustered DNA damage in the biological effects of heavy ion beam radiation. In this study, we analyzed the yield of clustered base damage (comprising multiple base lesions) in cultured cells irradiated with various heavy ion beams, and investigated isolated base damage and the repair process in post-irradiation cultured cells. Chinese hamster ovary (CHO) cells were irradiated by carbon, silicon, argon and iron ion beams with LETs of 13, 55, 90 and 200 keV µm(-1), respectively. Agarose gel electrophoresis of the cells with enzymatic treatments indicated that clustered base damage yields decreased as the LET increased. The aldehyde reactive probe procedure showed that isolated base damage yields in the irradiated cells followed the same pattern. To analyze the cellular base damage process, clustered DNA damage repair was investigated using DNA repair mutant cells. DNA double-strand breaks accumulated in CHO mutant cells lacking Xrcc1 after irradiation, and the cell viability decreased. On the other hand, mouse embryonic fibroblast (Mef) cells lacking both Nth1 and Ogg1 became more resistant than the wild type Mef. Thus, clustered base damage seems to be involved in the expression of heavy ion beam biological effects via the repair process. © The Author 2015. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.
A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L., Jr.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-03-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated to its BCG, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing an meaningful role. We have argued that old stars, often invoked to explain LINER emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power-laws with slopes in the range expected from shock models. These models also show, however, that only ˜10% of Hα luminosity can be explained by shocks. We conclude that shocks probably associated to the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but can not be the major source of ionizing photons.
Single and multiple ionization of C{sub 60} fullerenes and collective effects in collisions with highly charged C, F, and Si ions with energy 3 MeV/u

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelkar, A. H.; Kadhane, U.; Misra, D.

2010-10-15

We have measured absolute cross sections for single, double, triple, and quadruple ionization of C{sub 60} in collisions with 3 MeV/u C, F, and Si projectile ions at various projectile charge states. The experiment was performed using the recoil-ion time-of-flight technique. Projectile charge state dependence of the ionization yields was compared mainly with a model based on the giant dipole plasmon resonance (GDPR). In some cases, the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) model which is normally applied for ion-atom collisions was also used as a reference. An excellent qualitative agreement between the experimental data for single and double ionization and the GDPR modelmore » predictions was found for all projectile charge states.« less
Nano-jewellery: C5Au12--a gold-plated diamond at molecular level.

PubMed

Naumkin, F

2006-06-07

A mixed carbon-metal cluster is designed by combining the tetrahedral C(5) radical (with a central atom-the skeleton of the C(5)H(12) molecule) and the spherical Au(12) layer (the external atomic shell of the Au(13) cluster). The C(5)Au(12) cluster and its negative and positive ionic derivatives, C(5)Au(12)(+/-), are investigated ab initio (DFT) in terms of optimized structures and relative energies of a few spin-states, for the icosahedral-like and octahedral-like isomers. The cluster is predicted to be generally more stable in its octahedral shape (similar to C(5)H(12)) which prevails for the negative ion and may compete with the icosahedral shape for the neutral system and positive ion. Adiabatic ionization energies (AIE) and electron affinities (AEA) of C(5)Au(12), vertical electron-detachment (VDE) energies of C(5)Au(12)(-), and vertical ionization and electron-attachment energies (VIE, VEA) of C(5)Au(12) are calculated as well, and compared with those for the corresponding isomers of the Au(13) cluster. The AIE and VIE values are found to be close for the two systems, while the AEA and VDE values are significantly reduced for the radical-based species. A simple fragment-based model is proposed for the decomposition of the total interaction into carbon-gold and gold-gold components.
High Intensity Femtosecond XUV Pulse Interactions with Atomic Clusters: Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ditmire, Todd

We propose to expand our recent studies on the interactions of intense extreme ultraviolet (XUV) femtosecond pulses with atomic and molecular clusters. The work described follows directly from work performed under BES support for the past grant period. During this period we upgraded the THOR laser at UT Austin by replacing the regenerative amplifier with optical parametric amplification (OPA) using BBO crystals. This increased the contrast of the laser, the total laser energy to ~1.2 J , and decreased the pulse width to below 30 fs. We built a new all reflective XUV harmonic beam line into expanded lab space. This enabled an increase influence by a factor ofmore » 25 and an increase in the intensity by a factor of 50. The goal of the program proposed in this renewal is to extend this class of experiments to available higher XUV intensity and a greater range of wavelengths. In particular we plan to perform experiments to confirm our hypothesis about the origin of the high charge states in these exploding clusters, an effect which we ascribe to plasma continuum lowering (ionization potential depression) in a cluster nano-plasma. To do this we will perform experiments in which XUV pulses of carefully chosen wavelength irradiate clusters composed of only low-Z atoms and clusters with a mixture of this low-Z atom with higher Z atoms. The latter clusters will exhibit higher electron densities and will serve to lower the ionization potential further than in the clusters composed only of low Z atoms. This should have a significant effect on the charge states produced in the exploding cluster. We will also explore the transition of explosions in these XUV irradiated clusters from hydrodynamic expansion to Coulomb explosion. The work proposed here will explore clusters of a wider range of constituents, including clusters from solids. Experiments on clusters from solids will be enabled by development we performed during the past grant period in which we constructed and tested a cluster generator based on the Laser Ablation of Microparticles (LAM) method.« less
Higher-order equation-of-motion coupled-cluster methods for ionization processes.

PubMed

Kamiya, Muneaki; Hirata, So

2006-08-21

Compact algebraic equations defining the equation-of-motion coupled-cluster (EOM-CC) methods for ionization potentials (IP-EOM-CC) have been derived and computer implemented by virtue of a symbolic algebra system largely automating these processes. Models with connected cluster excitation operators truncated after double, triple, or quadruple level and with linear ionization operators truncated after two-hole-one-particle (2h1p), three-hole-two-particle (3h2p), or four-hole-three-particle (4h3p) level (abbreviated as IP-EOM-CCSD, CCSDT, and CCSDTQ, respectively) have been realized into parallel algorithms taking advantage of spin, spatial, and permutation symmetries with optimal size dependence of the computational costs. They are based on spin-orbital formalisms and can describe both alpha and beta ionizations from open-shell (doublet, triplet, etc.) reference states into ionized states with various spin magnetic quantum numbers. The application of these methods to Koopmans and satellite ionizations of N2 and CO (with the ambiguity due to finite basis sets eliminated by extrapolation) has shown that IP-EOM-CCSD frequently accounts for orbital relaxation inadequately and displays errors exceeding a couple of eV. However, these errors can be systematically reduced to tenths or even hundredths of an eV by IP-EOM-CCSDT or CCSDTQ. Comparison of spectroscopic parameters of the FH+ and NH+ radicals between IP-EOM-CC and experiments has also underscored the importance of higher-order IP-EOM-CC treatments. For instance, the harmonic frequencies of the A 2Sigma- state of NH+ are predicted to be 1285, 1723, and 1705 cm(-1) by IP-EOM-CCSD, CCSDT, and CCSDTQ, respectively, as compared to the observed value of 1707 cm(-1). The small adiabatic energy separation (observed 0.04 eV) between the X 2Pi and a 4Sigma- states of NH+ also requires IP-EOM-CCSDTQ for a quantitative prediction (0.06 eV) when the a 4Sigma- state has the low-spin magnetic quantum number (s(z) = 1/2). When the state with s(z) = 3/2 is sought, the energy separations converge much more rapidly with the IP-EOM-CCSD value (0.03 eV) already being close to the observed (0.04 eV).
Toward single-cell analysis by plume collimation in laser ablation electrospray ionization mass spectrometry.

PubMed

Stolee, Jessica A; Vertes, Akos

2013-04-02

Ambient ionization methods for mass spectrometry have enabled the in situ and in vivo analysis of biological tissues and cells. When an etched optical fiber is used to deliver laser energy to a sample in laser ablation electrospray ionization (LAESI) mass spectrometry, the analysis of large single cells becomes possible. However, because in this arrangement the ablation plume expands in three dimensions, only a small portion of it is ionized by the electrospray. Here we show that sample ablation within a capillary helps to confine the radial expansion of the plume. Plume collimation, due to the altered expansion dynamics, leads to greater interaction with the electrospray plume resulting in increased ionization efficiency, reduced limit of detection (by a factor of ~13, reaching 600 amol for verapamil), and extended dynamic range (6 orders of magnitude) compared to conventional LAESI. This enhanced sensitivity enables the analysis of a range of metabolites from small cell populations and single cells in the ambient environment. This technique has the potential to be integrated with flow cytometry for high-throughput metabolite analysis of sorted cells.
APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

PubMed Central

Short, Luke Chandler; Cai, Sheng-Suan; Syage, Jack A.

2009-01-01

The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of non-polar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e., ≤100 μL/min), while at a higher flow, photon absorption and ion-molecule reactions become significant. Under certain circumstances, APPI signal and S/N have been observed to excel at higher flow, which may be due to a non-photoionzation mechanism. To better understand APPI at higher flow rates, we have selected three lamps (Xe, Kr and Ar) and four mobile phases typical for reverse-phase, high-pressure liquid chromatography: acetonitrile, methanol, (1:1) acetonitrile:water and (1:1) methanol:water. As test compounds, three polyaromatic hydrocarbons are studied: benzo[a]pyrene, indeno[1,2,3-c,d]pyrene and benz[a]anthracene. We find that solvent photoabsorption cross-section is not the only parameter in explaining relative signal intensity, but that solvent photo-ion chemistry can also play a significant role. Three conclusions from this investigation are: (i) Methanol photoionization leads to protonated methanol clusters that can result in chemical ionization of analyte molecule; (ii) Use of the Ar lamp often results in greater signal and S/N; (iii) Acetonitrile photoionization is less efficient and resulting clusters are too strongly bound to efficiently chemically ionize the analyte, so that analyte ion formation is dominated by direct photoionization. PMID:17188507
APPI-MS: effects of mobile phases and VUV lamps on the detection of PAH compounds.

PubMed

Short, Luke Chandler; Cai, Sheng-Suan; Syage, Jack A

2007-04-01

The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of nonpolar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e.,
Spitzer Infrared Spectrograph Observations of the Galactic Center: Quantifying the Extreme Ultraviolet/Soft X-ray Fluxes

NASA Astrophysics Data System (ADS)

Simpson, Janet P.

2018-04-01

It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of H II regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal H II regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5 Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.
Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Yunteng; Zhang, Jie; Li, Yang

2015-08-15

We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He{sub 2}{sup +} and He{sub 4}{sup +}, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl{sub 4} doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He){sub n}C{sup +}, (He){sub n}Cl{sup +}, and (He){sub n}CCl{sup +}. Usingmore » both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.« less

Photoionization in Ultraviolet Processing of Astrophysical Ice Analogs at Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Woon, David E.

2004-01-01

Two recent experimental studies have demonstrated that amino acids or amino acid precursors are generated when astrophysical ice analogs are subjected to ultraviolet (UV) irradiation at cryogenic temperatures. Understanding the complete phenomenology of photoprocessing is critical to elucidating chemical reaction mechanisms that can function within an ice matrix under very cold conditions. Pushing beyond the much better characterized study of photolytic dissociation of chemical bonds through electronic excitation, this work explored the ability of UV radiation present in the interstellar medium to ionize small molecules embedded in ices. Quantum chemical calculations, including bulk solvation effects, were used to study the ionization of hydrogen (H2), water, and methanol (CH3OH) bound in small clusters of water. Ionization potentials were found to be much smaller in the condensed phase than in the gas phase; even a small cluster can account for large changes in the ionization potentials in ice, as well as the known formation of an OH--H3O+ pair in the case of H2O photoionization. To gauge the impact of photoionization on subsequent grain chemistry, the reaction between OH and CO in the presence of H3O+ was studied and compared with the potential energy surface without hydronium present, which is relevant to chemistry following photolysis. The differences indicate that the reaction is somewhat more likely to proceed to products (H + CO2) in the case of photoionization.
Quantum-Size Dependence of the Energy for Vacancy Formation in Charged Small Metal Clusters. Drop Model

NASA Astrophysics Data System (ADS)

Pogosov, V. V.; Reva, V. I.

2018-04-01

Self-consistent computations of the monovacancy formation energy are performed for Na N , Mg N , and Al N (12 < N ≤ 168) spherical clusters in the drop model for stable jelly. Scenarios of the Schottky vacancy formation and "bubble vacancy blowing" are considered. It is shown that the asymptotic behavior of the size dependences of the energy for the vacancy formation by these two mechanisms is different and the difference between the characteristics of a charged and neutral cluster is entirely determined by the difference between the ionization potentials of clusters and the energies of electron attachment to them.
Electron ionization of SiCl4

NASA Astrophysics Data System (ADS)

King, Simon J.; Price, Stephen D.

2011-02-01

Relative partial ionization cross sections (PICS) for the formation of fragment ions following electron ionization of SiCl4, in the electron energy range 30-200 eV, have been determined using time-of-flight mass spectrometry coupled with an ion coincidence technique. By this method, the contributions to the yield of each fragment ion from dissociative single, double, and triple ionization, are distinguished. These yields are quantified in the form of relative precursor-specific PICS, which are reported here for the first time for SiCl4. For the formation of singly charged ionic fragments, the low-energy maxima appearing in the PICS curves are due to contributions from single ionization involving predominantly indirect ionization processes, while contributions to the yields of these ions at higher electron energies are often dominated by dissociative double ionization. Our data, in the reduced form of relative PICS, are shown to be in good agreement with a previous determination of the PICS of SiCl4. Only for the formation of doubly charged fragment ions are the current relative PICS values lower than those measured in a previous study, although both datasets agree within combined error limits. The relative PICS data presented here include the first quantitative measurements of the formation of Cl2+ fragment ions and of the formation of ion pairs via dissociative double ionization. The peaks appearing in the 2D ion coincidence data are analyzed to provide further information concerning the mechanism and energetics of the charge-separating dissociations of SiCl42+. The lowest energy dicationic precursor state, leading to SiCl3+ + Cl+ formation, lies 27.4 ± 0.3 eV above the ground state of SiCl4 and is in close agreement with a calculated value of the adiabatic double ionization energy (27.3 eV).
Electron ionization of SiCl4.

PubMed

King, Simon J; Price, Stephen D

2011-02-21

Relative partial ionization cross sections (PICS) for the formation of fragment ions following electron ionization of SiCl(4), in the electron energy range 30-200 eV, have been determined using time-of-flight mass spectrometry coupled with an ion coincidence technique. By this method, the contributions to the yield of each fragment ion from dissociative single, double, and triple ionization, are distinguished. These yields are quantified in the form of relative precursor-specific PICS, which are reported here for the first time for SiCl(4). For the formation of singly charged ionic fragments, the low-energy maxima appearing in the PICS curves are due to contributions from single ionization involving predominantly indirect ionization processes, while contributions to the yields of these ions at higher electron energies are often dominated by dissociative double ionization. Our data, in the reduced form of relative PICS, are shown to be in good agreement with a previous determination of the PICS of SiCl(4). Only for the formation of doubly charged fragment ions are the current relative PICS values lower than those measured in a previous study, although both datasets agree within combined error limits. The relative PICS data presented here include the first quantitative measurements of the formation of Cl(2) (+) fragment ions and of the formation of ion pairs via dissociative double ionization. The peaks appearing in the 2D ion coincidence data are analyzed to provide further information concerning the mechanism and energetics of the charge-separating dissociations of SiCl(4) (2+). The lowest energy dicationic precursor state, leading to SiCl(3) (+) + Cl(+) formation, lies 27.4 ± 0.3 eV above the ground state of SiCl(4) and is in close agreement with a calculated value of the adiabatic double ionization energy (27.3 eV).
Systematization of actinides using cluster analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kopyrin, A.A.; Terent`eva, T.N.; Khramov, N.N.

1994-11-01

A representation of the actinides in multidimensional property space is proposed for systematization of these elements using cluster analysis. Literature data for their atomic properties are used. Owing to the wide variation of published ionization potentials, medians are used to estimate them. Vertical dendograms are used for classification on the basis of distances between the actinides in atomic-property space. The properties of actinium and lawrencium are furthest removed from the main group. Thorium and mendelevium exhibit individualized properties. A cluster based on the einsteinium-fermium pair is joined by californium.
Dynamics of the Coulomb explosion of large hydrogen iodide clusters irradiated by superintense ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Krainov, V. P.; Roshchupkin, A. S.

2001-12-01

Dynamics of the inner and outer above-barrier ionization and of the Coulomb explosion are calculated for large hydrogen iodide clusters irradiated by superintense ultrashort laser pulses. We have found that the Coulomb forces predominate in the expansion of these clusters in comparison with the hydrodynamic forces. The energy distribution of the iodine multiple atomic ions in laser focal volume is derived. Results of our calculations are in a good agreement with the recent experimental data of Tisch et al. [Phys. Rev. A 60, 3076 (1999)].
grid-model: Semi-numerical reionization code

NASA Astrophysics Data System (ADS)

Hutter, Anne

2018-05-01

grid-model computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). It accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual HI fraction in ionized regions. The ionizing emissivity is directly derived from the RT simulation spectra.
Indirect contributions to electron-impact ionization of Li+ (1 s 2 s S31 ) ions: Role of intermediate double-K -vacancy states

NASA Astrophysics Data System (ADS)

Müller, A.; Borovik, A.; Huber, K.; Schippers, S.; Fursa, D. V.; Bray, I.

2018-02-01

Fine details of the cross section for electron-impact ionization of metastable two-electron Li+(1 s 2 s S31) ions are scrutinized by both experiment and theory. Beyond direct knockoff ionization, indirect ionization mechanisms proceeding via formation of intermediate double-K-vacancy (hollow) states either in a Li+ ion or in a neutral lithium atom and subsequent emission of one or two electrons, respectively, can contribute to the net production of Li2 + ions. The partial cross sections for such contributions are less than 4% of the total single-ionization cross section. The characteristic steps, resonances, and interference phenomena in the indirect ionization contribution are measured with an experimental energy spread of less than 0.9 eV and with a statistical relative uncertainty of the order of 1.7%, requiring a level of statistical uncertainty in the total single-ionization cross section of better than 0.05%. The measurements are accompanied by convergent-close-coupling calculations performed on a fine energy grid. Theory and experiment are in remarkable agreement concerning the fine details of the ionization cross section. Comparison with previous R-matrix results is less favorable.
X-ray radiative transfer in protoplanetary disks. The role of dust and X-ray background fields

NASA Astrophysics Data System (ADS)

Rab, Ch.; Güdel, M.; Woitke, P.; Kamp, I.; Thi, W.-F.; Min, M.; Aresu, G.; Meijerink, R.

2018-01-01

Context. The X-ray luminosities of T Tauri stars are about two to four orders of magnitude higher than the luminosity of the contemporary Sun. As these stars are born in clusters, their disks are not only irradiated by their parent star but also by an X-ray background field produced by the cluster members. Aims: We aim to quantify the impact of X-ray background fields produced by young embedded clusters on the chemical structure of disks. Further, we want to investigate the importance of the dust for X-ray radiative transfer in disks. Methods: We present a new X-ray radiative transfer module for the radiation thermo-chemical disk code PRODIMO (PROtoplanetary DIsk MOdel), which includes X-ray scattering and absorption by both the gas and dust component. The X-ray dust opacities can be calculated for various dust compositions and dust-size distributions. For the X-ray radiative transfer we consider irradiation by the star and by X-ray background fields. To study the impact of X-rays on the chemical structure of disks we use the well established disk ionization tracers N2H+ and HCO+. Results: For evolved dust populations (e.g. grain growth), X-ray opacities are mostly dominated by the gas; only for photon energies E ≳ 5-10 keV do dust opacities become relevant. Consequently the local disk X-ray radiation field is only affected in dense regions close to the disk midplane. X-ray background fields can dominate the local X-ray disk ionization rate for disk radii r ≳ 20 au. However, the N2H+ and HCO+ column densities are only significantly affected in cases of low cosmic-ray ionization rates (≲10-19 s-1), or if the background flux is at least a factor of ten higher than the flux level of ≈10-5 erg cm-2 s-1 expected for clusters typical for the solar vicinity. Conclusions: Observable signatures of X-ray background fields in low-mass star-formation regions, like Taurus, are only expected for cluster members experiencing a strong X-ray background field (e.g. due to their location within the cluster). For the majority of the cluster members, the X-ray background field has relatively little impact on the disk chemical structure.
Compendium of Single Event Effects, Total Ionizing Dose, and Displacement Damage for Candidate Spacecraft Electronics for NASA

NASA Technical Reports Server (NTRS)

LaBel, Kenneth A.; O'Bryan, Martha V.; Chen, Dakai; Campola, Michael J.; Casey, Megan C.; Pellish, Jonathan A.; Lauenstein, Jean-Marie; Wilcox, Edward P.; Topper, Alyson D.; Ladbury, Raymond L.;

2014-01-01

We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to proton and heavy ion-induced single-event effects (SEE), proton-induced displacement damage (DD), and total ionizing dose (TID). This paper is a summary of test results.

Gas-Phase Stability of Negatively Charged Organophosphate Metabolites Produced by Electrospray Ionization and Matrix-Assisted Laser Desorption/Ionization

NASA Astrophysics Data System (ADS)

Asakawa, Daiki; Mizuno, Hajime; Toyo'oka, Toshimasa

2017-12-01

The formation mechanisms of singly and multiply charged organophosphate metabolites by electrospray ionization (ESI) and their gas phase stabilities were investigated. Metabolites containing multiple phosphate groups, such as adenosine 5'-diphosphate (ADP), adenosine 5'-triphosphate (ATP), and D- myo-inositol-1,4,5-triphosphate (IP3) were observed as doubly deprotonated ions by negative-ion ESI mass spectrometry. Organophosphates with multiple negative charges were found to be unstable and often underwent loss of PO3 -, although singly deprotonated analytes were stable. The presence of fragments due to the loss of PO3 - in the negative-ion ESI mass spectra could result in the misinterpretation of analytical results. In contrast to ESI, matrix-assisted laser desorption ionization (MALDI) produced singly charged organophosphate metabolites with no associated fragmentation, since the singly charged anions are stable. The stability of an organophosphate metabolite in the gas phase strongly depends on its charge state. The fragmentations of multiply charged organophosphates were also investigated in detail through density functional theory calculations. [Figure not available: see fulltext.
FT-ICR mass spectrometric and density functional theory studies of sulfate prenucleation clusters

NASA Astrophysics Data System (ADS)

Lemke, K. H.

2012-12-01

Recent mass spectrometric1 and relaxation spectroscopic studies2 of metal sulfate salts have demonstrated that aqueous clusters play an important role in sulfate prenucleation processes. While such studies provide evidence that that ion clusters are nucleation relevant species, ultra-high resolution mass spectrumetry, in particular, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) can provide additional valuable information about the molecular composition and stability of individual ion clusters. Prompted by the above studies, our group has begun a systematic survey of metal sulfate clusters using FT-ICR mass spectrometry. Here, I report stoichiometries, structures and thermodynamic properties of calcium sulfate ion clusters, both "dry" and microsolvated, using electrospray ionization FT-ICR mass spectrometry in combination with semi-empirical methods and M062X/aug-cc-PVXZ level density functional theory calculations. In electrosprayed dilute aqueous solutions of CaSO4 (1-20mM), droplet desolvation results in the formation of stable doubly-charged clusters of [Ca(CaSO4)m(H2O)n]+2 (m≤10 & n≤9) as well as larger quadruply-charged ion clusters [Ca2(CaSO4)m(H2O)n]+4 with m≤23 and n≤10, demonstrating considerable sulfate nucleation potential in undersaturated electrolyte solutions. An attempt was also made to assess the extent of ion cluster aggregation in solution prior to electrospray ionization by measuring ion mass spectra at different solution concentrations. In brief, an increase in calcium sulfate concentration from 1-10mM results in a continuous increase in polynuclear ion cluster species, while smaller clusters, for instance, Ca[CaSO4]+2 and corresponding hydrated forms, become increasingly less abundant. Building on semi-empirical methods, M062X calculations have been applied to predict calcium sulfate cluster geometries, both "dry" and microsolvated, as well as the size-dependent evolution of clustering and hydration energies. 1Schoeder et al. (2011) J.Am.Chem.Soc., 133, 2444; 2Chen et al. (2005) J.Sol.Chem., 34, 1045;
Luminous phenomena and electromagnetic VHF wave emission originated from earthquake-related radon exhalation

NASA Astrophysics Data System (ADS)

Seki, A.; Tobo, I.; Omori, Y.; Muto, J.; Nagahama, H.

2013-12-01

Anomalous luminous phenomena and electromagnetic wave emission before or during earthquakes have been reported (e.g., the 1965 Matsushiro earthquake swarm). However, their mechanism is still unsolved, in spite of many models for these phenomena. Here, we propose a new model about luminous phenomena and electromagnetic wave emission during earthquake by focusing on atmospheric radon (Rn-222) and its daughter nuclides (Po-218 and Po-214). Rn-222, Po-218 and Po-214 are alpha emitters, and these alpha particles ionize atmospheric molecules. A light emission phenomenon, called 'the air luminescence', is caused by de-excitation of the ionized molecules of atmospheric nitrogen due to electron impact ionization from alpha particles. The de-excitation is from the second positive system of neutral nitrogen molecules and the first negative system of nitrogen molecule ion. Wavelengths of lights by these transitions include the visible light wavelength. So based on this mechanism, we proposed a new luminous phenomenon model before or during earthquake: 1. The concentration of atmospheric radon and its daughter nuclides increase anomalously before or during earthquakes, 2. Nitrogen molecules and their ions are excited by alpha particles emitted from Rn-222, Po-218 and Po-214, and air luminescence is generated by their de-excitation. Similarly, electromagnetic VHF wave emission can be explained by ionizing effect of radon and its daughter nuclides. Boyarchuk et al. (2005) proposed a model that electromagnetic VHF wave emission is originated when excited state of neutral clusters changes. Radon gas ionizes atmosphere and forms positively and negatively charged heavy particles. The process of ion hydration in ordinary air can be determined by the formation of complex chemically active structures of the various types of ion radicals. As a result of the association of such hydration radical ions, a neutral cluster, which is dipole quasi-molecules, is formed. A neutral cluster's rotation-rotation transition causes electromagnetic VHF wave emission. We also discuss a possibility of electromagnetic VHF wave emission from excitation of polyatomic molecules by alpha particles from Rn-222 and its daughter nuclides, similar to air luminescence by excitation of nitrogen molecule in the viewpoint of electromagnetic radiation in quantum theory.
Properties of QSO Metal-line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies

NASA Astrophysics Data System (ADS)

Boksenberg, Alec; Sargent, Wallace L. W.

2015-05-01

Using Voigt-profile-fitting procedures on Keck High Resolution Spectrograph spectra of nine QSOs, we identify 1099 C IV absorber components clumped in 201 systems outside the Lyman forest over 1.6 <~ z <~ 4.4. With associated Si IV, C II, Si II and N V where available, we investigate the bulk statistical and ionization properties of the components and systems and find no significant change in redshift for C IV and Si IV while C II, Si II and N V change substantially. The C IV components exhibit strong clustering, but no clustering is detected for systems on scales from 150 km s-1 out to 50,000 km s-1. We conclude that the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios, we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find that the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence, and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample, the collective escape of radiation is sufficient to maintain the intergalactic medium ionized over the full range 1.9 < z <~ 4.4. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
HST-WFPC2 Observations of the Star Clusters in the Giant H II Regions of M33

NASA Astrophysics Data System (ADS)

Lee, Myung Gyoon; Park, Hong Soo; Kim, Sang Chul; Waller, William H.; Parker, Joel Wm.; Malumuth, Eliot M.; Hodge, Paul W.

We present a photometric study of the stars in ionizing star clusters embedded in several giant H II regions of M33 (CC93, IC 142, NGC 595, MA2, NGC 604 and NGC 588). Our photometry is based on the HST-WFPC2 images of these clusters. Color-magnitude diagrams and color-color diagrams of these clusters are obtained and are used for estimating the reddenings and ages of the clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of the massive stars in these clusters are also derived. The slopes of the IMFs range from Γ = -0.5 to -2.1. Interestingly, it is found that the IMFs get steeper with increasing galactocentric distance and with decreasing [O/H] abundance.
Structure, electronic and magnetic properties of Mn{sub n} (n=2-8) clusters: A DFT investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Vipin; Roy, Debesh R., E-mail: drr@ashd.svnit.ac.in

2016-05-06

A detail studyon the stability, electronic and magnetic properties of Mn{sub n} (n=2-8) cluster series is performed under the utilization ofdensity functional theory (DFT). The binding energy (B.E.), HOMO-LUMO energy gap (HLG), chemical hardness (η), ionization potential (I.P.), electron affinity (E.A)and electronegativity (χ) of these clusters are predicted. We have also studied the magnetic moments associated with the stable cluster isomers. The lowest energy structures for each cluster sizes aredetermined with a systematic search imposing all possible initial magnetic configuration on the cluster. All the calculations are carried out using a popular GGA functional PBE as proposed by Pardew, Burkemore » and Ernzerhof and implemented in the VASP program.« less
Quantum dynamics of charge state in silicon field evaporation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silaeva, Elena P.; Uchida, Kazuki; Watanabe, Kazuyuki, E-mail: kazuyuki@rs.kagu.tus.ac.jp

2016-08-15

The charge state of an ion field-evaporating from a silicon-atom cluster is analyzed using time-dependent density functional theory coupled to molecular dynamics. The final charge state of the ion is shown to increase gradually with increasing external electrostatic field in agreement with the average charge state of silicon ions detected experimentally. When field evaporation is triggered by laser-induced electronic excitations the charge state also increases with increasing intensity of the laser pulse. At the evaporation threshold, the charge state of the evaporating ion does not depend on the electrostatic field due to the strong contribution of laser excitations to themore » ionization process both at low and high laser energies. A neutral silicon atom escaping the cluster due to its high initial kinetic energy is shown to be eventually ionized by external electrostatic field.« less
Characterization of the reactive and dissociative behavior of transition metal oxide cluster ions in the gas phase.

PubMed

Maleknia, S; Brodbelt, J; Pope, K

1991-05-01

The reactive and dissociative behavior of molybdenum and tungsten oxide cluster ions has been studied in the gas phase using a triple quadrupole mass spectrometer. Cluster ions (MO3) n (-) were formed via a simple thermal desorption/electron capture negative ionization method, and their structures were characterized by collision-activated dissociation (CAD). Typically, the clusters fragment by losses of neutral (MO3) units. Reactions of the oxide cluster ions with ethylene oxide, cyclohexene oxide, ethylene sulfide cyclohexene sulfide, 2,3-butanedione, and 2,4-pentanedione were examined, and product ions were characterized by CAD. The clusters react with ethylene oxide by addition of ethylene oxide or net addition of oxygen, whereas the clusters react with ethylene sulfide via net addition of one or two sulfur atoms. Reactions of the clusters with the diones result in addition of one or two dione units, in some cases with dehydration.
Reaction Dynamics Following Ionization of Ammonia Dimer Adsorbed on Ice Surface.

PubMed

Tachikawa, Hiroto

2016-09-22

The ice surface provides an effective two-dimensional reaction field in interstellar space. However, how the ice surface affects the reaction mechanism is still unknown. In the present study, the reaction of an ammonia dimer cation adsorbed both on water ice and cluster surface was theoretically investigated using direct ab initio molecular dynamics (AIMD) combined with our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, and the results were compared with reactions in the gas phase and on water clusters. A rapid proton transfer (PT) from NH3(+) to NH3 takes place after the ionization and the formation of intermediate complex NH2(NH4(+)) is found. The reaction rate of PT was significantly affected by the media connecting to the ammonia dimer. The time of PT was calculated to be 50 fs (in the gas phase), 38 fs (on ice), and 28-33 fs (on water clusters). The dissociation of NH2(NH4(+)) occurred on an ice surface. The reason behind the reaction acceleration on an ice surface is discussed.
The Emergence of Star Clusters

NASA Astrophysics Data System (ADS)

Calzetti, Daniela

2017-08-01

We propose to measure the timescale for the clearing of natal dust by young star clusters. We will augment existing archival UV-to-I imaging data with new WFC3/IR images at J, H, and Paschen-beta for a sample of six nearby star forming galaxies. Under the standard scenario that the clearing is performed by supernovae (> 3 Myr), simulations show that not enough ionizing photons can escape galaxies and reionize the Universe at z>6. However, the actual clearing timescale is poorly established. We will obtain accurate ages and extinctions for the embedded and emergent young clusters in our target galaxies, in order to: (1) determine whether dust clearing occurs before or after 3 Myr, (2) investigate environmental dependencies for the timescale, and (3) establish the principal mechanisms for enabling the escape of ionizing photons from galaxies. Our project provides the physical footing for future JWST observations aimed at determining the sources of reionization of the Universe. The combination of archival and new images will also equip the community with a lasting legacy of homogeneous UV-to-IR coverage for a sample of nearby galaxies.

Exploration of dynamical regimes of irradiated small protonated water clusters

NASA Astrophysics Data System (ADS)

Ndongmouo Taffoti, U. F.; Dinh, P. M.; Reinhard, P.-G.; Suraud, E.; Wang, Z. P.

2010-05-01

We explore from a theoretical perspective the dynamical response of small water clusters, (H2O)nH3O+ with n=1,2,3, to a short laser pulse for various frequencies, from infrared (IR) to ultra-violet (UV) and intensities (from 6×10^{13} W/cm^2 to 5×10^{14} W/cm^2). To that end, we use time-dependent local-density approximation for the electrons, coupled to molecular dynamics for the atomic cores (TDLDA-MD). The local-density approximation is augmented by a self-interaction correction (SIC) to allow for a correct description of electron emission. For IR frequencies, we see a direct coupling of the laser field to the very light H+ ions in the clusters. Resonant coupling (in the UV) and/or higher intensities lead to fast ionization with subsequent Coulomb explosion. The stability against Coulomb pressure increases with system size. Excitation to lower ionization stages induced strong ionic vibrations. The latter maintain a rather harmonic pattern in spite of the sizeable amplitudes (often 10% of the bond length).
Double-frequency microwave ionization of Na

NASA Astrophysics Data System (ADS)

Ruff, G. A.; Dietrick, K. M.; Gallagher, T. F.

1990-11-01

We report the ionization of Na atoms by the simultaneous application of microwave fields of two different frequencies. We conclude that the salient features of double-frequency ionization can be readily understood. Both the hydrogenlike ||m||=2 states and the nonhydrogenic ||m||=0 and 1 states ionize when the sum of the field amplitudes, the peak field, reaches the field required for ionization by a single microwave frequency, E=1/9n4 and E=1/3n5, respectively.
A VLT/MUSE galaxy survey towards QSO Q1410: looking for a WHIM traced by BLAs in inter-cluster filaments

NASA Astrophysics Data System (ADS)

Pessa, Ismael; Tejos, Nicolas; Barrientos, L. Felipe; Werk, Jessica; Bielby, Richard; Padilla, Nelson; Morris, Simon L.; Prochaska, J. Xavier; Lopez, Sebastian; Hummels, Cameron

2018-07-01

Cosmological simulations predict that a significant fraction of the low-z baryon budget resides in large-scale filaments in the form of a diffuse plasma at temperatures T ˜ 105 - 107 K. However, direct observation of this so-called warm-hot intergalactic medium (WHIM) has been elusive. In the Λcold dark matter paradigm, galaxy clusters correspond to the nodes of the cosmic web at the intersection of several large-scale filamentary threads. In previous work, we used HST/COS data to conduct the first survey of broad H I Lyα absorbers (BLAs) potentially produced by WHIM in inter-cluster filaments. We targeted a single QSO, namely Q1410, whose sightline intersects seven independent inter-cluster axes at impact parameters <3 Mpc (comoving), and found a tentative excess of a factor of ˜4 with respect to the field. Here, we further investigate the origin of these BLAs by performing a blind galaxy survey within the Q1410 field using VLT/MUSE. We identified 77 sources and obtained the redshifts for 52 of them. Out of the total sample of seven BLAs in inter-cluster axes, we found three without any galaxy counterpart to stringent luminosity limits (˜4 × 108 L⊙ ˜0.01 L*), providing further evidence that these BLAs may represent genuine WHIM detections. We combined this sample with other suitable BLAs from the literature and inferred the corresponding baryon mean density for these filaments in the range Ω ^fil_bar= 0.02-0.04. Our rough estimates are consistent with the predictions from numerical simulations but still subject to large systematic uncertainties, mostly from the adopted geometry, ionization corrections, and density profile.
Hyperfine Interactions in the Electron Paramagnetic Resonance Spectra of Point Defects in Wide-Band-Gap Semiconductors

DTIC Science & Technology

2014-09-18

compensation) during growth due to their preferred trivalent charge states. The electron paramagnetic resonance spectrum of the singly ionized chromium ...neutral nitrogen acceptor in ZnO . . . . . . . . . . . . . . . . . . 45 16 Spectrum of the singly ionized chromium acceptor in TiO2 . . . . . . . . . 49...is a single crystal of magnesium oxide that has been doped with chromium . Chromium Cr3+ substitutes for magnesium Mg2+ and creates a paramagnetic
Correlated proton-electron hole dynamics in protonated water clusters upon extreme ultraviolet photoionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zheng; Vendrell, Oriol

2016-01-13

The ultrafast nuclear and electronic dynamics of protonated water clusters H+(H2O)n after extreme ultraviolet photoionization is investigated. In particular, we focus on cluster cations with n = 3, 6, and 21. Upon ionization, two positive charges are present in the cluster related to the excess proton and the missing electron, respectively. A correlation is found between the cluster's geometrical conformation and initial electronic energy with the size of the final fragments produced. As a result, for situations in which the electron hole and proton are initially spatially close, the two entities become correlated and separate in a time-scale of 20more » to 40 fs driven by strong non-adiabatic effects.« less
Visualization of complex DNA damage along accelerated ions tracks

NASA Astrophysics Data System (ADS)

Kulikova, Elena; Boreyko, Alla; Bulanova, Tatiana; Ježková, Lucie; Zadneprianetc, Mariia; Smirnova, Elena

2018-04-01

The most deleterious DNA lesions induced by ionizing radiation are clustered DNA double-strand breaks (DSB). Clustered or complex DNA damage is a combination of a few simple lesions (single-strand breaks, base damage etc.) within one or two DNA helix turns. It is known that yield of complex DNA lesions increases with increasing linear energy transfer (LET) of radiation. For investigation of the induction and repair of complex DNA lesions, human fibroblasts were irradiated with high-LET 15N ions (LET = 183.3 keV/μm, E = 13MeV/n) and low-LET 60Co γ-rays (LET ≈ 0.3 keV/μm) radiation. DNA DSBs (γH2AX and 53BP1) and base damage (OGG1) markers were visualized by immunofluorecence staining and high-resolution microscopy. The obtained results showed slower repair kinetics of induced DSBs in cells irradiated with accelerated ions compared to 60Co γ-rays, indicating induction of more complex DNA damage. Confirming previous assumptions, detailed 3D analysis of γH2AX/53BP1 foci in 15N ions tracks revealed more complicated structure of the foci in contrast to γ-rays. It was shown that proteins 53BP1 and OGG1 involved in repair of DNA DSBs and modified bases, respectively, were colocalized in tracks of 15N ions and thus represented clustered DNA DSBs.
ON-LINE ANALYSIS OF AQUEOUS AEROSOLS BY LASER DESORPTION IONIZATION. (R823980)

EPA Science Inventory

In this work the effects of water on the laser desorption ionization mass spectra of single aerosol particles are explored. Aqueous aerosols are produced by passing dry particles through a humid environment so that they undergo deliquescent growth. Laser desorption ionization is ...
Compendium of Current Single Event Effects for Candidate Spacecraft Electronics for NASA

NASA Technical Reports Server (NTRS)

O'Bryan, Martha V.; Label, Kenneth A.; Chen, Dakai; Campola, Michael J.; Casey, Megan C.; Lauenstein, Jean-Marie; Pellish, Jonathan A.; Ladbury, Raymond L.; Berg, Melanie D.

2015-01-01

NASA spacecraft are subjected to a harsh space environment that includes exposure to various types of ionizing radiation. The performance of electronic devices in a space radiation environment are often limited by their susceptibility to single event effects (SEE). Ground-based testing is used to evaluate candidate spacecraft electronics to determine risk to spaceflight applications. Interpreting the results of radiation testing of complex devices is and adequate understanding of the test condition is critical. Studies discussed herein were undertaken to establish the application-specific sensitivities of candidate spacecraft and emerging electronic devices to single-event upset (SEU), single-event latchup (SEL), single-event gate rupture (SEGR), single-event burnout (SEB), and single-event transient (SET). For total ionizing dose (TID) and displacement damage dose (DDD) results, see a companion paper submitted to the 2015 Institute of Electrical and Electronics Engineers (IEEE) Nuclear and Space Radiation Effects Conference (NSREC) Radiation Effects Data Workshop (REDW) entitled "compendium of Current Total Ionizing Dose and Displacement Damage for Candidate Spacecraft Electronics for NASA by M. Campola, et al.
Electron-helium S-wave model benchmark calculations. II. Double ionization, single ionization with excitation, and double excitation

NASA Astrophysics Data System (ADS)

Bartlett, Philip L.; Stelbovics, Andris T.

2010-02-01

The propagating exterior complex scaling (PECS) method is extended to all four-body processes in electron impact on helium in an S-wave model. Total and energy-differential cross sections are presented with benchmark accuracy for double ionization, single ionization with excitation, and double excitation (to autoionizing states) for incident-electron energies from threshold to 500 eV. While the PECS three-body cross sections for this model given in the preceding article [Phys. Rev. A 81, 022715 (2010)] are in good agreement with other methods, there are considerable discrepancies for these four-body processes. With this model we demonstrate the suitability of the PECS method for the complete solution of the electron-helium system.
Matilda: A mass filtered nanocluster source

NASA Astrophysics Data System (ADS)

Kwon, Gihan

Cluster science provides a good model system for the study of the size dependence of electronic properties, chemical reactivity, as well as magnetic properties of materials. One of the main interests in cluster science is the nanoscale understanding of chemical reactions and selectivity in catalysis. Therefore, a new cluster system was constructed to study catalysts for applications in renewable energy. Matilda, a nanocluster source, consists of a cluster source and a Retarding Field Analyzer (RFA). A moveable AJA A310 Series 1"-diameter magnetron sputtering gun enclosed in a water cooled aggregation tube served as the cluster source. A silver coin was used for the sputtering target. The sputtering pressure in the aggregation tube was controlled, ranging from 0.07 to 1torr, using a mass flow controller. The mean cluster size was found to be a function of relative partial pressure (He/Ar), sputtering power, and aggregation length. The kinetic energy distribution of ionized clusters was measured with the RFA. The maximum ion energy distribution was 2.9 eV/atom at a zero pressure ratio. At high Ar flow rates, the mean cluster size was 20 ˜ 80nm, and at a 9.5 partial pressure ratio, the mean cluster size was reduced to 1.6nm. Our results showed that the He gas pressure can be optimized to reduce the cluster size variations. Results from SIMION, which is an electron optics simulation package, supported the basic function of an RFA, a three-element lens and the magnetic sector mass filter. These simulated results agreed with experimental data. For the size selection experiment, the channeltron electron multiplier collected ionized cluster signal at different positions during Ag deposition on a TEM grid for four and half hours. The cluster signal was high at the position for neutral clusters, which was not bent by a magnetic field, and the signal decreased rapidly far away from the neutral cluster region. For cluster separation according to mass to charge ratio in a magnetic sector mass filter, the ion energy of the cluster and its distribution must be precisely controlled by acceleration or deceleration. To verify the size separation, a high resolution microscope was required. Matilda provided narrow particle sized distribution from atomic scale to 4nm in size with different pressure ratio without additional mass filter. It is very economical way to produce relatively narrow particle size distribution.
Single ionization and capture cross sections from biological molecules by bare projectile impact*

NASA Astrophysics Data System (ADS)

Quinto, Michele A.; Monti, Juan M.; Montenegro, Pablo D.; Fojón, Omar A.; Champion, Christophe; Rivarola, Roberto D.

2017-02-01

We report calculations on single differential and total cross sections for single ionization and single electron capture from biological targets, namely, vapor water and DNA nucleobasese molecules, by bare projectile impact: H+, He2+, and C6+. They are performed within the Continuum Distorted Wave - Eikonal Initial State approximation and compared to several existing experimental data. This study is oriented to the obtention of a reliable set of theoretical data to be used as input in a Monte Carlo code destined to micro- and nano- dosimetry.
Total Dose Effects on Single Event Transients in Digital CMOS and Linear Bipolar Circuits

NASA Technical Reports Server (NTRS)

Buchner, S.; McMorrow, D.; Sibley, M.; Eaton, P.; Mavis, D.; Dusseau, L.; Roche, N. J-H.; Bernard, M.

2009-01-01

This presentation discusses the effects of ionizing radiation on single event transients (SETs) in circuits. The exposure of integrated circuits to ionizing radiation changes electrical parameters. The total ionizing dose effect is observed in both complementary metal-oxide-semiconductor (CMOS) and bipolar circuits. In bipolar circuits, transistors exhibit grain degradation, while in CMOS circuits, transistors exhibit threshold voltage shifts. Changes in electrical parameters can cause changes in single event upset(SEU)/SET rates. Depending on the effect, the rates may increase or decrease. Therefore, measures taken for SEU/SET mitigation might work at the beginning of a mission but not at the end following TID exposure. The effect of TID on SET rates should be considered if SETs cannot be tolerated.
Changes in interstellar atomic abundances from the galactic plane to the halo

NASA Technical Reports Server (NTRS)

Jenkins, E. B.

1982-01-01

A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron.
THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 5253

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calzetti, D.; Johnson, K. E.; Adamo, A.

2015-10-01

The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses,more » and extinctions of the nine optically brightest clusters (M{sub V} < −8.8) and the two young radio nebula clusters. The clusters have ages ∼1–15 Myr and masses ∼1 × 10{sup 4}–2.5 × 10{sup 5} M{sub ⊙}. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ∼15 Myr. The most massive cluster is in the radio nebula; with a mass ∼2.5 × 10{sup 5} M{sub ⊙} and an age ∼1 Myr, it is 2–4 times less massive and younger than previously estimated. It is within a dust cloud with A{sub V} ∼ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ∼1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.« less
The Brightest Young Star Clusters in NGC 5253.

NASA Astrophysics Data System (ADS)

Calzetti, D.; Johnson, K. E.; Adamo, A.; Gallagher, J. S., III; Andrews, J. E.; Smith, L. J.; Clayton, G. C.; Lee, J. C.; Sabbi, E.; Ubeda, L.; Kim, H.; Ryon, J. E.; Thilker, D.; Bright, S. N.; Zackrisson, E.; Kennicutt, R. C.; de Mink, S. E.; Whitmore, B. C.; Aloisi, A.; Chandar, R.; Cignoni, M.; Cook, D.; Dale, D. A.; Elmegreen, B. G.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Krumholz, M. R.; Walterbos, R.; Wofford, A.; Brown, T. M.; Christian, C.; Dobbs, C.; Herrero, A.; Kahre, L.; Messa, M.; Nair, P.; Nota, A.; Östlin, G.; Pellerin, A.; Sacchi, E.; Schaerer, D.; Tosi, M.

2015-10-01

The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (MV < -8.8) and the two young radio nebula clusters. The clusters have ages ˜1-15 Myr and masses ˜1 × 104-2.5 × 105 M⊙. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ˜15 Myr. The most massive cluster is in the radio nebula; with a mass ˜2.5 × 105 M⊙ and an age ˜1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV ˜ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ˜1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Experimental and theoretical study of the reactions between neutral vanadium oxide clusters and ethane, ethylene, and acetylene.

PubMed

Dong, Feng; Heinbuch, Scott; Xie, Yan; Rocca, Jorge J; Bernstein, Elliot R; Wang, Zhe-Chen; Deng, Ke; He, Sheng-Gui

2008-02-13

Reactions of neutral vanadium oxide clusters with small hydrocarbons, namely C2H6, C2H4, and C2H2, are investigated by experiment and density functional theory (DFT) calculations. Single photon ionization through extreme ultraviolet (EUV, 46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is used to detect neutral cluster distributions and reaction products. The most stable vanadium oxide clusters VO2, V2O5, V3O7, V4O10, etc. tend to associate with C2H4 generating products V(m)O(n)C2H4. Oxygen-rich clusters VO3(V2O5)(n=0,1,2...), (e.g., VO3, V3O8, and V5O13) react with C2H4 molecules to cause a cleavage of the C=C bond of C2H4 to produce (V2O5)(n)VO2CH2 clusters. For the reactions of vanadium oxide clusters (V(m)O(n)) with C2H2 molecules, V(m)O(n)C2H2 are assigned as the major products of the association reactions. Additionally, a dehydration reaction for VO3 + C2H2 to produce VO2C2 is also identified. C2H6 molecules are quite stable toward reaction with neutral vanadium oxide clusters. Density functional theory calculations are employed to investigate association reactions for V2O5 + C2H(x). The observed relative reactivity of C2 hydrocarbons toward neutral vanadium oxide clusters is well interpreted by using the DFT calculated binding energies. DFT calculations of the pathways for VO3+C2H4 and VO3+C2H2 reaction systems indicate that the reactions VO3+C2H4 --> VO2CH2 + H2CO and VO3+C2H2 --> VO2C2 + H2O are thermodynamically favorable and overall barrierless at room temperature, in good agreement with the experimental observations.
Comparison of Three Plasma Sources for Ambient Desorption/Ionization Mass Spectrometry

NASA Astrophysics Data System (ADS)

McKay, Kirsty; Salter, Tara L.; Bowfield, Andrew; Walsh, James L.; Gilmore, Ian S.; Bradley, James W.

2014-09-01

Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources.
Comparison of three plasma sources for ambient desorption/ionization mass spectrometry.

PubMed

McKay, Kirsty; Salter, Tara L; Bowfield, Andrew; Walsh, James L; Gilmore, Ian S; Bradley, James W

2014-09-01

Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources.
Reducing the Matrix Effect in Organic Cluster SIMS Using Dynamic Reactive Ionization

NASA Astrophysics Data System (ADS)

Tian, Hua; Wucher, Andreas; Winograd, Nicholas

2016-12-01

Dynamic reactive ionization (DRI) utilizes a reactive molecule, HCl, which is doped into an Ar cluster projectile and activated to produce protons at the bombardment site on the cold sample surface with the presence of water. The methodology has been shown to enhance the ionization of protonated molecular ions and to reduce salt suppression in complex biomatrices. In this study, we further examine the possibility of obtaining improved quantitation with DRI during depth profiling of thin films. Using a trehalose film as a model system, we are able to define optimal DRI conditions for depth profiling. Next, the strategy is applied to a multilayer system consisting of the polymer antioxidants Irganox 1098 and 1010. These binary mixtures have demonstrated large matrix effects, making quantitative SIMS measurement not feasible. Systematic comparisons of depth profiling of this multilayer film between directly using GCIB, and under DRI conditions, show that the latter enhances protonated ions for both components by 4- to 15-fold, resulting in uniform depth profiling in positive ion mode and almost no matrix effect in negative ion mode. The methodology offers a new strategy to tackle the matrix effect and should lead to improved quantitative measurement using SIMS.
Simulating 3D Stellar Winds and Diffuse X-ray Emissions from Gases in Non-equilibrium Ionization State

NASA Astrophysics Data System (ADS)

Long, Min; Sun, Wei; Niu, Shu; Zhou, Xin; Ji, Li

2017-08-01

We investigate the physical properties of stellar winds launched in super stellar clusters (SSCs). Chandra observations have detected the presence of diffuse X-ray emission caused by hot gas from such winds in SSCs, and provide the best probe for understanding interactions between the stellar winds and the complex nursery regions. However, the details of the origin of cluster winds, the mass and energy ejection, the formation of diffuse X-ray emission, the fraction of winds contribution to the distribution of diffuse X-ray emission still remain unclear. We developed a multiphysics hydrodynamic model including self-gravity, head conduction and performed 3D simulations with an unprecedented grid resolution due to adaptive mesh refinement (AMR) capability in a case study of NGC 3603, as a supplement to the analysis of the archived 500 ks Chandra observations. The synthetic emission will be computed by assuming the gas in a non-equilibrium ionization (NEI) state indicated by Chandra observation, not coronal ionization equilibrium (CIE) that most works assumed, by using a customized NEI calculation module based on AtomDB. The results will be compared to the Chandra observations.

7.87 eV Laser Desorption Postionization Mass Spectrometry of Adsorbed and Covalently Bound Bisphenol A Diglycidyl Methacrylate

PubMed Central

Zhou, Manshui; Wu, Chunping; Akhmetov, Artem; Edirisinghe, Praneeth D.; Drummond, James L.; Hanley, Luke

2007-01-01

Bisphenol A diglycidyl methacrylate (Bis-GMA) was adsorbed onto or covalently bound to a porous silicon oxide surface. Laser desorption 10.5 eV postionization mass spectrometry (LDPI-MS) was previously demonstrated for surface analysis of adsorbed and surface bound Bis-GMA, but signal to noise levels were low and ion fragmentation was extensive. 7.87 eV postionization using the fluorine laser was demonstrated here for Bis-GMA. However, signal levels remained low for LDPI-MS of Bis-GMA as its ionization potential was only ∼7.8 eV, near threshold for single photon ionization by the 7.87 eV fluorine laser. It is known that aromatic tagging of molecular analytes can lower the overall IP of the tagged molecular complex, allowing 7.87 eV single photon ionization. Therefore, Bis-GMA was also derivatized with several tags whose IPs were either below or above 7.87 eV: the tag with an IP below 7.87 eV enhanced single photon ionization while the tags with higher IPs did not. However, signal intensities were enhanced by resonant laser desorption for two of the derivatized Bis-GMAs. Intact ions of Bis-GMA and its derivatives were generally observed by 7.87 eV LDPI-MS, consistent with the formation of ions with relatively little internal energy upon threshold single photon ionization. PMID:17449273
A pseudoatom in a cage: trimetallofullerene Y(3)@C(80) mimics y(3)n@c(80) with nitrogen substituted by a pseudoatom.

PubMed

Popov, Alexey A; Zhang, Lin; Dunsch, Lothar

2010-02-23

Y(3)C(80) obtained in the synthesis of nitride clusterfullerenes Y(3)N@C(2n) (2n = 80-88) by the reactive atmosphere method is found to be a genuine trimetallofullerene, Y(3)@C(80), with low ionization potential and divalent state of yttrium atoms. DFT studies of the electronic structure of Y(3)@C(80) show that this molecule mimics Y(3)N@C(80) with the pseudoatom (PA) instead of the nitrogen atom. Topology analysis of the electron density and electron localization function show that yttrium atoms form Y-PA bonds rather than direct Y-Y bonds. Molecular dynamics simulations show that the Y(3)PA cluster is as rigid as Y(3)N and rotates inside the fullerene cage as a single entity.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuomo, J.J.; Rossnagel, S.M.; Kaufman, H.R.

The work presented in this book deals with ion beam processing for basic sputter etching of samples, for sputter deposition of thin films, for the synthesis of material in thin form, and for the modification of the properties of thin films. The ion energy range covered is from a few tens of eV to about 10,000 eV, with primary interest in the range of about 20 to 1-2 keV, where implantation of the incident ion is a minor effect. Of the types of ion sources and devices available, this book examines principally broad beam ion sources, characterized by high fluxesmore » and large work areas. These sources include the ECR ion source, the Kaufman-type single- and multiple-grid sources, gridless sources such as the Hall effect or closed-drift source, and hydrid sources such as the ionized cluster beam system.« less
Nanomanipulation-Coupled Matrix-Assisted Laser Desorption/ Ionization-Direct Organelle Mass Spectrometry: A Technique for the Detailed Analysis of Single Organelles

NASA Astrophysics Data System (ADS)

Phelps, Mandy S.; Sturtevant, Drew; Chapman, Kent D.; Verbeck, Guido F.

2016-02-01

We describe a novel technique combining precise organelle microextraction with deposition and matrix-assisted laser desorption/ionization (MALDI) for a rapid, minimally invasive mass spectrometry (MS) analysis of single organelles from living cells. A dual-positioner nanomanipulator workstation was utilized for both extraction of organelle content and precise co-deposition of analyte and matrix solution for MALDI-direct organelle mass spectrometry (DOMS) analysis. Here, the triacylglycerol (TAG) profiles of single lipid droplets from 3T3-L1 adipocytes were acquired and results validated with nanoelectrospray ionization (NSI) MS. The results demonstrate the utility of the MALDI-DOMS technique as it enabled longer mass analysis time, higher ionization efficiency, MS imaging of the co-deposited spot, and subsequent MS/MS capabilities of localized lipid content in comparison to NSI-DOMS. This method provides selective organellar resolution, which complements current biochemical analyses and prompts for subsequent subcellular studies to be performed where limited samples and analyte volume are of concern.
Light/negative bias stress instabilities in indium gallium zinc oxide thin film transistors explained by creation of a double donor

NASA Astrophysics Data System (ADS)

Migliorato, Piero; Delwar Hossain Chowdhury, Md; Gwang Um, Jae; Seok, Manju; Jang, Jin

2012-09-01

The analysis of current-voltage (I-V) and capacitance-voltage (C-V) characteristics for amorphous indium gallium zinc oxide Thin film transistors as a function of active layer thickness shows that negative bias under illumination stress (NBIS) is quantitatively explained by creation of a bulk double donor, with a shallow singly ionized state ɛ(0/+) > EC-0.073 eV and a deep doubly ionized state ɛ(++/+) < EC-0.3 eV. The gap density of states, extracted from the capacitance-voltage curves, shows a broad peak between EC-E = 0.3 eV and 1.0 eV, which increases in height with NBIS stress time and corresponds to the broadened transition energy between singly and doubly ionized states. We propose that the center responsible is an oxygen vacancy and that the presence of a stable singly ionized state, necessary to explain our experimental results, could be due to the defect environment provided by the amorphous network.
Direct Delta-MBPT(2) method for ionization potentials, electron affinities, and excitation energies using fractional occupation numbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beste, Ariana; Vazquez-Mayagoitia, Alvaro; Ortiz, J. Vincent

2013-01-01

A direct method (D-Delta-MBPT(2)) to calculate second-order ionization potentials (IPs), electron affinities (EAs), and excitation energies is developed. The Delta-MBPT(2) method is defined as the correlated extension of the Delta-HF method. Energy differences are obtained by integrating the energy derivative with respect to occupation numbers over the appropriate parameter range. This is made possible by writing the second-order energy as a function of the occupation numbers. Relaxation effects are fully included at the SCF level. This is in contrast to linear response theory, which makes the D-Delta-MBPT(2) applicable not only to single excited but also higher excited states. We showmore » the relationship of the D-Delta-MBPT(2) method for IPs and EAs to a second-order approximation of the effective Fock-space coupled-cluster Hamiltonian and a second-order electron propagator method. We also discuss the connection between the D-Delta-MBPT(2) method for excitation energies and the CIS-MP2 method. Finally, as a proof of principle, we apply our method to calculate ionization potentials and excitation energies of some small molecules. For IPs, the Delta-MBPT(2) results compare well to the second-order solution of the Dyson equation. For excitation energies, the deviation from EOM-CCSD increases when correlation becomes more important. When using the numerical integration technique, we encounter difficulties that prevented us from reaching the Delta-MBPT(2) values. Most importantly, relaxation beyond the Hartree Fock level is significant and needs to be included in future research.« less
Analysis of the Structures and Properties of (GaSb)n (n = 4-9) Clusters through Density Functional Theory.

PubMed

Lu, Qi Liang; Luo, Qi Quan; Huang, Shou Guo; Li, Yi De; Wan, Jian Guo

2016-07-07

An optimization strategy combining global semiempirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (GaSb)n clusters up to n = 9. The growth pattern of the clusters differed from those of previously reported group III-V binary clusters. A cagelike configuration was found for cluster sizes n ≤ 7. The structure of (GaSb)6 deviated from that of other III-V clusters. Competition existed between core-shell and hollow cage structures of (GaSb)7. Novel noncagelike structures were energetically preferred over the cages for the (GaSb)8 and (GaSb)9 clusters. Electronic properties, such as vertical ionization potential, adiabatic electron affinities, HOMO-LUMO gaps, and average on-site charges on Ga or Sb atoms, as well as binding energies, were computed.
The new ClusterTrap setup

NASA Astrophysics Data System (ADS)

Martinez, F.; Marx, G.; Schweikhard, L.; Vass, A.; Ziegler, F.

2011-07-01

ClusterTrap has been designed to investigate properties of atomic clusters in the gas phase with particular emphasis on the dependence on the cluster size and charge state. The combination of cluster source, Penning trap and time-of-flight mass spectrometry allows a variety of experimental schemes including collision-induced dissociation, photo-dissociation, further ionization by electron impact, and electron attachment. Due to the storage capability of the trap extended-delay reaction experiments can be performed. Several recent modifications have resulted in an improved setup. In particular, an electrostatic quadrupole deflector allows the coupling of several sources or detectors to the Penning trap. Furthermore, a linear radio-frequency quadrupole trap has been added for accumulation and ion bunching and by switching the potential of a drift tube the kinetic energy of the cluster ions can be adjusted on their way towards or from the Penning trap. Recently, experiments on multiply negatively charged clusters have been resumed.
Comparison of Internal Energy Distributions of Ions Created by Electrospray Ionization and Laser Ablation-Liquid Vortex Capture-Electrospray Ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cahill, John F.; Kertesz, Vilmos; Ovchinnikova, Olga S.

2015-06-27

Recently a number of techniques have combined laser ablation with liquid capture for mass spectrometry spot sampling and imaging applications. The newly developed non-contact liquid-vortex capture probe has been used to efficiently collect 355 nm UV laser ablated material in a continuous flow solvent stream in which the captured material dissolves and then undergoes electrospray ionization. This sampling and ionization approach has produced what appear to be classic electrospray ionization spectra; however, the softness of this sampling/ionization process versus simple electrospray ionization has not been definitely determined. A series of benzlypyridinium salts, known as thermometer ions, were used to comparemore » internal energy distributions between electrospray ionization and the UV laser ablation liquid-vortex capture probe electrospray combination. Measured internal energy distributions were identical between the two techniques, even with differences in laser fluence (0.7-3.1 J cm-2) and when using UV-absorbing or non-UV-absorbing sample substrates. This data indicates ions formed directly by UV laser ablation, if any, are likely an extremely small constituent of the total ion signal observed. Instead, neutral molecules, clusters or particulates ejected from the surface during laser ablation, subsequently captured and dissolved in the flowing solvent stream then electrosprayed are the predominant source of ion signal observed. The electrospray ionization process used controls the softness of the technique.« less
Electron Impact Ionization and Dissociative Ionization of C2H2

NASA Technical Reports Server (NTRS)

Srivastava, S. K.

1995-01-01

By utilizing a crossed electron beam collision geometry, a combination of time-of-flight (TOF) and quadrupole mass spectrometers, and the relative flow technique1 normalized values of cross sections and appearance energies (AP) were obtained for the formation of singly and multiply ionized species resulting from the ionization and dissociation of C2H2. Details ont he apparatus and technique have been published previously.2,3.
Simultaneous ESI-APCI+ ionization and fragmentation pathways for nine benzodiazepines and zolpidem using single quadrupole LC-MS.

PubMed

Galaon, Toma; Vacaresteanu, Catalina; Anghel, Dan-Florin; David, Victor

2014-05-01

Nine important 1,4-benzodiazepines and zolpidem were characterized by liquid chromatography-mass spectrometry using a multimode ionization source able to generate ions using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and a single quadrupole mass analyzer. An optimum chromatographic separation was applied for all target compounds in less than 8 minutes using a Zorbax Eclipse Plus column (100 × 4.6 mm, 3.5 µm) kept at 35°C and a 0.3% HCOOH/ACN/IPA (61:34:5) mobile phase pumped at 1 ml/min. Optimization of LC-MS method generated low limit of quantitation (LOQ) values situated in the range 0.3-20.5 ng/ml. Comparison between differences in method sensitivity, under specified chromatographic conditions, when using ESI-only, APCI-only, and simultaneous ESI-APCI ionization with such a multimode source was discussed. Mixed ESI-APCI(+) mode proved to be the most sensitive ionization generating an average 35% detector response increase compared to ESI-only ionization and 350% detector response increase with respect to APCI-only ionization. Characterization of the nine benzodiazepines and zolpidem concerning their MS fragmentation pathway following 'in-source' collision-induced dissociation is discussed in detail and some general trends regarding these fragmentations are set. Copyright © 2013 John Wiley & Sons, Ltd.
Photoemission spectra and density functional theory calculations of 3d transition metal-aqua complexes (Ti-Cu) in aqueous solution.

PubMed

Yepes, Diana; Seidel, Robert; Winter, Bernd; Blumberger, Jochen; Jaque, Pablo

2014-06-19

Photoelectron spectroscopy measurements and density functional calculations are combined to determine the lowest electron binding energies of first-row transition-metal aqua ions, titanium through copper, with 3d(1) through 3d(9) electronic configurations, in their most common oxidation states. Vertical ionization energies are found to oscillate considerably between 6.76 and 9.65 eV for the dications and between 7.05 and 10.28 eV for the respective trivalent cations. The metal cations are modeled as [M(H2O)n](q+) clusters (q = 2, 3, and 4; n = 6 and 18) surrounded by continuum solvent. The performance of 10 exchange-correlation functionals, two GGAs, three MGGAs, two HGGAs and three HMGGAs, combined with the MDF10(ECP)/6-31+G(d,p) basis set is assessed for 11 M-O bond distances, 10 vertical ionization energies, 6 adiabatic ionization energies, and the associated reorganization free energies. We find that for divalent cations the HGGA and HMGGA functionals in combination with the 18 water model show the best agreement with experimental vertical ionization energies and geometries; for trivalent ions, the MGGA functionals perform best. The corresponding reorganization free energies (λo) of the oxidized ions are significantly underestimated with all DFT functionals and cluster models. This indicates that the structural reorganization of the solvation shell upon ionization is not adequately accounted for by the simple solvation models used, emphasizing the importance of extended sampling of thermally accessible solvation structures for an accurate computation of this quantity. The photoelectron spectroscopy measurements reported herein provide a comprehensive set of transition-metal redox energetic quantities for future electronic structure benchmarks.
Halorhodopsin pumps Cl– and bacteriorhodopsin pumps protons by a common mechanism that uses conserved electrostatic interactions

PubMed Central

Gunner, M. R.

2014-01-01

Key mutations differentiate the functions of homologous proteins. One example compares the inward ion pump halorhodopsin (HR) and the outward proton pump bacteriorhodopsin (BR). Of the nine essential buried ionizable residues in BR, six are conserved in HR. However, HR changes three BR acids, D85 in a central cluster of ionizable residues, D96, nearer the intracellular, and E204, nearer the extracellular side of the membrane to the small, neutral amino acids T111, V122, and T230, respectively. In BR, acidic amino acids are stationary anions whose proton affinity is modulated by conformational changes, establishing a sequence of directed binding and release of protons. Multiconformation continuum electrostatics calculations of chloride affinity and residue protonation show that, in reaction intermediates where an acid is ionized in BR, a Cl– is bound to HR in a position near the deleted acid. In the HR ground state, Cl– binds tightly to the central cluster T111 site and weakly to the extracellular T230 site, recovering the charges on ionized BR-D85 and neutral E204 in BR. Imposing key conformational changes from the BR M intermediate into the HR structure results in the loss of Cl– from the central T111 site and the tight binding of Cl– to the extracellular T230 site, mirroring the changes that protonate BR-D85 and ionize E204 in BR. The use of a mobile chloride in place of D85 and E204 makes HR more susceptible to the environmental pH and salt concentrations than BR. These studies shed light on how ion transfer mechanisms are controlled through the interplay of protein and ion electrostatics. PMID:25362051
Communication: Two-step explosion processes of highly charged fullerene cations C{sub 60}{sup q+} (q = 20–60)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamazaki, Kaoru; Nakamura, Takashi; Kanno, Manabu

2014-09-28

To establish the fundamental understanding of the fragmentation dynamics of highly positive charged nano- and bio-materials, we carried out on-the-fly classical trajectory calculations on the fragmentation dynamics of C{sub 60}{sup q+} (q = 20–60). We used the UB3LYP/3-21G level of density functional theory and the self-consistent charge density-functional based tight-binding theory. For q ≥ 20, we found that a two-step explosion mechanism governs the fragmentation dynamics: C{sub 60}{sup q+} first ejects singly and multiply charged fast atomic cations C{sup z+} (z ≥ 1) via Coulomb explosions on a timescale of 10 fs to stabilize the remaining core cluster. Thermal evaporationsmore » of slow atomic and molecular fragments from the core cluster subsequently occur on a timescale of 100 fs to 1 ps. Increasing the charge q makes the fragments smaller. This two-step mechanism governs the fragmentation dynamics in the most likely case that the initial kinetic energy accumulated upon ionization to C{sub 60}{sup q+} by ion impact or X-ray free electron laser is larger than 100 eV.« less
Lowest-energy structures and electronic properties of Na-Si binary clusters from ab initio global search.

PubMed

Sai, Linwei; Tang, Lingli; Zhao, Jijun; Wang, Jun; Kumar, Vijay

2011-11-14

The ground state structures of neutral and anionic clusters of Na(n)Si(m) (1 ≤ n ≤ 3, 1 ≤ m ≤ 11) have been determined using genetic algorithm incorporated in first principles total energy code. The size dependence of the structural and electronic properties is discussed in detail. It is found that the lowest-energy structures of Na(n)Si(m) clusters resemble those of the pure Si clusters. Interestingly, Na atoms in neutral Na(n)Si(m) clusters are usually well separated by the Si(m) skeleton, whereas Na atoms can form Na-Na bonds in some anionic clusters. The ionization potentials, adiabatic electron affinities, and photoelectron spectra are also calculated and the results compare well with the experimental data. © 2011 American Institute of Physics
Exploration of the Ionizable Metal Cluster-Electrode Surface Analogy: Infrared Spectroelectrochemistry of (Pt24(CO)30)n, (Pt26(CO)32)n, and (Pt38(CO) 44)n (n=0 to -10), and Comparisons with Potential-Dependent Spectra of CO adlayers on Platinum Surfaces

DTIC Science & Technology

1992-05-01

100"C under vacuum for 24 hours. The corresponding tetraethylammonium hexafluorophosphate (TEAH) was prepared similarly by using ammonium...the four electrolytes examined in acetonitrile (Table III). Nevertheless, use of lithium perchlorate in acetonitrile restricted the range of cluster
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry combined with multidimensional scaling, binary hierarchical cluster tree and selected diagnostic masses improves species identification of Neolithic keratin sequences from furs of the Tyrolean Iceman Oetzi.

PubMed

Hollemeyer, Klaus; Altmeyer, Wolfgang; Heinzle, Elmar; Pitra, Christian

2012-08-30

The identification of fur origins from the 5300-year-old Tyrolean Iceman's accoutrement is not yet complete, although definite identification is essential for the socio-cultural context of his epoch. Neither have all potential samples been identified so far, nor there has a consensus been reached on the species identified using the classical methods. Archaeological hair often lacks analyzable hair scale patterns in microscopic analyses and polymer chain reaction (PCR)-based techniques are often inapplicable due to the lack of amplifiable ancient DNA. To overcome these drawbacks, a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method was used exclusively based on hair keratins. Thirteen fur specimens from his accoutrement were analyzed after tryptic digest of native hair. Peptide mass fingerprints (pmfs) from ancient samples and from reference species mostly occurring in the Alpine surroundings at his lifetime were compared to each other using multidimensional scaling and binary hierarchical cluster tree analysis. Both statistical methods highly reflect spectral similarities among pmfs as close zoological relationships. While multidimensional scaling was useful to discriminate specimens on the zoological order level, binary hierarchical cluster tree reached the family or subfamily level. Additionally, the presence and/or absence of order, family and/or species-specific diagnostic masses in their pmfs allowed the identification of mammals mostly down to single species level. Red deer was found in his shoe vamp, goat in the leggings, cattle in his shoe sole and at his quiver's closing flap as well as sheep and chamois in his coat. Canid species, like grey wolf, domestic dog or European red fox, were discovered in his leggings for the first time, but could not be differentiated to species level. This is widening the spectrum of processed fur-bearing species to at least one member of the Canidae family. His fur cap was allocated to a carnivore species, but differentiation between brown bear and a canid species could not be made with certainty. Copyright © 2012 John Wiley & Sons, Ltd.
Closed-cage tungsten oxide clusters in the gas phase.

PubMed

Singh, D M David Jeba; Pradeep, T; Thirumoorthy, Krishnan; Balasubramanian, Krishnan

2010-05-06

During the course of a study on the clustering of W-Se and W-S mixtures in the gas phase using laser desorption ionization (LDI) mass spectrometry, we observed several anionic W-O clusters. Three distinct species, W(6)O(19)(-), W(13)O(29)(-), and W(14)O(32)(-), stand out as intense peaks in the regular mass spectral pattern of tungsten oxide clusters suggesting unusual stabilities for them. Moreover, these clusters do not fragment in the postsource decay analysis. While trying to understand the precursor material, which produced these clusters, we found the presence of nanoscale forms of tungsten oxide. The structure and thermodynamic parameters of tungsten clusters have been explored using relativistic quantum chemical methods. Our computed results of atomization energy are consistent with the observed LDI mass spectra. The computational results suggest that the clusters observed have closed-cage structure. These distinct W(13) and W(14) clusters were observed for the first time in the gas phase.
Chirally directed formation of nanometer-scale proline clusters.

PubMed

Myung, Sunnie; Fioroni, Marco; Julian, Ryan R; Koeniger, Stormy L; Baik, Mu-Hyun; Clemmer, David E

2006-08-23

Ion mobility measurements, combined with molecular mechanics simulations, are used to study enantiopure and racemic proline clusters formed by electrospray ionization. Broad distributions of cluster sizes and charge states are observed, ranging from clusters containing only a few proline units to clusters that contain more than 100 proline units (i.e., protonated clusters of the form [xPro + nH](n+) with x = 1 to >100 and n = 1-7). As the sizes of clusters increase, there is direct evidence for nanometer scale, chirally induced organization into specific structures. For n = 4 and 5, enantiopure clusters of approximately 50 to 100 prolines assemble into structures that are more elongated than the most compact structure that is observed from the racemic proline clusters. A molecular analogue, cis-4-hydroxy-proline, displays significantly different behavior, indicating that in addition to the rigidity of the side chain ring, intermolecular interactions are important in the formation of chirally directed clusters. This is the first case in which assemblies of chirally selective elongated structures are observed in this size range of amino acid clusters. Relationships between enantiopurity, cluster shape, and overall energetics are discussed.
First-principle interaction potentials for metastable He(3S) and Ne(3P) with closed-shell molecules: Application to Penning-ionizing systems

NASA Astrophysics Data System (ADS)

Hapka, Michał; Chałasiński, Grzegorz; Kłos, Jacek; Żuchowski, Piotr S.

2013-07-01

We present new interaction potential curves, calculated from first-principles, for the He(3S, 1s12s1)⋯H2 and He(3S)⋯Ar systems, relevant in recent Penning ionization experiments of Henson et al. [Science 338, 234 (2012), 10.1126/science.1229141]. Two different approaches were applied: supermolecular using coupled cluster (CC) theory and perturbational within symmetry-adapted perturbation theory (SAPT). Both methods gave consistent results, and the potentials were used to study the elastic scattering and determine the positions of shape resonances for low kinetic energy (up to 1 meV). We found a good agreement with the experiment. In addition, we investigated two other dimers composed of metastable Ne (3P, 2p53s1) and ground state He and Ar atoms. For the Ne(3P)⋯He system, a good agreement between CC and SAPT approaches was obtained. The Ne(3P)⋯Ar dimer was described only with SAPT, as CC gave divergent results. Ne* systems exhibit extremely small electronic orbital angular momentum anisotropy of the potentials. We attribute this effect to screening of an open 2p shell by a singly occupied 3s shell.

Theoretical and experimental quantification of doubly and singly differential cross sections for electron-induced ionization of isolated tetrahydrofuran molecules

DOE PAGES

Champion, Christophe; Quinto, Michele A.; Bug, Marion U.; ...

2014-07-29

Electron-induced ionization of the commonly used surrogate of the DNA sugar-phosphate backbone, namely, the tetrahydrofuran molecule, is here theoretically described within the 1 st Born approximation by means of quantum-mechanical approach. Comparisons between theory and recent experiments are reported in terms of doubly and singly differential cross sections.
A Radical-Mediated Pathway for the Formation of [M + H](+) in Dielectric Barrier Discharge Ionization.

PubMed

Wolf, Jan-Christoph; Gyr, Luzia; Mirabelli, Mario F; Schaer, Martin; Siegenthaler, Peter; Zenobi, Renato

2016-09-01

Active capillary plasma ionization is a highly efficient ambient ionization method. Its general principle of ion formation is closely related to atmospheric pressure chemical ionization (APCI). The method is based on dielectric barrier discharge ionization (DBDI), and can be constructed in the form of a direct flow-through interface to a mass spectrometer. Protonated species ([M + H](+)) are predominantly formed, although in some cases radical cations are also observed. We investigated the underlying ionization mechanisms and reaction pathways for the formation of protonated analyte ([M + H](+)). We found that ionization occurs in the presence and in the absence of water vapor. Therefore, the mechanism cannot exclusively rely on hydronium clusters, as generally accepted for APCI. Based on isotope labeling experiments, protons were shown to originate from various solvents (other than water) and, to a minor extent, from gaseous impurities and/or self-protonation. By using CO2 instead of air or N2 as plasma gas, additional species like [M + OH](+) and [M - H](+) were observed. These gas-phase reaction products of CO2 with the analyte (tertiary amines) indicate the presence of a radical-mediated ionization pathway, which proceeds by direct reaction of the ionized plasma gas with the analyte. The proposed reaction pathway is supported with density functional theory (DFT) calculations. These findings add a new ionization pathway leading to the protonated species to those currently known for APCI. Graphical Abstract ᅟ.
Ion formation mechanisms in UV-MALDI.

PubMed

Knochenmuss, Richard

2006-09-01

Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion-molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.
THE NATURE AND FREQUENCY OF OUTFLOWS FROM STARS IN THE CENTRAL ORION NEBULA CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

O’Dell, C. R.; Ferland, G. J.; Henney, W. J.

Recent Hubble Space Telescope images have allowed the determination with unprecedented accuracy of motions and changes of shocks within the inner Orion Nebula. These originate from collimated outflows from very young stars, some within the ionized portion of the nebula and others within the host molecular cloud. We have doubled the number of Herbig–Haro objects known within the inner Orion Nebula. We find that the best-known Herbig–Haro shocks originate from relatively few stars, with the optically visible X-ray source COUP 666 driving many of them. While some isolated shocks are driven by single collimated outflows, many groups of shocks aremore » the result of a single stellar source having jets oriented in multiple directions at similar times. This explains the feature that shocks aligned in opposite directions in the plane of the sky are usually blueshifted because the redshifted outflows pass into the optically thick photon-dominated region behind the nebula. There are two regions from which optical outflows originate for which there are no candidate sources in the SIMBAD database.« less
Rapid Quantitative Analysis of Multiple Explosive Compound Classes on a Single Instrument via Flow-Injection Analysis Tandem Mass Spectrometry.

PubMed

Ostrinskaya, Alla; Kunz, Roderick R; Clark, Michelle; Kingsborough, Richard P; Ong, Ta-Hsuan; Deneault, Sandra

2018-05-24

A flow-injection analysis tandem mass spectrometry (FIA MSMS) method was developed for rapid quantitative analysis of 10 different inorganic and organic explosives. Performance is optimized by tailoring the ionization method (APCI/ESI), de-clustering potentials, and collision energies for each specific analyte. In doing so, a single instrument can be used to detect urea nitrate, potassium chlorate, 2,4,6-trinitrotoluene, 2,4,6-trinitrophenylmethylnitramine, triacetone triperoxide, hexamethylene triperoxide diamine, pentaerythritol tetranitrate, 1,3,5-trinitroperhydro-1,3,5-triazine, nitroglycerin, and octohy-dro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine with sensitivities all in the picogram per milliliter range. In conclusion, FIA APCI/ESI MSMS is a fast (<1 min/sample), sensitive (~pg/mL LOQ), and precise (intraday RSD < 10%) method for trace explosive detection that can play an important role in criminal and attributional forensics, counterterrorism, and environmental protection areas, and has the potential to augment or replace several of the existing explosive detection methods. © 2018 American Academy of Forensic Sciences.
Modeling the gain of inner-shell X-ray laser transitions in neon, argon, and copper driven by X-ray free electron laser radiation using photo-ionization and photo-excitation processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nilsen, Joseph

2015-12-16

Using an X-ray free electron laser (XFEL) at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p-1s transition in singly-ionized neon, an inner-shell X-ray laser was demonstrated at 849 eV in singly-ionized neon gas several years ago. It took decades to demonstrate this scheme, because it required a very strong X-ray source that could photo-ionize the 1s (K shell) electron in neon on a timescale comparable to the intrinsic Auger lifetime in neon of 2 fs. In this paper, we model the neon inner shell X-ray laser under similar conditions to those usedmore » in the XFEL experiments at the SLAC Linac Coherent Light Source (LCLS), and show how we can improve the efficiency of the neon laser and reduce the drive requirements by tuning the XFEL to the 1s-3p transition in neutral neon in order to create gain on the 2p-1s line in neutral neon. We also show how the XFEL could be used to photo-ionize L-shell electrons to drive gain on n = 3–2 transitions in singly-ionized Ar and Cu plasmas. Furthermore, these bright, coherent, and monochromatic X-ray lasers may prove very useful for doing high-resolution spectroscopy and for studying non-linear process in the X-ray regime.« less
Ionizing Shocks in Argon. Part 2: Transient and Multi-Dimensional Effects (Preprint)

DTIC Science & Technology

2010-09-09

stability in ionizing monatomic gases. Part 1. Argon ,” J. Fluid Mech., 84, 55 (1978). 2M. P. F. Bristow and I. I. Glass, “ Polarizability of singly...Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Ionizing Shocks in Argon . Part 2: Transient...Physics. 14. ABSTRACT We extend the computations of ionizing shocks in argon to unsteady and multi-dimensional, using a collisional-radiative
Transition-matrix theory for two-photon ionization of rare-gas atoms and isoelectronic ions with application to argon

NASA Astrophysics Data System (ADS)

Starace, Anthony F.; Jiang, Tsin-Fu

1987-08-01

A transition-matrix theory for two-photon ionization processes in rare-gas atoms or isoelectronic ions is presented. Uncoupled ordinary differential equations are obtained for the radial functions needed to calculate the two-photon transition amplitude. The implications of these equations are discussed in detail. In particular, the role of correlations involving virtually excited electron pairs, which are known to be essential to the description of single-photon processes, is examined for multiphoton ionization processes. Additionally, electron scattering interactions between two electron-hole pairs are introduced into our transition amplitude in the boson approximation since these have been found important in two-photon ionization of xenon by L'Huillier and Wendin [J. Phys. B 20, L37 (1987)]. Application of our theory is made to two-photon ionization of the 3p subshell of argon below the one-photon ionization threshold. Our results are compared to previous calculations of McGuire [Phys. Rev. A 24, 835 (1981)], of Moccia, Rahman, and Rizzo [J. Phys. B 16, 2737 (1983)], and of Pindzola and Kelly [Phys. Rev. A 11, 1543 (1975)]. Results are presented for both circularly and linearly polarized photons. Among our findings are, firstly, that the electron scattering interactions, which have not been included in previous calculations for argon, produce a substantial reduction in the two-photon single-ionization cross section below the one-photon ionization threshold, which is in agreement with findings of L'Huillier and Wendin for xenon. Secondly, we find that de-excitation of virtually excited electron pairs by absorption of a photon is important for describing the interaction of the atom with the photon field, as in the case of single-photon ionization processes, but that further excitation of virtually excited electron pairs by the photon field has completely negligible effects, indicating a major simplification of the theory for higher-order absorption processes.
Wavelengths, Transition Probabilities, and Energy Levels for the Spectra of Strontium Ions (Sr II through Sr XXXVIII)

NASA Astrophysics Data System (ADS)

Sansonetti, J. E.

2012-03-01

Energy levels, with designations and uncertainties, have been compiled for the spectra of strontium (Z=38) ions from singly ionized to hydrogen-like. Wavelengths with classifications, intensities, and transition probabilities are also tabulated. In addition, ground states and ionization energies are listed. For many ionization stages experimental data are available; however for those for which only theoretical calculations or fitted values exist, these are reported. There are a few ionization stages for which only a calculated ionization potential is available.
Structural, electronic, vibrational and optical properties of Bin clusters

NASA Astrophysics Data System (ADS)

Liang, Dan; Shen, Wanting; Zhang, Chunfang; Lu, Pengfei; Wang, Shumin

2017-10-01

The neutral, anionic and cationic bismuth clusters with the size n up to 14 are investigated by using B3LYP functional within the regime of density functional theory and the LAN2DZ basis set. By analysis of the geometries of the Bin (n = 2-14) clusters, where cationic and anionic bismuth clusters are largely similar to those of neutral ones, a periodic effect by adding units with one to four atoms into smaller cluster to form larger cluster is drawn for the stable structures of bismuth clusters. An even-odd alteration is shown for the properties of the clusters, such as the calculated binding energies and dissociation energies, as well as frontier orbital energies, electron affinities, ionization energies. All the properties indicate that the Bi4 cluster is the most possible existence in bismuth-containing materials, which supports the most recent experiment. The orbital compositions, infrared and Raman activities and the ultraviolet absorption of the most possible tetramer bismuth cluster are given in detail to reveal the periodic tendency of adding bismuth atoms and the stability of tetramer bismuth cluster.
The Technical and Biological Reproducibility of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) Based Typing: Employment of Bioinformatics in a Multicenter Study

PubMed Central

Oberle, Michael; Wohlwend, Nadia; Jonas, Daniel; Maurer, Florian P.; Jost, Geraldine; Tschudin-Sutter, Sarah; Vranckx, Katleen; Egli, Adrian

2016-01-01

Background The technical, biological, and inter-center reproducibility of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI TOF MS) typing data has not yet been explored. The aim of this study is to compare typing data from multiple centers employing bioinformatics using bacterial strains from two past outbreaks and non-related strains. Material/Methods Participants received twelve extended spectrum betalactamase-producing E. coli isolates and followed the same standard operating procedure (SOP) including a full-protein extraction protocol. All laboratories provided visually read spectra via flexAnalysis (Bruker, Germany). Raw data from each laboratory allowed calculating the technical and biological reproducibility between centers using BioNumerics (Applied Maths NV, Belgium). Results Technical and biological reproducibility ranged between 96.8–99.4% and 47.6–94.4%, respectively. The inter-center reproducibility showed a comparable clustering among identical isolates. Principal component analysis indicated a higher tendency to cluster within the same center. Therefore, we used a discriminant analysis, which completely separated the clusters. Next, we defined a reference center and performed a statistical analysis to identify specific peaks to identify the outbreak clusters. Finally, we used a classifier algorithm and a linear support vector machine on the determined peaks as classifier. A validation showed that within the set of the reference center, the identification of the cluster was 100% correct with a large contrast between the score with the correct cluster and the next best scoring cluster. Conclusions Based on the sufficient technical and biological reproducibility of MALDI-TOF MS based spectra, detection of specific clusters is possible from spectra obtained from different centers. However, we believe that a shared SOP and a bioinformatics approach are required to make the analysis robust and reliable. PMID:27798637
Cationic Gold Clusters Ligated with Differently Substituted Phosphines: Effect of Substitution on Ligand Reactivity and Binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Grant E.; Olivares, Astrid M.; Hill, David E.

2015-01-01

We present a systematic study of the effect of the number of methyl (Me) and cyclohexyl (Cy) functional groups in monodentate phosphine ligands on the solution-phase synthesis of ligated sub-nanometer gold clusters and their gas-phase fragmentation pathways. Small mixed ligand cationic gold clusters were synthesized using ligand exchange reactions between pre-formed triphenylphosphine ligated (PPh3) gold clusters and monodentate Me- and Cy-substituted ligands in solution and characterized using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation (CID) experiments. Under the same experimental conditions, larger gold-PPh3 clusters undergo efficient exchange of unsubstituted PPh3 ligands for singly Me- and Cy-substituted PPh2Me and PPh2Cymore » ligands. The efficiency of ligand exchange decreases with an increasing number of Me or Cy groups in the substituted phosphine ligands. CID experiments performed for a series of ligand-exchanged gold clusters indicate that loss of a neutral Me-substituted ligand is preferred over loss of a neutral PPh¬3 ligand while the opposite trend is observed for Cy-substituted ligands. The branching ratio of the competing ligand loss channels is strongly correlated with the electron donating ability of the phosphorous lone pair as determined by the relative proton affinity of the ligand. The results indicate that the relative ligand binding energies increase in the order PMe3 < PPhMe2 < PPh2Me < PPh3< PPh2Cy < PPhCy2< PCy3. Furthermore, the difference in relative ligand binding energies increases with the number of substituted PPh3-mMem or PPh3-mCym ligands (L) exchanged onto each cluster. This study provides the first experimental determination of the relative binding energies of ligated gold clusters containing differently substituted monophosphine ligands, which are important to controlling their synthesis and reactivity in solution. The results also indicate that ligand substitution is an important parameter that must be considered in theoretical modeling of these complex systems« less
C=C bond cleavage on neutral VO3(V2O5)n clusters.

PubMed

Dong, Feng; Heinbuch, Scott; Xie, Yan; Bernstein, Elliot R; Rocca, Jorge J; Wang, Zhe-Chen; Ding, Xun-Lei; He, Sheng-Gui

2009-01-28

The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V(2)O(5))(n)VO(2)CH(2), (V(2)O(5))(n)VO(2)C(2)H(4), (V(2)O(5))(n)VO(2)C(3)H(4), and (V(2)O(5))(n)VO(2)C(3)H(6), for neural V(m)O(n) clusters in reactions with C(2)H(4), C(3)H(6), C(4)H(6), and C(4)H(8), respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO(3)(V(2)O(5))(n=0,1,2...). DFT calculations demonstrate that the reaction VO(3) + C(3)H(6) --> VO(2)C(2)H(4) + H(2)CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO(3)(V(2)O(5))(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V(m)O(n) with C(6)H(6) and C(2)F(4) are also investigated by experiments. The products VO(2)(V(2)O(5))(n)C(6)H(4) are observed for dehydration reactions between V(m)O(n) clusters and C(6)H(6). No product is detected for V(m)O(n) clusters reacting with C(2)F(4). The mechanisms of the reactions between VO(3) and C(2)F(4)/C(6)H(6) are also investigated by calculations at the B3LYP/TZVP level.
Nuclear fusion driven by Coulomb explosion of homonuclear and heteronuclear deuterium- and tritium-containing clusters

NASA Astrophysics Data System (ADS)

Last, Isidore; Jortner, Joshua

2001-12-01

The ionization and Coulomb explosion of homonuclear Dn and Tn (n=959-8007) and heteronuclear (D2O)n and (T2O)n (n=459-2171) clusters in very intense (I=5×1014-5×1018 W cm-2) laser fields is studied using classical dynamics simulations. The efficiency of the d+d and d+t nuclear fusion driven by the Coulomb explosion (NFDCE) is explored. The d+d NFDCE of (D2O)n heteronuclear clusters is enhanced by energetic and kinematic effects for D+, while for (T2O)n heteronuclear clusters the kinetic energy of T+ is dominated by energetic effects. The cluster size dependence of the fusion reaction yield has been established. The heteronuclear clusters provide considerably higher d+d and d+t fusion reaction yields than the homonuclear clusters of the same size. The clusters consisting of both D and T atoms can provide highly efficient d+t fusion reactions.
Partial cross sections of helium satellites at medium photon energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wehlitz, R.; Sellin, I.A.; Hemmers, O.

1997-04-01

Still of current interest is the important role of single ionization with excitation compared to single ionization alone. The coupling between the electrons and the incoming photon is a single-particle operator. Thus, an excitation in addition to an ionization, leading to a so-called satellite line in a photoelectron spectrum, is entirely due to electron-electron interaction and probes the electron correlation in the ground and final state. Therefore the authors have undertaken the study of the intensity of helium satellites He{sup +}nl (n = 2 - 6) relative to the main photoline (n = 1) as a function of photon energymore » at photon energies well above threshold up to 900 eV. From these results they could calculate the partial cross-sections of the helium satellites. In order to test the consistency of their satellite-to-1s ratios with published double-to-single photoionization ratios, the authors calculated the double-to-single photoionization ratio from their measured ratios using the theoretical energy-distribution curves of Chang and Poe and Le Rouzo and Dal Cappello which proved to be valid for photon energies below 120 eV. These calculated double-to-single ionization ratios agree fairly well with recent ion measurements. In the lower photon energy range the authors ratios agree better with the ratios of Doerner et al. while for higher photon energies the agreement is better with the values of Levin et al.« less
Delineation of Stenotrophomonas maltophilia isolates from cystic fibrosis patients by fatty acid methyl ester profiles and matrix-assisted laser desorption/ionization time-of-flight mass spectra using hierarchical cluster analysis and principal component analysis.

PubMed

Vidigal, Pedrina Gonçalves; Mosel, Frank; Koehling, Hedda Luise; Mueller, Karl Dieter; Buer, Jan; Rath, Peter Michael; Steinmann, Joerg

2014-12-01

Stenotrophomonas maltophilia is an opportunist multidrug-resistant pathogen that causes a wide range of nosocomial infections. Various cystic fibrosis (CF) centres have reported an increasing prevalence of S. maltophilia colonization/infection among patients with this disease. The purpose of this study was to assess specific fingerprints of S. maltophilia isolates from CF patients (n = 71) by investigating fatty acid methyl esters (FAMEs) through gas chromatography (GC) and highly abundant proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and to compare them with isolates obtained from intensive care unit (ICU) patients (n = 20) and the environment (n = 11). Principal component analysis (PCA) of GC-FAME patterns did not reveal a clustering corresponding to distinct CF, ICU or environmental types. Based on the peak area index, it was observed that S. maltophilia isolates from CF patients produced significantly higher amounts of fatty acids in comparison with ICU patients and the environmental isolates. Hierarchical cluster analysis (HCA) based on the MALDI-TOF MS peak profiles of S. maltophilia revealed the presence of five large clusters, suggesting a high phenotypic diversity. Although HCA of MALDI-TOF mass spectra did not result in distinct clusters predominantly composed of CF isolates, PCA revealed the presence of a distinct cluster composed of S. maltophilia isolates from CF patients. Our data suggest that S. maltophilia colonizing CF patients tend to modify not only their fatty acid patterns but also their protein patterns as a response to adaptation in the unfavourable environment of the CF lung. © 2014 The Authors.
Strong-field ionization of clusters using two-cycle pulses at 1.8 μm

PubMed Central

Schütte, Bernd; Ye, Peng; Patchkovskii, Serguei; Austin, Dane R.; Brahms, Christian; Strüber, Christian; Witting, Tobias; Ivanov, Misha Yu.; Tisch, John W. G.; Marangos, Jon P.

2016-01-01

The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale. PMID:28009012
New method for estimating clustering of DNA lesions induced by physical/chemical mutagens using fluorescence anisotropy.

PubMed

Akamatsu, Ken; Shikazono, Naoya; Saito, Takeshi

2017-11-01

We have developed a new method for estimating the localization of DNA damage such as apurinic/apyrimidinic sites (APs) on DNA using fluorescence anisotropy. This method is aimed at characterizing clustered DNA damage produced by DNA-damaging agents such as ionizing radiation and genotoxic chemicals. A fluorescent probe with an aminooxy group (AlexaFluor488) was used to label APs. We prepared a pUC19 plasmid with APs by heating under acidic conditions as a model for damaged DNA, and subsequently labeled the APs. We found that the observed fluorescence anisotropy (r obs ) decreases as averaged AP density (λ AP : number of APs per base pair) increases due to homo-FRET, and that the APs were randomly distributed. We applied this method to three DNA-damaging agents, 60 Co γ-rays, methyl methanesulfonate (MMS), and neocarzinostatin (NCS). We found that r obs -λ AP relationships differed significantly between MMS and NCS. At low AP density (λ AP < 0.001), the APs induced by MMS seemed to not be closely distributed, whereas those induced by NCS were remarkably clustered. In contrast, the AP clustering induced by 60 Co γ-rays was similar to, but potentially more likely to occur than, random distribution. This simple method can be used to estimate mutagenicity of ionizing radiation and genotoxic chemicals. Copyright © 2017 Elsevier Inc. All rights reserved.
Single and double multiphoton ionization of Li and Be atoms by strong laser fields

NASA Astrophysics Data System (ADS)

Telnov, Dmitry; Heslar, John; Chu, Shih-I.

2011-05-01

The time-dependent density functional theory with self-interaction correction and proper asymptotic long-range potential is extended for nonperturbative treatment of multiphoton single and double ionization of Li and Be atoms by strong 800 nm laser fields. We make use of the time-dependent Krieger-Li-Iafrate (TDKLI) exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. However, we have found that the discontinuity of the TDKLI potential is not sufficient to reproduce the characteristic feature of double ionization. This may happen because the discontinuity of the TDKLI potential is related to the spin particle numbers only and not to the total particle number. Introducing a discontinuity with respect to the total particle number to the exchange-correlation potential, we were able to obtain the knee structure in the intensity dependence of the double ionization probability of Be. This work was partially supported by DOE and NSF and by NSC-Taiwan.
Gas-phase lifetimes of nucleobase analogues by picosecond pumpionization and streak techniques.

PubMed

Blaser, Susan; Frey, Hans-Martin; Heid, Cornelia G; Leutwyler, Samuel

2014-01-01

The picosecond (ps) timescale is relevant for the investigation of many molecular dynamical processes such as fluorescence, nonradiative relaxation, intramolecular vibrational relaxation, molecular rotation and intermolecular energy transfer, to name a few. While investigations of ultrafast (femtosecond) processes of biological molecules, e.g. nucleobases and their analogues in the gas phase are available, there are few investigations on the ps time scale. We have constructed a ps pump-ionization setup and a ps streak camera fluorescence apparatus for the determination of lifetimes of supersonic jet-cooled and isolated molecules and clusters. The ps pump-ionization setup was used to determine the lifetimes of the nucleobase analogue 2-aminopurine (2AP) and of two 2AP˙(H2O)n water cluster isomers with n=1 and 2. Their lifetimes lie between 150 ps and 3 ns and are strongly cluster-size dependent. The ps streak camera setup was used to determine accurate fluorescence lifetimes of the uracil analogue 2-pyridone (2PY), its self-dimer (2PY)2, two isomers of its trimer (2PY)3 and its tetramer (2PY)4, which lie in the 7-12 ns range.

The application of Gaussian mixture models for signal quantification in MALDI-TOF mass spectrometry of peptides.

PubMed

Spainhour, John Christian G; Janech, Michael G; Schwacke, John H; Velez, Juan Carlos Q; Ramakrishnan, Viswanathan

2014-01-01

Matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) coupled with stable isotope standards (SIS) has been used to quantify native peptides. This peptide quantification by MALDI-TOF approach has difficulties quantifying samples containing peptides with ion currents in overlapping spectra. In these overlapping spectra the currents sum together, which modify the peak heights and make normal SIS estimation problematic. An approach using Gaussian mixtures based on known physical constants to model the isotopic cluster of a known compound is proposed here. The characteristics of this approach are examined for single and overlapping compounds. The approach is compared to two commonly used SIS quantification methods for single compound, namely Peak Intensity method and Riemann sum area under the curve (AUC) method. For studying the characteristics of the Gaussian mixture method, Angiotensin II, Angiotensin-2-10, and Angiotenisn-1-9 and their associated SIS peptides were used. The findings suggest, Gaussian mixture method has similar characteristics as the two methods compared for estimating the quantity of isolated isotopic clusters for single compounds. All three methods were tested using MALDI-TOF mass spectra collected for peptides of the renin-angiotensin system. The Gaussian mixture method accurately estimated the native to labeled ratio of several isolated angiotensin peptides (5.2% error in ratio estimation) with similar estimation errors to those calculated using peak intensity and Riemann sum AUC methods (5.9% and 7.7%, respectively). For overlapping angiotensin peptides, (where the other two methods are not applicable) the estimation error of the Gaussian mixture was 6.8%, which is within the acceptable range. In summary, for single compounds the Gaussian mixture method is equivalent or marginally superior compared to the existing methods of peptide quantification and is capable of quantifying overlapping (convolved) peptides within the acceptable margin of error.
The shape and size distribution of H II regions near the percolation transition

NASA Astrophysics Data System (ADS)

Bag, Satadru; Mondal, Rajesh; Sarkar, Prakash; Bharadwaj, Somnath; Sahni, Varun

2018-06-01

Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (H I) density fields, simulated using seminumerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the `largest cluster statistic' (LCS), originally proposed in Klypin & Shandarin, to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction x_{H I}≲ 0.728 (or equivalently z ≲ 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders - `thickness' (T) and `breadth' (B) - of the largest ionized region do not vary much, while the third Shapefinder - `length' (L) - abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T × B, provides a measure of the `cross-section' of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ˜7 Mpc2 (in comoving scale) while its length increases with time. Interestingly, all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V0.72, at the onset of percolation.
HEAO-A2 observations of the X-ray spectra of the Centaurus and A1060 clusters of galaxies

NASA Technical Reports Server (NTRS)

Mitchell, R.; Mushotzky, R.

1979-01-01

The X-ray spectral observations of two low luminosity clusters of galaxies, Centaurus and A1060, are presented. An emission feature of the Centaurus cluster at 7.9 keV is detected at about one third of the strength of the 6.7 keV line. This higher energy line represents K sub beta emission from highly ionized iron. An isothermal model with an Fe emission line is discussed and it is shown that the model cannot fit the data of the Centaurus or the A1060 clusters. The implications of the two component nature of the continuum on the Fe abundance and the X-ray surface brightness distribution are discussed.
Nova-driven winds in globular clusters

NASA Technical Reports Server (NTRS)

Scott, E. H.; Durisen, R. H.

1978-01-01

Recent sensitive searches for H-alpha emission from ionized intracluster gas in globular clusters have set upper limits that conflict with theoretical predictions. It is suggested that nova outbursts heat the gas, producing winds that resolve this discrepancy. The incidence of novae in globular clusters, the conversion of kinetic energy of the nova shell to thermal energy of the intracluster gas, and the characteristics of the resultant winds are discussed. Calculated emission from the nova-driven models does not conflict with any observations to date. Some suggestions are made concerning the most promising approaches for future detection of intracluster gas on the basis of these models. The possible relationship of nova-driven winds to globular cluster X-ray sources is also considered.
Correlation-driven charge migration following double ionization and attosecond transient absorption spectroscopy

NASA Astrophysics Data System (ADS)

Hollstein, Maximilian; Santra, Robin; Pfannkuche, Daniela

2017-05-01

We theoretically investigate charge migration following prompt double ionization. Thereby, we extend the concept of correlation-driven charge migration, which was introduced by Cederbaum and coworkers for single ionization [Chem. Phys. Lett. 307, 205 (1999), 10.1016/S0009-2614(99)00508-4], to doubly ionized molecules. This allows us to demonstrate that compared to singly ionized molecules, in multiply ionized molecules, electron dynamics originating from electronic relaxation and correlation are particularly prominent. In addition, we also discuss how these correlation-driven electron dynamics might be evidenced and traced experimentally using attosecond transient absorption spectroscopy. For this purpose, we determine the time-resolved absorption cross section and find that the correlated electron dynamics discussed are reflected in it with exceptionally great detail. Strikingly, we find that features in the cross section can be traced back to electron hole populations and time-dependent partial charges and hence, can be interpreted with surprising ease. By taking advantage of element-specific core-to-valence transitions even atomic spatial resolution can be achieved. Thus, with the theoretical considerations presented, not only do we predict particularly diverse and correlated electron dynamics in molecules to follow prompt multiple ionization but we also identify a promising route towards their experimental investigation.
Electron-helium S-wave model benchmark calculations. I. Single ionization and single excitation

NASA Astrophysics Data System (ADS)

Bartlett, Philip L.; Stelbovics, Andris T.

2010-02-01

A full four-body implementation of the propagating exterior complex scaling (PECS) method [J. Phys. B 37, L69 (2004)] is developed and applied to the electron-impact of helium in an S-wave model. Time-independent solutions to the Schrödinger equation are found numerically in coordinate space over a wide range of energies and used to evaluate total and differential cross sections for a complete set of three- and four-body processes with benchmark precision. With this model we demonstrate the suitability of the PECS method for the complete solution of the full electron-helium system. Here we detail the theoretical and computational development of the four-body PECS method and present results for three-body channels: single excitation and single ionization. Four-body cross sections are presented in the sequel to this article [Phys. Rev. A 81, 022716 (2010)]. The calculations reveal structure in the total and energy-differential single-ionization cross sections for excited-state targets that is due to interference from autoionization channels and is evident over a wide range of incident electron energies.
Unprecedented Ionization Processes in Mass Spectrometry Provide Missing Link between ESI and MALDI.

PubMed

Trimpin, Sarah; Lee, Chuping; Weidner, Steffen M; El-Baba, Tarick J; Lutomski, Corinne A; Inutan, Ellen D; Foley, Casey D; Ni, Chi-Kung; McEwen, Charles N

2018-03-05

In the field of mass spectrometry, producing intact, highly-charged protein ions from surfaces is a conundrum with significant potential payoff in application areas ranging from biomedical to clinical research. Here, we report on the ability to form intact, highly-charged protein ions on high vacuum time-of-flight mass spectrometers in the linear and reflectron modes achievable using experimental conditions that allow effective matrix removal from both the sample surfaces and from the charged clusters formed by the laser ablation event. The charge states are the highest reported on high vacuum mass spectrometers, yet they remain at only around a third of the highest charge obtained using laser ablation with a suitable matrix at atmospheric pressure. Other than physical instrument modifications, the key to forming abundant and stable highly-charged ions appears to be the volatility of the matrix used. Cumulative results suggest mechanistic links between the ionization process reported here and traditional ionization methods of electrospray ionization and matrix-assisted laser desorption/ionization. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Observing the real time formation of phosphine-ligated gold clusters by electrospray ionization mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ligare, Marshall R.; Johnson, Grant E.; Laskin, Julia

Early stages of the reduction and nucleation of solution-phase gold clusters are largely unknown. This is due, in part, to the high reaction rates and the complexity of the cluster synthesis process. Through the addition of a diphosphine ligand, 1-4,Bis(diphenylphosphino)butane (L4) to the gold precursor, chloro(triphenylphosphine) gold(I) (Au(PPh3)Cl), in methanol organometallic complexes of the type, [Au(L4)x(L4O)y(PPh3)z]+, are formed. These complexes lower the rate of reduction so that the reaction can be directly monitored from 1 min to over an hour using on-line electrospray ionization mass spectrometry (ESI-MS). Our results indicate that the formation of Au8(L4)42+, Au9(L4)4H2+ and Au10(L4)52+ cationic clustersmore » occurs through different reaction pathways that may be kinetically controlled either through the reducing agent concentration or the extent of oxidation of L4. Through comparison of selected ion chronograms our results indicate that Au2(L4)2H+ may be an intermediate in the formation of Au8(L4)42+and Au10(L4)52+ while a variety of chlorinated clusters are involved in the formation of Au9(L4)4H2+. Additionally, high-resolution mass spectrometry was employed to identify 53 gold containing species produced under highly oxidative conditions. New intermediate species are identified which help understand how different gold cluster nuclearities can be stabilized during the growth process.« less
Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources

NASA Astrophysics Data System (ADS)

Newsome, G. Asher; Ackerman, Luke K.; Johnson, Kevin J.

2016-01-01

Post-plasma ambient desorption/ionization (ADI) sources are fundamentally dependent on surrounding water vapor to produce protonated analyte ions. There are two reports of humidity effects on ADI spectra. However, it is unclear whether humidity will affect all ADI sources and analytes, and by what mechanism humidity affects spectra. Flowing atmospheric pressure afterglow (FAPA) ionization and direct analysis in real time (DART) mass spectra of various surface-deposited and gas-phase analytes were acquired at ambient temperature and pressure across a range of observed humidity values. A controlled humidity enclosure around the ion source and mass spectrometer inlet was used to create programmed humidity and temperatures. The relative abundance and fragmentation of molecular adduct ions for several compounds consistently varied with changing ambient humidity and also were controlled with the humidity enclosure. For several compounds, increasing humidity decreased protonated molecule and other molecular adduct ion fragmentation in both FAPA and DART spectra. For others, humidity increased fragment ion ratios. The effects of humidity on molecular adduct ion fragmentation were caused by changes in the relative abundances of different reagent protonated water clusters and, thus, a change in the average difference in proton affinity between an analyte and the population of water clusters. Control of humidity in ambient post-plasma ion sources is needed to create spectral stability and reproducibility.
Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources.

PubMed

Newsome, G Asher; Ackerman, Luke K; Johnson, Kevin J

2016-01-01

Post-plasma ambient desorption/ionization (ADI) sources are fundamentally dependent on surrounding water vapor to produce protonated analyte ions. There are two reports of humidity effects on ADI spectra. However, it is unclear whether humidity will affect all ADI sources and analytes, and by what mechanism humidity affects spectra. Flowing atmospheric pressure afterglow (FAPA) ionization and direct analysis in real time (DART) mass spectra of various surface-deposited and gas-phase analytes were acquired at ambient temperature and pressure across a range of observed humidity values. A controlled humidity enclosure around the ion source and mass spectrometer inlet was used to create programmed humidity and temperatures. The relative abundance and fragmentation of molecular adduct ions for several compounds consistently varied with changing ambient humidity and also were controlled with the humidity enclosure. For several compounds, increasing humidity decreased protonated molecule and other molecular adduct ion fragmentation in both FAPA and DART spectra. For others, humidity increased fragment ion ratios. The effects of humidity on molecular adduct ion fragmentation were caused by changes in the relative abundances of different reagent protonated water clusters and, thus, a change in the average difference in proton affinity between an analyte and the population of water clusters. Control of humidity in ambient post-plasma ion sources is needed to create spectral stability and reproducibility.
Properties of R136a as derived from its optical light distribution

NASA Technical Reports Server (NTRS)

Chu, Y.-H.; Wolfire, M. G.; Cassinelli, J. P.

1984-01-01

Short exposure 4 m prime focus plates taken with interference filters centered on blue continuum 4765 A, He II 4686 line, red continuum 6485 A, and H-alpha line have been used to study the light distribution within R136a. R136a contains a bright component and several fainter components superposed on an extended background. The brightest component, unresolved under sub-arcsec seeing condition, contributes about 37 percent of the total light from a 3 in. diameter aperture. Combining the optical and UV information, it is found that this brightest component R136a1 may be a single star with a mass of approximately 750 solar masses with a brightness of six HD 93129A or 20 O3 V stars, or it could be a cluster of such stars. In either case, R136a1 supplies no more than one-half of the ionization of the 30 Doradus nebula.
Properties of R136a as derived from its optical light distribution

NASA Astrophysics Data System (ADS)

Chu, Y. H.; Cassinelli, J. P.; Wolfire, M. G.

1984-08-01

Short exposure 4 m prime focus plates taken with interference filters centered on blue continuum 4765 A, He II 4686 line, red continuum 6485 A, and H-alpha line have been used to study the light distribution within R136a. R136a contains a bright component and several fainter components superposed on an extended background. The brightest component, unresolved under sub-arcsec seeing condition, contributes about 37 percent of the total light from a 3 in. diameter aperture. Combining the optical and UV information, it is found that this brightest component R136a1 may be a single star with a mass of approximately 750 solar masses with a brightness of six HD 93129A or 20 O3 V stars, or it could be a cluster of such stars. In either case, R136a1 supplies no more than one-half of the ionization of the 30 Doradus nebula.
Charge transfer to ground-state ions produces free electrons

PubMed Central

You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K

2017-01-01

Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne–Kr mixed clusters. PMID:28134238
Extending Quantum Chemistry of Bound States to Electronic Resonances

NASA Astrophysics Data System (ADS)

Jagau, Thomas-C.; Bravaya, Ksenia B.; Krylov, Anna I.

2017-05-01

Electronic resonances are metastable states with finite lifetime embedded in the ionization or detachment continuum. They are ubiquitous in chemistry, physics, and biology. Resonances play a central role in processes as diverse as DNA radiolysis, plasmonic catalysis, and attosecond spectroscopy. This review describes novel equation-of-motion coupled-cluster (EOM-CC) methods designed to treat resonances and bound states on an equal footing. Built on complex-variable techniques such as complex scaling and complex absorbing potentials that allow resonances to be associated with a single eigenstate of the molecular Hamiltonian rather than several continuum eigenstates, these methods extend electronic-structure tools developed for bound states to electronic resonances. Selected examples emphasize the formal advantages as well as the numerical accuracy of EOM-CC in the treatment of electronic resonances. Connections to experimental observables such as spectra and cross sections, as well as practical aspects of implementing complex-valued approaches, are also discussed.
Single Low-Dose Ionizing Radiation Induces Genotoxicity in Adult Zebrafish and its Non-Irradiated Progeny.

PubMed

Lemos, J; Neuparth, T; Trigo, M; Costa, P; Vieira, D; Cunha, L; Ponte, F; Costa, P S; Metello, L F; Carvalho, A P

2017-02-01

This study investigated to what extent a single exposure to low doses of ionizing radiation can induce genotoxic damage in irradiated adult zebrafish (Danio rerio) and its non-irradiated F1 progeny. Four groups of adult zebrafish were irradiated with a single dose of X-rays at 0 (control), 100, 500 and 1000 mGy, respectively, and couples of each group were allowed to reproduce following irradiation. Blood of parental fish and whole-body offspring were analysed by the comet assay for detection of DNA damage. The level of DNA damage in irradiated parental fish increased in a radiation dose-dependent manner at day 1 post-irradiation, but returned to the control level thereafter. The level of DNA damage in the progeny was directly correlated with the parental irradiation dose. Results highlight the genotoxic risk of a single exposure to low-dose ionizing radiation in irradiated individuals and also in its non-irradiated progeny.
Critical Assessment of Theoretical Methods for Li3+ Collisions with He at Intermediate and High Impact Energies

NASA Astrophysics Data System (ADS)

Belkić, Dževad; Mančev, Ivan; Milojevićb, Nenad

2013-09-01

The total cross sections for the various processes for Li3+-He collisions at intermediate-to-high impact energies are compared with the corresponding theories. The possible reasons for the discrepancies among various theoretical predictions are thoroughly discussed. Special attention has been paid to single and double electron capture, simultaneous transfer and ionization, as well as to single and double ionization.
Metal-atom Interactions and Clustering in Organic Semiconductor Systems

NASA Astrophysics Data System (ADS)

Tomita, Yoko; Park, Tea-uk; Nakayama, Takashi

2017-07-01

The interatomic interactions and clustering of metal atoms have been studied by first-principles calculations in graphene, pentacene, and polyacetylene as representative organic systems. It is shown that long-range repulsive Coulomb interaction appears between metal atoms with small electronegativity such as Al due to their ionization on host organic molecules, inducing their scattered distribution in organic systems. On the other hand, metal atoms with large electronegativity such as Au are weakly bonded to organic molecules, easily diffuse in molecular solids, and prefer to combine with each other owing to their short-range strong metallic-bonding interaction, promoting metal cluster generation in organic systems.
Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. II. Three- and four-photon ionization of fenchone and camphor.

PubMed

Müller, Anne D; Artemyev, Anton N; Demekhin, Philipp V

2018-06-07

Angle-resolved multiphoton ionization of fenchone and camphor by short intense laser pulses is computed by the time-dependent single center method. Thereby, the photoelectron circular dichroism (PECD) in the three-photon resonance enhanced ionization and four-photon above-threshold ionization of these molecules is investigated in detail. The computational results are in satisfactory agreement with the available experimental data, measured for randomly oriented fenchone and camphor molecules at different wavelengths of the exciting pulses. We predict a significant enhancement of the multiphoton PECD for uniaxially oriented fenchone and camphor.
Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. II. Three- and four-photon ionization of fenchone and camphor

NASA Astrophysics Data System (ADS)

Müller, Anne D.; Artemyev, Anton N.; Demekhin, Philipp V.

2018-06-01

Angle-resolved multiphoton ionization of fenchone and camphor by short intense laser pulses is computed by the time-dependent single center method. Thereby, the photoelectron circular dichroism (PECD) in the three-photon resonance enhanced ionization and four-photon above-threshold ionization of these molecules is investigated in detail. The computational results are in satisfactory agreement with the available experimental data, measured for randomly oriented fenchone and camphor molecules at different wavelengths of the exciting pulses. We predict a significant enhancement of the multiphoton PECD for uniaxially oriented fenchone and camphor.
Compendium of Current Total Ionizing Dose and Displacement Damage Results from NASA Goddard Space Flight Center and NASA Electronic Parts and Packaging Program

NASA Technical Reports Server (NTRS)

Topper, Alyson D.; Campola, Michael J.; Chen, Dakai; Casey, Megan C.; Yau, Ka-Yen; Cochran, Donna J.; Label, Kenneth A.; Ladbury, Raymond L.; Mondy, Timothy K.; O'Bryan, Martha V.;

2017-01-01

Total ionizing dose and displacement damage testing was performed to characterize and determine the suitability of candidate electronics for NASA space utilization. Devices tested include optoelectronics, digital, analog, linear bipolar devices, and hybrid devices. Displacement Damage, Optoelectronics, Proton Damage, Single Event Effects, and Total Ionizing Dose.

Dissociation kinetics of excited ions: PEPICO measurements of Os3(CO)12 - The 7-35 eV single ionization binding energy region.

PubMed

Schalk, Oliver; Josefsson, Ida; Geng, Ting; Richter, Robert; Sa'adeh, Hanan; Thomas, Richard D; Mucke, Melanie

2018-02-28

In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os 3 (CO) 12 , in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behavior was observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 ± 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 ± 0.4 eV, corresponding to one electron being ejected from the Os 3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.
Experimental optimization of directed field ionization

NASA Astrophysics Data System (ADS)

Liu, Zhimin Cheryl; Gregoric, Vincent C.; Carroll, Thomas J.; Noel, Michael W.

2017-04-01

The state distribution of an ensemble of Rydberg atoms is commonly measured using selective field ionization. The resulting time resolved ionization signal from a single energy eigenstate tends to spread out due to the multiple avoided Stark level crossings atoms must traverse on the way to ionization. The shape of the ionization signal can be modified by adding a perturbation field to the main field ramp. Here, we present experimental results of the manipulation of the ionization signal using a genetic algorithm. We address how both the genetic algorithm and the experimental parameters were adjusted to achieve an optimized result. This work was supported by the National Science Foundation under Grants No. 1607335 and No. 1607377.
Threshold photoionization and density functional theory studies of bimetallic-carbide nanocrystals and fragments: Ta3ZrC(y) (y = 0-4).

PubMed

Dryza, V; Metha, G F

2009-06-28

Gas-phase bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta(3)ZrC(y) (y = 0-4) clusters are examined by photoionization efficiency spectroscopy to extract experimental ionization energies (IEs). The IE trend for the Ta(3)ZrC(y) cluster series is reasonably similar to that of the Ta(4)C(y) cluster series [V. Dryza et al., J. Phys. Chem. A 109, 11180 (2005)], although the IE reductions upon carbon addition are greater for the former. Complementary density functional theory calculations are performed for the various isomers constructed by attaching carbon atoms to the different faces of the tetrahedral Ta(3)Zr cluster. The good agreement between the experimental IE trend and that calculated for these isomers support a 2x2x2 face centered cubic nanocrystal structure for Ta(4)ZrC(4) and nanocrystal fragment structures for the smaller clusters.
Photoinduced intermolecular dynamics and subsequent fragmentation in VUV-ionized acetamide clusters

NASA Astrophysics Data System (ADS)

Tarkanovskaja, Marta; Kooser, Kuno; Levola, Helena; Nõmmiste, Ergo; Kukk, Edwin

2016-09-01

Photofragmentation of small gas-phase acetamide clusters (CH3CONH2)n (n ≤ 10) produced by a supersonic expansion source has been studied using time-of-flight ion mass spectroscopy combined with tunable vacuum-ultraviolet (VUV) synchrotron radiation. Fragmentation channels of acetamide clusters under VUV photoionization resulting in protonated and ammoniated clusters formation were identified with the discussion about the preceding intramolecular rearrangements. Acetamide-2,2,2-d3 clusters were also studied in an experiment with a gas discharge lamp as a VUV light source; comparison with the main experiment gave insights into the mechanism of formation of protonated acetamide clusters, indicating that proton transfer from amino group plays a dominant role in that process. Geometry of the acetamide dimer was discussed and the most stable arrangement was concluded to be achieved when subunits of the dimer are connected via two N—H⋯O —C hydrogen bonds. Also, the influence of the photon energy on the stability of the clusters and their fragmentation channels has been examined.
Mass spectrometric identification of intermediates in the O2-driven [4Fe-4S] to [2Fe-2S] cluster conversion in FNR

PubMed Central

Crack, Jason C.; Thomson, Andrew J.

2017-01-01

The iron-sulfur cluster containing protein Fumarate and Nitrate Reduction (FNR) is the master regulator for the switch between anaerobic and aerobic respiration in Escherichia coli and many other bacteria. The [4Fe-4S] cluster functions as the sensory module, undergoing reaction with O2 that leads to conversion to a [2Fe-2S] form with loss of high-affinity DNA binding. Here, we report studies of the FNR cluster conversion reaction using time-resolved electrospray ionization mass spectrometry. The data provide insight into the reaction, permitting the detection of cluster conversion intermediates and products, including a [3Fe-3S] cluster and persulfide-coordinated [2Fe-2S] clusters [[2Fe-2S](S)n, where n = 1 or 2]. Analysis of kinetic data revealed a branched mechanism in which cluster sulfide oxidation occurs in parallel with cluster conversion and not as a subsequent, secondary reaction to generate [2Fe-2S](S)n species. This methodology shows great potential for broad application to studies of protein cofactor–small molecule interactions. PMID:28373574
Unrepaired clustered DNA lesions induce chromosome breakage in human cells

PubMed Central

Asaithamby, Aroumougame; Hu, Burong; Chen, David J.

2011-01-01

Clustered DNA damage induced by ionizing radiation is refractory to repair and may trigger carcinogenic events for reasons that are not well understood. Here, we used an in situ method to directly monitor induction and repair of clustered DNA lesions in individual cells. We showed, consistent with biophysical modeling, that the kinetics of loss of clustered DNA lesions was substantially compromised in human fibroblasts. The unique spatial distribution of different types of DNA lesions within the clustered damages, but not the physical location of these damages within the subnuclear domains, determined the cellular ability to repair the damage. We then examined checkpoint arrest mechanisms and yield of gross chromosomal aberrations. Induction of nonrepairable clustered damage affected only G2 accumulation but not the early G2/M checkpoint. Further, cells that were released from the G2/M checkpoint with unrepaired clustered damage manifested a spectrum of chromosome aberrations in mitosis. Difficulties associated with clustered DNA damage repair and checkpoint release before the completion of clustered DNA damage repair appear to promote genome instability that may lead to carcinogenesis. PMID:21527720
From clusters to bulk: A relativistic density functional investigation on a series of gold clusters Aun, n=6,…,147

NASA Astrophysics Data System (ADS)

Häberlen, Oliver D.; Chung, Sai-Cheong; Stener, Mauro; Rösch, Notker

1997-03-01

A series of gold clusters spanning the size range from Au6 through Au147 (with diameters from 0.7 to 1.7 nm) in icosahedral, octahedral, and cuboctahedral structure has been theoretically investigated by means of a scalar relativistic all-electron density functional method. One of the main objectives of this work was to analyze the convergence of cluster properties toward the corresponding bulk metal values and to compare the results obtained for the local density approximation (LDA) to those for a generalized gradient approximation (GGA) to the exchange-correlation functional. The average gold-gold distance in the clusters increases with their nuclearity and correlates essentially linearly with the average coordination number in the clusters. An extrapolation to the bulk coordination of 12 yields a gold-gold distance of 289 pm in LDA, very close to the experimental bulk value of 288 pm, while the extrapolated GGA gold-gold distance is 297 pm. The cluster cohesive energy varies linearly with the inverse of the calculated cluster radius, indicating that the surface-to-volume ratio is the primary determinant of the convergence of this quantity toward bulk. The extrapolated LDA binding energy per atom, 4.7 eV, overestimates the experimental bulk value of 3.8 eV, while the GGA value, 3.2 eV, underestimates the experiment by almost the same amount. The calculated ionization potentials and electron affinities of the clusters may be related to the metallic droplet model, although deviations due to the electronic shell structure are noticeable. The GGA extrapolation to bulk values yields 4.8 and 4.9 eV for the ionization potential and the electron affinity, respectively, remarkably close to the experimental polycrystalline work function of bulk gold, 5.1 eV. Gold 4f core level binding energies were calculated for sites with bulk coordination and for different surface sites. The core level shifts for the surface sites are all positive and distinguish among the corner, edge, and face-centered sites; sites in the first subsurface layer show still small positive shifts.
Improving liquid chromatography-mass spectrometry sensitivity using a subambient pressure ionization with nanoelectrospray (SPIN) interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Keqi; Page, Jason S.; Marginean, Ioan

2011-04-22

In this work the Subambient Pressure Ionization with Nanoelectrospray (SPIN) ion source and interface which operates at ~15-30 Torr is demonstrated to be compatible with gradient reversed-phase liquid chromatography-MS applications, exemplified here with the analysis of complex samples (a protein tryptic digest and a whole cell lysate). A low liquid chromatographic flow rate (100-400 nL/min) allowed stable electrospray to be established while avoiding electrical breakdown. Efforts to increase the operating pressure of the SPIN source relative to previously reported designs prevented solvent freezing and enhanced charged cluster/droplet desolvation. A 5-12-fold improvement in sensitivity relative to a conventional atmospheric pressure nanoelectrospraymore » ionization (ESI) source was obtained for detected peptides.« less
Unexpected methyl migrations of ethanol dimer under synchrotron VUV radiation

NASA Astrophysics Data System (ADS)

Xiao, Weizhan; Hu, Yongjun; Li, Weixing; Guan, Jiwen; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

2015-01-01

While methyl transfer is well known to occur in the enzyme- and metal-catalyzed reactions, the methyl transfer in the metal-free organic molecules induced by the photon ionization has been less concerned. Herein, vacuum ultraviolet single photon ionization and dissociation of ethanol dimer are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical methods. Besides the protonated clusters cation (C2H5OH) ṡ H+ (m/z = 47) and the β-carbon-carbon bond cleavage fragment CH2O ṡ (C2H5OH)H+ (m/z = 77), the measured mass spectra revealed that a new fragment (C2H5OH) ṡ (CH3)+ (m/z = 61) appeared at the photon energy of 12.1 and 15.0 eV, where the neutral dimer could be vertically ionized to higher ionic state. Thereafter, the generated carbonium ions are followed by a Wagner-Meerwein rearrangement and then dissociate to produce this new fragment, which is considered to generate after surmounting a few barriers including intra- and inter-molecular methyl migrations by the aid of theoretical calculations. The appearance energy of this new fragment is measured as 11.55 ± 0.05 eV by scanning photoionization efficiency curve. While the signal intensity of fragment m/z = 61 starts to increase, the fragments m/z = 47 and 77 tend to slowly incline around 11.55 eV photon energy. This suggests that the additional fragment channels other than (C2H5OH) ṡ H+ and CH2O ṡ (C2H5OH)H+ have also been opened, which consume some dimer cations. The present report provides a clear description of the photoionization and dissociation processes of the ethanol dimer in the range of the photon energy 12-15 eV.
Single electron dynamics in a Hall thruster electromagnetic field profile

NASA Astrophysics Data System (ADS)

Marini, Samuel; Pakter, Renato

2017-05-01

In this work, the single electron dynamics in a simplified three dimensional Hall thruster model is studied. Using Hamiltonian formalism and the concept of limiting curves, one is able to determine confinement conditions for the electron in the acceleration channel. It is shown that as a given parameter of the electromagnetic field is changed, the particle trajectory may transit from regular to chaotic without affecting the confinement, which allows one to make a detailed analysis of the role played by the chaos. The ionization volume is also computed, which measures the probability of an electron to ionize background gas atoms. It is found that there is a great correlation between chaos and increased effective ionization volume. This indicates that a complex dynamical behavior may improve the device efficiency by augmenting the ionization capability of each electron, requiring an overall lower electron current.
The study of ionization by electron impact of a substance simulating spent nuclear fuel components

NASA Astrophysics Data System (ADS)

Antonov, N. N.; Bochkarev, E. I.; Gavrikov, A. V.; Samokhin, A. A.; Smirnov, V. P.

2015-11-01

Plasma sources of model substances are necessary to solve problems associated with development of the spent nuclear fuel (SNF) plasma separation method. Lead was chosen to simulate kinetic and dynamic properties of the heavy SNF components. In this paper we present the results of a study of a lead vapor discharge with a lead concentration of 1012-1013 cm-3. Ionization was carried out by an electron beam (with energy of up to 500 eV per electron) inside a centimeter gap between planar electrodes. The discharge was numerically modeled using the hydrodynamic and single-particle approximation. Current-voltage characteristics and single ionization efficiency were obtained as functions of the vapors concentration and thermoelectric current. An ion current of hundreds of microamperes at the ionization efficiency near tenths of a percent was experimentally obtained. These results are in good agreement with our model.
IR signature of the photoionization-induced hydrophobic-->hydrophilic site switching in phenol-Arn clusters

NASA Astrophysics Data System (ADS)

Ishiuchi, Shun-ichi; Sakai, Makoto; Tsuchida, Yuji; Takeda, Akihiro; Kawashima, Yasutake; Dopfer, Otto; Müller-Dethlefs, Klaus; Fujii, Masaaki

2007-09-01

IR spectra of phenol-Arn (PhOH-Arn) clusters with n =1 and 2 were measured in the neutral and cationic electronic ground states in order to determine the preferential intermolecular ligand binding motifs, hydrogen bonding (hydrophilic interaction) versus π bonding (hydrophobic interaction). Analysis of the vibrational frequencies of the OH stretching motion, νOH, observed in nanosecond IR spectra demonstrates that neutral PhOH-Ar and PhOH -Ar2 as well as cationic PhOH +-Ar have a π-bound structure, in which the Ar atoms bind to the aromatic ring. In contrast, the PhOH +-Ar2 cluster cation is concluded to have a H-bound structure, in which one Ar atom is hydrogen-bonded to the OH group. This π →H binding site switching induced by ionization was directly monitored in real time by picosecond time-resolved IR spectroscopy. The π-bound νOH band is observed just after the ionization and disappears simultaneously with the appearance of the H-bound νOH band. The analysis of the picosecond IR spectra demonstrates that (i) the π →H site switching is an elementary reaction with a time constant of ˜7ps, which is roughly independent of the available internal vibrational energy, (ii) the barrier for the isomerization reaction is rather low(<100cm-1), (iii) both the position and the width of the H-bound νOH band change with the delay time, and the time evolution of these spectral changes can be rationalized by intracluster vibrational energy redistribution occurring after the site switching. The observation of the ionization-induced switch from π bonding to H bonding in the PhOH +-Ar2 cation corresponds to the first manifestation of an intermolecular isomerization reaction in a charged aggregate.
Bipolar H II regions produced by cloud-cloud collisions

NASA Astrophysics Data System (ADS)

Whitworth, Anthony; Lomax, Oliver; Balfour, Scott; Mège, Pierre; Zavagno, Annie; Deharveng, Lise

2018-05-01

We suggest that bipolar H II regions may be the aftermath of collisions between clouds. Such a collision will produce a shock-compressed layer, and a star cluster can then condense out of the dense gas near the center of the layer. If the clouds are sufficiently massive, the star cluster is likely to contain at least one massive star, which emits ionizing radiation, and excites an H II region, which then expands, sweeping up the surrounding neutral gas. Once most of the matter in the clouds has accreted onto the layer, expansion of the H II region meets little resistance in directions perpendicular to the midplane of the layer, and so it expands rapidly to produce two lobes of ionized gas, one on each side of the layer. Conversely, in directions parallel to the midplane of the layer, expansion of the H II region stalls due to the ram pressure of the gas that continues to fall towards the star cluster from the outer parts of the layer; a ring of dense neutral gas builds up around the waist of the bipolar H II region, and may spawn a second generation of star formation. We present a dimensionless model for the flow of ionized gas in a bipolar H II region created according to the above scenario, and predict the characteristics of the resulting free-free continuum and recombination-line emission. This dimensionless model can be scaled to the physical parameters of any particular system. Our intention is that these predictions will be useful in testing the scenario outlined above, and thereby providing indirect support for the role of cloud-cloud collisions in triggering star formation.
Ion time-of-flight determinations of doubly to singly ionized mercury ion ratios from a mercury electron bombardment discharge

NASA Technical Reports Server (NTRS)

Sellen, J. M., Jr.; Kemp, R. F.; Hall, D. F.

1973-01-01

Doubly to singly charged mercury ion ratios in electron bombardment ion thruster exhaust beams have been determined as functions of bombardment discharge potential, thrust beam current, thrust beam radial position, acceleration-deceleration voltage ratio, and propellant utilization fraction. A mathematical model for two-step ionization processes has been derived, and calculated ion ratios are compared to observed ratios. Production of Hg(++) appears to result primarily from sequential ionization of Hg(+) in the discharge. Experimental and analytical results are presented, and design, construction, and operation features of an electrostatic deflection ion time-of-flight analyzer for the determination of the above-mentioned ratios are reviewed.
An atomic model for neutral and singly ionized uranium

NASA Technical Reports Server (NTRS)

Maceda, E. L.; Miley, G. H.

1979-01-01

A model for the atomic levels above ground state in neutral, U(0), and singly ionized, U(+), uranium is described based on identified atomic transitions. Some 168 states in U(0) and 95 in U(+) are found. A total of 1581 atomic transitions are used to complete this process. Also discussed are the atomic inverse lifetimes and line widths for the radiative transitions as well as the electron collisional cross sections.
Preliminary Experimental Measurements for a Gallium Electromagnetic (GEM) Thruster

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Burton, Rodney L.; Glumac, Nick G.; Polzin, Kurt A.

2007-01-01

A low-energy gallium plasma source is used to perform a spatially and temporally broad spectroscopic survey in the 220-520 nm range. Neutral, singly, and doubly ionized gallium are present in a 20 J, 1.8 kA (peak) arc discharge operating with a central cathode. When the polarity of the inner electrode is reversed the discharge current and arc voltage waveforms remain similar. Utilizing a central anode configuration, multiple Ga lines are absent in the 270-340 nm range. In addition, neutral and singly ionized Fe spectral lines are present, indicating erosion of the outer electrode. With graphite present on the insulator to facilitate breakdown, line emission from the gallium species is further reduced and while emissions from singly and doubly ionized carbon atoms and molecular carbon (C2) radicals are observed. These data indicate that a significant fraction of energy is shifted from the gallium and deposited into the various carbon species.
High-energy accelerator for beams of heavy ions

DOEpatents

Martin, Ronald L.; Arnold, Richard C.

1978-01-01

An apparatus for accelerating heavy ions to high energies and directing the accelerated ions at a target comprises a source of singly ionized heavy ions of an element or compound of greater than 100 atomic mass units, means for accelerating the heavy ions, a storage ring for accumulating the accelerated heavy ions and switching means for switching the heavy ions from the storage ring to strike a target substantially simultaneously from a plurality of directions. In a particular embodiment the heavy ion that is accelerated is singly ionized hydrogen iodide. After acceleration, if the beam is of molecular ions, the ions are dissociated to leave an accelerated singly ionized atomic ion in a beam. Extraction of the beam may be accomplished by stripping all the electrons from the atomic ion to switch the beam from the storage ring by bending it in magnetic field of the storage ring.
The escape of Lyman photons from a young starburst: the case of Haro11†

NASA Astrophysics Data System (ADS)

Hayes, Matthew; Östlin, Göran; Atek, Hakim; Kunth, Daniel; Mas-Hesse, J. Miguel; Leitherer, Claus; Jiménez-Bailón, Elena; Adamo, Angela

2007-12-01

Lyman α (Lyα) is one of the dominant tools used to probe the star-forming galaxy population at high redshift (z). However, astrophysical interpretations of data drawn from Lyα alone hinge on the Lyα escape fraction which, due to the complex radiative transport, may vary greatly. Here, we map the Lyα emission from the local luminous blue compact galaxy Haro11, a known emitter of Lyα and the only known candidate for low-z Lyman continuum emission. To aid in the interpretation, we perform a detailed ultraviolet and optical multiwavelength analysis and model the stellar population, dust distribution, ionizing photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the neutral hydrogen column density. The Lyα morphology is found to be largely symmetric around a single young star-forming knot and is strongly decoupled from other wavelengths. From general surface photometry, only very slight correlation is found between Lyα and Hα, E(B - V), and the age of the stellar population. Only around the central Lyα bright cluster do we find the Lyα/Hα ratio at values predicted by the recombination theory. The total Lyα escape fraction is found to be just 3 per cent. We compute that ~90 per cent of the Lyα photons that escape do so after undergoing multiple resonance scattering events, masking their point of origin. This leads to a largely symmetric distribution and, by increasing the distance that photons must travel to escape, decreases the escape probability significantly. While dust must ultimately be responsible for the destruction of Lyα, it plays a little role in governing the observed morphology, which is regulated more by interstellar medium kinematics and geometry. We find tentative evidence for local Lyα equivalent width in the immediate vicinity of star clusters being a function of cluster age, consistent with hydrodynamic studies. We estimate the intrinsic production of ionizing photons and put further constraints of ~9 per cent on the escaping fraction of photons at 900Å. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-26555. These observations are associated with programmes #GO9470 and #GO10575. Based on observations made with ESO Telescopes at the La Silla Observatories under programme ID 073.B-0785. ‡ E-mail: matthew@astro.su.se
Interatomic Coulombic decay cascades in multiply excited neon clusters

PubMed Central

Nagaya, K.; Iablonskyi, D.; Golubev, N. V.; Matsunami, K.; Fukuzawa, H.; Motomura, K.; Nishiyama, T.; Sakai, T.; Tachibana, T.; Mondal, S.; Wada, S.; Prince, K. C.; Callegari, C.; Miron, C.; Saito, N.; Yabashi, M.; Demekhin, Ph. V.; Cederbaum, L. S.; Kuleff, A. I.; Yao, M.; Ueda, K.

2016-01-01

In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation. PMID:27917867
Method and apparatus for confinement of ions in the presence of a neutral gas

DOEpatents

Peurrung, Anthony J.; Barlow, Stephan E.

1999-01-01

The present invention is an apparatus and method for combining ions with a neutral gas and flowing the mixture with a radial flow component through a magnetic field so that the weakly ionized gas is confined by the neutral gas. When the weakly ionized gas is present in sufficient density, a weakly ionized non-neutral plasma is formed that may be trapped in accordance with the present invention. Applications for a weakly ionized non-neutral plasma exploit the trap's ability to store and manipulate ionic species in the presence of neutral gas. The trap may be connected to a mass spectrometer thereby permitting species identification after a fixed period of time. Delicate and/or heavy particles such as clusters may be held and studied in a "gentle" environment. In addition, the trap can provide a relatively intense, low-energy source of a particular ion species for surface implantation or molecular chemistry. Finally, a long trap may permit spectroscopy of unprecedented accuracy to be performed on ionic species.

Onset of carbon-carbon bonding in Ta(5)C(y) (y = 0-6) clusters: a threshold photoionization and density functional theory study.

PubMed

Dryza, Viktoras; Alvino, Jason F; Metha, Gregory F

2010-04-01

We have used photoionization efficiency spectroscopy to determine ionization energies (IEs) of the gas-phase tantalum-carbide clusters Ta(5)C(y) (y = 0-6). The structures of the clusters observed in the experiment are assigned by comparing the experimental IEs with those of candidate isomers, calculated by density functional theory. Two competing geometries of the underlying Ta(5) cluster are found to be present in the assigned Ta(5)C(y) structures; either a "prolate" or "distorted oblate" trigonal bipyramid geometry. The onset of carbon-carbon bonding in the Ta(5)C(y) series is proposed to occur at y = 6, with the structure of Ta(5)C(6) containing two molecular C(2) units.
Effects of Ion Atomic Number on Single-Event Gate Rupture (SEGR) Susceptibility of Power MOSFETs

NASA Technical Reports Server (NTRS)

Lauenstein, J.-M.; Goldsman, N.; Liu, S.; Titus, J.; Ladbury, R. L.; Kim, H. S.; Phan, A. M.; Zafrani, M.; Sherman, P.

2011-01-01

The relative importance of heavy-ion interaction with the oxide, charge ionized in the epilayer, and charge ionized in the drain substrate, on the bias for SEGR failure is experimentally investigated.
Multiple hydrogen bonds. Mass spectra of hydrogen bonded heterodimers. A comparison of ESI- and REMPI-ReTOF-MS.

PubMed

Taubitz, Jörg; Lüning, Ulrich; Grotemeyer, Jürgen

2004-11-07

Resonance enhanced multi-photon ionization-reflectron time of flight mass spectrometry is the analytical method of choice to observe hydrogen bonded supramolecules in the gas phase when protonation of basic centers competes with cluster formation.
Studying Townsend and glow modes in an atmospheric-pressure DBD using mass spectrometry

NASA Astrophysics Data System (ADS)

McKay, Kirsty; Donaghy, David; He, Feng; Bradley, James W.

2018-01-01

Ambient molecular beam mass spectrometry has been employed to examine the effects of the mode of operation and the excitation waveform on the ionic content of a helium-based atmospheric-pressure parallel plate dielectric barrier discharge. By applying 10 kHz microsecond voltage pulses with a nanosecond rise times and 10 kHz sinusoidal voltage waveforms, distinctly different glow and Townsend modes were produced, respectively. Results showed a significant difference in the dominant ion species between the two modes. In the Townsend mode, molecular oxygen ions, atomic oxygen anions and nitric oxide anions are the most abundant species, however, in the glow mode water clusters ions and hydrated nitric oxygen anions dominate. Several hypotheses are put forward to explain these differences, including low electron densities and energies in the Townsend mode, more efficient ionization of water molecules through penning ionization and charge exchange with other species in glow mode, and large temperature gradients due to the pulsed nature of the glow mode, leading to more favorable conditions for cluster formation.
Influence of oxygen on the chemical stage of radiobiological mechanism

NASA Astrophysics Data System (ADS)

Barilla, Jiří; Lokajíček, Miloš V.; Pisaková, Hana; Simr, Pavel

2016-07-01

The simulation of the chemical stage of radiobiological mechanism may be very helpful in studying the radiobiological effect of ionizing radiation when the water radical clusters formed by the densely ionizing ends of primary or secondary charged particle may form DSBs damaging DNA molecules in living cells. It is possible to study not only the efficiency of individual radicals but also the influence of other species or radiomodifiers (mainly oxygen) being present in water medium during irradiation. The mathematical model based on Continuous Petri nets (proposed by us recently) will be described. It makes it possible to analyze two main processes running at the same time: chemical radical reactions and the diffusion of radical clusters formed during energy transfer. One may study the time change of radical concentrations due to the chemical reactions running during diffusion process. Some orientation results concerning the efficiency of individual radicals in DSB formation (in the case of Co60 radiation) will be presented; the influence of oxygen present in water medium during irradiation will be shown, too.
Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.

PubMed

Hua, Lei; Wu, Qinghao; Hou, Keyong; Cui, Huapeng; Chen, Ping; Wang, Weiguo; Li, Jinghua; Li, Haiyang

2011-07-01

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.
Single hair analysis of small molecules using MALDI-triple quadrupole MS imaging and LC-MS/MS: investigations on opportunities and pitfalls.

PubMed

Poetzsch, Michael; Steuer, Andrea E; Roemmelt, Andreas T; Baumgartner, Markus R; Kraemer, Thomas

2014-12-02

Single hair analysis normally requires extensive sample preparation microscale protocols including time-consuming steps like segmentation and extraction. Matrix assisted laser desorption and ionization mass spectrometric imaging (MALDI-MSI) was shown to be an alternative tool in single hair analysis, but still, questions remain. Therefore, an investigation of MALDI-MSI in single hair analysis concerning the extraction process, usage of internal standard (IS), and influences on the ionization processes were systematically investigated to enable the reliable application to hair analysis. Furthermore, single dose detection, quantitative correlation to a single hair, and hair strand LC-MS/MS results were performed, and the performance was compared to LC-MS/MS single hair monitoring. The MALDI process was shown to be independent from natural hair color and not influenced by the presence of melanin. Ionization was shown to be reproducible along and in between different hair samples. MALDI image intensities in single hair and hair snippets showed good semiquantitative correlation to zolpidem hair concentrations obtained from validated routine LC-MS/MS methods. MALDI-MSI is superior to LC-MS/MS analysis when a fast, easy, and cheap sample preparation is necessary, whereas LC-MS/MS showed higher sensitivity with the ability of single dose detection for zolpidem. MALDI-MSI and LC-MS/MS segmental single hair analysis showed good correlation, and both are suitable for consumption monitoring of drugs of abuse with a high time resolution.
Strong-field ionization of Li and Be: a time-dependent density functional theory with self-interaction correction

NASA Astrophysics Data System (ADS)

Telnov, Dmitry A.; Heslar, John T.; Chu, Shih-I.

2011-11-01

In the framework of the time-dependent density functional theory, we have performed 3D calculations of multiphoton ionization of Li and Be atoms by strong near-infrared laser fields. The results for the intensity-dependent probabilities of single and double ionization are presented. We make use of the time-dependent Krieger-Li-Iafrate exchange-correlation potential with self-interaction correction (TD-KLI-SIC). Such a potential possesses an integer discontinuity which improves description of the ionization process. However, we have found that the discontinuity of the TD-KLI-SIC potential is not sufficient to reproduce characteristic feature of double ionization.
Strong-field ionization of H{sub 2} from ultraviolet to near-infrared wavelengths: Photoelectron energy and angular identifications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilbois, Timo; Helm, Hanspeter

2011-11-15

Strong-field ionization of molecular hydrogen is studied at wavelengths ranging from 300 to 800 nm using pulses of 100-fs duration. We find that over this wide wavelength range, from nominally 4-photon to 11-photon ionization, resonance features dominate the ionization probability at intensities below 10{sup 14} W/cm{sup 2}. Photoelectron momentum maps recorded by an imaging spectrometer are analyzed to identify the wavelength-dependent ionization pathways in single ionization of molecular hydrogen. A number of models, some empirical, which are appropriate for a quantitative interpretation of the spectra and the ionization yield are introduced. A near-absolute comparison of measured ionization yields at 398more » nm is made with the predictions based on a numerical solution [Y. V. Vanne and A. Saenz, Phys. Rev. A 79, 023421 (2009)] of the time-dependent Schroedinger equation for two correlated electrons.« less
Assessing the sensitivity of benzene cluster cation chemical ionization mass spectrometry toward a wide array of biogenic volatile organic compounds

NASA Astrophysics Data System (ADS)

Lavi, Avi; Vermeuel, Michael; Novak, Gordon; Bertram, Timothy

2017-04-01

Chemical ionization mass spectrometry is a real-time, sensitive and selective measurement technique for the detection of volatile organic compounds (VOCs). The benefits of CIMS technology make it highly suitable for field measurements that requires fast (10Hz and higher) response rates, such as the study of surface-atmosphere exchange processes by the eddy covariance method. The use of benzene cluster cations as a regent ion was previously demonstrated as a sensitive and selective method for the detection of select biogenic VOCs (e.g. isoprene, monoterpenes and sesquiterpenes) [Kim et al., 2016; Leibrock and Huey, 2000]. Quantitative analysis of atmospheric trace gases necessitates calibration for each analyte as a function of atmospheric conditions. We describe a custom designed calibration system, based on liquid evaporation, for determination of the sensitivity of the benzene-CIMS to a wide range of organic compounds at atmospherically relevant mixing ratios (<200 ppt). We report on the effect of atmospheric water vapor and oxygen concentrations on instrument response for isoprene and a wide range of monoterpenes and sesquiterpenes. To gain mechanistic insight into the ion-molecule reactions and the role of water vapor and oxygen, we compare our measured sensitivities with a computational analysis of the charge distribution between the analyte, reagent ion and water molecules in the gas phase. These parameters provide insight on the ionization mechanism and provide parameters for quantification of organic molecules measured during field campaigns. References Kim, M. J., M. C. Zoerb, N. R. Campbell, K. J. Zimmermann, B. W. Blomquist, B. J. Huebert, and T. H. Bertram (2016), Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds, Atmos Meas Tech, 9(4), 1473-1484, doi:10.5194/amt-9-1473-2016. Leibrock, E., and L. G. Huey (2000), Ion chemistry for the detection of isoprene and other volatile organic compounds in ambient air, Geophys Res Lett, 27(12), 1719-1722, doi:Doi 10.1029/1999gl010804.
Fluctuations in microwave background radiation due to secondary ionization of the intergalactic gas in the universe

NASA Technical Reports Server (NTRS)

Sunyayev, R. A.

1979-01-01

Secondary heating and ionization of the intergalactic gas at redshifts z approximately 10-30 could lead to the large optical depth of the Universe for Thomson scattering and could smooth the primordial fluctuations formed at z approximately 1500. It is shown that the gas motions connected with the large scale density perturbations at z approximately 10-15 must lead to the generation of secondary fluctuations of microwave background. The contribution of the rich clusters of galaxies and young galaxies to the fluctuations of microwave background is also estimated.
Quantum mechanical calculations related to ionization and charge transfer in DNA

NASA Astrophysics Data System (ADS)

Cauët, E.; Valiev, M.; Weare, J. H.; Liévin, J.

2012-07-01

Ionization and charge migration in DNA play crucial roles in mechanisms of DNA damage caused by ionizing radiation, oxidizing agents and photo-irradiation. Therefore, an evaluation of the ionization properties of the DNA bases is central to the full interpretation and understanding of the elementary reactive processes that occur at the molecular level during the initial exposure and afterwards. Ab initio quantum mechanical (QM) methods have been successful in providing highly accurate evaluations of key parameters, such as ionization energies (IE) of DNA bases. Hence, in this study, we performed high-level QM calculations to characterize the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration between DNA bases. In particular, we examined the IEs of guanine, the most easily oxidized base, isolated and embedded in base clusters, and investigated the mechanism of charge migration over two and three stacked guanines. The IE of guanine in the human telomere sequence has also been evaluated. We report a simple molecular orbital analysis to explain how modifications in the base sequence are expected to change the efficiency of the sequence as a hole trap. Finally, the application of a hybrid approach combining quantum mechanics with molecular mechanics brings an interesting discussion as to how the native aqueous DNA environment affects the IE threshold of nucleobases.
Complex DNA Damage: A Route to Radiation-Induced Genomic Instability and Carcinogenesis

PubMed Central

Mavragani, Ifigeneia V.; Nikitaki, Zacharenia; Souli, Maria P.; Aziz, Asef; Nowsheen, Somaira; Aziz, Khaled; Rogakou, Emmy

2017-01-01

Cellular effects of ionizing radiation (IR) are of great variety and level, but they are mainly damaging since radiation can perturb all important components of the cell, from the membrane to the nucleus, due to alteration of different biological molecules ranging from lipids to proteins or DNA. Regarding DNA damage, which is the main focus of this review, as well as its repair, all current knowledge indicates that IR-induced DNA damage is always more complex than the corresponding endogenous damage resulting from endogenous oxidative stress. Specifically, it is expected that IR will create clusters of damage comprised of a diversity of DNA lesions like double strand breaks (DSBs), single strand breaks (SSBs) and base lesions within a short DNA region of up to 15–20 bp. Recent data from our groups and others support two main notions, that these damaged clusters are: (1) repair resistant, increasing genomic instability (GI) and malignant transformation and (2) can be considered as persistent “danger” signals promoting chronic inflammation and immune response, causing detrimental effects to the organism (like radiation toxicity). Last but not least, the paradigm shift for the role of radiation-induced systemic effects is also incorporated in this picture of IR-effects and consequences of complex DNA damage induction and its erroneous repair. PMID:28718816
Complex DNA Damage: A Route to Radiation-Induced Genomic Instability and Carcinogenesis.

PubMed

Mavragani, Ifigeneia V; Nikitaki, Zacharenia; Souli, Maria P; Aziz, Asef; Nowsheen, Somaira; Aziz, Khaled; Rogakou, Emmy; Georgakilas, Alexandros G

2017-07-18

Cellular effects of ionizing radiation (IR) are of great variety and level, but they are mainly damaging since radiation can perturb all important components of the cell, from the membrane to the nucleus, due to alteration of different biological molecules ranging from lipids to proteins or DNA. Regarding DNA damage, which is the main focus of this review, as well as its repair, all current knowledge indicates that IR-induced DNA damage is always more complex than the corresponding endogenous damage resulting from endogenous oxidative stress. Specifically, it is expected that IR will create clusters of damage comprised of a diversity of DNA lesions like double strand breaks (DSBs), single strand breaks (SSBs) and base lesions within a short DNA region of up to 15-20 bp. Recent data from our groups and others support two main notions, that these damaged clusters are: (1) repair resistant, increasing genomic instability (GI) and malignant transformation and (2) can be considered as persistent "danger" signals promoting chronic inflammation and immune response, causing detrimental effects to the organism (like radiation toxicity). Last but not least, the paradigm shift for the role of radiation-induced systemic effects is also incorporated in this picture of IR-effects and consequences of complex DNA damage induction and its erroneous repair.
Imaging and spectroscopic observations of a strange elliptical bubble in the northern arm of the spiral galaxy NGC 6946

NASA Astrophysics Data System (ADS)

Efremov, Yuri N.; Moiseev, Alexei V.

2016-09-01

NGC 6946, known as the Fireworks galaxy because of its high supernova rate and high star formation, is embedded in a very extended H I halo. Its northern spiral arm is well detached from the galactic main body. We found that this arm contains a large (˜300 pc in size) Red Ellipse, named according to a strong contamination of the Hα emission line on its optical images. The ellipse is accompanied by a short parallel arc and a few others still smaller and less regular; a bright star cluster is seen inside these features. The complicated combination of arcs seems to be unique; it is only a bit similar to some SNRs. However, the long-slit spectral data obtained with the Russian 6-m telescope did not confirm the origin of the nebula as a result of a single SN outburst. The emission-line spectrum corresponds to the photoionization by young hot stars with a small contribution of shock ionization. The most likely explanation of the Red Ellipse is a superbubble created by a collective feedback of massive stars in the star cluster located in the NE side of the Red Ellipse. However, the very regular elliptical shape of the nebulae seems strange.
Clusters of DNA induced by ionizing radiation: formation of short DNA fragments. I. Theoretical modeling

NASA Technical Reports Server (NTRS)

Holley, W. R.; Chatterjee, A.

1996-01-01

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber comprised of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and delta rays due to knock-on collisions involving energy transfers >100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of OH, H, eaq, etc.; (2) OH attack on sugar molecules leading to strand breaks: (3) OH attack on bases; (4) direct ionization of the sugar molecules leading to strand breaks; (5) direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 bp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. The shapes of the spectra of DNA fragment lengths depend on the symmetries or approximate symmetries of the chromatin structure. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper (B. Rydberg, Radiat, Res. 145, 200-209, 1996) after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the chromatin fibers in mammalian DNA.
Redox-linked ionization of sulredoxin, an archaeal Rieske-type [2Fe-2S] protein from Sulfolobus sp. strain 7.

PubMed

Iwasaki, T; Imai, T; Urushiyama, A; Oshima, T

1996-11-01

"Sulredoxin" of Sulfolobus sp. strain 7 is an archaeal soluble Rieske-type [2Fe-2S] protein and was initially characterized by several spectroscopic techniques (Iwasaki, T., Isogai, T., Iizuka, T. , and Oshima, T. (1995) J. Bacteriol. 177, 2576-2582). It appears to have tightly linked ionization affecting the redox properties of the protein, which is characteristic of the Rieske FeS proteins found as part of the respiratory chain. Sulredoxin had an Em(low pH) value of +188 +/- 9 mV, and the slope of pH dependence of the midpoint redox potential indicated two ionization equilibria in the oxidized form with pKa(ox1) of 6.23 +/- 0.22 and pKa(ox2) of 8.57 +/- 0.20. The absorption, CD, and resonance Raman spectra of oxidized sulredoxin are consistent with the proposed St2FeSb2Fe[N(His)]t2 core structure, and deprotonation of one of the two putative coordinated histidine imidazoles, having the pKa(ox2) of 8.57 +/- 0.20, causes a decrease in the midpoint redox potential, the change in the optical and CD spectra, and the appearance of a new Raman transition at 278 cm-1, without major structural rearrangement of the [2Fe-2S] cluster as well as the overall protein conformation. The redox-linked ionization of sulredoxin is also contributed by local changes involving another ionizable group having the pKa(ox1) of 6.23 +/- 0. 22, which is probably attributed to a certain positively charged amino acid residue that may not be a ligand by itself but located very close to the cluster. We suggest that sulredoxin provides a new tractable model of the membrane-bound homologue of the respiratory chain, the Rieske FeS proteins of the cytochrome bc1-b6f complexes.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Konstantopoulos, I. S.; Charlton, J. C.; Gronwall, C.

The environment where galaxies are found heavily influences their evolution. Close groupings, like the ones in the cores of galaxy clusters or compact groups, evolve in ways far more dramatic than their isolated counterparts. We have conducted a multi-wavelength study of Hickson Compact Group 7 (HCG 7), consisting of four giant galaxies: three spirals and one lenticular. We use Hubble Space Telescope (HST) imaging to identify and characterize the young and old star cluster populations. We find young massive clusters (YMCs) mostly in the three spirals, while the lenticular features a large, unimodal population of globular clusters (GCs) but nomore » detectable clusters with ages less than a few Gyr. The spatial and approximate age distributions of the {approx}300 YMCs and {approx}150 GCs thus hint at a regular star formation history in the group over a Hubble time. While at first glance the HST data show the galaxies as undisturbed, our deep ground-based, wide-field imaging that extends the HST coverage reveals faint signatures of stellar material in the intragroup medium (IGM). We do not, however, detect the IGM in H I or Chandra X-ray observations, signatures that would be expected to arise from major mergers. Despite this fact, we find that the H I gas content of the individual galaxies and the group as a whole are a third of the expected abundance. The appearance of quiescence is challenged by spectroscopy that reveals an intense ionization continuum in one galaxy nucleus, and post-burst characteristics in another. Our spectroscopic survey of dwarf galaxy members yields a single dwarf elliptical galaxy in an apparent stellar tidal feature. Based on all this information, we suggest an evolutionary scenario for HCG 7, whereby the galaxies convert most of their available gas into stars without the influence of major mergers and ultimately result in a dry merger. As the conditions governing compact groups are reminiscent of galaxies at intermediate redshift, we propose that HCGs are appropriate for studying galaxy evolution at z {approx} 1-2.« less
Loss of cellular transformation efficiency induced by DNA irradiation with low-energy (10 eV) electrons.

PubMed

Kouass Sahbani, Saloua; Sanche, Leon; Cloutier, Pierre; Bass, Andrew D; Hunting, Darel J

2014-11-20

Low energy electrons (LEEs) of energies less than 20 eV are generated in large quantities by ionizing radiation in biological matter. While LEEs are known to induce single (SSBs) and double strand breaks (DSBs) in DNA, their ability to inactivate cells by inducing nonreparable lethal damage has not yet been demonstrated. Here we observe the effect of LEEs on the functionality of DNA, by measuring the efficiency of transforming Escherichia coli with a [pGEM-3Zf (-)] plasmid irradiated with 10 eV electrons. Highly ordered DNA films were prepared on pyrolitic graphite by molecular self-assembly using 1,3-diaminopropane ions (Dap(2+)). The uniformity of these films permits the inactivation of approximately 50% of the plasmids compared to <10% using previous methods, which is sufficient for the subsequent determination of their functionality. Upon LEE irradiation, the fraction of functional plasmids decreased exponentially with increasing electron fluence, while LEE-induced isolated base damage, frank DSB, and non DSB-cluster damage increased linearly with fluence. While DSBs can be toxic, their levels were too low to explain the loss of plasmid functionality observed upon LEE irradiation. Similarly, non-DSB cluster damage, revealed by transforming cluster damage into DSBs by digestion with repair enzymes, also occurred relatively infrequently. The exact nature of the lethal damage remains unknown, but it is probably a form of compact cluster damage in which the lesions are too close to be revealed by purified repair enzymes. In addition, this damage is either not repaired or is misrepaired by E. coli, since it results in plasmid inactivation, when they contain an average of three lesions. Comparison with previous results from a similar experiment performed with γ-irradiated plasmids indicates that the type of clustered DNA lesions, created directly on cellular DNA by LEEs, may be more difficult to repair than those produced by other species from radiolysis.
Xeroderma Pigmentosum Group A Suppresses Mutagenesis Caused by Clustered Oxidative DNA Adducts in the Human Genome.

PubMed

Sassa, Akira; Kamoshita, Nagisa; Kanemaru, Yuki; Honma, Masamitsu; Yasui, Manabu

2015-01-01

Clustered DNA damage is defined as multiple sites of DNA damage within one or two helical turns of the duplex DNA. This complex damage is often formed by exposure of the genome to ionizing radiation and is difficult to repair. The mutagenic potential and repair mechanisms of clustered DNA damage in human cells remain to be elucidated. In this study, we investigated the involvement of nucleotide excision repair (NER) in clustered oxidative DNA adducts. To identify the in vivo protective roles of NER, we established a human cell line lacking the NER gene xeroderma pigmentosum group A (XPA). XPA knockout (KO) cells were generated from TSCER122 cells derived from the human lymphoblastoid TK6 cell line. To analyze the mutagenic events in DNA adducts in vivo, we previously employed a system of tracing DNA adducts in the targeted mutagenesis (TATAM), in which DNA adducts were site-specifically introduced into intron 4 of thymidine kinase genes. Using the TATAM system, one or two tandem 7,8-dihydro-8-oxoguanine (8-oxoG) adducts were introduced into the genomes of TSCER122 or XPA KO cells. In XPA KO cells, the proportion of mutants induced by a single 8-oxoG (7.6%) was comparable with that in TSCER122 cells (8.1%). In contrast, the lack of XPA significantly enhanced the mutant proportion of tandem 8-oxoG in the transcribed strand (12%) compared with that in TSCER122 cells (7.4%) but not in the non-transcribed strand (12% and 11% in XPA KO and TSCER122 cells, respectively). By sequencing the tandem 8-oxoG-integrated loci in the transcribed strand, we found that the proportion of tandem mutations was markedly increased in XPA KO cells. These results indicate that NER is involved in repairing clustered DNA adducts in the transcribed strand in vivo.

Xeroderma Pigmentosum Group A Suppresses Mutagenesis Caused by Clustered Oxidative DNA Adducts in the Human Genome

PubMed Central

Sassa, Akira; Kamoshita, Nagisa; Kanemaru, Yuki; Honma, Masamitsu; Yasui, Manabu

2015-01-01

Clustered DNA damage is defined as multiple sites of DNA damage within one or two helical turns of the duplex DNA. This complex damage is often formed by exposure of the genome to ionizing radiation and is difficult to repair. The mutagenic potential and repair mechanisms of clustered DNA damage in human cells remain to be elucidated. In this study, we investigated the involvement of nucleotide excision repair (NER) in clustered oxidative DNA adducts. To identify the in vivo protective roles of NER, we established a human cell line lacking the NER gene xeroderma pigmentosum group A (XPA). XPA knockout (KO) cells were generated from TSCER122 cells derived from the human lymphoblastoid TK6 cell line. To analyze the mutagenic events in DNA adducts in vivo, we previously employed a system of tracing DNA adducts in the targeted mutagenesis (TATAM), in which DNA adducts were site-specifically introduced into intron 4 of thymidine kinase genes. Using the TATAM system, one or two tandem 7,8-dihydro-8-oxoguanine (8-oxoG) adducts were introduced into the genomes of TSCER122 or XPA KO cells. In XPA KO cells, the proportion of mutants induced by a single 8-oxoG (7.6%) was comparable with that in TSCER122 cells (8.1%). In contrast, the lack of XPA significantly enhanced the mutant proportion of tandem 8-oxoG in the transcribed strand (12%) compared with that in TSCER122 cells (7.4%) but not in the non-transcribed strand (12% and 11% in XPA KO and TSCER122 cells, respectively). By sequencing the tandem 8-oxoG-integrated loci in the transcribed strand, we found that the proportion of tandem mutations was markedly increased in XPA KO cells. These results indicate that NER is involved in repairing clustered DNA adducts in the transcribed strand in vivo. PMID:26559182
Ionization Electron Signal Processing in Single Phase LArTPCs II. Data/Simulation Comparison and Performance in MicroBooNE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, C.; et al.

The single-phase liquid argon time projection chamber (LArTPC) provides a large amount of detailed information in the form of fine-grained drifted ionization charge from particle traces. To fully utilize this information, the deposited charge must be accurately extracted from the raw digitized waveforms via a robust signal processing chain. Enabled by the ultra-low noise levels associated with cryogenic electronics in the MicroBooNE detector, the precise extraction of ionization charge from the induction wire planes in a single-phase LArTPC is qualitatively demonstrated on MicroBooNE data with event display images, and quantitatively demonstrated via waveform-level and track-level metrics. Improved performance of inductionmore » plane calorimetry is demonstrated through the agreement of extracted ionization charge measurements across different wire planes for various event topologies. In addition to the comprehensive waveform-level comparison of data and simulation, a calibration of the cryogenic electronics response is presented and solutions to various MicroBooNE-specific TPC issues are discussed. This work presents an important improvement in LArTPC signal processing, the foundation of reconstruction and therefore physics analyses in MicroBooNE.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Hargreaves, L. R.; Colyer, C.; Stevenson, M. A.

A number of previous studies have suggested the possibility of two-center interference effects in the single ionization of diatomic molecules such as H{sub 2} and N{sub 2}. While interference effects have been successfully observed in the ionization of H{sub 2}, to date evidence for interference in N{sub 2} ionization has yet to be conclusively demonstrated. This study presents triply differential cross sections for electron impact ionization of N{sub 2}, measured using the (e,2e) technique. The data are probed for signatures of two-center interference effects. Evidence for interference manifesting in the cross sections is observed.
Double ionization in R -matrix theory using a two-electron outer region

NASA Astrophysics Data System (ADS)

Wragg, Jack; Parker, J. S.; van der Hart, H. W.

2015-08-01

We have developed a two-electron outer region for use within R -matrix theory to describe double ionization processes. The capability of this method is demonstrated for single-photon double ionization of He in the photon energy region between 80 and 180 eV. The cross sections are in agreement with established data. The extended R -matrix with time dependence method also provides information on higher-order processes, as demonstrated by the identification of signatures for sequential double ionization processes involving an intermediate He+ state with n =2 .
Lattice Boltzmann method for weakly ionized isothermal plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Huayu; Ki, Hyungson

2007-12-15

In this paper, a lattice Boltzmann method (LBM) for weakly ionized isothermal plasmas is presented by introducing a rescaling scheme for the Boltzmann transport equation. Without using this rescaling, we found that the nondimensional relaxation time used in the LBM is too large and the LBM does not produce physically realistic results. The developed model was applied to the electrostatic wave problem and the diffusion process of singly ionized helium plasmas with a 1-3% degree of ionization under an electric field. The obtained results agree well with theoretical values.
Infrared Multiple Photon Dissociation Spectroscopy Of Metal Cluster-Adducts

NASA Astrophysics Data System (ADS)

Cox, D. M.; Kaldor, A.; Zakin, M. R.

1987-01-01

Recent development of the laser vaporization technique combined with mass-selective detection has made possible new studies of the fundamental chemical and physical properties of unsupported transition metal clusters as a function of the number of constituent atoms. A variety of experimental techniques have been developed in our laboratory to measure ionization threshold energies, magnetic moments, and gas phase reactivity of clusters. However, studies have so far been unable to determine the cluster structure or the chemical state of chemisorbed species on gas phase clusters. The application of infrared multiple photon dissociation IRMPD to obtain the IR absorption properties of metal cluster-adsorbate species in a molecular beam is described here. Specifically using a high power, pulsed CO2 laser as the infrared source, the IRMPD spectrum for methanol chemisorbed on small iron clusters is measured as a function of the number of both iron atoms and methanols in the complex for different methanol isotopes. Both the feasibility and potential utility of IRMPD for characterizing metal cluster-adsorbate interactions are demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only upon the availability of appropriate high power infrared sources.
"Trampoline" ejection of organic molecules from graphene and graphite via keV cluster ions impacts.

PubMed

Verkhoturov, Stanislav V; Gołuński, Mikołaj; Verkhoturov, Dmitriy S; Geng, Sheng; Postawa, Zbigniew; Schweikert, Emile A

2018-04-14

We present the data on ejection of molecules and emission of molecular ions caused by single impacts of 50 keV C 60 2+ on a molecular layer of deuterated phenylalanine (D8Phe) deposited on free standing, 2-layer graphene. The projectile impacts on the graphene side stimulate the abundant ejection of intact molecules and the emission of molecular ions in the transmission direction. To gain insight into the mechanism of ejection, Molecular Dynamic simulations were performed. It was found that the projectile penetrates the thin layer of graphene, partially depositing the projectile's kinetic energy, and molecules are ejected from the hot area around the hole that is made by the projectile. The yield, Y, of negative ions of deprotonated phenylalanine, (D8Phe-H) - , emitted in the transmission direction is 0.1 ions per projectile impact. To characterize the ejection and ionization of molecules, we have performed the experiments on emission of (D8Phe-H) - from the surface of bulk D8Phe (Y = 0.13) and from the single molecular layer of D8Phe deposited on bulk pyrolytic graphite (Y = 0.15). We show that, despite the similar yields of molecular ions, the scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. The projectile impact on the graphene-D8Phe sample stimulates the collective radial movement of analyte atoms, which compresses the D8Phe layer radially from the hole. At the same time, this compression bends and stretches the graphene membrane around the hole thus accumulating potential energy. The accumulated potential energy is transformed into the kinetic energy of correlated movement upward for membrane atoms, thus the membrane acts as a trampoline for the molecules. The ejected molecules are effectively ionized; the ionization probability is ∼30× higher compared to that obtained for the bulk D8Phe target. The proposed mechanism of ionization involves tunneling of electrons from the vibrationally excited area around the hole to the molecules. Another proposed mechanism is a direct proton transfer exchange, which is suitable for a bulk target: ions of molecular fragments (i.e., CN - ) generated in the impact area interact with intact molecules from the rim of this area. There is a direct proton exchange process for the system D8Phe molecule + CN - .
"Trampoline" ejection of organic molecules from graphene and graphite via keV cluster ions impacts

NASA Astrophysics Data System (ADS)

Verkhoturov, Stanislav V.; Gołuński, Mikołaj; Verkhoturov, Dmitriy S.; Geng, Sheng; Postawa, Zbigniew; Schweikert, Emile A.

2018-04-01

We present the data on ejection of molecules and emission of molecular ions caused by single impacts of 50 keV C602+ on a molecular layer of deuterated phenylalanine (D8Phe) deposited on free standing, 2-layer graphene. The projectile impacts on the graphene side stimulate the abundant ejection of intact molecules and the emission of molecular ions in the transmission direction. To gain insight into the mechanism of ejection, Molecular Dynamic simulations were performed. It was found that the projectile penetrates the thin layer of graphene, partially depositing the projectile's kinetic energy, and molecules are ejected from the hot area around the hole that is made by the projectile. The yield, Y, of negative ions of deprotonated phenylalanine, (D8Phe-H)-, emitted in the transmission direction is 0.1 ions per projectile impact. To characterize the ejection and ionization of molecules, we have performed the experiments on emission of (D8Phe-H)- from the surface of bulk D8Phe (Y = 0.13) and from the single molecular layer of D8Phe deposited on bulk pyrolytic graphite (Y = 0.15). We show that, despite the similar yields of molecular ions, the scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. The projectile impact on the graphene-D8Phe sample stimulates the collective radial movement of analyte atoms, which compresses the D8Phe layer radially from the hole. At the same time, this compression bends and stretches the graphene membrane around the hole thus accumulating potential energy. The accumulated potential energy is transformed into the kinetic energy of correlated movement upward for membrane atoms, thus the membrane acts as a trampoline for the molecules. The ejected molecules are effectively ionized; the ionization probability is ˜30× higher compared to that obtained for the bulk D8Phe target. The proposed mechanism of ionization involves tunneling of electrons from the vibrationally excited area around the hole to the molecules. Another proposed mechanism is a direct proton transfer exchange, which is suitable for a bulk target: ions of molecular fragments (i.e., CN-) generated in the impact area interact with intact molecules from the rim of this area. There is a direct proton exchange process for the system D8Phe molecule + CN-.
Ionization Potentials for Isoelectronic Series.

ERIC Educational Resources Information Center

Agmon, Noam

1988-01-01

Presents a quantitative treatment of ionization potentials of isoelectronic atoms. By looking at the single-electron view of calculating the total energy of an atom, trends in the screening and effective quantum number parameters are examined. Approaches the question of determining electron affinities. (CW)
Singlet-paired coupled cluster theory for open shells

NASA Astrophysics Data System (ADS)

Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

2016-06-01

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.
Carbon atom and cluster sputtering under low-energy noble gas plasma bombardment

NASA Astrophysics Data System (ADS)

Oyarzabal, E.; Doerner, R. P.; Shimada, M.; Tynan, G. R.

2008-08-01

Exit-angle resolved carbon atom and cluster (C2 and C3) sputtering yields are measured during different noble gas (Xe, Kr, Ar, Ne, and He) ion bombardments from a plasma, for low incident energies (75-225 eV). A quadrupole mass spectrometer (QMS) is used to detect the fraction of sputtered neutrals that is ionized in the plasma and to obtain the angular distribution by changing the angle between the target normal and the QMS aperture. A one-dimensional Monte Carlo code is used to simulate the interaction of the plasma and the sputtered particles in the region between the sample and the QMS. The effective elastic scattering cross sections of C, C2, and C3 with the different bombarding gas neutrals are obtained by varying the distance between the sample and the QMS and by performing a best fit of the simulation results to the experimental results. The total sputtering yield (C+C2+C3) for each bombarding gas is obtained from weight-loss measurements and the sputtering yield for C, C2, and C3 is then calculated from the integration of the measured angular distribution, taking into account the scattering and ionization of the sputtered particles between the sample and the QMS. We observe undercosine angular distributions of the sputtered atoms and clusters for all the studied bombarding gases and a clear decrease of the atom to cluster (C2 and C3) sputtering ratio as the incident ion mass increases, changing from a carbon atom preferential erosion for the lower incident ion masses (He, Ne, and Ar) to a cluster preferential erosion for the higher incident ion masses (Kr and Xe).
Effects of Ion Atomic Number on Single-Event Gate Rupture (SEGR) Susceptibility of Power MOSFETs

NASA Technical Reports Server (NTRS)

Lauenstein, Jean-Marie; Goldsman, Neil; Liu, Sandra; Titus, Jeffrey L.; Ladbury, Raymond L.; Kim, Hak S.; Phan, Anthony M.; LaBel, Kenneth A.; Zafrani, Max; Sherman, Phillip

2012-01-01

The relative importance of heavy-ion interaction with the oxide, charge ionized in the epilayer, and charge ionized in the drain substrate, on the bias for SEGR failure in vertical power MOSFETs is experimentally investigated. The results indicate that both the charge ionized in the epilayer and the ion atomic number are important parameters of SEGR failure. Implications on SEGR hardness assurance are discussed.
Development of a Portable Single Photon Ionization-Photoelectron Ionization Time-of-Flight Mass Spectrometer

PubMed Central

Huang, Yunguang; Li, Jinxu; Tang, Bin; Zhu, Liping; Hou, Keyong; Li, Haiyang

2015-01-01

A vacuum ultraviolet lamp based single photon ionization- (SPI-) photoelectron ionization (PEI) portable reflecting time-of-flight mass spectrometer (TOFMS) was designed for online monitoring gas samples. It has a dual mode ionization source: SPI for analyte with ionization energy (IE) below 10.6 eV and PEI for IE higher than 10.6 eV. Two kinds of sampling inlets, a capillary inlet and a membrane inlet, are utilized for high concentration and trace volatile organic compounds, respectively. A mass resolution of 1100 at m/z 64 has been obtained with a total size of 40 × 31 × 29 cm, the weight is 27 kg, and the power consumption is only 70 W. A mixture of benzene, toluene, and xylene (BTX), SO2, and discharging products of SF6 were used to test its performance, and the result showed that the limit of quantitation for BTX is as low as 5 ppbv (S/N = 10 : 1) with linear dynamic ranges greater than four orders of magnitude. The portable TOFMS was also evaluated by analyzing volatile organic compounds from wine and decomposition products of SF6 inside of a gas-insulated switchgear. PMID:26587023
An explicitly spin-free compact open-shell coupled cluster theory using a multireference combinatoric exponential ansatz: formal development and pilot applications.

PubMed

Datta, Dipayan; Mukherjee, Debashis

2009-07-28

In this paper, we present a comprehensive account of an explicitly spin-free compact state-universal multireference coupled cluster (CC) formalism for computing the state energies of simple open-shell systems, e.g., doublets and biradicals, where the target open-shell states can be described by a few configuration state functions spanning a model space. The cluster operators in this formalism are defined in terms of the spin-free unitary generators with respect to the common closed-shell component of all model functions (core) as vacuum. The spin-free cluster operators are either closed-shell-like n hole-n particle excitations (denoted by T(mu)) or involve excitations from the doubly occupied (nonvalence) orbitals to the singly occupied (valence) orbitals (denoted by S(e)(mu)). In addition, there are cluster operators with exchange spectator scatterings involving the valence orbitals (denoted by S(re)(mu)). We propose a new multireference cluster expansion ansatz for the wave operator with the above generally noncommuting cluster operators which essentially has the same physical content as the Jeziorski-Monkhorst ansatz with the commuting cluster operators defined in the spin-orbital basis. The T(mu) operators in our ansatz are taken to commute with all other operators, while the S(e)(mu) and S(re)(mu) operators are allowed to contract among themselves through the spectator valence orbitals. An important innovation of this ansatz is the choice of an appropriate automorphic factor accompanying each contracted composite of cluster operators in order to ensure that each distinct excitation generated by this composite appears only once in the wave operator. The resulting CC equations consist of two types of terms: a "direct" term and a "normalization" term containing the effective Hamiltonian operator. It is emphasized that the direct term is almost quartic in the cluster amplitudes, barring only a handful of terms and termination of the normalization term depends on the valence rank of the effective Hamiltonian operator and the excitation rank of the cluster operators at which the theory is truncated. Illustrative applications are presented by computing the state energies of neutral doublet radicals and doublet molecular cations and ionization energies of neutral molecules and comparing our results with the other open-shell CC theories, benchmark full CI results (when available) in the same basis, and the experimental results. Highly encouraging results show the efficacy of the method.
The NGC 281 west cluster. I. Star formation in photoevaporating clumps.

NASA Astrophysics Data System (ADS)

Megeath, S. T.; Wilson, T. L.

1997-09-01

The NGC281 West molecular cloud is an excellent test case for studying star formation in the clumpy interface between a \\hii region and a giant molecular cloud. We present here a study based on new high resolution radio and near-infrared data. Using the IRAM 30-meter telescope, we have mapped the interface in the \\cotwo, \\coone, and \\cs transitions with FWHP beamwidths <= 22''. We have imaged the same region with the VLA in the 20, 6 and 2 cm continuum bands to obtain complementary maps of the ionized gas distribution with angular resolutions <= 13''. In addition, we have obtained near-infrared J and K'-band images to detect young stars in the interface. The 30-meter data shows the molecular gas is concentrated into three clumps with masses of 570, > 210, and 300 \\msun and average volume densities of 1.4, >1, and 2 x 10(4) \\cm. We detect \\cs emission in two of the clumps, indicating peak densities in excess of 5x 10(5) \\cm are attained in the clumps. A comparison of the \\co line data with the 20 cm continuum image suggests that the molecular clumps are being photoevaporated through their direct exposure to the UV radiation from neighboring OB stars. The luminosity and extent of the observed 20 cm emission is in good agreement with theoretical predictions. We use models of photoevaporative flows to estimate the pressure exerted on the clumps by the ionized gas and find that it exceeds the internal, turbulent pressure of the clumps by a factor of a 2.5. Although a pressure equilibrium is not excluded given the uncertainties inherent in determining the pressures of the ionized and molecular gases, our best estimates of the clumps and flow parameters favor the the existence of low velocity shocks (1.5 \\kms) in the clumps. The clumps exhibit broad, non-gaussian lineshapes and complex kinematical structures suggestive of shocks. Further evidence for shocks is found in a comparison of position-velocity diagrams with published numerical simulations of imploding spherical clumps. We discuss the possibility that the knots of \\cs emission may trace gas compressed by converging shock waves. The K'-band observations show a rich cluster of primarily low mass stars in the \\hii/molecular interface, which we argue is divided into two distinct sub-clusters. We associate one sub-cluster with the two clumps nearest the OB stars, and the second sub-cluster with the third clump. The two clumps nearest the OB stars contain an embedded population, suggesting that star formation is ongoing. We discuss the impact photoevaporation is having on star formation in these two clumps. We find that photoevaporation is dispersing the molecular gas from which the cluster is forming and estimate that the molecular gas will be completely evaporated in 5 Myr. Deep K'-band imaging of the two clumps show that the stars are detected primarily on the sides of the clumps facing the OB stars and in the adjoining \\hii region. We examine three explanations for this asymmetry: displacement of the clump centers from the cluster center by the acceleration of the molecular gas through photoevaporation (i.e. the rocket effect), unveiling of young, embedded stars by ionization-shock fronts, and the triggered formation of stars by shocks advancing into the clumps. If shock compression is indeed ongoing in the clumps, then we argue that there is a good case for shock triggered star formation.
Ultra-performance liquid chromatography/tandem mass spectrometric quantification of structurally diverse drug mixtures using an ESI-APCI multimode ionization source.

PubMed

Yu, Kate; Di, Li; Kerns, Edward; Li, Susan Q; Alden, Peter; Plumb, Robert S

2007-01-01

We report in this paper an ultra-performance liquid chromatography/tandem mass spectrometric (UPLC(R)/MS/MS) method utilizing an ESI-APCI multimode ionization source to quantify structurally diverse analytes. Eight commercial drugs were used as test compounds. Each LC injection was completed in 1 min using a UPLC system coupled with MS/MS multiple reaction monitoring (MRM) detection. Results from three separate sets of experiments are reported. In the first set of experiments, the eight test compounds were analyzed as a single mixture. The mass spectrometer was switching rapidly among four ionization modes (ESI+, ESI-, APCI-, and APCI+) during an LC run. Approximately 8-10 data points were collected across each LC peak. This was insufficient for a quantitative analysis. In the second set of experiments, four compounds were analyzed as a single mixture. The mass spectrometer was switching rapidly among four ionization modes during an LC run. Approximately 15 data points were obtained for each LC peak. Quantification results were obtained with a limit of detection (LOD) as low as 0.01 ng/mL. For the third set of experiments, the eight test compounds were analyzed as a batch. During each LC injection, a single compound was analyzed. The mass spectrometer was detecting at a particular ionization mode during each LC injection. More than 20 data points were obtained for each LC peak. Quantification results were also obtained. This single-compound analytical method was applied to a microsomal stability test. Compared with a typical HPLC method currently used for the microsomal stability test, the injection-to-injection cycle time was reduced to 1.5 min (UPLC method) from 3.5 min (HPLC method). The microsome stability results were comparable with those obtained by traditional HPLC/MS/MS.
Three-body Coulomb problem probed by mapping the Bethe surface in ionizing ion-atom collisions.

PubMed

Moshammer, R; Perumal, A; Schulz, M; Rodríguez, V D; Kollmus, H; Mann, R; Hagmann, S; Ullrich, J

2001-11-26

The three-body Coulomb problem has been explored in kinematically complete experiments on single ionization of helium by 100 MeV/u C(6+) and 3.6 MeV/u Au(53+) impact. Low-energy electron emission ( E(e)<150 eV) as a function of the projectile deflection theta(p) (momentum transfer), i.e., the Bethe surface [15], has been mapped with Delta theta(p)+/-25 nanoradian resolution at extremely large perturbations ( 3.6 MeV/u Au(53+)) where single ionization occurs at impact parameters of typically 10 times the He K-shell radius. The experimental data are not in agreement with state-of-the-art continuum distorted wave-eikonal initial state theory.
Comparison of experimental and theoretical triple differential cross sections for the single ionization of C O2 (1 πg ) by electron impact

NASA Astrophysics Data System (ADS)

Ozer, Zehra N.; Ali, Esam; Dogan, Mevlut; Yavuz, Murat; Alwan, Osman; Naja, Adnan; Chuluunbaatar, Ochbadrakh; Joulakian, Boghos B.; Ning, Chuan-Gang; Colgan, James; Madison, Don

2016-06-01

Experimental and theoretical triple differential cross sections for intermediate-energy (250 eV) electron-impact single ionization of the CO2 are presented for three fixed projectile scattering angles. Results are presented for ionization of the outermost 1 πg molecular orbital of C O2 in a coplanar asymmetric geometry. The experimental data are compared to predictions from the three-center Coulomb continuum approximation for triatomic targets, and the molecular three-body distorted wave (M3DW) model. It is observed that while both theories are in reasonable qualitative agreement with experiment, the M3DW is in the best overall agreement with experiment.
SC3 - consensus clustering of single-cell RNA-Seq data

PubMed Central

Kiselev, Vladimir Yu.; Kirschner, Kristina; Schaub, Michael T.; Andrews, Tallulah; Yiu, Andrew; Chandra, Tamir; Natarajan, Kedar N; Reik, Wolf; Barahona, Mauricio; Green, Anthony R; Hemberg, Martin

2017-01-01

Single-cell RNA-seq (scRNA-seq) enables a quantitative cell-type characterisation based on global transcriptome profiles. We present Single-Cell Consensus Clustering (SC3), a user-friendly tool for unsupervised clustering which achieves high accuracy and robustness by combining multiple clustering solutions through a consensus approach. We demonstrate that SC3 is capable of identifying subclones based on the transcriptomes from neoplastic cells collected from patients. PMID:28346451
Direct mass spectrometric peptide profiling and sequencing of nervous tissues to identify peptides involved in male copulatory behavior in Lymnaea stagnalis

NASA Astrophysics Data System (ADS)

Dreisewerd, Klaus; Kingston, Robert; Geraerts, Wijnand P. M.; Li, Ka Wan

1997-12-01

Matrix-assisted laser desorption mass spectrometry (MALDI-MS) was performed directly on a small piece of single penis nerve of the pond snail, Lymnaea stagnalis, and reveals the presence of complex peptide profiles, including many hitherto undescribed peptides. Two of the peptides have molecular weights corresponding exactly to the previously described Lymnaea small cardioactive peptides (SCP) A and B. We confirmed their identities by structural characterization of the two peptides directly from a single penis nerve by matrix-assisted laser desorption ionization high-energy collision tandem MS analysis. MALDI-MS of nervous tissues also demonstrates that a cluster of central neurons, which send their axons to the penis nerve, contain the two peptides. As the penis nerve is the nerve that innervates the penis complex, we propose that the peptides are involved in the modulation of male copulatory processes. A bioassay indeed showed that the peptides increase the contraction frequency of the vas deference in a dose-dependent manner. The results demonstrate the potential of direct MALDI-MS analysis of nervous tissue to complement or substitute conventional biochemical techniques for the identification and localization of neuropeptides.

Röntgen spheres around active stars

NASA Astrophysics Data System (ADS)

Locci, Daniele; Cecchi-Pestellini, Cesare; Micela, Giuseppina; Ciaravella, Angela; Aresu, Giambattista

2018-01-01

X-rays are an important ingredient of the radiation environment of a variety of stars of different spectral types and age. We have modelled the X-ray transfer and energy deposition into a gas with solar composition, through an accurate description of the electron cascade following the history of the primary photoelectron energy deposition. We test and validate this description studying the possible formation of regions in which X-rays are the major ionization channel. Such regions, called Röntgen spheres may have considerable importance in the chemical and physical evolution of the gas embedding the emitting star. Around massive stars the concept of Röntgen sphere appears to be of limited use, as the formation of extended volumes with relevant levels of ionization is efficient just in a narrow range of gas volume densities. In clouds embedding low-mass pre-main-sequence stars significant volumes of gas are affected by ionization levels exceeding largely the cosmic-ray background ionization. In clusters arising in regions of vigorous star formation X-rays create an ionization network pervading densely the interstellar medium, and providing a natural feedback mechanism, which may affect planet and star formation processes.
Fast Atom Ionization in Strong Electromagnetic Radiation

NASA Astrophysics Data System (ADS)

Apostol, M.

2018-05-01

The Goeppert-Mayer and Kramers-Henneberger transformations are examined for bound charges placed in electromagnetic radiation in the non-relativistic approximation. The consistent inclusion of the interaction with the radiation field provides the time evolution of the wavefunction with both structural interaction (which ensures the bound state) and electromagnetic interaction. It is shown that in a short time after switching on the high-intensity radiation the bound charges are set free. In these conditions, a statistical criterion is used to estimate the rate of atom ionization. The results correspond to a sudden application of the electromagnetic interaction, in contrast with the well-known ionization probability obtained by quasi-classical tunneling through classically unavailable non-stationary states, or other equivalent methods, where the interaction is introduced adiabatically. For low-intensity radiation the charges oscillate and emit higher-order harmonics, the charge configuration is re-arranged and the process is resumed. Tunneling ionization may appear in these circumstances. Extension of the approach to other applications involving radiation-induced charge emission from bound states is discussed, like ionization of molecules, atomic clusters or proton emission from atomic nuclei. Also, results for a static electric field are included.
Single cyanide-bridged Mo(W)/S/Cu cluster-based coordination polymers: Reactant- and stoichiometry-dependent syntheses, effective photocatalytic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jinfang, E-mail: zjf260@jiangnan.edu.cn; Wang, Chao; Wang, Yinlin

2015-11-15

The systematic study on the reaction variables affecting single cyanide-bridged Mo(W)/S/Cu cluster-based coordination polymers (CPs) is firstly demonstrated. Five anionic single cyanide-bridged Mo(W)/S/Cu cluster-based CPs {[Pr_4N][WS_4Cu_3(CN)_2]}{sub n} (1), {[Pr_4N][WS_4Cu_4(CN)_3]}{sub n} (2), {[Pr_4N][WOS_3Cu_3(CN)_2]}{sub n} (3), {[Bu_4N][WOS_3Cu_3(CN)_2]}{sub n} (4) and {[Bu_4N][MoOS_3Cu_3(CN)_2]}{sub n} (5) were prepared by varying the molar ratios of the starting materials, and the specific cations, cluster building blocks and central metal atoms in the cluster building blocks. 1 possesses an anionic 3D diamondoid framework constructed from 4-connected T-shaped clusters [WS{sub 4}Cu{sub 3}]{sup +} and single CN{sup −} bridges. 2 is fabricated from 6-connected planar ‘open’ clusters [WS{sub 4}Cu{sub 4}]{supmore » 2+} and single CN{sup −} bridges, forming an anionic 3D architecture with an “ACS” topology. 3 and 4 exhibit novel anionic 2-D double-layer networks, both constructed from nest-shaped clusters [WOS{sub 3}Cu{sub 3}]{sup +} linked by single CN{sup −} bridges, but containing the different cations [Pr{sub 4}N]{sup +} and [Bu{sub 4}N]{sup +}, respectively. 5 is constructed from nest-shaped clusters [MoOS{sub 3}Cu{sub 3}]{sup +} and single CN{sup −} bridges, with an anionic 3D diamondoid framework. The anionic frameworks of 1-5, all sustained by single CN{sup −} bridges, are non-interpenetrating and exhibit huge potential void volumes. Employing differing molar ratios of the reactants and varying the cluster building blocks resulted in differing single cyanide-bridged Mo(W)/S/Cu cluster-based CPs, while replacing the cation ([Pr{sub 4}N]{sup +} vs. [Bu{sub 4}N]{sup +}) was found to have negligible impact on the nature of the architecture. Unexpectedly, replacement of the central metal atom (W vs. Mo) in the cluster building blocks had a pronounced effect on the framework. Furthermore, the photocatalytic activities of heterothiometallic cluster-based CPs were firstly explored by monitoring the photodegradation of methylene blue (MB) under visible light irradiation, which reveals that 2 exhibits effective photocatalytic properties. - Highlights: • Reaction variables affecting Mo(W)/S/Cu cluster-based CPs is firstly explored. • Replacing central metal atom had a pronounced effect on W/S/Cu cluster-based CPs. • Photocatalytic activities of Mo(W)/S/Cu cluster-based CPs are firstly investigated.« less
Evidence for formation of DNA repair centers and dose-response nonlinearity in human cells

PubMed Central

Neumaier, Teresa; Swenson, Joel; Pham, Christopher; Polyzos, Aris; Lo, Alvin T.; Yang, PoAn; Dyball, Jane; Asaithamby, Aroumougame; Chen, David J.; Bissell, Mina J.; Thalhammer, Stefan; Costes, Sylvain V.

2012-01-01

The concept of DNA “repair centers” and the meaning of radiation-induced foci (RIF) in human cells have remained controversial. RIFs are characterized by the local recruitment of DNA damage sensing proteins such as p53 binding protein (53BP1). Here, we provide strong evidence for the existence of repair centers. We used live imaging and mathematical fitting of RIF kinetics to show that RIF induction rate increases with increasing radiation dose, whereas the rate at which RIFs disappear decreases. We show that multiple DNA double-strand breaks (DSBs) 1 to 2 μm apart can rapidly cluster into repair centers. Correcting mathematically for the dose dependence of induction/resolution rates, we observe an absolute RIF yield that is surprisingly much smaller at higher doses: 15 RIF/Gy after 2 Gy exposure compared to approximately 64 RIF/Gy after 0.1 Gy. Cumulative RIF counts from time lapse of 53BP1-GFP in human breast cells confirmed these results. The standard model currently in use applies a linear scale, extrapolating cancer risk from high doses to low doses of ionizing radiation. However, our discovery of DSB clustering over such large distances casts considerable doubts on the general assumption that risk to ionizing radiation is proportional to dose, and instead provides a mechanism that could more accurately address risk dose dependency of ionizing radiation. PMID:22184222
A New Method Using Single-Particle Mass Spectrometry Data to Distinguish Mineral Dust and Biological Aerosols

NASA Astrophysics Data System (ADS)

Al-Mashat, H.; Kristensen, L.; Sultana, C. M.; Prather, K. A.

2016-12-01

The ability to distinguish types of particles present within a cloud is important for determining accurate inputs to climate models. The chemical composition of particles within cloud liquid droplets and ice crystals can have a significant impact on the timing, location, and amount of precipitation that falls. Precipitation efficiency is increased by the presence of ice crystals in clouds, and both mineral dust and biological aerosols have been shown to be effective ice nucleating particles (INPs) in the atmosphere. A current challenge in aerosol science is distinguishing mineral dust and biological material in the analysis of real-time, ambient, single-particle mass spectral data. Single-particle mass spectrometers are capable of measuring the size-resolved chemical composition of individual atmospheric particles. However, there is no consistent analytical method for distinguishing dust and biological aerosols. Sampling and characterization of control samples (i.e. of known identity) of mineral dust and bacteria were performed by the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) as part of the Fifth Ice Nucleation (FIN01) Workshop at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility in Karlsruhe, Germany. Using data collected by the ATOFMS of control samples, a new metric has been developed to classify single particles as dust or biological independent of spectral cluster analysis. This method, involving the use of a ratio of mass spectral peak areas for organic nitrogen and silicates, is easily reproducible and does not rely on extensive knowledge of particle chemistry or the ionization characteristics of mass spectrometers. This represents a step toward rapidly distinguishing particle types responsible for ice nucleation activity during real-time sampling in clouds. The ability to distinguish types of particles present within a cloud is important for determining accurate inputs to climate models. The chemical composition of particles within cloud liquid droplets and ice crystals can have a significant impact on the timing, location, and amount of precipitation that falls. Precipitation efficiency is increased by the presence of ice crystals in clouds, and both mineral dust and biological aerosols have been shown to be effective ice nucleating particles (INPs) in the atmosphere. A current challenge in aerosol science is distinguishing mineral dust and biological material in the analysis of real-time, ambient, single-particle mass spectral data. Single-particle mass spectrometers are capable of measuring the size-resolved chemical composition of individual atmospheric particles. However, there is no consistent analytical method for distinguishing dust and biological aerosols. Sampling and characterization of control samples (i.e. of known identity) of mineral dust and bacteria were performed by the Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) as part of the Fifth Ice Nucleation (FIN01) Workshop at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility in Karlsruhe, Germany. Using data collected by the ATOFMS of control samples, a new metric has been developed to classify single particles as dust or biological independent of spectral cluster analysis. This method, involving the use of a ratio of mass spectral peak areas for organic nitrogen and silicates, is easily reproducible and does not rely on extensive knowledge of particle chemistry or the ionization characteristics of mass spectrometers. This represents a step toward rapidly distinguishing particle types responsible for ice nucleation activity during real-time sampling in clouds.
Simulation of the GEM detector for BM@N experiment

NASA Astrophysics Data System (ADS)

Baranov, Dmitriy; Rogachevsky, Oleg

2017-03-01

The Gas Electron Multiplier (GEM) detector is one of the basic parts of the BM@N experiment included in the NICA project. The simulation model that takes into account features of signal generation process in an ionization GEM chamber is presented in this article. Proper parameters for the simulation were extracted from data retrieved with the help of Garfield++ (a toolkit for the detailed simulation of particle detectors). Due to this, we are able to generate clusters in layers of the micro-strip readout that correspond to clusters retrieved from a real physics experiment.
Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies

NASA Astrophysics Data System (ADS)

Vidal-García, A.; Charlot, S.; Bruzual, G.; Hubeny, I.

2017-09-01

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (∼10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.
Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhijun; Gu, Quanli; Department of Chemistry, University of Oklahoma, Norman, Oklahoma 73019

2015-07-21

4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S{sub 1}, using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D{sub 0}, using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar{sub 1} and aniline-Ar{sub 2}, which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm{sup −1} and 89 cm{sup −1} from the S{sub 1} origin bands and 83more » cm{sup −1} and 148 cm{sup −1} from the ionization potential assigned to the Ar{sub 1} and Ar{sub 2} complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm{sup −1} and 109 cm{sup −1} for the S{sub 1} origin bands, and 61 cm{sup −1} and 125 cm{sup −1} for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm{sup −1} in the D{sub 0} state, 496 ± 5 cm{sup −1} in the S{sub 1} state, and 467 ± 5 cm{sup −1} in the neutral ground state, S{sub 0}.« less
Wiggler magnetic field assisted third harmonic generation in expanding clusters

NASA Astrophysics Data System (ADS)

Vij, Shivani

2018-04-01

A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.
Thermophysics Characterization of Multiply Ionized Air Plasma Absorption of Laser Radiation

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Rhodes, Robert; Turner, Jim (Technical Monitor)

2002-01-01

The impact of multiple ionization of air plasma on the inverse Bremsstrahlung absorption of laser radiation is investigated for air breathing laser propulsion. Thermochemical properties of multiply ionized air plasma species are computed for temperatures up to 200,000 deg K, using hydrogenic approximation of the electronic partition function; And those for neutral air molecules are also updated for temperatures up to 50,000 deg K, using available literature data. Three formulas for absorption are calculated and a general formula is recommended for multiple ionization absorption calculation. The plasma composition required for absorption calculation is obtained by increasing the degree of ionization sequentially, up to quadruple ionization, with a series of thermal equilibrium computations. The calculated second ionization absorption coefficient agrees reasonably well with that of available data. The importance of multiple ionization modeling is demonstrated with the finding that area under the quadruple ionization curve of absorption is found to be twice that of single ionization. The effort of this work is beneficial to the computational plasma aerodynamics modeling of laser lightcraft performance.
Effects of the nanoplasma on the energetics of Coulomb explosion of molecular clusters in ultraintense laser fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Last, Isidore; Jortner, Joshua

We report on theoretical and computational studies of electron and nuclear energies in the Coulomb explosion of (D{sub 2}){sub n/2} clusters (n=250-33 000, cluster radius R{sub 0}=11 A-55 A) coupled to ultraintense Gaussian laser fields (laser peak intensities I{sub M}=10{sup 15}-10{sup 18} W cm{sup -2}, pulse widths {tau}=25-50 fs, and frequency {nu}=0.35 fs{sup -1}). Molecular dynamics simulations were fit by semiempirical relations for the average E{sub av} and maximal E{sub M} ion energies and for their dependence on the cluster radius (R{sub 0}) and on the laser parameters. This revealed two kinds of Coulomb explosion domains separated by the bordermore » radius R{sub 0}{sup (I)}, which marks complete cluster outer ionization and which depends on I{sub M} and {tau}, (i) the cluster vertical ionization (CVI) domain (R{sub 0}R{sub 0}{sup (I)}), which prevails at lower laser intensities over a broad region of cluster sizes (i.e., at I{sub M}=10{sup 15} W cm{sup -2}, R{sub 0}>R{sub 0}{sup (I)}=6.2 A for {tau}=25 fs, and R{sub 0}>R{sub 0}{sup (I)}=9.5 A for {tau}=50 fs). The effects of the persistent nanoplasma on Coulomb explosion in the non-CVI domain are manifested by a distinct cluster size dependence, i.e., E{sub av}{proportional_to}R{sub 0}{sup {eta}} ({eta}=0) and E{sub M}{proportional_to}R{sub 0}{sup {eta}} ({eta}=1) for R{sub 0}>(2.0-2.5)R{sub 0}{sup (I)}, and by a bimodal distribution of the ion kinetic energies. The energetics of Coulomb explosion in the non-CVI domain and its dependence (or independence) on the cluster size and laser parameters was semiquantitatively described by a cold nanoplasma model, which is based on a lychee configuration of the cluster charge, and which induces Coulomb explosion in the presence of the persistent nanoplasma. The results of our analyses are general for the cluster size dependence of the energetics of Coulomb explosion of multicharged elemental and molecular Xe{sub n}, (CH{sub 4}){sub n}, and (DI){sub n} clusters in the non-CVI domain.« less
DIMM-SC: a Dirichlet mixture model for clustering droplet-based single cell transcriptomic data.

PubMed

Sun, Zhe; Wang, Ting; Deng, Ke; Wang, Xiao-Feng; Lafyatis, Robert; Ding, Ying; Hu, Ming; Chen, Wei

2018-01-01

Single cell transcriptome sequencing (scRNA-Seq) has become a revolutionary tool to study cellular and molecular processes at single cell resolution. Among existing technologies, the recently developed droplet-based platform enables efficient parallel processing of thousands of single cells with direct counting of transcript copies using Unique Molecular Identifier (UMI). Despite the technology advances, statistical methods and computational tools are still lacking for analyzing droplet-based scRNA-Seq data. Particularly, model-based approaches for clustering large-scale single cell transcriptomic data are still under-explored. We developed DIMM-SC, a Dirichlet Mixture Model for clustering droplet-based Single Cell transcriptomic data. This approach explicitly models UMI count data from scRNA-Seq experiments and characterizes variations across different cell clusters via a Dirichlet mixture prior. We performed comprehensive simulations to evaluate DIMM-SC and compared it with existing clustering methods such as K-means, CellTree and Seurat. In addition, we analyzed public scRNA-Seq datasets with known cluster labels and in-house scRNA-Seq datasets from a study of systemic sclerosis with prior biological knowledge to benchmark and validate DIMM-SC. Both simulation studies and real data applications demonstrated that overall, DIMM-SC achieves substantially improved clustering accuracy and much lower clustering variability compared to other existing clustering methods. More importantly, as a model-based approach, DIMM-SC is able to quantify the clustering uncertainty for each single cell, facilitating rigorous statistical inference and biological interpretations, which are typically unavailable from existing clustering methods. DIMM-SC has been implemented in a user-friendly R package with a detailed tutorial available on www.pitt.edu/∼wec47/singlecell.html. wei.chen@chp.edu or hum@ccf.org. Supplementary data are available at Bioinformatics online. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com
HEAO A-2 observations of the X-ray spectra of the Centaurus and A1060 clusters of galaxies

NASA Technical Reports Server (NTRS)

Mitchell, R.; Mushotzky, R.

1980-01-01

X-ray spectral observations of two nearby low-luminosity clusters of galaxies are presented. For the Centaurus cluster an emission feature at 7.9 keV is detected at about one-third of the strength of the 6.7 keV line. This higher energy line represents K-beta emission from highly ionized iron. In addition, it is demonstrated that for neither the Centaurus nor the A1060 cluster can an isothermal model with an Fe emission line adequately fit the data. Instead, the simplest models which provide acceptable fits include a second, harder component which may be either a second exponential or a power law. The implications of the two-component nature of the continuum on the Fe abundance and the X-ray surface-brightness distribution are discussed.
Integrative analysis of signaling pathways and diseases associated with the miR-106b/25 cluster and their function study in berberine-induced multiple myeloma cells.

PubMed

Gu, Chunming; Li, Tianfu; Yin, Zhao; Chen, Shengting; Fei, Jia; Shen, Jianping; Zhang, Yuan

2017-05-01

Berberine (BBR), a traditional Chinese herbal medicine compound, has emerged as a novel class of anti-tumor agent. Our previous microRNA (miRNA) microarray demonstrated that miR-106b/25 was significantly down-regulated in BBR-treated multiple myeloma (MM) cells. Here, systematic integration showed that miR-106b/25 cluster is involved in multiple cancer-related signaling pathways and tumorigenesis. MiREnvironment database revealed that multiple environmental factors (drug, ionizing radiation, hypoxia) affected the miR-106b/25 cluster expression. By targeting the seed region in the miRNA, tiny anti-mir106b/25 cluster (t-anti-mir106b/25 cluster) significantly induced suppression in cell viability and colony formation. Western blot validated that t-anti-miR-106b/25 cluster effectively inhibited the expression of P38 MAPK and phospho-P38 MAPK in MM cells. These findings indicated the miR-106b/25 cluster functioned as oncogene and might provide a novel molecular insight into MM.
Laser separation of lithium isotopes by double resonance enhanced multiphoton ionization of Li/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balz, J.G.; Bernheim, R.A.; Gold, L.P.

1987-01-01

Multiphoton ionization spectra of /sup 7/Li/sub 2/, /sup 6/Li/sub 2/, and /sup 7/Li/sup 6/Li vapors have been measured in the 570--650 nm region using a single, low resolution, multimode cw dye laser. A number of wavelengths provide selective multiphoton ionization of one isotopic species demonstrating the possibility of efficient laser-driven isotopic separation in lithium in this wavelength region.
Two-photon spectroscopy of autoionizing states of Xe² near threshold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pratt, Stephen T.; Dehmer, Patricia M.; Dehmer, Joseph L.

1990-01-01

The two-photon ionization spectrum of Xe² in the region of the first ionization threshold is presented. Vibronic bands corresponding to at least four different autoionizing electronic states of Xe² are observed for the first time and are tentatively assigned. The observed appearance potential is significantly higher (by 415 cm-1) than the earlier single-photon ionization result (Ng, Trevor, Mahan and Lee, - J. Chem. Phys. 65 (1976) 4327).
Resonant ionization spectroscopy of autoionizing Rydberg states in cobalt and redetermination of its ionization potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yuan; Gottwald, T.; Mattolat, C.

We obtained multi-step resonance ionization spectroscopy of cobalt using a hot-cavity laser ion source and three Ti:Sapphire lasers. Furthermore, the photoionization spectra revealed members of five new autoionizing Rydberg series that originate from three different lower levels of 3d 74s5s h 4F 9/2, 3d 74s4d f 4G 11/2, and 3d 74s4d f 4H 13/2 and converge to the first four excited states of singly ionized Co. Our analyses of the Rydberg series yield 63564.689 0.036 cm -1 as the first ionization potential of Co, which is an order of magnitude more accurate than the previous estimation. Using a three-step resonancemore » ionization scheme that employs an autoinizing Rydberg state in the last transition, we obtained an overall ionization efficiency of about 18% for Co.« less
Resonant ionization spectroscopy of autoionizing Rydberg states in cobalt and redetermination of its ionization potential

DOE PAGES

Liu, Yuan; Gottwald, T.; Mattolat, C.; ...

2017-03-20

We obtained multi-step resonance ionization spectroscopy of cobalt using a hot-cavity laser ion source and three Ti:Sapphire lasers. Furthermore, the photoionization spectra revealed members of five new autoionizing Rydberg series that originate from three different lower levels of 3d 74s5s h 4F 9/2, 3d 74s4d f 4G 11/2, and 3d 74s4d f 4H 13/2 and converge to the first four excited states of singly ionized Co. Our analyses of the Rydberg series yield 63564.689 0.036 cm -1 as the first ionization potential of Co, which is an order of magnitude more accurate than the previous estimation. Using a three-step resonancemore » ionization scheme that employs an autoinizing Rydberg state in the last transition, we obtained an overall ionization efficiency of about 18% for Co.« less
Electron-Atom Ionization Calculations using Propagating Exterior Complex Scaling

NASA Astrophysics Data System (ADS)

Bartlett, Philip

2007-10-01

The exterior complex scaling method (Science 286 (1999) 2474), pioneered by Rescigno, McCurdy and coworkers, provided highly accurate ab initio solutions for electron-hydrogen collisions by directly solving the time-independent Schr"odinger equation in coordinate space. An extension of this method, propagating exterior complex scaling (PECS), was developed by Bartlett and Stelbovics (J. Phys. B 37 (2004) L69, J. Phys. B 39 (2006) R379) and has been demonstrated to provide computationally efficient and accurate calculations of ionization and scattering cross sections over a large range of energies below, above and near the ionization threshold. An overview of the PECS method for three-body collisions and the computational advantages of its propagation and iterative coupling techniques will be presented along with results of: (1) near-threshold ionization of electron-hydrogen collisions and the Wannier threshold laws, (2) scattering cross section resonances below the ionization threshold, and (3) total and differential cross sections for electron collisions with excited targets and hydrogenic ions from low through to high energies. Recently, the PECS method has been extended to solve four-body collisions using time-independent methods in coordinate space and has initially been applied to the s-wave model for electron-helium collisions. A description of the extensions made to the PECS method to facilitate these significantly more computationally demanding calculations will be given, and results will be presented for elastic, single-excitation, double-excitation, single-ionization and double-ionization collisions.
Electron and fluorescence spectra of a water molecule irradiated by an x-ray free-electron laser pulse

NASA Astrophysics Data System (ADS)

Schäfer, Julia M.; Inhester, Ludger; Son, Sang-Kil; Fink, Reinhold F.; Santra, Robin

2018-05-01

With the highly intense x-ray light generated by x-ray free-electron lasers (XFELs), molecular samples can be ionized many times in a single pulse. Here we report on a computational study of molecular spectroscopy at the high x-ray intensity provided by XFELs. Calculated photoelectron, Auger electron, and x-ray fluorescence spectra are presented for a single water molecule that reaches many electronic hole configurations through repeated ionization steps. The rich details shown in the spectra depend on the x-ray pulse parameters in a nonintuitive way. We discuss how the observed trends can be explained by the competition of microscopic electronic transition processes. A detailed comparison between spectra calculated within the independent-atom model and within the molecular-orbital framework highlights the chemical sensitivity of the spectral lines of multiple-hole configurations. Our results demonstrate how x-ray multiphoton ionization-related effects such as charge-rearrangement-enhanced x-ray ionization of molecules and frustrated absorption manifest themselves in the electron and fluorescence spectra.

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