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Sample records for photoelectron photoion molecular

  1. Photoelectron photoion molecular beam spectroscopy

    SciTech Connect

    Trevor, D.J.

    1980-12-01

    The use of supersonic molecular beams in photoionization mass spectroscopy and photoelectron spectroscopy to assist in the understanding of photoexcitation in the vacuum ultraviolet is described. Rotational relaxation and condensation due to supersonic expansion were shown to offer new possibilities for molecular photoionization studies. Molecular beam photoionization mass spectroscopy has been extended above 21 eV photon energy by the use of Stanford Synchrotron Radiation Laboratory (SSRL) facilities. Design considerations are discussed that have advanced the state-of-the-art in high resolution vuv photoelectron spectroscopy. To extend gas-phase studies to 160 eV photon energy, a windowless vuv-xuv beam line design is proposed.

  2. Photoionization-photoelectron research

    SciTech Connect

    Berkowitz, J.; Ruscic, B.

    1993-12-01

    The photoionization research program is aimed at understanding the basic processes of interaction of vacuum ultraviolet (VUV) light with atoms and molecules. This research provides valuable information on both thermochemistry and dynamics. Recent studies include atoms, clusters, hydrides, sulfides and an important fluoride.

  3. Photoionization-photoelectron research.

    SciTech Connect

    Ruscic, B.

    1998-03-06

    In the broad sense of a general definition, the fundamental goal of this research program is to explore, understand, and utilize the basic processes of interaction of vacuum UV light with atoms and molecules. In practical terms, this program uses photoionization mass spectrometry and other related techniques to study chemically relevant transient and metastable species that are intimately connected to energy-producing processes, such as combustion, or play-prominent roles in the associated environmental issues. Some recent examples of species that have been studied are: CH{sub 3}, CH{sub 2}, CH{sub 3}O, CH{sub 2}OH, CH{sub 3}S, CH{sub 2}SH, HCS, HNCO, NCO, HNCS, NCS, the isomers of C{sub 2}H{sub 5}O, HOBr, CF{sub 3} and CF{sub 3}OH. The ephemeral species of interest are produced in situ using various suitable techniques, such as sublimation, pyrolysis, microwave discharge, chemical abstraction reactions with H or F atoms, laser photodissociation, on-line synthesis, and others. The desired information is obtained by applying a variety of suitable photoionization methods, which use both conventional and coherent light sources in the vacuum W region. The spiritus movens of our studies is the need to provide the chemical community with essential information on the species of interest, such as accurate and reliable thermochemical, spectroscopic and structural data, and thus contribute to the global comprehension of the underlying chemical processes. The scientific motivation is also fueled by the necessity to unveil useful generalities, such as bonding patterns within a class of related compounds, or systematic behavior in the ubiquitous autoionization processes. In addition, the nature of the results obtained in this program is such that it generates a significant impetus for further theoretical work. The experimental work of this program is coordinated with other related experimental and theoretical efforts of the Chemical Dynamics Group to provide a broad perspective

  4. Photoelectron wave function in photoionization: plane wave or Coulomb wave?

    PubMed

    Gozem, Samer; Gunina, Anastasia O; Ichino, Takatoshi; Osborn, David L; Stanton, John F; Krylov, Anna I

    2015-11-19

    The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectron wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. The results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion. PMID:26509428

  5. Molecular photoionization studies

    SciTech Connect

    Dehmer, P.M.

    1983-01-01

    This program is concerned with the study of the electronic structure of small molecules and clusters of molecules. Of particular interest is the interaction of discrete electronic states with one another and with the various ionization and dissociation continua. Since the Second Annual Meeting of the DOE-OHER Program on The Physics and Chemistry of Energy-Related Atmospheric Pollutants in April 1981, significant progress has been made in the following areas: (1) the study of the electronic structure of dimers and small clusters of rare gas atoms using photoionization techniques; (2) similar studies on clusters of CO/sub 2/ molecules; (3) the study of electronic structure of rare gas dimers and trimers using photoelectron and photoelectron-photoion coincidence techniques; (4) the investigation of the relationship between Rydberg states in atoms, van der Waals molecules, and chemically-bonded molecules; (5) the extension of the study of photoabsorption, photoionization, and predissociation processes in H/sub 2/ to the unsymmetric isotope HD; (6) the study of photoelectron spectra of H/sub 2/ and C/sub 2/H/sub 2/; (7) a review of some of the aspects of dissociation processes in small molecules; and (8) the creation of a new program to study the spectra and dynamics of the photoionization processes in small molecules using the technique of multiphoton ionization followed by mass and electron energy analysis of the product ions and electrons. Some of the highlights of this work are reviewed.

  6. Molecular photoionization dynamics

    SciTech Connect

    Dehmer, Joseph L.

    1982-05-01

    This program seeks to develop both physical insight and quantitative characterization of molecular photoionization processes. Progress is briefly described, and some publications resulting from the research are listed. (WHK)

  7. Molecular Isomer Identification of Titan's Tholins Organic Aerosols by Photoelectron/Photoion Coincidence Spectroscopy Coupled to VUV Synchrotron Radiation.

    PubMed

    Cunha de Miranda, Barbara; Garcia, Gustavo A; Gaie-Levrel, François; Mahjoub, Ahmed; Gautier, Thomas; Fleury, Benjamin; Nahon, Laurent; Pernot, Pascal; Carrasco, Nathalie

    2016-08-25

    The chemical composition of Titan organic haze is poorly known. To address this issue, laboratory analogues named tholins are synthesized and analyzed by methods often requiring an extraction process in a carrier solvent. These methods exclude the analysis of the insoluble tholins' fraction and assume a hypothetical chemical equivalence between soluble and insoluble fractions. In this work, we present a powerful complementary analysis method recently developed on the DESIRS VUV synchrotron beamline at SOLEIL. It involves soft pyrolysis of tholins at ∼230 °C and electron/ion coincidence analysis of the emitted volatile compounds photoionized by tunable synchrotron radiation. By comparison with reference photoelectron spectra (PES), the spectral information collected on the detected molecules yields their isomeric structure. The method is more readily applied to light species (m/z ≤ 69), while for heavier ones, the number of possibilities and the lack of PES reference spectra in the literature limit its analysis. A notable pattern in the analyzed tholins is the presence of species containing adjacent doubly bonded N atoms, which might be a signature of heterogeneous incorporation of N2 in tholins. PMID:27471793

  8. Effects of molecular rotation after ionization and prior to fragmentation on observed recoil-frame photoelectron angular distributions in the dissociative photoionization of nonlinear molecules

    NASA Astrophysics Data System (ADS)

    López-Domínguez, Jesús A.; Lucchese, Robert R.

    2016-03-01

    Experimental angle-resolved photoelectron-photoion coincidence experiments measure photoelectron angular distributions (PADs) in dissociative photoionization (DPI) in the reference frame provided by the momenta of the emitted heavy fragments. By extension of the nomenclature used with DPI of diatomic molecules, we refer to such a PAD as a recoil-frame PAD (RFPAD). When the dissociation is fast compared to molecular rotational and bending motions, the emission directions of the heavy fragments can be used to determine the orientation of the bonds that are broken in the DPI at the time of the ionization, which is known as the axial-recoil approximation (ARA). When the ARA is valid, the RFPADs correspond to molecular-frame photoelectron angular distributions (MFPADs) when the momenta of a sufficient number of the heavy fragments are determined. When only two fragments are formed, the experiment cannot measure the orientation of the fragments about the recoil axes so that the resulting measured PAD is an azimuthally averaged RFPAD (AA-RFPAD). In this study we consider how the breakdown of the ARA due to rotation will modify the observed RFPADs for DPI processes in nonlinear molecules for ionization by light of arbitrary polarization. This model is applied to the core C 1 s DPI of CH4, with the results compared to experimental measurements and previous theoretical calculations done within the ARA. The published results indicate that there is a breakdown in the ARA for two-fragment events where the heavy-fragment kinetic energy release was less than 9 eV. Including the breakdown of the ARA due to rotation in our calculations gives very good agreement with the experimental AA-RFPAD, leading to an estimate of upper bounds on the predissociative lifetimes as a function of the kinetic energy release of the intermediate ion states formed in the DPI process.

  9. Imaging molecular orbitals using photoionization

    NASA Astrophysics Data System (ADS)

    Santra, Robin

    2006-10-01

    The interpretation of a recent experiment using high-order harmonic generation [Itatani et al., Nature 432 (2004) 867] as a measurement of the highest occupied molecular orbital of a molecule is conceptually problematic, even if the independent-particle picture is taken seriously. Guided by the relationship between the amplitude for one-photon-induced electron emission and the electron-ion recombination amplitude in the three-step model of high-order harmonic generation, it is argued that synchrotron-based photoionization might be a superior approach to imaging molecular orbitals. Within the Hartree-Fock independent-particle picture, the molecular-frame photoelectron angular distributions, measured as a function of photon energy, could be used to reconstruct all orbitals occupied in the Hartree-Fock ground state of the molecule investigated. It is suggested that laser alignment techniques could be employed to facilitate the measurement of the molecular-frame photoelectron angular distributions.

  10. An unambiguous signature in molecular frame photoelectron angular distributions of core hole localization in fluorine K-edge photoionization of CF4

    NASA Astrophysics Data System (ADS)

    McCurdy, C. W.; Rescigno, T. N.; Trevisan, C. S.; Lucchese, R. R.

    2016-05-01

    Molecular Frame Photoelectron Angular Distributions (MFPADs) are calculated using the Complex Kohn variational method for core-hole ionization of the carbon and fluorines in CF4 at photoelectron energies below 15 eV. The angular distributions for localized versus delocalized core-hole creation on the four equivalent fluorines are radically different. A strong propensity for the dissociation to take place via the mechanism hν +CF4 -->CF 4 + +e- -->CF 3 + +F(1s-1) -->CF 3 + +F+ + 2e- in which a core excited neutral fluorine atom ionizes during or after dissociation creates the conditions for experimental observation of core hole localization. Comparison with recent unpublished experiments at the Advanced Light Source that measured the Recoil Frame Photoelectron Angular Distributions (averaged over CF3 rotations around the recoil axis) for fluorine K-edge ionization gives unambiguous evidence that these experiments directly observed the creation of an almost completely localized core hole on the dissociating fluorine atom when the molecule was initially photoionized. Work supported by USDOE, OBES Chemical Sciences, Geosciences, and Biosciences Division.

  11. Attosecond Delays in Molecular Photoionization.

    PubMed

    Huppert, Martin; Jordan, Inga; Baykusheva, Denitsa; von Conta, Aaron; Wörner, Hans Jakob

    2016-08-26

    We report measurements of energy-dependent photoionization delays between the two outermost valence shells of N_{2}O and H_{2}O. The combination of single-shot signal referencing with the use of different metal foils to filter the attosecond pulse train enables us to extract delays from congested spectra. Remarkably large delays up to 160 as are observed in N_{2}O, whereas the delays in H_{2}O are all smaller than 50 as in the photon-energy range of 20-40 eV. These results are interpreted by developing a theory of molecular photoionization delays. The long delays measured in N_{2}O are shown to reflect the population of molecular shape resonances that trap the photoelectron for a duration of up to ∼110 as. The unstructured continua of H_{2}O result in much smaller delays at the same photon energies. Our experimental and theoretical methods make the study of molecular attosecond photoionization dynamics accessible. PMID:27610849

  12. Photoionization and photoelectron spectroscopy of doped helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Neumark, Daniel

    2006-03-01

    Photoionization and photoelectron spectra for helium nanodroplets doped with rare gas atoms and SF6 will be reported. The experiments were conducted using tunable synchrotron radiation at the Advanced Light Source in the photon energy range of 14-26 eV. Time-of-flight mass spectra will be presented, along with photoion and photoelectron images. The results will be compared to previous electron impact ionization data.

  13. Fine- and hyperfine-structure effects in molecular photoionization. I. General theory and direct photoionization.

    PubMed

    Germann, Matthias; Willitsch, Stefan

    2016-07-28

    We develop a model for predicting fine- and hyperfine intensities in the direct photoionization of molecules based on the separability of electron and nuclear spin states from vibrational-electronic states. Using spherical tensor algebra, we derive highly symmetrized forms of the squared photoionization dipole matrix elements from which we derive the salient selection and propensity rules for fine- and hyperfine resolved photoionizing transitions. Our theoretical results are validated by the analysis of the fine-structure resolved photoelectron spectrum of O2 reported by Palm and Merkt [Phys. Rev. Lett. 81, 1385 (1998)] and are used for predicting hyperfine populations of molecular ions produced by photoionization. PMID:27475368

  14. Time delay in molecular photoionization

    NASA Astrophysics Data System (ADS)

    Hockett, P.; Frumker, E.; Villeneuve, D. M.; Corkum, P. B.

    2016-05-01

    Time-delays in the photoionization of molecules are investigated. As compared to atomic ionization, the time-delays expected from molecular ionization present a much richer phenomenon, with a strong spatial dependence due to the anisotropic nature of the molecular scattering potential. We investigate this from a scattering theory perspective, and make use of molecular photoionization calculations to examine this effect in representative homonuclear and hetronuclear diatomic molecules, nitrogen and carbon monoxide. We present energy and angle-resolved maps of the Wigner delay time for single-photon valence ionization, and discuss the possibilities for experimental measurements.

  15. Photoion-photoelectron coincidence studies clusters and transient molecules

    SciTech Connect

    Norwood, K.

    1990-11-16

    Experimental photoion-photoelectron coincidence (PIPECO) spectra have been obtained at different nozzle stagnation pressures for Ar, Kr, Xe, and CO dimers and trimers in the wavelength regions corresponding to the respective ground states through all states accessible with a photon energy of 20 eV. Ionization energies for all ground states were measured and agree well with previously reported values. The formation of stable dimer ions from fragmentation of larger cluster ions initially produced by photoionization is efficient. For nozzle expansion conditions which minimize the formation of clusters larger than dimers, the intensities of the excited PIPECO bands for all clusters, except Ar{sub 2}{sup +} and Ar{sub 3}{sup +}, are found to be negligible with respect to the ground state PIPECO bands. The PIPECO technique has been used successfully to obtain the mass-selected threshold photoelectron spectra of the SO and S{sub 2}O transient molecules formed from a microwave discharge, effusive beam source. Analysis of the PIPECO spectra of all the clusters and transient molecules are presented. 177 refs., 32 figs., 6 tabs.

  16. Imaging photoelectron photoion coincidence spectroscopy with velocity focusing electron optics

    SciTech Connect

    Bodi, Andras; Johnson, Melanie; Gerber, Thomas; Gengeliczki, Zsolt; Sztaray, Balint; Baer, Tomas

    2009-03-15

    An imaging photoelectron photoion coincidence spectrometer at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source is presented and a few initial measurements are reported. Monochromatic synchrotron VUV radiation ionizes the cooled or thermal gas-phase sample. Photoelectrons are velocity focused, with better than 1 meV resolution for threshold electrons, and also act as start signal for the ion time-of-flight analysis. The ions are accelerated in a relatively low, 40-80 V cm{sup -1} field, which enables the direct measurement of rate constants in the 10{sup 3}-10{sup 7} s{sup -1} range. All electron and ion events are recorded in a triggerless multiple-start/multiple-stop setup, which makes it possible to carry out coincidence experiments at >100 kHz event frequencies. As examples, the threshold photoelectron spectrum of the argon dimer and the breakdown diagrams for hydrogen atom loss in room temperature methane and the chlorine atom loss in cold chlorobenzene are shown and discussed.

  17. A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of {sigma}=18 ps and energy resolution {delta}E/E=3.5%

    SciTech Connect

    Vredenborg, Arno; Roeterdink, Wim G.; Janssen, Maurice H. M.

    2008-06-15

    We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 {mu}m) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to {sigma}=18 ps. We observed that our electron coincidence detector has a timing resolution better than {sigma}=16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of {delta}E{sub FWHM}/E=3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about {delta}m{sub FWHM}/m=1/4150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to {sigma}=115 {mu}m.

  18. Molecular photoionization studies of nucleobases and correlated systems

    SciTech Connect

    Poliakoff, Erwin D.

    2015-03-11

    We proposed molecular photoionization studies in order to probe correlated events in fundamental scattering phenomena. In particular, we suggested that joint theoretical-experimental studies would provide a window into the microscopic aspects that are of central importance in AMO and chemical physics generally, and would generate useful data for wide array of important DOE topics, such as ultrafast dynamics, high harmonic generation, and probes of nonadiabatic processes. The unifying theme is that correlations between electron scattering dynamics and molecular geometry highlight inherently molecular aspects of the photoelectron behavior.

  19. Energy Correlation among Three Photoelectrons Emitted in Core-Valence-Valence Triple Photoionization of Ne

    SciTech Connect

    Hikosaka, Y.; Soejima, K.; Lablanquie, P.; Penent, F.; Palaudoux, J.; Andric, L.; Shigemasa, E.; Suzuki, I. H.; Nakano, M.; Ito, K.

    2011-09-09

    The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne{sup 3+} in the 1s2s{sup 2}2p{sup 4} configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

  20. Energy Correlation among Three Photoelectrons Emitted in Core-Valence-Valence Triple Photoionization of Ne

    NASA Astrophysics Data System (ADS)

    Hikosaka, Y.; Lablanquie, P.; Penent, F.; Palaudoux, J.; Andric, L.; Soejima, K.; Shigemasa, E.; Suzuki, I. H.; Nakano, M.; Ito, K.

    2011-09-01

    The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s2s22p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

  1. Energy correlation among three photoelectrons emitted in core-valence-valence triple photoionization of Ne.

    PubMed

    Hikosaka, Y; Lablanquie, P; Penent, F; Palaudoux, J; Andric, L; Soejima, K; Shigemasa, E; Suzuki, I H; Nakano, M; Ito, K

    2011-09-01

    The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons. PMID:22026663

  2. Double imaging photoelectron photoion coincidence sheds new light on the dissociation of energy-selected CH3Cl(+) ions.

    PubMed

    Tang, Xiaofeng; Lin, Xiaoxiao; Zhang, Weijun; Garcia, Gustavo A; Nahon, Laurent

    2016-09-14

    The vacuum ultraviolet (VUV) photoionization and dissociative photoionization of CH3Cl in the energy range of 11-17 eV have been investigated in detail by combining synchrotron radiation and double imaging photoelectron photoion coincidences (i(2)PEPICO). Three low-lying electronic states of the CH3Cl(+) molecular ion, X(2)E, A(2)A1 and B(2)E, were prepared and analyzed. The appearance energies of the energetically accessible fragment ions, CH2Cl(+), CHCl(+), CH3(+) and CH2(+), have been obtained from their respective mass-selected threshold photoelectron spectra (TPES) or photoionization efficiency (PIE) curves. The dissociation mechanisms of energy-selected CH3Cl(+) ions, prepared in the A(2)A1 and the B(2)E electronic states, as well as outside the Franck-Condon region, have been revealed to be state-specific via ion/electron kinetic energy correlation diagrams. In particular, the umbrella mode vibrational progression of the CH3(+) fragment ion in the direct dissociation of the A(2)A1 electronic state was identified and assigned indicating that this state correlates to the CH3(+)(1(1)A1') + Cl((2)P1/2) dissociation limit, in agreement with the theoretical calculations performed in this work. PMID:27524637

  3. Short-time Chebyshev wave packet method for molecular photoionization

    NASA Astrophysics Data System (ADS)

    Sun, Zhaopeng; Zheng, Yujun

    2016-08-01

    In this letter we present the extended usage of short-time Chebyshev wave packet method in the laser induced molecular photoionization dynamics. In our extension, the polynomial expansion of the exponential in the time evolution operator, the Hamiltonian operator can act on the wave packet directly which neatly avoids the matrix diagonalization. This propagation scheme is of obvious advantages when the dynamical system has large Hamiltonian matrix. Computational simulations are performed for the calculation of photoelectronic distributions from intense short pulse ionization of K2 and NaI which represent the Born-Oppenheimer (BO) model and Non-BO one, respectively.

  4. In situ flame chemistry tracing by imaging photoelectron photoion coincidence spectroscopy

    SciTech Connect

    Oßwald, P.; Köhler, M.; Hemberger, P.; Bodi, A.; Gerber, T.; Bierkandt, T.; Akyildiz, E.; Kasper, T.

    2014-02-15

    Adaptation of a low-pressure flat flame burner with a flame-sampling interface to the imaging photoelectron photoion coincidence spectrometer (iPEPICO) of the VUV beamline at the Swiss Light Source is presented. The combination of molecular-beam mass spectrometry and iPEPICO provides a new powerful analytical tool for the detailed investigation of reaction networks in flames. First results demonstrate the applicability of the new instrument to comprehensive flame diagnostics and the potentially high impact for reaction mechanism development for conventional and alternative fuels. Isomer specific identification of stable and radical flame species is demonstrated with unrivaled precision. Radical detection and identification is achieved for the initial H-abstraction products of fuel molecules as well as for the reaction controlling H, O, and OH radicals. Furthermore, quantitative evaluation of changing species concentrations during the combustion process and the applicability of respective results for kinetic model validation are demonstrated. Utilization of mass-selected threshold photoelectron spectra is shown to ensure precise signal assignment and highly reliable spatial profiles.

  5. High-Resolution Threshold Photoionization and Photoelectron Spectroscopy of Propene and 2-BUTYNE

    NASA Astrophysics Data System (ADS)

    Michaud, Julie M.; Vasilatou, Konstantina; Merkt, Frédéric

    2009-06-01

    The high-resolution photoionization and pulsed-field ionization zero-kinetic energy (PFI-ZEKE) photoelectron spectra of propene and 2-butyne and their perdeuterated isotopologues have been recorded in the vicinity of the first adiabatic ionization energy following single-photon excitation from the neutral ground state using a narrowband vacuum ultraviolet laser system. The spectral resolution of better than 0.1 cm^{-1} achieved in these spectra has enabled us to partially resolve the rotational structure of the photoelectron spectra and to obtain information on the internal rotation/torsional vibration of the methyl groups in the cationic ground state. The intensity distributions observed in the photoelectron spectra will be discussed in terms of rovibronic photoionization selection rules and Franck-Condon factors for transitions between the neutral and ionized molecules.

  6. The ionisation energy of cyclopentadienone: a photoelectron-photoion coincidence study

    NASA Astrophysics Data System (ADS)

    Ormond, Thomas K.; Hemberger, Patrick; Troy, Tyler P.; Ahmed, Musahid; Stanton, John F.; Ellison, G. Barney

    2015-08-01

    Imaging photoelectron photoion coincidence (iPEPICO) spectra of cyclopentadienone (C5H4=O and C5D4=O) have been measured at the Swiss Light Source Synchrotron (Paul Scherrer Institute, Villigen, Switzerland) at the Vacuum Ultraviolet (VUV) Beamline. Complementary to the photoelectron spectra, photoionisation efficiency curves were measured with tunable VUV radiation at the Chemical Dynamics Beamline at the Advanced Light Source Synchrotron (Lawrence Berkeley National Laboratory, Berkeley, CA, USA). For both experiments, molecular beams diluted in argon and helium were generated from the vacuum flash pyrolysis of o-phenylene sulphite in a resistively heated microtubular SiC flow reactor. The Franck-Condon profiles and ionisation energies were calculated at the CCSD(T) level of theory, and are in excellent agreement with the observed iPEPICO spectra. The ionisation energies of both cyclopentadienone-d0, IE(C5H4=O), and cyclopentadienone-d4, IE(C5D4=O), were observed to be the same: 9.41 ± 0.01 eV. The mass-selected threshold photoelectron spectrum (ms-TPES) of cyclopentadienone reveals that the C=C stretch in the ground state of the cation is excited upon ionisation, supporting computational evidence that the ground state of the cation is ? 2A2, and is in agreement with previous studies. However, the previously reported ionisation potential has been improved considerably in this work. In addition, since o-benzoquinone (o-O=C6H4=O and o-O=C6D4=O) is also produced in this process, its ms-TPES has been recorded. From the iPEPICO and photoionisation efficiency spectra, we infer an adiabatic ionisation energy of IE(o-O=C6H4=O) = 9.3 ± 0.1 eV, but the rather structureless spectrum indicates a strong change in geometry upon ionisation making this value less reliable.

  7. Photodissociation of Small Molecules and Photoionization of Free Radicals Using the VUV Velocity-Map Imaging Photoion and Photoelectron Method

    NASA Astrophysics Data System (ADS)

    Gao, Hong

    The tunable vacuum ultraviolet (VUV) laser generated through the two-photon resonance-enhanced four-wave mixing scheme is combined with the newly developed time-slice velocity map imaging photoion method to study the photodissociation of small molecules in the VUV region, and with the velocity map imaging photoelectron method to study the photoionization of free radicals. The photodissociation dynamics of NO in the energy region around 13.5 eV has been investigated. Branching ratios of the three lowest dissociation channels of 12C 16O that produce C(3P) + O(3P), C( 1D) + O(3P) and C(3P) + O(1D) are measured for the first time in the VUV region from 102,500 cm-1 to 110,500 cm-1, valuable information of the dissociation dynamics for this prototype system has been deduced. We demonstrated an experiment that has two independently tunable VUV lasers and a time-slice velocity map imaging setup, this provides us a global way to perform systematic state-selected photodissociation of small molecules via state-selected detection of the atomic products in the VUV region. The velocity map imaging photoelectron method was successfully used to obtain the photoelectron spectrum of the propargyl radical (C3H3) via a single VUV photoionization process. The propargyl radical is generated by the 193 nm laser photodissociation of the precursor C3H3Cl. This is the first time that the velocity map imaging photoelectron method is used to get the photoelectron spectra of free radicals, indicating that it is a powerful technique for studying the photoionization of free radicals which are always hard to be produced with high enough number densities for spectroscopic studies. This dissertation is mainly based on the following peer-reviewed journal articles: 1. Hong Gao, Yang Pan, Lei Yang, Jingang Zhou, C. Y. Ng and William M. Jackson. "Time-slice velocity-map ion imaging studies of the Photodissociation of NO in the vacuum ultraviolet region", the Journal of Chemical Physics, 136, 134302

  8. State-To Spectroscopy and Dynamics of Ions and Neutrals by Photoionization and Photoelectron Methods

    NASA Astrophysics Data System (ADS)

    Ng, Cheuk-Yiu

    2014-06-01

    Recent advances in high-resolution photoionization, photoelectron, and photodissociation studies based on single-photon vacuum ultraviolet (VUV) and two-color infrared (IR)-VUV, visible (VIS)-ultraviolet (UV), and VUV-VUV laser excitations are illustrated with selected examples. We show that VUV laser photoionization coupled with velocity-map-imaging (VMI)-threshold photoelectron (VMI-TPE) detection can achieve comparable energy resolutions, but higher detection sensitivities than those observed in VUV laser pulsed field ionization-photoelectron (PFI-PE) measurements. For molecules with known intermediate states, IR-VUV and VIS-UV excitation schemes are highly sensitive for rovibronically selected and resolved PFI-PE studies. The successful applications of the VUV-PFI-PE, VUV-VMI-TPE and VIS-UV-PFI-PE methods to state-resolved and state-to-state photoelectron studies of transient radicals and transitional metal-containing molecules are highlighted. The most recently established VUV-VUV pump-probe time-slice VMI-photoion method is shown to be promising for state-to-state photodissociation studies of small molecules relevant to planetary atmospheres and for the fundamental understanding of photodissociation dynamics.

  9. State-to-State Spectroscopy and Dynamics of Ions and Neutrals by Photoionization and Photoelectron Methods

    NASA Astrophysics Data System (ADS)

    Ng, Cheuk-Yiu

    2014-04-01

    Recent advances in high-resolution photoionization, photoelectron, and photodissociation studies based on single-photon vacuum ultraviolet (VUV) and two-color infrared (IR)-VUV, visible (Vis)-ultraviolet (UV), and VUV-VUV laser excitations are illustrated with selected examples. VUV laser photoionization coupled with velocity-map-imaging threshold photoelectron (VMI-TPE) detection can achieve comparable energy resolution but has higher-detection sensitivities than those observed in VUV laser pulsed field ionization photoelectron (PFI-PE) measurements. For molecules with known intermediate states, IR-VUV and Vis-UV excitation schemes are highly sensitive for rovibronically selected and resolved PFI-PE studies. The successful applications of the VUV-PFI-PE, VUV-VMI-TPE, and Vis-UV-PFI-PE methods to state-resolved and state-to-state photoelectron studies of transient radicals and transitional metal-containing molecules are highlighted. The most recently established VUV-VUV pump-probe time-slice VMI photoion method is shown to be promising for state-to-state photodissociation studies of small molecules relevant to planetary atmospheres and for the fundamental understanding of photodissociation dynamics.

  10. Velocity map photoelectron-photoion coincidence imaging on a single detector

    SciTech Connect

    Lehmann, C. Stefan; Ram, N. Bhargava; Janssen, Maurice H. M.

    2012-09-15

    Here we report on a new simplified setup for velocity map photoelectron-photoion coincidence imaging using only a single particle detector. We show that both photoelectrons and photoions can be extracted toward the same micro-channel-plate delay line detector by fast switching of the high voltages on the ion optics. This single detector setup retains essentially all the features of a standard two-detector coincidence imaging setup, viz., the high spatial resolution for electron and ion imaging, while only slightly decreasing the ion time-of-flight mass resolution. The new setup paves the way to a significant cost reduction in building a coincidence imaging setup for experiments aiming to obtain the complete correlated three-dimensional momentum distribution of electrons and ions.

  11. Rotationally resolved photoelectron spectroscopy of a triatomic molecule: Photoionization of the C (0.0.0) state of water

    SciTech Connect

    Glab, W.L.; Glynn, P.T.; Dehmer, P.M.; Dehmer, J.L.

    1996-05-01

    The authors have used a magnetic bottle photoelectron spectrometer to study the distribution of ion rotational states following photoionization of selected rotational states of the {tilde C}(0,0,0) state of water by 355 nm light. The spectrometer`s kinetic energy resolution of about 4 meV was sufficient to yield rotationally resolved time-of-flight photoelectron spectra. Comparison of the measured and calculated photoelectron spectra is encouraging and reveals unusual photoionization dynamics due to very nonatomic-like behavior in the photoionization continuum and to the presence of Cooper minima. This is the first time that such a test of photoionization theory for a polyatomic molecule at finite kinetic energy has been possible.

  12. Threshold Photoelectron Photoion Coincidence (TPEPICO) Studies. The Road to ± 0.1 kJ/mol Thermochemistry

    SciTech Connect

    Baer, Tomas

    2013-10-14

    The threshold photoelectron photoion coincidence (TPEPICO) technique is utilized to investigate the dissociation dynamics and thermochemistry of energy selected medium to large organic molecular ions. The reactions include parallel and consecutive steps that are modeled with the statistical theory in order to extract dissociation onsets for multiple dissociation paths. These studies are carried out with the aid of molecular orbital calculations of both ions and the transition states connecting the ion structure to their products. The results of these investigations yield accurate heats of formation of ions, free radicals, and stable molecules. In addition, they provide information about the potential energy surface that governs the dissociation process. Isomerization reactions prior to dissociation are readily inferred from the TPEPICO data.

  13. Photoionization study of Xe 5s: ionization cross sections and photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Aarthi, G.; Jose, J.; Deshmukh, S.; Radojevic, V.; Deshmukh, P. C.; Manson, S. T.

    2014-01-01

    We report studies of photoelectron angular distribution and cross-section for photoionization of xenon 5s electrons using the relativistic multiconfiguration Tamm-Dancoff (MCTD) approximation. We find that MCTD provides a significantly improved agreement with experiment, compared to some of the other relativistic many body approximations such as the relativistic random phase approximation and the relativistic random phase approximation with relaxation, over the entire photon energy region bracketing the near-threshold 5s Cooper minimum, from the 5s threshold up to about 70 eV. The MCTD results in the length form are in much better agreement with the experiment than those in the velocity form, suggesting residual correlations that must be of importance.

  14. Disentangling Multichannel Photodissociation Dynamics in Acetone by Time-Resolved Photoelectron-Photoion Coincidence Spectroscopy.

    PubMed

    Maierhofer, Paul; Bainschab, Markus; Thaler, Bernhard; Heim, Pascal; Ernst, Wolfgang E; Koch, Markus

    2016-08-18

    For the investigation of photoinduced dynamics in molecules with time-resolved pump-probe photoionization spectroscopy, it is essential to obtain unequivocal information about the fragmentation behavior induced by the laser pulses. We present time-resolved photoelectron-photoion coincidence (PEPICO) experiments to investigate the excited-state dynamics of isolated acetone molecules triggered by two-photon (269 nm) excitation. In the complex situation of different relaxation pathways, we unambiguously identify three distinct pump-probe ionization channels. The high selectivity of PEPICO detection allows us to observe the fragmentation behavior and to follow the time evolution of each channel separately. For channels leading to fragment ions, we quantitatively obtain the fragment-to-parent branching ratio and are able to determine experimentally whether dissociation occurs in the neutral molecule or in the parent ion. These results highlight the importance of coincidence detection for the interpretation of time-resolved photochemical relaxation and dissociation studies if multiple pathways are present. PMID:27459051

  15. PHOTOELECTRON AND AUGER ELECTRON ASYMMETRIES: ALIGNMENT OF Xe{sup +}({sup 2}D{sub 5/2}) BY PHOTOIONIZATION

    SciTech Connect

    Southworth, S. H.; Kobrin, P. H.; Truesdale, C. M.; Lindle, D.; Owaki, S.; Shirley, D. A.

    1980-12-01

    Angular distributions of photoelectrons from the Xe 4d subshell, and N{sub 4,5}oo Auger electrons, have been measured using synchrotron radiation. The 4d asymmetry parameter exhibits strong oscillations with energy, in agreement with several theoretical calculations. The Auger electrons show large asymmetries due to alignment of Xe{sup +} by photoionization.

  16. PHOTOELECTRON SPECTROSCOPY OF SUPERSONIC MOLECULAR BEAMS

    SciTech Connect

    Pollard, J.E.; Trevor, D.J.; Lee, Y.T.; Shirley, D.A.

    1981-06-01

    We report the development of an instrument for gas-phase ultraviolet photoelectron spectroscopy which opens several new areas for study through use of the supersonic molecular beam technique. The key features in which we have sought an improvement on earlier spectrometer designs are (1) the optimization of electron energy resolution and sensitivity, (2) vacuum isolation, and (3) the capability for mass spectrometric analysis. Our principal interests are in the high resolution spectroscopy of small molecules and in studies of weakly bound complexes formed under collisionless conditions. As shown in Fig. 1 the apparatus is essentially a molecular beam chamber with allowance for access by a beam source, an electron energy analyzer, and a quadrupole mass spectrometer. These three plug-in units are equipped with individual differential pumping systems. The photon source is a rare-gas resonance lamp which may be directed toward the molecular beam either 90{sup o} or 54.7{sup o} from the direction of electron collection. Electrons which pass through entrance aperture are transported by a series of electrostatic lenses to a 90{sup o} spherical sector pre-analyzer (R{sub 0} = 3.8 cm) and then on to a 180{sup o} hemispherical analyzer (R{sub 0} = 10.2 cm). The detector consists of a microchannel plate electron multiplier (40 mm diam.) with a resistive-anode position encoder. The function of the pre-analyzer is to improve the signal-to-noise ratio by reducing the background of scattered electrons incident upon the microchannel plate. The electron optical system is designed such that the energy bandpass (FWHN) leaving the pre-analyzer just fills the energy window presented by the multichannel detector. The multichannel capability of this analyzer is very advantageous for working with the rather low number density (< 10{sup 13} cm{sup -3}) of molecular beam samples, since the data collection rate is improved by more than an order of magnitude over single channel operation. To

  17. Rovibronically Selected and Resolved Laser Photoionization and Photoelectron Studies of Transition Metal Carbides, Nitrides, and Oxides.

    NASA Astrophysics Data System (ADS)

    Luo, Zhihong; Chang, Yih-Chung; Huang, Huang; Ng, Cheuk-Yiu

    2014-06-01

    Transition metal (M) carbides, nitrides, and oxides (MX, X = C, N, and O) are important molecules in astrophysics, catalysis, and organometallic chemistry. The measurements of the ionization energies (IEs), bond energies, and spectroscopic constants for MX/MX+ in the gas phase by high-resolution photoelectron methods represent challenging but profitable approaches to gain fundamental understandings of the electronic structures and bonding properties of these compounds and their cations. We have developed a two-color laser excitation scheme for high-resolution pulse field ionization photoelectron (PFI-PE) measurements of MX species. By exciting the neutral MX species to a single rovibronic state using a visible laser prior to photoionization by a UV laser, we have obtained fully rotational resolved PFI-PE spectra for TiC+, TiO+, VCH+, VN+, CoC+, ZrO+, and NbC+. The unambiguous rotational assignments of these spectra have provided highly accurate IE values for TiC, TiO, VCH, VN, CoC, ZrO, and NbC, and spectroscopic constants for their cations.

  18. Molecular Frame Photoemission: Probe of the Photoionization Dynamics for Molecules in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Dowek, D.; Picard, Y. J.; Billaud, P.; Elkharrat, C.; Houver, J. C.

    2009-04-01

    Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. This paper reports a comparative study of non-resonant and resonant photoionization of D2 induced by VUV circularly polarized synchrotron radiation at SOLEIL at the level of the molecular frame photoelectron angular distributions (MFPADs). We use the vector correlation method which combines imaging and time-of-flight resolved electron-ion coincidence techniques, and a generalized formalism for the expression of the I(χ, θe, varphie) MFPADs, where χ is the orientation of the molecular axis with respect to the light quantization axis and (θe, varphie) the electron emission direction in the molecular frame. Selected MFPADs for a molecule aligned parallel or perpendicular to linearly polarized light, or perpendicular to the propagation axis of circularly polarized light, are presented for dissociative photoionization (DPI) of D2 at two photon excitation energies, hν = 19 eV, where direct PI is the only channel opened, and hν = 32.5 eV, i.e. in the region involving resonant excitation of Q1 and Q2 doubly excited state series. We discuss in particular the properties of the circular dichroism characterizing photoemission in the molecular frame for direct and resonant PI. In the latter case, a remarkable behavior is observed which may be attributed to the interference occurring between undistinguishable autoionization decay channels.

  19. Photoelectron imaging of XUV photoionization of CO2 by 13-40 eV synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Furch, Federico J.; Birkner, Sascha; Jungmann, Julia H.; Kelkensberg, Freek; Schulz, Claus Peter; Rouzée, Arnaud; Vrakking, Marc J. J.

    2013-09-01

    Valence band photoionization of CO2 has been studied by photoelectron spectroscopy using a velocity map imaging spectrometer and synchrotron radiation. The measured data allow retrieving electronic and vibrational branching ratios, vibrationally resolved asymmetry parameters, and the total electron yield which includes multiple strong resonances. Additionally, the spectrum of low kinetic energy electrons has been studied in the resonant region, and the evolution with photon energy of one of the forbidden transitions present in the slow photoelectrons spectrum has been carefully analyzed, indicating that in the presence of auto-ionizing resonances the vibrational populations of the ion are significantly redistributed.

  20. Double Photoionization of Aligned Molecular Hydrogen

    SciTech Connect

    Vanroose, Wim; Horner, Daniel A.; Martin, Fernando; Rescigno,Thomas N.; McCurdy, C. William

    2006-07-21

    We present converged, completely ab initio calculations ofthe triple differential cross sections for double photoionization ofaligned H2 molecules for a photon energy of 75.0 eV. The method ofexterior complex scaling, implemented with both the discrete variablerepresentation and B-splines, is used to solve the Schroedinger equationfor a correlated continuum wave function corresponding to a single photonhaving been absorbed by a correlated initial state. Results for a fixedinternuclear distance are compared with recent experiments and show thatintegration over experimental angular and energy resolutions is necessaryto produce good qualitative agreement, but does not eliminate somediscrepancies. Limitations of current experimental resolution are shownto sometimes obscure interesting details of the crosssection.

  1. Retrieving transient conformational molecular structure information from inner-shell photoionization of laser-aligned molecules

    DOE PAGESBeta

    Wang, Xu; Le, Anh -Thu; Yu, Chao; Lucchese, R. R.; Lin, C. D.

    2016-03-30

    We discuss a scheme to retrieve transient conformational molecular structure information using photoelectron angular distributions (PADs) that have averaged over partial alignments of isolated molecules. The photoelectron is pulled out from a localized inner-shell molecular orbital by an X-ray photon. We show that a transient change in the atomic positions from their equilibrium will lead to a sensitive change in the alignment-averaged PADs, which can be measured and used to retrieve the former. Exploiting the experimental convenience of changing the photon polarization direction, we show that it is advantageous to use PADs obtained from multiple photon polarization directions. Lastly, amore » simple single-scattering model is proposed and benchmarked to describe the photoionization process and to do the retrieval using a multiple-parameter fitting method.« less

  2. Retrieving transient conformational molecular structure information from inner-shell photoionization of laser-aligned molecules

    NASA Astrophysics Data System (ADS)

    Wang, Xu; Le, Anh-Thu; Yu, Chao; Lucchese, R. R.; Lin, C. D.

    2016-03-01

    We discuss a scheme to retrieve transient conformational molecular structure information using photoelectron angular distributions (PADs) that have averaged over partial alignments of isolated molecules. The photoelectron is pulled out from a localized inner-shell molecular orbital by an X-ray photon. We show that a transient change in the atomic positions from their equilibrium will lead to a sensitive change in the alignment-averaged PADs, which can be measured and used to retrieve the former. Exploiting the experimental convenience of changing the photon polarization direction, we show that it is advantageous to use PADs obtained from multiple photon polarization directions. A simple single-scattering model is proposed and benchmarked to describe the photoionization process and to do the retrieval using a multiple-parameter fitting method.

  3. Retrieving transient conformational molecular structure information from inner-shell photoionization of laser-aligned molecules

    PubMed Central

    Wang, Xu; Le, Anh-Thu; Yu, Chao; Lucchese, R. R.; Lin, C. D.

    2016-01-01

    We discuss a scheme to retrieve transient conformational molecular structure information using photoelectron angular distributions (PADs) that have averaged over partial alignments of isolated molecules. The photoelectron is pulled out from a localized inner-shell molecular orbital by an X-ray photon. We show that a transient change in the atomic positions from their equilibrium will lead to a sensitive change in the alignment-averaged PADs, which can be measured and used to retrieve the former. Exploiting the experimental convenience of changing the photon polarization direction, we show that it is advantageous to use PADs obtained from multiple photon polarization directions. A simple single-scattering model is proposed and benchmarked to describe the photoionization process and to do the retrieval using a multiple-parameter fitting method. PMID:27025410

  4. Near-Threshold, Vibrationally-Resolved Photoionization of Molecular Nitrogen

    NASA Astrophysics Data System (ADS)

    Vangyseghem, Gaetan; Gorczyca, Thomas; Ballance, Connor

    2016-05-01

    Photoionization of molecular nitrogen N2 is investigated near the first ionization threshold using an R-matrix, multi-channel quantum defect theory (MQDT) approach. Building on an existing fixed-nuclei R-matrix photoionization model, which, in turn, is built on the UKRmol suite of codes, photoionization cross sections, as well as scattering and dipole matrices, are computed in the Born-Oppenheimer approximation. By varying the internuclear separation, potential energy curves have been constructed for the N2 and N 2 + states and compared to quantum chemistry calculations. Using these fixed-nuclei potential energy curves, and corresponding vibronic eigenenergies and eigenfunctions, a frame transformation is enacted on the fixed-nuclei scattering and dipole matrices, allowing for the calculation of vibrationally-resolved photoionization cross sections. The resultant photoionization cross sections are compared to high-resolution experimental data near threshold, a region complicated by multiple vibrationally-resolved, interacting Rydberg series.

  5. Molecular photoelectron momentum distributions by intense orthogonally polarized attosecond ultraviolet laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2015-10-01

    We study molecular photoelectron momentum distributions (MPMDs) of aligned H2+ by intense orthogonally polarized attosecond ultraviolet laser pulses. Photoionization is simulated by numerically solving corresponding three-dimensional time dependent Schrödinger equations with static nuclei. It is found that altering pulse phases ϕ varies the structure of MPMDs, which is attributed to the interference effect between orthogonal polarization ionizations. The phase ϕ dependent MPMDs are also a function of molecular alignment and pulse wavelengths. Altering the symmetry of initial electronic states offers the possibility of imaging molecular orbitals by orthogonal polarization attosecond MPMDs.

  6. Dissociative Ionization Mechanism and Appearance Energies in Adipic Acid Revealed by Imaging Photoelectron Photoion Coincidence, Selective Deuteration, and Calculations.

    PubMed

    Heringa, Maarten F; Slowik, Jay G; Prévôt, André S H; Baltensperger, Urs; Hemberger, Patrick; Bodi, Andras

    2016-05-26

    Adipic acid, a model compound for oxygenated organic aerosol, has been studied at the VUV beamline of the Swiss Light Source. Internal energy selected cations were prepared by threshold photoionization using vacuum ultraviolet synchrotron radiation and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). The threshold photoelectron spectrum yields a vertical ionization energy (IE) of 10.5 eV, significantly above the calculated adiabatic IE of 8.6 eV. The cationic minimum is accessible after vertical ionization by H-transfer from one of the γ-carbons to a carbonyl oxygen and is sufficiently energetic to decay by water loss at the ionization onset. The slope of the breakdown curves, quantum chemical calculations, and selective deuteration of the carboxylic hydrogens establish the dissociative photoionization mechanism. After ionization, one γ-methylene hydrogen and the two carboxylic hydrogens are randomized prior to H2O loss. On the basis of the deuteration degree in the H2O + CO-loss product at higher energies, a direct water-loss channel without complete randomization also exists. The breakdown diagram and center of gravity of the H2O + CO-loss peak were modeled to obtain 0 K appearance energies of 10.77, 10.32, and 11.53 eV for H2O + CO loss, CH2COOH loss, and H2O + CH2COOH loss from adipic acid. These agree well with the CBS-QB3 calculated values of 10.68, 10.45, and 11.57 eV, respectively, which shows that threshold photoionization can yield energetics data as long as the dissociation is statistical, even when the parent ion cannot be observed. The results can be used as a starting point for a deeper understanding of the ionization and low-energy fragmentation of organic aerosol components. PMID:27100102

  7. Hybrid Gaussian-discrete-variable representation approach to molecular continuum processes: Application to photoionization of diatomic Li2+

    NASA Astrophysics Data System (ADS)

    Yip, F. L.; McCurdy, C. W.; Rescigno, T. N.

    2008-08-01

    We describe an approach for studying molecular photoionization with a hybrid basis that combines the functionality of analytic basis sets to represent electronic coordinates near the nuclei of a molecule with numerically defined grid-based functions. We discuss the evaluation of the various classes of two-electron integrals that occur in a hybrid basis consisting of Gaussian-type orbitals and discrete-variable representation functions. This combined basis is applied to calculate single photoionization cross sections for molecular Li2+ , which has a large equilibrium bond distance (R=5.86a0) . The highly nonspherical nature of Li2+ molecules causes higher angular momentum components to contribute significantly to the cross section even at low photoelectron energies, resulting in angular distributions that appear to be f -wave dominated near the photoionization threshold. At higher energies, where the de Broglie wavelength of the photoelectron becomes comparable with the bond distance, interference effects appear in the photoionization cross section. These interference phenomena appear at much lower energies than would be expected for diatomic targets with shorter internuclear separations.

  8. A hybridGaussian-discrete variable representation approach to molecular continuum processes II: application to photoionization of diatomic Li2+

    SciTech Connect

    Rescigno, Thomas N; Yip, Frank L.; McCurdy, C. William; Rescigno, Thomas N.

    2008-08-01

    We describe an approach for studying molecular photoionization with a hybrid basis that combines the functionality of analytic basis sets to represent electronic coordinates near the nuclei of a molecule with numerically-defined grid-based functions. We discuss the evaluation of the various classes of two-electron integrals that occur in a hybrid basis consisting of Gaussian type orbitals (GTOs) and discrete variable representation (DVR) functions. This combined basis is applied to calculate single photoionization cross sections for molecular Li_2+, which has a large equilibrium bond distance (R=5.86a_0). The highly non-spherical nature of Li_2+ molecules causes higher angular momentum components to contribute significantly to the cross section even at low photoelectron energies, resulting in angular distributions that appear to be f-wave dominated near the photoionization threshold. At higher energies, where the de Broglie wavelength of the photoelectron becomes comparable with the bond distance, interference effects appear in the photoionization cross section. These interference phenomena appear at much lower energies than would be expected for diatomic targets with shorter internuclear separations.

  9. Communication: State-to-state photoionization and photoelectron study of vanadium methylidyne radical (VCH)

    SciTech Connect

    Luo, Zhihong; Zhang, Zheng; Huang, Huang; Chang, Yih-Chung; Ng, C. Y.

    2014-05-14

    By employing the infrared (IR)-ultraviolet (UV) laser excitation scheme, we have obtained rotationally selected and resolved pulsed field ionization-photoelectron (PFI-PE) spectra for vanadium methylidyne cation (VCH{sup +}). This study supports that the ground state electronic configuration for VCH{sup +} is …7σ{sup 2}8σ{sup 2}3π{sup 4}9σ{sup 1} (X{sup ~2}Σ{sup +}), and is different from that of …7σ{sup 2}8σ{sup 2}3π{sup 4}1δ{sup 1} (X{sup ~2}Δ) for the isoelectronic TiO{sup +} and VN{sup +} ions. This observation suggests that the addition of an H atom to vanadium carbide (VC) to form VCH has the effect of stabilizing the 9σ orbital relative to the 1δ orbital. The analysis of the state-to-state IR-UV-PFI-PE spectra has provided precise values for the ionization energy of VCH, IE(VCH) = 54 641.9 ± 0.8 cm{sup −1} (6.7747 ± 0.0001 eV), the rotational constant B{sup +} = 0.462 ± 0.002 cm{sup −1}, and the v{sub 2}{sup +} bending (626 ± 1 cm{sup −1}) and v{sub 3}{sup +} V–CH stretching (852 ± 1 cm{sup −1}) vibrational frequencies for VCH{sup +}(X{sup ~2}Σ{sup +}). The IE(VCH) determined here, along with the known IE(V) and IE(VC), allows a direct measure of the change in dissociation energy for the V–CH as well as the VC–H bond upon removal of the 1δ electron of VCH(X{sup ~3}Δ{sub 1}). The formation of VCH{sup +}(X{sup ~2}Σ{sup +}) from VCH(X{sup ~3}Δ{sub 1}) by photoionization is shown to strengthen the VC–H bond by 0.3559 eV, while the strength of the V–CH bond remains nearly unchanged. This measured change of bond dissociation energies reveals that the highest occupied 1δ orbital is nonbonding for the V–CH bond; but has anti-bonding or destabilizing character for the VC–H bond of VCH(X{sup ~3}Δ{sub 1})

  10. Dynamical Relativistic Effects in Photoionization: Spin-Orbit-Resolved Angular Distributions of Xenon 4d Photoelectrons near the Cooper Minimum

    SciTech Connect

    Wang, H.; Snell, G.; Hemmers, O.; Sant'Anna, M. M.; Sellin, I.; Berrah, N.; Lindle, D. W.; Deshmukh, P. C.; Haque, N.; Manson, S. T.

    2001-09-17

    Two decades ago, it was predicted [Y.S.Kim et al., Phys.Rev.Lett.46, 1326 (1981)] that relativistic effects should alter the dynamics of the photoionization process in the vicinity of Cooper minima. The present experimental and theoretical study of the angular distributions of Xe 4d{sub 3/2} and 4d{sub 5/2} photoelectrons demonstrates this effect for the first time. The results clearly imply that relativistic effects are likely to be important for intermediate-Z atoms at most energies.

  11. Molecular photoelectron angular distributions with intense attosecond circularly polarized UV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2014-01-01

    We investigate effects of intermediate resonant electronic states on molecular photoelectron angular distributions (MPADs) by intense circularly polarized attosecond UV laser pulses. Simulations are performed on aligned H2+ by numerically solving the corresponding three dimensional time dependent Schrödinger equations. MPADs exhibit signature of rotations, which is shown to be critically sensitive to the symmetry of the intermediate resonant electronic state and the pulse intensity. This sensitivity is attributed to the coherent population transfer in the initial and intermediate resonant states, thus suggesting a method to control molecular photoionization on attosecond time scale.

  12. Molecular-frame photoelectron angular distributions Molecular-frame photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Lucchese, Robert R.; Stolow, Albert

    2012-10-01

    Angle-resolved photoelectron measurements in molecular ionization continue to grow in importance due to their sensitivity to molecular dynamics combined with their avoidance of deleterious averaging over molecular orientation. This special issue contains only regularly refereed articles and provides an account of current experimental and theoretical studies of such molecular-frame photoelectron angular distributions (MFPADs). Recent experimental activity in this field has been stimulated by advances in light sources such as x-ray free electron lasers, attosecond XUV laser pulses and phase-stable ultrashort strong laser fields. This effort is further amplified by recent developments in coincidence detection and molecular-frame alignment/orientation techniques. Beyond perturbative light-matter interactions, strong field processes such as tunnel ionization, above threshold ionization and rescattering phenomena such as high harmonic generation and laser-induced electron diffraction are beginning to probe molecular-frame photoelectron-molecule scattering dynamics. Theoretical developments are playing an equally important role in furthering molecular-frame photoelectron science. This issue contains several purely theoretical papers that aim to provide insight into possible schemes for using MFPADs in the study of molecular dynamics. Because the details of the electron-molecule scattering dynamics are important to the interpretation of experimental data, significant progress is made by a close collaboration between theory and experiment. There are a number of such contributions in this issue that combine theory and experiment to obtain a detailed understanding of the observed processes. One recurring theme is the use of measured MFPADs as probes of the molecular state and to uncover information about the dynamics of molecular systems. Contributions in this issue consider using MFPADs to investigate molecular geometry or the rotational, vibrational or electronic state of a

  13. K-shell photoionization of CO: I. Angular distributions of photoelectrons from fixed-in-space molecules

    NASA Astrophysics Data System (ADS)

    Motoki, S.; Adachi, J.; Hikosaka, Y.; Ito, K.; Sano, M.; Soejima, K.; Yagishita, A.; Raseev, G.; Cherepkov, N. A.

    2000-10-01

    Angular distributions of photoelectrons from both C and O K-shells of the fixed-in-space CO molecule have been measured using the angle-resolved photoelectron-photoion coincidence technique. The measurements have been performed at several photon energies from the ionization thresholds up to about 30 eV above them, where the σ* shape resonances occur. Experimental results are compared with the multiple-scattering calculations of Dill et al (1976 J. Chem. Phys. 65 3158) and with our new calculations in the relaxed-core Hartree-Fock approximation. Our calculations are in a better agreement with the experimental data though numerical discrepancies remain. The experimental angular distributions are fitted by the expansion in Legendre polynomials containing up to ten terms and the extracted parameters are compared with the corresponding theoretical values.

  14. Synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy of radicals produced in a flow tube: OH and OD

    NASA Astrophysics Data System (ADS)

    Garcia, Gustavo A.; Tang, Xiaofeng; Gil, Jean-François; Nahon, Laurent; Ward, Michael; Batut, Sebastien; Fittschen, Christa; Taatjes, Craig A.; Osborn, David L.; Loison, Jean-Christophe

    2015-04-01

    We present a microwave discharge flow tube coupled with a double imaging electron/ion coincidence device and vacuum ultraviolet (VUV) synchrotron radiation. The system has been applied to the study of the photoelectron spectroscopy of the well-known radicals OH and OD. The coincidence imaging scheme provides a high selectivity and yields the spectra of the pure radicals, removing the ever-present contributions from excess reactants, background, or secondary products, and therefore obviating the need for a prior knowledge of all possible byproducts. The photoelectron spectra encompassing the X3Σ- ground state of the OH+ and OD+ cations have been extracted and the vibrational constants compared satisfactorily to existing literature values. Future advantages of this approach include measurement of high resolution VUV spectroscopy of radicals, their absolute photoionization cross section, and species/isomer identification in chemical reactions as a function of time.

  15. Synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy of radicals produced in a flow tube: OH and OD

    DOE PAGESBeta

    Garcia, Gustavo A.; Tang, Xiaofeng; Gil, Jean -Francois; Nahon, Laurent; Ward, Michael; Batut, Sebastien; Fittschen, Christa; Taatjes, Craig A.; Osborn, David L.; Loison, Jean -Christophe

    2015-04-23

    In this study, we present a microwave discharge flow tube coupled with a double imaging electron/ion coincidence device and vacuum ultraviolet (VUV) synchrotron radiation. The system has been applied to the study of the photoelectron spectroscopy of the well-known radicals OH and OD. The coincidence imaging scheme provides a high selectivity and yields the spectra of the pure radicals, removing the ever-present contributions from excess reactants, background, or secondary products, and therefore obviating the need for a prior knowledge of all possible byproducts. The photoelectron spectra encompassing the X3Σ– ground state of the OH+ and OD+ cations have been extractedmore » and the vibrational constants compared satisfactorily to existing literature values. Future advantages of this approach include measurement of high resolution VUV spectroscopy of radicals, their absolute photoionization cross section, and species/isomer identification in chemical reactions as a function of time.« less

  16. Synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy of radicals produced in a flow tube: OH and OD

    SciTech Connect

    Garcia, Gustavo A.; Tang, Xiaofeng; Gil, Jean-François; Nahon, Laurent; Ward, Michael; Batut, Sebastien; Fittschen, Christa; Taatjes, Craig A.; Osborn, David L.; Loison, Jean-Christophe

    2015-04-28

    We present a microwave discharge flow tube coupled with a double imaging electron/ion coincidence device and vacuum ultraviolet (VUV) synchrotron radiation. The system has been applied to the study of the photoelectron spectroscopy of the well-known radicals OH and OD. The coincidence imaging scheme provides a high selectivity and yields the spectra of the pure radicals, removing the ever-present contributions from excess reactants, background, or secondary products, and therefore obviating the need for a prior knowledge of all possible byproducts. The photoelectron spectra encompassing the X{sup 3}Σ{sup −} ground state of the OH{sup +} and OD{sup +} cations have been extracted and the vibrational constants compared satisfactorily to existing literature values. Future advantages of this approach include measurement of high resolution VUV spectroscopy of radicals, their absolute photoionization cross section, and species/isomer identification in chemical reactions as a function of time.

  17. Synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy of radicals produced in a flow tube: OH and OD

    SciTech Connect

    Garcia, Gustavo A.; Tang, Xiaofeng; Gil, Jean -Francois; Nahon, Laurent; Ward, Michael; Batut, Sebastien; Fittschen, Christa; Taatjes, Craig A.; Osborn, David L.; Loison, Jean -Christophe

    2015-04-23

    In this study, we present a microwave discharge flow tube coupled with a double imaging electron/ion coincidence device and vacuum ultraviolet (VUV) synchrotron radiation. The system has been applied to the study of the photoelectron spectroscopy of the well-known radicals OH and OD. The coincidence imaging scheme provides a high selectivity and yields the spectra of the pure radicals, removing the ever-present contributions from excess reactants, background, or secondary products, and therefore obviating the need for a prior knowledge of all possible byproducts. The photoelectron spectra encompassing the X3Σ ground state of the OH+ and OD+ cations have been extracted and the vibrational constants compared satisfactorily to existing literature values. Future advantages of this approach include measurement of high resolution VUV spectroscopy of radicals, their absolute photoionization cross section, and species/isomer identification in chemical reactions as a function of time.

  18. Enantioselective femtosecond laser photoionization spectrometry of limonene using photoelectron circular dichroism.

    PubMed

    Rafiee Fanood, Mohammad M; Janssen, Maurice H M; Powis, Ivan

    2015-04-14

    Limonene is ionized by circularly polarized 420 nm femtosecond laser pulses. Ion mass and photoelectron energy spectra identify the dominant (2 + 1) multiphoton ionization mechanism, aided by TDDFT calculations of the Rydberg excitations. Photoelectron circular dichroism measurements on pure enantiomers reveal a chiral asymmetry of ±4 %. PMID:25744283

  19. Rotations of molecular photoelectron angular distributions with intense ultrashort circularly polarized attosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2013-04-01

    Molecular photoelectron angular distributions (MPADs) by intense (I0 ⩾ 1014 W/cm2) circularly polarized ultrashort, few cycle (attosecond) ultraviolet laser pulses are presented from numerical solutions of time dependent Schrödinger equations. For the aligned molecular ion H_2^+, the MPADs exhibit rotations with respect to the polarization and molecular symmetry axes which are determined by the symmetry of the initial electronics states. It is also found that the rotation angle of MPADs is insensitive to the pulse intensity. We attribute these effects to the asymmetry between the parallel and perpendicular (to the molecular axis) polarization photoionization. Influence of the molecular alignment and ionizing pulse ellipticity on the rotation of MPADs is also shown to allow control of the nonsymmetric ionization.

  20. Probing photoelectron multiple interferences via Fourier spectroscopy in energetic photoionization of Xe-C{sub 60}

    SciTech Connect

    Potter, Andrea; McCune, Matthew A.; De, Ruma; Chakraborty, Himadri S.; Madjet, Mohamed E.

    2010-09-15

    Considering the photoionization of the Xe-C{sub 60} endohedral compound, we study in detail the ionization cross sections of various levels of the system at energies higher than the plasmon resonance region. Five classes of single-electron levels are identified depending on their spectral character. Each class engenders distinct oscillations in the cross section, emerging from the interference between active ionization modes specific to that class. Analysis of the cross sections based on their Fourier transforms unravels oscillation frequencies that carry unique fingerprints of the emitting level.

  1. Probing confinement resonances by photoionizing Xe inside a C60+ molecular cage

    NASA Astrophysics Data System (ADS)

    Phaneuf, R. A.; Kilcoyne, A. L. D.; Aryal, N. B.; Baral, K. K.; Thomas, C. M.; Esteves-Macaluso, D. A.; Lomsadze, R.; Gorczyca, T. W.; Ballance, C. P.; Manson, S. T.; Hasoglu, M. F.; Hellhund, J.; Schippers, S.; Müller, A.

    2014-05-01

    Double photoionization accompanied by loss of n C atoms (n = 0 , 2 , 4 , 6) was investigated by merging beams of Xe@C60+ ions and synchrotron radiation and measuring the yields of product ions. The giant 4 d dipole resonance of the caged Xe atom has a prominent signature in the cross section for these product channels, which together account for 6 . 2 +/- 1 . 4 of the total Xe 4 d oscillator strength of 10. Compared to that for a free Xe atom, the oscillator strength is redistributed in photon energy due to multipath interference of outgoing Xe 4 d photoelectron waves that may be transmitted or reflected by the spherical C60+ molecular cage, yielding so-called confinement resonances. The data are compared with an earlier measurement and with theoretical predictions for this single-molecule photoelectron interferometer system. Relativistic R-matrix calculations for the Xe atom in a spherical potential shell representing the fullerene cage show the sensitivity of the interference pattern to the molecular geometry.

  2. Photoionization and photofragmentation of the C60+ molecular ion

    NASA Astrophysics Data System (ADS)

    Baral, K. K.; Aryal, N. B.; Esteves-Macaluso, D. A.; Thomas, C. M.; Hellhund, J.; Lomsadze, R.; Kilcoyne, A. L. D.; Müller, A.; Schippers, S.; Phaneuf, R. A.

    2016-03-01

    Cross-section measurements are reported for single and double photoionization of C60+ ions in the photon energy range 18-150 eV accompanied by the loss of zero to seven pairs of carbon atoms, as well as for fragmentation without ionization resulting in loss of two to eight pairs of C atoms in the photon energy range 18-65 eV. Absolute measurements were performed by merging a beam of C60+ molecular ions with a beam of monochromatized synchrotron radiation. Product channels involving dissociation yielding smaller fullerene fragment ions account for nearly half of the total measured oscillator strength in this energy range. The sum of cross sections for the measured product channels is compared to a published calculation of the total photoabsorption cross section of neutral C60 based on time-dependent density-functional theory. This comparison and an accounting of oscillator strengths indicate that with the exception of C58+, the most important product channels resulting from photoabsorption were accounted for in the experiment. Threshold energies for the successive removal of carbon atom pairs accompanying photoionization are also determined from the measurements.

  3. Photoelectron Angular Distribution and Molecular Structure in Multiply Charged Anions

    SciTech Connect

    Xing, Xiaopeng; Wang, Xue B.; Wang, Lai S.

    2009-02-12

    Photoelectrons emitted from multiply charged anions (MCAs) carry information of the intramolecular Coulomb repulsion (ICR), which is dependent on molecular structures. Using photoelectron imaging, we observed the effects of ICR on photoelectron angular distributions (PAD) of the three isomers of benzene dicarboxylate dianions C6H4(CO2)22– (o-, m- and p-BDC2–). Photoelectrons were observed to peak along the laser polarization due to the ICR, but the anisotropy was the largest for p-BDC2–, followed by the m- and o-isomer. The observed anisotropy is related to the direction of the ICR or the detailed molecular structures, suggesting that photoelectron imaging may allow structural information to be obtained for complex multiply charged anions.

  4. Photoionization of He above the N =2 threshold. II. Angular distribution of photoelectrons and asymmetry parameter

    SciTech Connect

    Sanchez, I.; Martin, F. )

    1992-04-01

    We report theoretical calculations for the {beta}{sub 2{ital p}}-asymmetry parameter in the photoionization of He(1{ital s}{sup 2}) above the {ital N}=2 ionization threshold. We use an extension of a method recently proposed (I. Sanchez and F. Martin, Phys. Rev. A 44, 7318 (1991)) that makes use of a Feshbach partitioning of the final-state wave function and an {ital L}{sup 2} representation of the coupled continuum states. Partial differential cross sections at emission angles 0{degree} and 90{degree} are also provided. Our results are in good agreement with the experimental data, thus showing the accuracy of the present method to study electron angular-distribution properties.

  5. Photoionization Dynamics of Small Molecules

    SciTech Connect

    Dehmer, Joseph L.; Dill, Dan; Parr, Albert C.

    1985-01-01

    The last decade has witnessed remarkable progress in characterizing dynamical aspects of the molecular photoionization process. The general challenge is to gain physical insight into those processes occuring during photo excitation and eventual escape of the photoelectron through the anisotropic molecular field, in terms of various observables such as photoionization cross-sections and branching ratios, photoelectron angular distributions and even newer probes mentioned below. Much of the progress in this field has mirrored earlier work in atomic photoionization dynamics where many key ideas were developed (e.g., channel interaction, quantum defect analysis, potential barrier phenomena and experimental techniques). However, additional concepts and techniques were required to deal with the strictly molecular aspects of the problem, particularly the anisotropy of the multicenter molecular field and the interaction among rovibronic modes.

  6. Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging

    NASA Astrophysics Data System (ADS)

    Tang, Xiaofeng; Zhou, Xiaoguo; Sun, Zhongfa; Liu, Shilin; Liu, Fuyi; Sheng, Liusi; Yan, Bing

    2014-01-01

    Dissociative photoionization of methyl bromide (CH3Br) in an excitation energy range of 10.45-16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X2E of CH3Br+ is stable, and both A2A1 and B2E ionic excited states are fully dissociative to produce the unique fragment ion of CH3+. From TPEPICO 3D time-sliced velocity images of CH3+ dissociated from specific state-selected CH3Br+ ion, kinetic energy release distribution (KERD) and angular distribution of CH3+ fragment ion are directly obtained. Both spin-orbit states of Br(2P) atom can be clearly observed in fast dissociation of CH3Br+(A2A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br+(B2E) ion. With the aid of the re-calculated potential energy curves of CH3Br+ including spin-orbit coupling, dissociation mechanisms of CH3Br+ ion in A2A1 and B2E states along C-Br rupture are revealed. For CH3Br+(A2A1) ion, the CH3+ + Br(2P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br(2P3/2) formation is through vibronic coupling to the high vibrational level of X2E state followed by rapid dissociation. C-Br bond breaking of CH3Br+(B2E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

  7. A HIGH-RESOLUTION PHOTOIONIZATION AND PHOTOELECTRON STUDY OF {sup 58}Ni USING A VACUUM ULTRAVIOLET LASER

    SciTech Connect

    Shi Xiaoyu; Huang Huang; Jacobson, Brian; Chang, Yih-Chung; Ng, C. Y.; Yin Qingzhu

    2012-03-01

    In order to provide high-resolution spectroscopic data of nickel ({sup 58}Ni) and its cation ({sup 58}Ni{sup +}) for the assignment of vacuum ultraviolet (VUV) stellar spectra, we have obtained the photoionization efficiency (PIE) spectra of {sup 58}Ni by using a supersonically cooled laser ablation transition-metal beam source and a broadly tunable VUV laser in the range of 61,100-73,600 cm{sup -1}, covering the photoionization transitions: Ni{sup +} (3d{sup 92} D) <- Ni (3d{sup 8}4s{sup 23} D), Ni{sup +}(3d{sup 92} D) <- Ni(3d{sup 8}4s{sup 23} F), and Ni{sup +} (3d{sup 8}4s{sup 4} F) <- Ni(3d{sup 8}4s{sup 23} F). We have also measured the VUV laser pulsed-field-ionization-photoelectron (PFI-PE) spectra of {sup 58}Ni in these regions. The VUV-PFI-PE measurement has allowed the determination of a precise value of 61,619.89 {+-} 0.8 cm{sup -1} (7.6399 {+-} 0.0001 eV) for the ionization energy (IE) of {sup 58}Ni. Due to the narrow VUV laser optical bandwidth of 0.4 cm{sup -1} used in the present study, many complex autoionizing resonances exhibiting Fano line shape profiles are resolved in the PIE spectra. Four autoionizing Rydberg series originating from two-electron and one-electron excitations from the Ni(3d{sup 8}4s{sup 23} F{sub 4}) ground state to converge to the respective Ni{sup +}({sup 2} D{sub 3/2}) and Ni{sup +}({sup 4} F{sub J} ) (J = 9/2, 7/2, and 5/2) ion states are identified. The Rydberg analysis, along with VUV-PFI-PE measurements, has yielded highly precise IE values for the formation of these excited ionic states from the Ni(3d{sup 8}4s{sup 23} F{sub 4}) ground state. The IE values, relative photoionization cross sections, and autoionizing Rydberg resonances observed in the present study are relevant to astrophysics by enhancing the atomic database of iron group transition metal atoms and for understanding the Ni and Ni{sup +} contribution to the VUV opacity in the solar atmosphere.

  8. Molecular Photoionization Calculations Using the Complex Basis Function Method.

    NASA Astrophysics Data System (ADS)

    Yu, Chin-Hui

    The complex basis function method (CBF) using both real and complex basis functions has been applied to the calculation of photoionization cross sections. The CBF method requires less computational resources than rigorous full-scattering methods and is effective for the evaluation of shape-resonance features. Neither the number of electrons in the system nor the molecular geometry is restricted. Moreover, the cross section obtained by the CBF method satisfies a variational principle and provides a practical diagnostic tool for the calculation of cross sections. The photoionization cross sections of H _sp{2}{+}, H _2, N_2, CO _2, and SF_6 have been computed using the CBF method. The computed partial cross sections for linear molecules agreed fairly well with other theoretical and experimental values. Particularly encouraging is the nearly perfect agreement of the CBF results with the results by rigorous full-scattering methods in the regions of sharp resonance features such as the K-shell ionization of N_2 and the 4sigma_{rm g} --> ksigma_ {rm u} transition of CO _2. The effect of averaging over all vibrational modes on the ionization cross sections for the 4 sigma_{rm g} orbital in CO_2 has also been studied for the first time. The resonance peak in the totally vibrationally averaged cross sections was reduced by 20%, but still represents a feature which has not yet been detected experimentally. The photoionization of SF_6 valence shells, 1t_{1rm g} , 5t_{1rm u}, 1t_{2rm u}, 3e _{rm g}, 1t_ {2rm g}, 4t_{1 rm u}, and 5a_{1 rm g}, has also been studied for the continuum symmetries a_{1rm g }, t_{1rm u} , e_{rm g}, and t_{2rm g}. The CBF results of SF_6 are numerically stable and essentially approach the static-exchange limit. These static-exchange partial cross sections, however, do not compare well with the experimental measurements. The discrepancy may be attributed to the physical approximations made in the theoretical model and to the quality of the ground -state

  9. Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging

    SciTech Connect

    Tang, Xiaofeng; Zhou, Xiaoguo E-mail: yanbing@jlu.edu.cn; Liu, Shilin; Sun, Zhongfa; Liu, Fuyi; Sheng, Liusi; Yan, Bing E-mail: yanbing@jlu.edu.cn

    2014-01-28

    Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.45–16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X{sup 2}E of CH{sub 3}Br{sup +} is stable, and both A{sup 2}A{sub 1} and B{sup 2}E ionic excited states are fully dissociative to produce the unique fragment ion of CH{sub 3}{sup +}. From TPEPICO 3D time-sliced velocity images of CH{sub 3}{sup +} dissociated from specific state-selected CH{sub 3}Br{sup +} ion, kinetic energy release distribution (KERD) and angular distribution of CH{sub 3}{sup +} fragment ion are directly obtained. Both spin-orbit states of Br({sup 2}P) atom can be clearly observed in fast dissociation of CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion along C–Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH{sub 3}Br{sup +}(B{sup 2}E) ion. With the aid of the re-calculated potential energy curves of CH{sub 3}Br{sup +} including spin-orbit coupling, dissociation mechanisms of CH{sub 3}Br{sup +} ion in A{sup 2}A{sub 1} and B{sup 2}E states along C–Br rupture are revealed. For CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion, the CH{sub 3}{sup +} + Br({sup 2}P{sub 1/2}) channel is occurred via an adiabatic dissociation by vibration, while the Br({sup 2}P{sub 3/2}) formation is through vibronic coupling to the high vibrational level of X{sup 2}E state followed by rapid dissociation. C–Br bond breaking of CH{sub 3}Br{sup +}(B{sup 2}E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

  10. High-resolution threshold photoelectron-photoion coincidence experiments performed on beamline 9.0.2.2: Kinetic energy release study of the process SF{sub 6} + hv {yields} SF{sub 5}{sup +} F + e{sup -}

    SciTech Connect

    Evans, M.; Ng, C.Y.; Hsu, C.W.; Heimann, P.

    1997-04-01

    Vacuum ultraviolet (VUV) photoionization mass spectrometry has been used extensively to determine the energetics of neutral radicals and radical cations, as well as to study the dynamics of the dissociative photoionization process. Very often these measurements are concerned with determining the appearance energy (AE) for a dissociative ionization process, as well as determining the heats of formation of the species involved. One such photoionization mass spectrometric technique employed on End Station 2 of the Chemical Dynamics Beamline (9.0.2.2) at the Advanced Light Source is the threshold photoelectron-photoion coincidence (TPEPICO) method. TPEPICO involves measuring the time-of-flight (TOF) mass spectrum of a given cation in coincidence with threshold photoelectrons at a known photoionization energy.

  11. Theoretical study of asymmetric molecular-frame photoelectron angular distributions for C 1s photoejection from CO2

    SciTech Connect

    Rescigno, Thomas N; Miyabe, S.; McCurdy, C.W.; Orel, A.E.

    2009-02-18

    We report the results of ab initio calculations of cross sections and molecular-frame photoelectron angular distributions for C 1s ionization of CO2, and propose a mechanism for the recently observed asymmetry of those angular distributions with respect to the CO^+and O^+ions produced by subsequent Auger decay. The fixed-nuclei, photoionization amplitudes were constructed using variationally obtained electron-molecular ion scattering wave functions. We have also carried out electronic structure calculations which identify a dissociative state of the CO2^++ dication that is likely populated following Auger decay and which leads to O^+ + CO^+ fragment ions. We show that a proper accounting of vibrational motion in the computation of the photoelectron angular distributions, along with reasonable assumptions about the nuclear dissociation dynamics, gives results in good agreement with recent experimental observations. We also demonstrate that destructive interference between different partial waves accounts for sudden changes with photon energy in the observed angular distributions.

  12. PCI effects and the gradual formation of Rydberg series due to photoelectron recapture, in the Auger satellite lines upon Xe 4d-15/2 photoionization

    NASA Astrophysics Data System (ADS)

    Kosugi, Satoshi; Iizawa, Masatomi; Kawarai, Yu; Kuriyama, Yosuke; Kilcoyne, A. L. David; Koike, Fumihiro; Kuze, Nobuhiko; Slaughter, Daniel S.; Azuma, Yoshiro

    2015-06-01

    The Xe (N5O2,3O2,3) Auger electron spectra originating from 4d-15/2 inner-shell photoionization were measured, with photon energy tuned close to the ionization threshold. As the photon energy approaches the threshold from above the 4d-15/2 photoionization threshold, Rydberg series structures are formed within the Auger electron peak by the recapture of the photoelectron into high-lying ion orbitals. They emerge in the tail on the higher energy side of the post-collision interaction (PCI) profile of the Auger electron. Discrete Rydberg peaks replace the continuous PCI tail and gradually form a series with intensity distribution emulating the intensity profile of the continuous tail. Structures due to the Xe+5p4(1S0, 1D2, 3P2,1,0) ml series were observed and assigned.

  13. A threshold photoelectron-photoion coincidence study of the N2O+ dissociation between 15 and 20.5 eV

    NASA Astrophysics Data System (ADS)

    Nenner, Irene; Guyon, Paul-Marie; Baer, Tomas; Govers, Thomas R.

    1980-06-01

    Branching ratios and the kinetic energy released in the various fragmentation channels of energy selected N2O+ (15-20.5 eV) were investigated by the technique of threshold photoelectron-photoion coincidence. Pulsed synchrotron radiation from ACO, Orsay's storage ring, dispersed by a monochromator, was used as a photon source. Threshold electrons were energy selected on the basis of angular and temporal discrimination against energetic electrons. The energy region below 16.388 eV and the ? state were investigated in detail. Below the ? state the most abundant fragment ion is O+, while above the ? state NO+ dominates. Results for the ? and ? states are also reported.

  14. High-resolution threshold photoelectron spectrum of molecular oxygen

    NASA Astrophysics Data System (ADS)

    Merkt, F.; Guyon, P. M.; Hepburn, J.

    1993-07-01

    The threshold TPE photoelectron spectrum of molecular oxygen has been reinvestigated using a partially cooled effusive molecular jet and the monochromatised VUV synchrotron radiation from super-ACO in Orsay. Three vibrational progressions are identified. One of them corresponds to and confirms that observed recently by Baltzer et al. (Phys. Rev. A 45 (1992) 4374), the two other ones are observed for the first time in TPE spectroscopy. Possible assignments for these progressions are discussed. The vibrational progression in the X 2Π g state has been seen up to v+=26 and the two spin-orbit components 2Π 1/2 and 2Π 3/2) are for the first time fully resolved in TPES. High-lying vibrational levels with v+ >20 of the X state are seen to overlap with the a state levels. The relative contribution of both states is obtained through a deconvolution procedure. The vibrational progression in the b 4Σ -g is extended to v+=18. The threshold photoelectron spectrum around 20 eV shows a particularly high density of lines. Possible assignments of these lines to new progressions are discussed with the help of a series of time-of-flight photoelectron spectra (TOF-PES) measured at a series of excitation energies between 18 and 20 eV.

  15. Multi-electron coincidence spectroscopy: double photoionization from molecular inner-shell orbitals

    NASA Astrophysics Data System (ADS)

    Hikosaka, Y.; Lablanquie, P.; Penent, F.; Nakano, M.; Ito, K.

    2014-04-01

    We have studied double photoionization from molecular inner-shell orbitals and investigated the properties of the resultant double core-hole states in molecules, by multi-electron coincidence spectroscopy with a magnetic bottle electron spectrometer. A brief summary of our previous studies is presented.

  16. Molecular photoionization cross sections by Stieltjes-Chebyshev moment theory applied to Lanczos pseudospectra

    SciTech Connect

    Gokhberg, K.; Vysotskiy, V.; Cederbaum, L. S.; Storchi, L.; Tarantelli, F.; Averbukh, V.

    2009-02-14

    Stieltjes imaging technique is widely used for the ab initio computation of photoionization cross sections and decay widths. The main problem hampering the application of the standard Stieltjes imaging algorithms in conjunction with high-level ab initio methods to polyatomic molecules is the requirement of full diagonalization of excessively large Hamiltonian matrices. Here we show that the full diagonalization bottleneck can be overcome by applying the Stieltjes imaging procedure to Lanczos pseudospectrum of the atomic or molecular Hamiltonian. Using the helium and neon atoms as examples, we demonstrate that the Lanczos pseudospectrum obtained after only a relatively small number of iterations can be used for Stieltjes-type calculations of photoionization cross sections essentially without loss of accuracy. The new technique is applied to the calculation of the total photoionization cross section of benzene within an ab initio approach explicitly taking into account single and double electronic excitations. Good agreement with experimental results is obtained.

  17. Correlation of molecular valence- and K-shell photoionization resonances with bond lengths

    NASA Technical Reports Server (NTRS)

    Sheehy, J. A.; Gil, T. J.; Winstead, C. L.; Farren, R. E.; Langhoff, P. W.

    1989-01-01

    The relationship between the interatomic distance and the positions of valence-shell and K-shell sigma(asterisk) photoionization resonances is investigated theoretically for the molecules C2, F2, N2, O2, CO, NO, C2H2, C2H4, C2H6, HCN, H2CO, N20, CO2, and C2N2. The results of molecular-orbital computations are presented in three-dimensional diagrams, which are shown to be similar to the wave functions of a particle in a cylindrical well, confirming the validity of free-electron molecular-orbital (FEMO) approximations for modeling the potential along the symmetry axis. FEMO orbital energies and resonance positions are found to be in good agreement with previous theoretical and experimental results. Also included is a Feshbach-Fano analysis of the relevance of virtual-valence orbitals to the appearance of single-channel resonances in molecular photoionization cross sections.

  18. Two-center interference in molecular photoelectron energy spectra with intense attosecond circularly polarized XUV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bian, Xue-Bin; Bandrauk, André D.

    2014-08-01

    We study two-center electron interference in molecular photoionization processes by intense attosecond circularly polarized extreme ultraviolet (XUV) laser pulses in both symmetric H2+ and nonsymmetric HHe2+ one-electron diatomic systems. Simulations from numerical solutions of time-dependent Schrödinger equations for the oriented symmetric molecular ion H2+ exhibit a signature of interference with double peaks (minima) in molecular attosecond photoelectron energy spectra (MAPES) at critical angles ϑc between the continuum electron momentum pe and the molecular internuclear R axis. The interference patterns are shown to be influenced by the molecular Coulomb potential, leading to a shift of the critical angle ϑc. Dependence of the two-center interference on the pulse ellipticity is also investigated. Furthermore, it is found that the interference phenomena are critically sensitive to the molecular orbital symmetry. For the nonsymmetric molecular ion HHe2+, such double peaks in MAPES also occur, thus suggesting a method for imaging orbitals in molecules by intense ultrashort circularly polarized XUV pulses on the attosecond time scale.

  19. Theoretical study of asymmetric molecular-frame photoelectron angular distributions for C 1s photoejection from CO{sub 2}

    SciTech Connect

    Miyabe, S.; McCurdy, C. W.; Orel, A. E.; Rescigno, T. N.

    2009-05-15

    We report the results of ab initio calculations of cross sections and molecular-frame photoelectron angular distributions for C 1s ionization of CO{sub 2} and propose a mechanism for the recently observed asymmetry of those angular distributions with respect to the CO{sup +} and O{sup +} ions produced by subsequent Auger decay. The fixed-nuclei, photoionization amplitudes were constructed using variationally obtained electron-molecular ion scattering wave functions. We have also carried out electronic structure calculations which identify a dissociative state of the CO{sub 2}{sup 2+} dication that is likely populated following Auger decay and which leads to O{sup +}+CO{sup +} fragment ions. We show that a proper accounting of vibrational motion in the computation of the photoelectron angular distributions, along with reasonable assumptions about the nuclear dissociation dynamics, gives results in good agreement with recent experimental observations. We also demonstrate that destructive interference between different partial waves accounts for sudden changes with photon energy in the observed angular distributions.

  20. Role of nuclear dynamics in the Asymmetric molecular-frame photoelectron angular distributions for C 1s photoejection from CO{sub 2}

    SciTech Connect

    Miyabe, Shungo; Haxton, Dan; Rescigno, Tom; McCurdy, Bill

    2010-11-30

    We report the results of semiclassical calculations of the asymmetric molecular-frame photoelectron angular distributions for C 1s ionization of CO{sub 2} measured with respect to the CO{sup +} and O{sup +} ions produced by subsequent Auger decay, and show how the decay event can be used to probe ultrafast molecular dynamics of the transient cation. The fixed-nuclei photoionization amplitudes were constructed using variationally obtained electron-molecular ion scattering wave functions. The amplitudes are then used in a semiclassical manner to investigate their dependence on the nuclear dynamics of the cation. The method introduced here can be used to study other core-level ionization events.

  1. Rotationally resolved state-to-state photoionization and photoelectron study of titanium carbide and its cation (TiC/TiC{sup +})

    SciTech Connect

    Luo, Zhihong; Huang, Huang; Chang, Yih-Chung; Zhang, Zheng; Ng, C. Y.; Yin, Qing-Zhu

    2014-10-14

    Titanium carbide and its cation (TiC/TiC{sup +}) have been investigated by the two-color visible (VIS)-ultraviolet (UV) resonance-enhanced photoionization and pulsed field ionization-photoelectron (PFI-PE) methods. Two visible excitation bands for neutral TiC are observed at 16 446 and 16 930 cm{sup −1}. Based on rotational analyses, these bands are assigned as the respective TiC({sup 3}Π{sub 1}) ← TiC(X{sup 3}Σ{sup +}) and TiC({sup 3}Σ{sup +}) ← TiC(X{sup 3}Σ{sup +}) transition bands. This assignment supports that the electronic configuration and term symmetry for the neutral TiC ground state are …7σ{sup 2}8σ{sup 1}9σ{sup 1}3π{sup 4} (X{sup 3}Σ{sup +}). The rotational constant and the corresponding bond distance of TiC(X{sup 3}Σ{sup +}; v″ = 0) are determined to be B{sub 0}″ = 0.6112(10) cm{sup −1} and r{sub 0}″ = 1.695(2) Å, respectively. The rotational analyses of the VIS-UV-PFI-PE spectra for the TiC{sup +}(X; v{sup +} = 0 and 1) vibrational bands show that the electronic configuration and term symmetry for the ionic TiC{sup +} ground state are …7σ{sup 2}8σ{sup 1}3π{sup 4} (X{sup 2}Σ{sup +}) with the v{sup +} = 0 → 1 vibrational spacing of 870.0(8) cm{sup −1} and the rotational constants of B{sub e}{sup +} = 0.6322(28) cm{sup −1}, and α{sub e}{sup +} = 0.0085(28) cm{sup −1}. The latter rotational constants yield the equilibrium bond distance of r{sub e}{sup +} = 1.667(4) Å for TiC{sup +}(X{sup 2}Σ{sup +}). The cleanly rotationally resolved VIS-UV-PFI-PE spectra have also provided a highly precise value of 53 200.2(8) cm{sup −1} [6.5960(1) eV] for the adiabatic ionization energy (IE) of TiC. This IE(TiC) value along with the known IE(Ti) has made possible the determination of the difference between the 0 K bond dissociation energy (D{sub 0}) of TiC{sup +}(X{sup 2}Σ{sup +}) and that of TiC(X{sup 3}Σ{sup +}) to be D{sub 0}(Ti{sup +}−C) − D{sub 0}(Ti−C) = 0.2322(2) eV. Similar to previous experimental

  2. O1s photoionization dynamics in oriented NO2

    NASA Astrophysics Data System (ADS)

    Stener, Mauro; Decleva, Piero; Yamazaki, Masakazu; Adachi, Jun-ichi; Yagishita, Akira

    2011-05-01

    We have performed extensive density functional theory (DFT) calculations, partial cross sections, dipole prepared continuum orbitals, dipole amplitudes and phase shifts, asymmetry parameters β, and molecular frame photoelectron angular distributions, to elucidate the O1s photoionization dynamics of NO2 molecule with emphasis on the shape resonances in the O1s ionization continuum. In the shape resonance region, the β parameters and photoelectron angular distributions have been compared with our experimental results. Fairly good agreement between the theory and experiment has confirmed that the DFT level calculations can well describe the photoionization dynamics of the simple molecule such as NO2. Interference due to equivalent atom photoionization is theoretically considered, and the possibility of detection of the effect in the two degenerate channels with different combinations of light polarization and photoemission direction is discussed.

  3. High temperature and high resolution uv photoelectron spectroscopy using supersonic molecular beams

    SciTech Connect

    Wang, Lai-Sheng; Reutt-Robey, J.E.; Niu, B.; Lee, Y.T.; Shirley, D.A.; Maryland Univ., College Park, MD . Dept. of Chemistry and Biochemistry; Lawrence Berkeley Lab., CA )

    1989-07-01

    A high temperature molecular beam source with electron bombardment heating has been built for high resolution photoelectron spectroscopic studies of high temperature species and clusters. This source has the advantages of: producing an intense, continuous, seeded molecular beam, eliminating the interference of the heating mechanism from the photoelectron measurement. Coupling the source with our hemispherical electron energy analyzer, we can obtain very high resolution HeI{alpha} (584{angstrom}) photoelectron spectra of high temperature species. Vibrationally-resolved photoelectron spectra of PbSe, As{sub 2}, As{sub 4}, and ZnCl{sub 2} are shown to demonstrate the performance of the new source. 25 refs., 8 figs., 1 tab.

  4. Electron-Vibration Coupling in Molecular Materials: Assignment of Vibronic Modes from Photoelectron Momentum Mapping

    NASA Astrophysics Data System (ADS)

    Graus, M.; Grimm, M.; Metzger, C.; Dauth, M.; Tusche, C.; Kirschner, J.; Kümmel, S.; Schöll, A.; Reinert, F.

    2016-04-01

    Electron-phonon coupling is one of the most fundamental effects in condensed matter physics. We here demonstrate that photoelectron momentum mapping can reveal and visualize the coupling between specific vibrational modes and electronic excitations. When imaging molecular orbitals with high energy resolution, the intensity patterns of photoelectrons of the vibronic sidebands of molecular states show characteristic changes due to the distortion of the molecular frame in the vibronically excited state. By comparison to simulations, an assignment of specific vibronic modes is possible, thus providing unique information on the coupling between electronic and vibronic excitation.

  5. Electron-Vibration Coupling in Molecular Materials: Assignment of Vibronic Modes from Photoelectron Momentum Mapping.

    PubMed

    Graus, M; Grimm, M; Metzger, C; Dauth, M; Tusche, C; Kirschner, J; Kümmel, S; Schöll, A; Reinert, F

    2016-04-01

    Electron-phonon coupling is one of the most fundamental effects in condensed matter physics. We here demonstrate that photoelectron momentum mapping can reveal and visualize the coupling between specific vibrational modes and electronic excitations. When imaging molecular orbitals with high energy resolution, the intensity patterns of photoelectrons of the vibronic sidebands of molecular states show characteristic changes due to the distortion of the molecular frame in the vibronically excited state. By comparison to simulations, an assignment of specific vibronic modes is possible, thus providing unique information on the coupling between electronic and vibronic excitation. PMID:27104726

  6. Photoelectron Spectra

    ERIC Educational Resources Information Center

    Bock, Hans; Mollere, Phillip D.

    1974-01-01

    Presents an experimental approach to teaching molecular orbital models. Suggests utilizing photoelectron spectroscopy and molecular orbital theory as complementary approaches to teaching the qualitative concepts basic to molecular orbital theory. (SLH)

  7. Molecular Frame Photoelectron Angular Distributions for Core Ionization of CF4 and C2H2F2

    NASA Astrophysics Data System (ADS)

    Trevisan, C. S.; Williams, J. B.; Menssen, A. J.; Rescigno, T. N.; Dorner, R.; McCurdy, C. W.

    2015-05-01

    We present experimental and theoretical results for the angular dependence of electrons ejected from the core orbitals of tetrafluoromethane (CF4) which display a tendency to avoid molecular bonds if averaged over directions of polarization of the incident X-ray beam, in contrast to earlier cases (CH4, H2O and NH3) studied by the same methods. To investigate whether the imaging effect can be used to detect the creation of core holes by photoionization from one of two atoms of the same type in a molecule, we computed and measured MFPADs of difluoroethylene (C2H2F2). Good agreement with the experimentally measured angular distributions show that the MFPADs contain the clear signature of the core-hole origin of the photoelectron, and validate the use of computed MFPADs as promising tools for the interpretation of such experiments. Our measurements employ the COLTRIMS method and the calculations were performed with the Complex Kohn Variational method. Work supported in part by the USDOE, Office of Science, Office of WDTS under the Visiting Faculty Program.

  8. Molecular photoemission studies using synchrotron radiation

    SciTech Connect

    Truesdale, C.M.

    1983-04-01

    The angular distributions of photoelectrons and Auger electrons were measured by electron spectroscopy using synchrotron radiation. The experimental results are compared with theoretical calculations to interpret the electronic behavior of photoionization for molecular systems.

  9. Dissociative and double photoionization of CO2 from threshold to 90 A

    NASA Technical Reports Server (NTRS)

    Masuoka, T.; Samson, J. A. R.

    1979-01-01

    The molecular photoionization, dissociative photoionization and double photoionization cross sections for CO2 were measured from their onsets down to 90 A by using various combinations of mass spectrometers (a coincidence time-of-flight mass spectrometer and a magnetic mass spectrometer) and light sources (synchrotron radiation, and glow and spark discharge). It is concluded that the one broad peak and the three shoulders in the total adsorption cross section curve between 640 and 90 A are caused completely by dissociative ionization processes. Several peaks observed in the cross section curve for the total fragmentation CO(+)3, O(+) and C(+) are compared with those in the photoelectron spectrum reported for CO2.

  10. Structural and electronic characterization of self-assembled molecular nanoarchitectures by X-ray photoelectron spectroscopy.

    PubMed

    Gulino, Antonino

    2013-02-01

    Molecular monolayers and similar nanoarchitectures are indicative of the promising future of nanotechnology. Therefore, many scientists recently devoted their efforts to the synthesis, characterization, and properties of mono- and multilayer-based systems. In this context, X-ray photoelectron spectroscopy is an important technique for the in-depth chemical and structural characterization of nanoscopic systems. In fact, it is a surface technique suitable for probing thicknesses of the same order of the photoelectron inelastic mean free paths (a few tens of ångströms) and allows one to immediately obtain qualitative and quantitative data, film thickness, surface coverage, molecule footprint, oxidation states, and presence of functional groups. Nevertheless, other techniques are important in obtaining a complete spectroscopic characterization of the investigated systems. Therefore, in the present review we report on X-ray photoelectron spectroscopy of self-assembled molecular mono- and multilayer materials including some examples on which other characterization techniques produced important results. PMID:23014858

  11. Photoionization Dynamics in Pure Helium Droplets

    SciTech Connect

    Peterka, Darcy S.; Kim, Jeong Hyun; Wang, Chia C.; Poisson,Lionel; Neumark, Daniel M.

    2007-02-04

    The photoionization and photoelectron spectroscopy of pure He droplets are investigated at photon energies between 24.6 eV (the ionization energy of He) and 28 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, the photoelectron images are dominated by fast electrons produced via direct ionization of He atoms, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a 'dimer model', in which one assumes vertical ionization from two nearest neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanism for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core.

  12. Pulsed field-ionization photoelectron-photoion coincidence study of the process N{sub 2}+h{nu}{yields}N{sup +}+N+e{sup -}: Bond dissociation energies of N{sub 2} and N{sub 2}{sup +}

    SciTech Connect

    Tang Xiaonan; Hou Yu; Ng, C.Y.; Ruscic, Branko

    2005-08-15

    We have examined the dissociative photoionization reaction N{sub 2}+h{nu}{yields}N{sup +}+N+e{sup -} near its threshold using the pulsed field-ionization photoelectron-photoion coincidence (PFI-PEPICO) time-of-flight (TOF) method. By examining the kinetic-energy release based on the simulation of the N{sup +} PFI-PEPICO TOF peak profile as a function of vacuum ultraviolet photon energy and by analyzing the breakdown curves of N{sup +} and N{sub 2}{sup +}, we have determined the 0-K threshold or appearance energy (AE) of this reaction to be 24.2884{+-}0.0010 eV. Using this 0-K AE, together with known ionization energies of N and N{sub 2}, results in more precise values for the 0-K bond dissociation energies of N-N (9.7543{+-}0.0010 eV) and N-N{sup +} (8.7076{+-}0.0010 eV) and the 0-K heats of formation for N (112.469{+-}0.012 kcal/mol) and N{sup +} (447.634{+-}0.012 kcal/mol)

  13. Few-femtosecond sensitivity of ultrafast molecular dynamics with time-resolved photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Champenois, Elio G.; Cryan, James P.; Larsen, Kirk; Shivaram, Niranjan H.; Belkacem, Ali

    2016-05-01

    We explore ultrafast dynamics involving non-adiabatic couplings following valence electronic excitation of small molecular systems. By measuring the time-resolved photoelectron spectra (TRPES) resulting from ionization with ultraviolet light, the excited wave packet can be tracked with state specificity. If the nuclear motion is dominated by a limited number of degrees of freedom, the TRPES also yields information about the molecular geometry. Even with limited temporal resolution, the onset times of the signal at different photoelectron energies can lead to few-femtosecond sensitivity. Applying this technique to ethylene (C2 H4) excited to the ππ* state, ultrafast motion along the twist coordinate is observed along with transient population to the π 3 s state through non-adiabatic coupling. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Divison under Contract No. DE-AC02-05CH11231.

  14. Photoionization study of quasibound states of doubly charged molecular nitrogen ions

    NASA Astrophysics Data System (ADS)

    Hellner, L.; Besnard, M. J.; Dujardin, G.; Malinovich, Y.

    1988-01-01

    Doubly charged N 22+ ions were produced by double photoionization of neutral nitrogen molecules with the synchrotron radiation from ACO as a photon source of variable energy in the 40-70 eV range. From the double photoionization spectrum the threshold energy of the stable X 1Σ g+ state was found at 43.1 ± 0.1 eV. The D 1Σ g+ → X 1Σ g+ emission observed by using a photoion-photon of fluorescence coincidence (PIFCO) experiment. The onset energy of this emitting D 1Σ u+ state at 50.5 eV, was deduced from the variation of the fluorescence efficiency as a function of the excitation photon energy. The lifetime of this emitting state was measured to be τ = 8 ± 3 ns.

  15. Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions.

    PubMed

    Olivieri, Giorgia; Parry, Krista M; Powell, Cedric J; Tobias, Douglas J; Brown, Matthew A

    2016-04-21

    Over the past decade, energy-dependent ambient pressure X-ray photoelectron spectroscopy(XPS) has emerged as a powerful analytical probe of the ion spatial distributions at the vapor (vacuum)-aqueous electrolyteinterface. These experiments are often paired with complementary molecular dynamics (MD) simulations in an attempt to provide a complete description of the liquidinterface. There is, however, no systematic protocol that permits a straightforward comparison of the two sets of results. XPS is an integrated technique that averages signals from multiple layers in a solution even at the lowest photoelectron kinetic energies routinely employed, whereas MD simulations provide a microscopic layer-by-layer description of the solution composition near the interface. Here, we use the National Institute of Standards and Technology database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to quantitatively interpret atom-density profiles from MD simulations for XPS signal intensities using sodium and potassium iodide solutions as examples. We show that electron inelastic mean free paths calculated from a semi-empirical formula depend strongly on solution composition, varying by up to 30% between pure water and concentrated NaI. The XPS signal thus arises from different information depths in different solutions for a fixed photoelectron kinetic energy. XPS signal intensities are calculated using SESSA as a function of photoelectron kinetic energy (probe depth) and compared with a widely employed ad hoc method. SESSA simulations illustrate the importance of accounting for elastic-scattering events at low photoelectron kinetic energies (<300 eV) where the ad hoc method systematically underestimates the preferential enhancement of anions over cations. Finally, some technical aspects of applying SESSA to liquidinterfaces are discussed. PMID:27389231

  16. Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

    NASA Astrophysics Data System (ADS)

    Olivieri, Giorgia; Parry, Krista M.; Powell, Cedric J.; Tobias, Douglas J.; Brown, Matthew A.

    2016-04-01

    Over the past decade, energy-dependent ambient pressure X-ray photoelectron spectroscopy (XPS) has emerged as a powerful analytical probe of the ion spatial distributions at the vapor (vacuum)-aqueous electrolyte interface. These experiments are often paired with complementary molecular dynamics (MD) simulations in an attempt to provide a complete description of the liquid interface. There is, however, no systematic protocol that permits a straightforward comparison of the two sets of results. XPS is an integrated technique that averages signals from multiple layers in a solution even at the lowest photoelectron kinetic energies routinely employed, whereas MD simulations provide a microscopic layer-by-layer description of the solution composition near the interface. Here, we use the National Institute of Standards and Technology database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to quantitatively interpret atom-density profiles from MD simulations for XPS signal intensities using sodium and potassium iodide solutions as examples. We show that electron inelastic mean free paths calculated from a semi-empirical formula depend strongly on solution composition, varying by up to 30% between pure water and concentrated NaI. The XPS signal thus arises from different information depths in different solutions for a fixed photoelectron kinetic energy. XPS signal intensities are calculated using SESSA as a function of photoelectron kinetic energy (probe depth) and compared with a widely employed ad hoc method. SESSA simulations illustrate the importance of accounting for elastic-scattering events at low photoelectron kinetic energies (<300 eV) where the ad hoc method systematically underestimates the preferential enhancement of anions over cations. Finally, some technical aspects of applying SESSA to liquid interfaces are discussed.

  17. Relative Photoionization Cross Sections of Super-Atom Molecular Orbitals (SAMOs) in C60.

    PubMed

    Bohl, Elvira; Sokół, Katarzyna P; Mignolet, Benoit; Thompson, James O F; Johansson, J Olof; Remacle, Francoise; Campbell, Eleanor E B

    2015-11-25

    The electronic structure and photoinduced dynamics of fullerenes, especially C60, is of great interest because these molecules are model systems for more complex molecules and nanomaterials. In this work we have used Rydberg Fingerprint Spectroscopy to determine the relative ionization intensities from excited SAMO (Rydberg-like) states in C60 as a function of laser wavelength. The relative ionization intensities are then compared to the ratio of the photoionization widths of the Rydberg-like states, computed in time-dependent density functional theory (TD-DFT). The agreement is remarkably good when the same photon order is required to energetically access the excited states. This illustrates the predictive potential of quantum chemistry for studying photoionization of large, complex molecules as well as confirming the assumption that is often made concerning the multiphoton excitation and rapid energy redistribution in the fullerenes. PMID:26551039

  18. Classical two-split interference effects in double photoionization of molecular hydrogen at high energies

    SciTech Connect

    Horner, Daniel A; Miyabe, S; Rescigno, T N; Mccurdy, C W; Morales, F; Martin, F

    2009-01-01

    The authors report a thorough theoretical study of one photon double ionization of H{sub 2}. They suggest that interference effects reported in one photon ionization will be reproducible in the case of double ionization when one of the photons carriers most of the available energy and the other electron is not observed. These calculations reproduce recent double photoionization experiments of H{sub 2}.

  19. Exploring Ultrafast Molecular Dynamics using Photoelectron Spectra from UV/XUV Pump-Probe Experiments

    NASA Astrophysics Data System (ADS)

    Champenois, Elio; Cryan, James; Shivaram, Niranjan; Wright, Travis; Belkacem, Ali

    2015-05-01

    The motion of atoms in molecules can drive electron dynamics via non-adiabatic couplings. In small molecules such as Ethylene, Carbon Dioxide, and Nitrophenol, this can lead to isomerization, electronic relaxation, or other time-dependent effects following excitation from a bonding to an anti-bonding molecular orbital. To study these mechanisms, we use ultraviolet photons of various energies from a bright High Harmonic Generation source to first initiate dynamics and subsequently probe the system through ionization. We record the kinetic energy and angular distribution of the resultant photoelectrons using a Velocity Map Imaging spectrometer, allowing us to track the evolution of the electronic state.

  20. Combustion chemistry of the propanol isomers : investigated by electron ionization and VUV-photoionization molecular-beam mass spectrometry.

    SciTech Connect

    Wang, J.; Kohse-Hoinghaus, Katharina; Cool, Terrill A.; Taatjes, Craig A.; Struckmeier, Ulf; OBwald, Patrick; Morel, Aude; Westmoreland, Phillip R.; Kasper, Tina Silvia

    2008-10-01

    The combustion of 1-propanol and 2-propanol was studied in low-pressure, premixed flat flames using two independent molecular-beam mass spectrometry (MBMS) techniques. For each alcohol, a set of three flames with different stoichiometries was measured, providing an extensive data base with in total twelve conditions. Profiles of stable and intermediate species, including several radicals, were measured as a function of height above the burner. The major-species mole fraction profiles in the 1-propanol flames and the 2-propanol flames of corresponding stoichiometry are nearly identical, and only small quantitative variations in the intermediate species pool could be detected. Differences between flames of the isomeric fuels are most pronounced for oxygenated intermediates that can be formed directly from the fuel during the oxidation process. The analysis of the species pool in the set of flames was greatly facilitated by using two complementary MBMS techniques. One apparatus employs electron ionization (EI) and the other uses VUV light for single-photon ionization (VUV-PI). The photoionization technique offers a much higher energy resolution than electron ionization and as a consequence, near-threshold photoionization-efficiency measurements provide selective detection of individual isomers. The EI data are recorded with a higher mass resolution than the PI spectra, thus enabling separation of mass overlaps of species with similar ionization energies that may be difficult to distinguish in the photoionization data. The quantitative agreement between the EI- and PI-datasets is good. In addition, the information in the EI- and PI-datasets is complementary, aiding in the assessment of the quality of individual burner profiles. The species profiles are supplemented by flame temperature profiles. The considerable experimental efforts to unambiguously assign intermediate species and to provide reliable quantitative concentrations are thought to be valuable for improving

  1. Combustion chemistry of the propanol isomers - investigated by electron ionization and VUV-photoionization molecular-beam mass spectrometry

    SciTech Connect

    Kasper, T.; Osswald, P.; Struckmeier, U.; Kohse-Hoeinghaus, K.; Taatjes, C.A.; Wang, J.; Cool, T.A.; Law, M.E.; Morel, A.; Westmoreland, P.R.

    2009-06-15

    The combustion of 1-propanol and 2-propanol was studied in low-pressure, premixed flat flames using two independent molecular-beam mass spectrometry (MBMS) techniques. For each alcohol, a set of three flames with different stoichiometries was measured, providing an extensive data base with in total twelve conditions. Profiles of stable and intermediate species, including several radicals, were measured as a function of height above the burner. The major-species mole fraction profiles in the 1-propanol flames and the 2-propanol flames of corresponding stoichiometry are nearly identical, and only small quantitative variations in the intermediate species pool could be detected. Differences between flames of the isomeric fuels are most pronounced for oxygenated intermediates that can be formed directly from the fuel during the oxidation process. The analysis of the species pool in the set of flames was greatly facilitated by using two complementary MBMS techniques. One apparatus employs electron ionization (EI) and the other uses VUV light for single-photon ionization (VUV-PI). The photoionization technique offers a much higher energy resolution than electron ionization and as a consequence, near-threshold photoionization-efficiency measurements provide selective detection of individual isomers. The EI data are recorded with a higher mass resolution than the PI spectra, thus enabling separation of mass overlaps of species with similar ionization energies that may be difficult to distinguish in the photoionization data. The quantitative agreement between the EI- and PI-datasets is good. In addition, the information in the EI- and PI-datasets is complementary, aiding in the assessment of the quality of individual burner profiles. The species profiles are supplemented by flame temperature profiles. The considerable experimental efforts to unambiguously assign intermediate species and to provide reliable quantitative concentrations are thought to be valuable for improving

  2. Spin–orbit interaction mediated molecular dissociation

    SciTech Connect

    Kokkonen, E. Jänkälä, K.; Kettunen, J. A.; Heinäsmäki, S.; Karpenko, A.; Huttula, M.; Löytynoja, T.

    2014-05-14

    The effect of the spin–orbit interaction to photofragmentation is investigated in the mercury(II) bromide (HgBr{sub 2}) molecule. Changes in the fragmentation between the two spin–orbit components of Hg 5d photoionization, as well as within the molecular-field-splitted levels of these components are observed. Dissociation subsequent to photoionization is studied with synchrotron radiation and photoelectron-photoion coincidence spectroscopy. The experimental results are accompanied by relativistic ab initio analysis of the photoelectron spectrum.

  3. Spectral investigations of photoionized plasmas induced in atomic and molecular gases using nanosecond extreme ultraviolet (EUV) pulses

    SciTech Connect

    Bartnik, A.; Fiedorowicz, H.; Wachulak, P.

    2014-07-15

    In this paper, results of spectral investigations of low temperature photoionized plasmas, created by irradiation of gases with intense pulses of extreme ultraviolet (EUV) radiation from a laser-produced plasma (LPP) source, are presented. The LPP source was based on a double-stream KrXe/He gas-puff target irradiated with 4 ns/0.8 J/10 Hz Nd:YAG laser pulses. The most intense emission from the source spanned a relatively narrow spectral region λ ≈ 10–12 nm; however, spectrally integrated intensity at longer wavelengths was also significant. The EUV beam was focused on a gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Irradiation of gases resulted in formation of photoionized plasmas emitting radiation in the EUV range. Radiation spectra, measured for plasmas produced in various gases, are dominated by emission lines, originating from single charged ions. Significant differences in spectral intensities and distributions between plasmas created in neon and molecular gases were observed.

  4. Classical two-slit interference effects in double photoionization of molecular hydrogen at high energies

    SciTech Connect

    Horner, Daniel A.; Miyabe, Shungo; Rescigno, Thomas N; McCurdy, C. William; Morales, Felipe; Martin, Fernando

    2008-07-06

    Recent experiments on double photoionization of H$_2$ with photon energies between 160 and 240 eV have revealed body-frame angular distributions that suggest classical two-slit interference effects may be present when one electron carries most of the available energy and the second electron is not observed. We report precise quantum mechanical calculations that reproduce the experimental findings. They reveal that the interpretation in terms of classical diffraction is only appropriate atsubstantially higher photon energies. At the energies considered in the experiment we offer an alternative explanation based on the mixing of two non-diffractive contributions by circularly polarized light.

  5. Atomic and Molecular Photoelectron and Auger Electron SpectroscopyStudies Using Synchrotron Radiation

    SciTech Connect

    Southworth, Stephen H.

    1982-01-01

    Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were a 130 measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra o f the ejected electrons. The ''a double-angle-TOF'' method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collect ion efficiency and the elimination of certain systematic errors. Several results were obtained for Xe using photon energies in the range hv {approx_equal} 60-190 eV, where excitation and ionization of the inner-subshell 4d electrons dominates. The 4d asymmetry parameter {beta} exhibits strong oscillations with energy, in agreement with several theoretical calculations. As predicted, the 5p asymmetry parameter was observed to deviate strongly from that calculated using the independent-electron model, due to intershell correlation with the 4d electrons.

  6. Photoelectron spectroscopy of the nitrogen dimer (N2)2 and clusters (N2)n: N2 dimer revealed as the chromophore in photoionization of condensed nitrogen

    NASA Astrophysics Data System (ADS)

    Carnovale, Frank; Peel, J. Barrie; Rothwell, Richard G.

    1988-01-01

    The He i photoelectron spectra of gas-phase nitrogen dimer and nitrogen clusters have been measured in a pulsed cluster beam. The dimer (N2)2 is characterized by broad bands with vertical ionization energies which are 0.3±0.1 eV lower than for N2 monomer. The bands observed for a mixture of small clusters, estimated to be of average size N¯=10, are identical to the dimer bands except for further shifts of 0.3 eV to lower ionization energies. The clusters bandwidths and band shapes are virtually the same as measured for thin films of condensed N2, indicating that the nitrogen dimer (N2)2 is the ionization chromophore in each case. This offers support for Haberland's hypothesis that ionization of any Mn cluster produces the ion M+2Mn-2 provided M is a closed-shell atom or molecule. The theory of electronic relaxation polarization of the dielectric medium, which explains the gas-to-solid ionization energy shifts, is modified for the case of finite clusters and to account for dimer ion formation.

  7. High resolution photoelectron spectroscopy and femtosecond intramolecular dynamics using supersonic molecular beams

    SciTech Connect

    Niu, B.

    1992-09-01

    High resolution He I[alpha] photoelectron spectroscopy of formaldehyde and ketene and their deuterated compounds, are reported. The combination of a (H2CO) double-pass high-resolution electron-energy analyzer and effective rotational cooling of the sample by supersonic expansion enable the spectroscopy of these molecular cations. The vibrational autocorrelation functions are calculated from the high-resolution photoelectron spectra, shedding light on the ultrafast intramolecular dynamics of the molecular cations. This study reveals much more vibrational structural detail in the first electronic excited state of H2CO cations. The first electronic excited state of H2CO cations may have nonplanar equilibrium geometry. Strong isotope effects on vibronic (vibrational) coupling are observed in the second electronic excited state of H2CO. Vibrational autocorrelation functions are calculated for all four observed electronic states of H2CO. The correlation function of the first electronic excited state of H2CO shows a slow decay rate on the femtosecond time scale. The ultrafast decay of the H2CO cations in the third electronic excited state implies that dissociation and intramolecular processes are the main decay pathways. The present spectra of the ground states of ketene cations have more fine structure than before. The AIEs of the first and fifth excited states are determined unambiguously more accurately. The doublet-like fine structures present in the lint excited state of ketene implies the excitation of a soft'' mode not observed before. The vibrational autocorrelation functions are calculated for 4 of the 6 observed electronic states. The dynamics of the ground states of the cations are characterized by a wave packet oscillating with small amplitude around the minimum on the upper PES. The decay dynamics of the first and the fifth excited states of ketene are characterized by ultra-fast intramolecular processes like predissociation.

  8. High resolution photoelectron spectroscopy and femtosecond intramolecular dynamics using supersonic molecular beams

    SciTech Connect

    Niu, B.

    1992-09-01

    High resolution He I{alpha} photoelectron spectroscopy of formaldehyde and ketene and their deuterated compounds, are reported. The combination of a (H2CO) double-pass high-resolution electron-energy analyzer and effective rotational cooling of the sample by supersonic expansion enable the spectroscopy of these molecular cations. The vibrational autocorrelation functions are calculated from the high-resolution photoelectron spectra, shedding light on the ultrafast intramolecular dynamics of the molecular cations. This study reveals much more vibrational structural detail in the first electronic excited state of H2CO cations. The first electronic excited state of H2CO cations may have nonplanar equilibrium geometry. Strong isotope effects on vibronic (vibrational) coupling are observed in the second electronic excited state of H2CO. Vibrational autocorrelation functions are calculated for all four observed electronic states of H2CO. The correlation function of the first electronic excited state of H2CO shows a slow decay rate on the femtosecond time scale. The ultrafast decay of the H2CO cations in the third electronic excited state implies that dissociation and intramolecular processes are the main decay pathways. The present spectra of the ground states of ketene cations have more fine structure than before. The AIEs of the first and fifth excited states are determined unambiguously more accurately. The doublet-like fine structures present in the lint excited state of ketene implies the excitation of a ``soft`` mode not observed before. The vibrational autocorrelation functions are calculated for 4 of the 6 observed electronic states. The dynamics of the ground states of the cations are characterized by a wave packet oscillating with small amplitude around the minimum on the upper PES. The decay dynamics of the first and the fifth excited states of ketene are characterized by ultra-fast intramolecular processes like predissociation.

  9. Thickness determination of molecularly thin lubricant films by angle-dependent X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Pang, Chongjun; Bai, Mingwu

    2007-03-01

    An angle-dependent X-ray photoelectron spectroscopy (XPS) method used to measure the thickness of molecularly thin lubricants was developed. The method was built based on an island model of patched overlayer on a flat substrate by using the photoemission signal solely from the lubricant film. Typical molecularly thin Zdol films on the CHx overcoat of unused commercial magnetic disks were measured to verify the metrology. The lubricant thickness determined by the metrology was equal to the recent result by thermostatic high vacuum atomic force microscopy. The measured deduction in the thickness of the molecularly thin lubricant films, successively irradiated by the monochromatic source operated at 14 kV/250 W, was as low as 1 Ǻ during the first irradiation hour. XPS spectra showed that no hydrocarbons, water or oxygen were adsorbed over the Zdol outer surfaces in the tested XPS conditions. The inelastic mean free path (IMFP) of C 1s in Zdol or in CHx was found to be independent of take off angle (TOA) when TOA < 40°. The IMFP of C 1s in Zdol was ˜63.5 Ǻ and the lubricant island thickness was ˜35 Ǻ.

  10. Breakdown of ionic character of molecular alkali bromides in inner-valence photoionization

    SciTech Connect

    Karpenko, A. Iablonskyi, D.; Kettunen, J. A.; Cao, W.; Huttula, M.; Aksela, H.; Urpelainen, S.

    2014-05-28

    The inner-valence region of alkali bromide XBr (X=Li, Na, K, Rb) vapours has been studied experimentally by means of synchrotron radiation excited photoelectron spectroscopy. Experimental spectra were analyzed by comparing them with available theoretical results and previous experiments. Ionic character of alkali bromides is seen to change in the inner-valence region with increasing atomic number of the alkali atom. A mechanism involving mixing between Br 4s and Rb 4p orbitals has been suggested to account for the fine structure observed in inner-valence ionization region of RbBr.

  11. Photoelectron Spectroscopy of Doped Helium Nanodroplets

    SciTech Connect

    Loginov, Evgeniy; Rossi, Dominic; Drabbels, Marcel

    2005-10-14

    The photoionization dynamics of aniline doped helium droplets has been investigated by photoelectron spectroscopy. The photoelectron spectra resemble closely that of gas phase aniline, except for a droplet-size-dependent shift. This shift is caused by lowering of the ionization threshold upon solvation and can be readily estimated. The individual peaks in the photoelectron spectrum are broadened towards lower kinetic energy which is attributed to the relaxation of the photoelectrons as they pass through the helium droplet.

  12. Fine- and hyperfine-structure effects in molecular photoionization. II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations.

    PubMed

    Germann, Matthias; Willitsch, Stefan

    2016-07-28

    Resonance-enhanced multiphoton ionization (REMPI) is a widely used technique for studying molecular photoionization and producing molecular cations for spectroscopy and dynamics studies. Here, we present a model for describing hyperfine-structure effects in the REMPI process and for predicting hyperfine populations in molecular ions produced by this method. This model is a generalization of our model for fine- and hyperfine-structure effects in one-photon ionization of molecules presented in Paper I [M. Germann and S. Willitsch, J. Chem. Phys. 145, 044314 (2016)]. This generalization is achieved by covering two main aspects: (1) treatment of the neutral bound-bound transition including the hyperfine structure that makes up the first step of the REMPI process and (2) modification of our ionization model to account for anisotropic populations resulting from this first excitation step. Our findings may be used for analyzing results from experiments with molecular ions produced by REMPI and may serve as a theoretical background for hyperfine-selective ionization experiments. PMID:27475369

  13. Fine- and hyperfine-structure effects in molecular photoionization. II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations

    NASA Astrophysics Data System (ADS)

    Germann, Matthias; Willitsch, Stefan

    2016-07-01

    Resonance-enhanced multiphoton ionization (REMPI) is a widely used technique for studying molecular photoionization and producing molecular cations for spectroscopy and dynamics studies. Here, we present a model for describing hyperfine-structure effects in the REMPI process and for predicting hyperfine populations in molecular ions produced by this method. This model is a generalization of our model for fine- and hyperfine-structure effects in one-photon ionization of molecules presented in Paper I [M. Germann and S. Willitsch, J. Chem. Phys. 145, 044314 (2016)]. This generalization is achieved by covering two main aspects: (1) treatment of the neutral bound-bound transition including the hyperfine structure that makes up the first step of the REMPI process and (2) modification of our ionization model to account for anisotropic populations resulting from this first excitation step. Our findings may be used for analyzing results from experiments with molecular ions produced by REMPI and may serve as a theoretical background for hyperfine-selective ionization experiments.

  14. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  15. Fourier transform photoelectron diffraction and its application to molecular orbitals and surface structure

    SciTech Connect

    Zhou, Xin

    1998-11-30

    Photoemission intensities from the molecular orbitals of c(2x2)CO/Pt(111) over a wide photon energy range were measured and analyzed by the same methods developed for structural studies using core levels. The 4{sigma} orbital center of gravity is found to be concentrated between the C and O atoms, while that of the 5{sigma} orbital lies between the C atom and the Pt surface. The C 1s photoelectron diffraction was used to determine the adsorption geometry. The earlier ambiguity that multiple scattering is needed to correctly model a {chi} curve while single scattering is sufficient for understanding major peaks in the ARPEFS-FTS is clarified by studying the clean Ni(111) surface. In the normal emission case, several different combinations of scattering events have similar path length differences (PLDs), and can either cancel each other or enhance the corresponding FT peak. In the off-normal case the degeneracy is greatly reduced due to the lower degree of symmetry. In normal emission AR PEFS, up to third order multiple scattering is needed to describe fully both the {chi} curve and its FT spectrum. To improve the spectral resolution in the ARPEFS-FT analysis, several new spectral analysis methods are introduced. With both autocorrelation autoregression (ACAR) and autocorrelation eigenvector (ACE), we can produce a reliable power spectrum by following the order-closing procedure. The best spectra are usually obtained when the autocorrelation sequence is computed with lags up to half the data range. A simple way of determining surface adsorption sites is proposed as follows: First use a single scattering cluster for possible adsorption sites to construct the geometrical PLDs from the strong backscattering events; then compare these PLDs with those obtained from the ARPEFS-FT analysis of the experimental data. After the preferred adsorption site is determined, fine tune the interlayer distances according to the positional R-factor.

  16. Gadolinium photoionization process

    DOEpatents

    Paisner, J.A.; Comaskey, B.J.; Haynam, C.A.; Eggert, J.H.

    1993-04-13

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  17. Gadolinium photoionization process

    DOEpatents

    Paisner, Jeffrey A.; Comaskey, Brian J.; Haynam, Christopher A.; Eggert, Jon H.

    1993-01-01

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  18. Molecular Calculations of the Photoionization of Endohedral Atoms: Ar@C60

    NASA Astrophysics Data System (ADS)

    Ponzi, A.; Stener, M.; Decleva, P.; Manson, S. T.

    2014-05-01

    Endohedral fullerenes represent a particularly clean case of quantum confinement where the electronic properties of the guest atom or molecule are strongly modified by the encapsulating host.. Many theoretical studies, e.g, have been performed both on free C60 and endohedral systems, and the predicted confinement resonances have been confirmed by recent experiment. Most calculations have employed jellium models for the C60 moiety, allowing the treatment of electron response effects and interchannel coupling, while the few molecular calculations have been limited to a static description, either at the DFT or static-exchange level, giving, however, some conflicting evidence with interpretations based on jellium treatments. The development of large scale TDDFT codes allows full treatment of nonspherical and response effects, and this methods is applied to Ar@C60, to compare with results and assess the modifications brought about by the full inclusion of the ionic cores. It is found that molecular effects increase hybridization of the atomic orbitals with the cage and reduces the role of response effects, due to the stronger localization of the electron cloud.

  19. Correlation between photoeletron and photoion in ultrafast multichannel photoionization of Ar

    SciTech Connect

    Itakura, R.; Fushitani, M.; Hishikawa, A.; Sako, T.

    2015-12-31

    We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar{sup +} associated with a superposition of the spin-orbit states {sup 2}PJ (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth.

  20. Merging quantum-chemistry with B-splines to describe molecular photoionization

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Marante, C.; Klinker, M.; Corral, I.; Gonzalez, J.; Martin, F.

    2016-05-01

    Theoretical description of observables in attosecond pump-probe experiments requires a good representation of the system's ionization continuum. For polyelectronic atoms and molecules, however, this is still a challenge, due to the complicated short-range structure of correlated electronic wavefunctions. Whereas quantum chemistry packages (QCP) implementing sophisticated methods to compute bound electronic molecular states are well established, comparable tools for the continuum are not widely available yet. To tackle this problem, we have developed a new approach that, by means of a hybrid Gaussian-B-spline basis, interfaces existing QCPs with close-coupling scattering methods. To illustrate the viability of this approach, we report results for the multichannel ionization of the helium atom and of the hydrogen molecule that are in excellent agreement with existing accurate benchmarks. These findings, together with the flexibility of QCPs, make of this approach a good candidate for the theoretical study of the ionization of poly-electronic systems. FP7/ERC Grant XCHEM 290853.

  1. Ultraviolet photoionization in CO2 TEA lasers

    NASA Astrophysics Data System (ADS)

    Scott, S. J.; Smith, A. L. S.

    1988-07-01

    The effects of gas composition and spark parameters on the UV emission in CO2 TEA laser gas mixtures were investigated together with the nature of photoionization process and the photoelectron-loss mechanism. A linear relationship was found between N2 concentration and photoionization (with no such dependence on C concentration, from CO and CO2), but the increases in photoionization that could be effected by optimizing the spark discharge circuit parameters were much higher than those produced by changes in gas composition. UV emission was directly proportional to the amount of stored electrical energy in the spark-discharge circuit and to the cube of the peak current produced in the spark by the discharge of this energy. Photoionization was also found to be proportional to the spark electrode gap. It was found that free-space sparks gave a considerably broader emission pattern than a surface-guided notched spark.

  2. Photoionization of argon clusters

    SciTech Connect

    Dehmer, Patricia M.; Pratt, Stephen T.

    1982-01-01

    Argon clusters were produced in a free supersonic molecular beam expansion of pure argon at room temperature and the photoionization efficiency curves of the trimer through hexamer were measured in the wavelength regions from threshold to 700 Â. A study of the Ar⁺3 photoionization efficiency curve as a function of nozzle stagnation pressure shows that fragmentation of heavier clusters can dominate the spectrum, even near threshold, and even when the nozzle conditions are such that the Ar⁺4 intensity is only a small fraction of the Ar⁺3 intensity. The Ar⁺3 photoionization efficiency curve, obtained using nozzle stagnation conditions such that no heavier ions were detected, exhibits several broad peaks near threshold which show similarities to bands of the dimer. At high nozzle stagnation pressures, the photoionization efficiency curves for Ar⁺3 to Ar⁺6 are nearly identical due to the effects of fragmentation. These spectra exhibit two very broad features which are similar to features observed in the solid. The threshold regions for all the positive ions show extremely gradual onsets, making it difficult to determine the appearance potentials accurately. The appearance potentials for Ar⁺2 and Ar⁺3 are 855.0±1.5 and 865.0±1.5 Â, respectively, yielding a value of 0.18±0.05 eV for the dissociation energy of Ar⁺3. The appearance potentials for the heavier clusters Ar⁺4 through Ar⁺6 are all approximately 870±2 Â.

  3. Probing and extracting the structure of vibrating SF6 molecules with inner-shell photoelectrons

    NASA Astrophysics Data System (ADS)

    Nguyen, Ngoc-Ty; Lucchese, R. R.; Lin, C. D.; Le, Anh-Thu

    2016-06-01

    We propose a scheme for probing the structure of vibrating molecules with photoelectrons generated from ultrashort soft-x-ray pulses. As an example we analyze below-100-eV photoelectrons liberated from the S (2 p ) orbital of vibrating SF6 molecules to image very small structural changes of molecular vibration. In particular, photoionization cross sections and photoelectron angular distributions (PAD) at nonequilibrium geometries can be retrieved accurately with photoelectrons near the shape resonance at 13 eV. This is achieved with a pump-probe scheme, in which the symmetric stretch mode is first Raman excited predominantly by a relatively short laser pulse and then later probed at different time delays by a few-femtosecond soft-x-ray pulse with photon energy near 200 eV.

  4. Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

    PubMed Central

    Greif, Michael; Nagy, Tibor; Soloviov, Maksym; Castiglioni, Luca; Hengsberger, Matthias; Meuwly, Markus; Osterwalder, Jürg

    2015-01-01

    A THz-pump and x-ray-probe experiment is simulated where x-ray photoelectron diffraction (XPD) patterns record the coherent vibrational motion of carbon monoxide molecules adsorbed on a Pt(111) surface. Using molecular dynamics simulations, the excitation of frustrated wagging-type motion of the CO molecules by a few-cycle pulse of 2 THz radiation is calculated. From the atomic coordinates, the time-resolved XPD patterns of the C 1s core level photoelectrons are generated. Due to the direct structural information in these data provided by the forward scattering maximum along the carbon-oxygen direction, the sequence of these patterns represents the equivalent of a molecular movie. PMID:26798798

  5. 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)

  6. Characterizing reactions to fabricate thin films of charge transfer complexes by synchrotron photoelectron spectroscopy: A case study of DCNQI-Cu

    NASA Astrophysics Data System (ADS)

    Shimada, Toshihiro; Mochida, Michihiro; Koma, Atsushi

    1997-04-01

    Ultraviolet photoelectron spectroscopy with various photon energies using synchrotron radiation was used to characterize chemical reactions associated with thin film growth of organic charge transfer complex (DMe-DCNQI) 2Cu. Other molecular systems H 2Pc, CuPc and C 60 were also studied to clarify the origin of the systematic relation between the spectra and the incident photon energy. Characteristic photon energy dependence of the photo-ionization cross section of molecular orbitals is useful to analyze the intermolecular reactions.

  7. Vacuum Ultraviolet Photoionization of Complex Chemical Systems

    NASA Astrophysics Data System (ADS)

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-01

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

  8. Vacuum Ultraviolet Photoionization of Complex Chemical Systems.

    PubMed

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-27

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed. PMID:26980311

  9. Near-Edge X-Ray Absorption Fine Structures Revealed in Core Ionization Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakano, M.; Selles, P.; Lablanquie, P.; Hikosaka, Y.; Penent, F.; Shigemasa, E.; Ito, K.; Carniato, S.

    2013-09-01

    Simultaneous core ionization and core excitation have been observed in the C2H2n (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K-2V) core excited states of the K-1 molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude.

  10. Near-edge x-ray absorption fine structures revealed in core ionization photoelectron spectroscopy.

    PubMed

    Nakano, M; Selles, P; Lablanquie, P; Hikosaka, Y; Penent, F; Shigemasa, E; Ito, K; Carniato, S

    2013-09-20

    Simultaneous core ionization and core excitation have been observed in the C(2)H(2n) (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K(-2)V) core excited states of the K(-1) molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude. PMID:24093255

  11. Near threshold studies of photoelectron satellites

    SciTech Connect

    Heimann, P.A.

    1986-11-01

    Photoelectron spectroscopy and synchrotron radiation have been used to study correlation effects in the rare gases: He, Ne, Ar, Kr, and Xe. Two kinds of time-of-flight electron analyzers were employed to examine photoionization very close to threshold and at higher kinetic energies. Partial cross sections and angular distributions have been measured for a number of photoelectron satellites. The shake-off probability has been determined at some inner-shell resonances. 121 refs., 28 figs., 13 tabs.

  12. Shape resonant features in the photoionization spectra of NO

    SciTech Connect

    Wallace, Scott; Dill, Dan; Dehmer, Joseph L.

    1982-01-01

    Calculations of core and valence level photoionization spectra of NO are presented and compared with available experimental data. A low-lying continuum shape resonance is identified in the sigma photoionization channel, which is the analog of similar states found in other first-row diatomic molecules. Both partial cross sections and photoelectron angular distributions are discussed, and the effect of nuclear motion on these observables is treated.

  13. Effects of dimerization on the photoelectron angular distribution parameters from chiral camphor enantiomers obtained with circularly polarized vacuum-ultraviolet radiation

    SciTech Connect

    Nahon, Laurent; Garcia, Gustavo A.; Soldi-Lose, Heloiese; Daly, Steven; Powis, Ivan

    2010-09-15

    As an intermediate state of matter between the free monomeric gas phase and the solid state, clusters may exhibit a specific electronic structure and photoionization dynamics that can be unraveled by different types of electron spectroscopies. From mass-selected ion yield scans measured for photoionization of (R)-camphor, the ionization potentials (IPs) of the monomer (8.66{+-}0.01 eV), and of the homochiral dimer ({<=}8.37{+-}0.01 eV) and trimer ({<=}8.30{+-}0.01 eV) were obtained. These spectra, combined with threshold photoelectron spectroscopy and velocity map ion imaging, allow us to show that the camphor monomer and dimer photoionization channels are decoupled, i.e., that the highest occupied molecular orbital (HOMO) of the dimer does not undergo a dissociative ionization process that would lead to a spurious contribution to the monomer ion channel. Therefore mass selection, as achieved in our imaging photoelectron-photoion coincidence experiments, leads to size selection of the nascent monomer or dimer species. Since both the monomer and dimer are chiral, their photoelectron angular distribution (PAD) not only involves the usual {beta} anisotropy parameter but also a chiral asymmetry parameter b{sub 1} that can generate a forward-backward asymmetry in the PAD. This has been investigated using circularly polarized light (CPL) to record the photoelectron circular dichroism (PECD) in the near-threshold vacuum-ultraviolet (VUV) photoionization region. Analysis of size-selected electron images recorded with left- and right-handed CPL shows that over the first 1.5 eV above the HOMO orbital ionization potentials (IPs), the {beta} parameter is not affected by the dimerization process, while the chiral b{sub 1} parameter shows clear differences between the monomer and the dimer, confirming that PECD is a subtle long-range probe of the molecular potential.

  14. Effects of dimerization on the photoelectron angular distribution parameters from chiral camphor enantiomers obtained with circularly polarized vacuum-ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Nahon, Laurent; Garcia, Gustavo A.; Soldi-Lose, Héloïse; Daly, Steven; Powis, Ivan

    2010-09-01

    As an intermediate state of matter between the free monomeric gas phase and the solid state, clusters may exhibit a specific electronic structure and photoionization dynamics that can be unraveled by different types of electron spectroscopies. From mass-selected ion yield scans measured for photoionization of (R)-camphor, the ionization potentials (IPs) of the monomer (8.66±0.01 eV), and of the homochiral dimer (⩽8.37±0.01 eV) and trimer (⩽8.30±0.01 eV) were obtained. These spectra, combined with threshold photoelectron spectroscopy and velocity map ion imaging, allow us to show that the camphor monomer and dimer photoionization channels are decoupled, i.e., that the highest occupied molecular orbital (HOMO) of the dimer does not undergo a dissociative ionization process that would lead to a spurious contribution to the monomer ion channel. Therefore mass selection, as achieved in our imaging photoelectron-photoion coincidence experiments, leads to size selection of the nascent monomer or dimer species. Since both the monomer and dimer are chiral, their photoelectron angular distribution (PAD) not only involves the usual β anisotropy parameter but also a chiral asymmetry parameter b1 that can generate a forward-backward asymmetry in the PAD. This has been investigated using circularly polarized light (CPL) to record the photoelectron circular dichroism (PECD) in the near-threshold vacuum-ultraviolet (VUV) photoionization region. Analysis of size-selected electron images recorded with left- and right-handed CPL shows that over the first 1.5 eV above the HOMO orbital ionization potentials (IPs), the β parameter is not affected by the dimerization process, while the chiral b1 parameter shows clear differences between the monomer and the dimer, confirming that PECD is a subtle long-range probe of the molecular potential.

  15. Photoionization of epichlorohydrin enantiomers and clusters studied with circularly polarized vacuum ultraviolet radiation.

    PubMed

    Daly, Steven; Powis, Ivan; Garcia, Gustavo A; Soldi-Lose, Héloïse; Nahon, Laurent

    2011-02-14

    The photoionization of enantiomerically pure epichlorohydrin (C(3)H(5)OCl) has been studied using linearly and circularly polarized vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum was recorded and the first three bands assigned using molecular orbital calculations for the expected conformers, although uncertain experimental conformer populations and an anticipated breakdown in Koopmans' theorem leave some ambiguity. Measurements of the photoelectron circular dichroism (PECD) were obtained across a range of photon energies for each of these bands, using electron velocity map imaging to record the angular distributions, during which a record PECD chiral asymmetry factor of 32% was observed. A comparison with calculated PECD curves clarifies the assignment achieved using ionization energies alone and further suggests a likely relative population of the conformers. Threshold photoelectron-photoion coincidence methods were used to study the ionic fragmentation of epichlorohydrin. Fragment ion appearance energies show nonstatistical behavior with clear indications that the cationic epoxide ring is unstable and lower energy decay channels proceeding via ring breaking are generally open. Extensive neutral homochiral clusters of epichlorohydrin may be formed in supersonic molecular beam expansions seeded in Ar. Electron angular distribution measurements made in coincidence with dimer and trimer ions are used to effect an examination of the PECD associated with ionization of size-selected neutral cluster species, and these results differ clearly from PECD of the neutral monomer. The shifted ionization thresholds of the n-mers (n = 2, ..., 7) are shown to follow a simple linear relationship, but under intense beam expansion conditions the monomer deviates from this relationship, and the monomer electron spectra tail to below the expected monomer adiabatic ionization potential (IP). PECD measurements made in coincidence with monomer ions obtained

  16. Photoionization of epichlorohydrin enantiomers and clusters studied with circularly polarized vacuum ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Daly, Steven; Powis, Ivan; Garcia, Gustavo A.; Soldi-Lose, Héloïse; Nahon, Laurent

    2011-02-01

    The photoionization of enantiomerically pure epichlorohydrin (C3H5OCl) has been studied using linearly and circularly polarized vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum was recorded and the first three bands assigned using molecular orbital calculations for the expected conformers, although uncertain experimental conformer populations and an anticipated breakdown in Koopmans' theorem leave some ambiguity. Measurements of the photoelectron circular dichroism (PECD) were obtained across a range of photon energies for each of these bands, using electron velocity map imaging to record the angular distributions, during which a record PECD chiral asymmetry factor of 32% was observed. A comparison with calculated PECD curves clarifies the assignment achieved using ionization energies alone and further suggests a likely relative population of the conformers. Threshold photoelectron-photoion coincidence methods were used to study the ionic fragmentation of epichlorohydrin. Fragment ion appearance energies show nonstatistical behavior with clear indications that the cationic epoxide ring is unstable and lower energy decay channels proceeding via ring breaking are generally open. Extensive neutral homochiral clusters of epichlorohydrin may be formed in supersonic molecular beam expansions seeded in Ar. Electron angular distribution measurements made in coincidence with dimer and trimer ions are used to effect an examination of the PECD associated with ionization of size-selected neutral cluster species, and these results differ clearly from PECD of the neutral monomer. The shifted ionization thresholds of the n-mers (n = 2, …, 7) are shown to follow a simple linear relationship, but under intense beam expansion conditions the monomer deviates from this relationship, and the monomer electron spectra tail to below the expected monomer adiabatic ionization potential (IP). PECD measurements made in coincidence with monomer ions obtained

  17. Photoionization from excited states of helium

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The cross sections for photoionization from the 2 1S, 2 3S, 2 1P and 2 3P excited states of helium are calculated for photoelectron energies below the n = 2 threshold of He(+) using Hylleraas bound state wave functions and 1s-2s-2p close coupling final state wave functions. The resonant structures associated with the lowest-lying 1S, 1P, 3P, and 1D autoionizing states of helium are found to be characterized by large values of the line profile parameter q. The cross sections and the photoelectron angular distribution asymmetry parameters for the P-states are calculated for various polarization states of the target atom and the incident photon. Experiments which would lead to the separate determinations of the S- and D- wave partial photoionization cross sections are discussed.

  18. Time-dependent photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Wang, Xiangyang

    1999-09-01

    I show that the angular distribution of electrons photoionized from gas phase targets by short light pulses is time-dependent, when the orbital momentum composition of the photocurrent changes with excitation energy so evolves with the time of detection. A theory of time- dependent photoionization is outlined and general formulas of time-dependent photoelectron flux and angular distribution are given. Two general propagator methods suitable to describe the time-dependent photoionization and scattering processes are developed. The photoionization process is viewed as a local excitation followed by a half scattering. The local excitation process is solved theoretically in a small region around the target core. This approach has been generalized to describe the evolution of a wavepacket in an unbound system. An asymptotic propagator theorem is discovered and used to derive analytic expressions for asymptotic propagators. The origin of the time dependence is explored by parameterizing the time delay and orbital momentum coupling in a two channel model. K-shell photoionization of N2 and CO are calculated with this time- dependent photoionization theory, implemented using a multiple scattering model. Numerical results demonstrate that the time dependence of photoelectron angular distributions is a realistic effect.

  19. Photoinduced Reconfiguration Cycle in a Molecular Adsorbate Layer Studied by Femtosecond Inner-Shell Photoelectron Spectroscopy

    SciTech Connect

    Dachraoui, H.; Michelswirth, M.; Bartz, P.; Pfeiffer, W.; Heinzmann, U.; Siffalovic, P.; Schaefer, C.; Schnatwinkel, B.; Mattay, J.; Drescher, M.

    2011-03-11

    A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.

  20. Photoionization Dynamics and Ion State Distributions in Single-Photon and Resonance-Enhanced Multiphoton Ionization of Molecules.

    NASA Astrophysics Data System (ADS)

    Braunstein, Matthew

    This thesis presents results of theoretical studies of single-photon ionization and resonance enhanced multiphoton ionization (REMPI) of several small molecules. The first part of the thesis examines shape resonances in the photoionization of O_2. Studies reported here include investigations of branching ratios of electronic multiplet states in the 3sigma _{g} and 1pi_ {u} photoionization of O_2 and a comparison of photoionization of the singlet states, a ^1Delta_{g} and d ^1prod_{g } (3ssigma_{g} 1pi_{g}), with that of the ground state of O_2. These studies show that the electronic exchange interaction between the ion core and the photoelectron in shape resonant energy regions profoundly affects the electronic state distributions of the molecular ion. We also report vibrational branching ratios in the single-photon ionization of O_2 , and in REMPI of O_2 via the G^3prod_{g} Rydberg state. In these studies, we find that a shape resonance causes a dependence of the electronic transition moment on the molecular geometry leading to non-Franck -Condon ion vibrational distributions and a dependence of the rotational branch intensity on the ion vibrational state. The second part of this thesis examines shape resonances in other molecules, focusing on the more general aspects of the photoionization dynamics. Here we present studies of the vibrational state distributions in the 7 sigma photoionization of the polyatomic N_2O, where a shape resonance causes non-Franck-Condon vibrational state distributions, the degree of which depends on the nuclear displacements involved and whether the shape resonance is localized on a particular bond. We also study the photoionization dynamics of the valence shell of Cl_2, where a shape resonance is also seen. Finally, we present studies of the K-shell ionization of CO. Studies in this energy region have assumed a new importance with the development of tunable X-ray synchrotron sources. Here, electronic relaxation in the production of a K

  1. Simulation of time resolved photoelectron spectra with Stieltjes imaging illustrated on ultrafast internal conversion in pyrazine

    NASA Astrophysics Data System (ADS)

    Werner, Ute; Mitrić, Roland; Bonačić-Koutecký, Vlasta

    2010-05-01

    We present an approach for the simulation of time resolved photoelectron spectra based on the combination of the ab initio nonadiabatic molecular dynamics "on the fly" with the Stieltjes imaging method utilizing discrete neutral states above the ionization limit for the approximate description of the ionization continuum. Our approach has been implemented in the framework of the time-dependent density functional theory and has been applied to interrogate the ultrafast internal conversion between the S2 and S1 states in pyrazine. The simulations reveal that, parallel to the S2→S1 internal conversion, a change in the dominant ionization process (S2→D1 versus S1→D0) occurs on the time scale of 20 fs such that no significant change in the photoelectron kinetic energy distribution is observed. The presented results are in full agreement with the experimental results presented in the accompanying paper [Suzuki et al., J. Chem. Phys. 132, 174302 (2010)] and provide an insight into the interplay between the nonradiative relaxation and the photoionization process in pyrazine as reflected in the time resolved photoelectron spectrum. Our approach represents a general tool for the investigation of ultrafast photoionization processes in complex systems and thus can be used to investigate the ultrafast femtochemistry of complex molecular systems including all degrees of freedom.

  2. Atomic photoelectron-spectroscopy studies using synchrotron radiation

    SciTech Connect

    Kobrin, P.H.

    1983-02-01

    Photoelectron spectroscopy combined with tunable synchrotron radiation has been used to study the photoionization process in several atomic systems. The time structure of the synchrotron radiation source at the Stanford Synchrotron Radiation Laboratory (SSRL) was used to record time-of-flight (TOF) photoelectron spectra of gaseous Cd, Hg, Ne, Ar, Ba, and Mn. The use of two TOF analyzers made possible the measurement of photoelectron angular distributions as well as branching ratios and partial cross sections.

  3. Rotations of molecular photoelectron angular distributions in above threshold ionization of H2+ by intense circularly polarized attosecond UV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2014-10-01

    We present molecular photoelectron angular distributions (MPADs) in multi-photon ionization processes by circularly polarized attosecond UV laser pulses. Simulations are performed on the single electron aligned molecular ion H_2^+ by solving corresponding 3D time-dependent Schrödinger equations. Numerical results of molecular above threshold ionization (MATI) show that rotations of MPADs with respect to the molecular and polarization axes depend on pulse intensities and photoelectron kinetic energies. We attribute the rotation to Γ, the difference between parallel and perpendicular ionization probabilities. It is found that in a resonant ionization process, the rotation angle is also a function of the symmetry of intermediate electronic states. The coherent population transfer between the initial and the resonant electronic states is controlled by pulse intensities. Such dependence of rotations on the pulse intensity is absent in Rydberg resonant ionizations as well as in MATI at large energy photons ℏω > Ip, where ω is angular frequency of photons and Ip is the molecular ionization potential. We describe these processes by a multi-photon perturbation theory model. Effects of molecular alignment and pulse ellipticities on rotations are investigated, confirming the essence of the ionization parameter Γ in rotations of MPADs.

  4. High efficiency photoionization detector

    DOEpatents

    Anderson, David F.

    1984-01-01

    A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36.+-.0.02 eV, and a vapor pressure of 0.35 torr at 20.degree. C.

  5. High efficiency photoionization detector

    DOEpatents

    Anderson, D.F.

    1984-01-31

    A high efficiency photoionization detector is described using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 [+-] 0.02 eV, and a vapor pressure of 0.35 torr at 20 C. 6 figs.

  6. Vacuum ultraviolet photoelectron spectroscopy of atoms and molecules

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1978-01-01

    For a complete study of the photoionization of atoms and molecules it is essential to make use of the technique of Photoelectron Spectroscopy and the continuum characteristics of synchrotron radiation. A brief review is given of the application of the above techniques in measuring partial photoionization cross sections and the angular distribution assymetry parameter beta. Selected results are given, which are compared to theoretical values.

  7. Spin effects in double photoionization of lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Hines, C. W.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-02-15

    We apply the nonperturbative convergent close-coupling (CCC) and time-dependent close coupling (TDCC) formalisms to calculate fully differential energy and angular resolved cross sections of double photoionization (DPI) of lithium. The equal energy sharing case is considered in which dynamics of the DPI process can be adequately described by two symmetrized singlet and triplet amplitudes. The angular width of these amplitudes serves as a measure of the strength of the angular correlation between the two ejected electrons. This width is interpreted in terms of the spin of the photoelectron pair.

  8. Effect of electron correlation and shape resonance on photoionization from the S1 and S2 states of pyrazine

    NASA Astrophysics Data System (ADS)

    Suzuki, Yoshi-Ichi; Suzuki, Toshinori

    2012-11-01

    In a previous study [T. Horio, T. Fuji, Y.-I. Suzuki, and T. Suzuki, J. Am. Chem. Soc. 131, 10392 (2009), 10.1021/ja904780b], we demonstrated that the time-energy map of photoelectron angular anisotropy enables unambiguous identification of ultrafast S2(ππ*)-S1(nπ*) internal conversion in pyrazine. A notable characteristic of this map is that the forbidden ionization process of D0(n-1) ← S2(ππ*) gives a negative photoelectron anisotropy parameter. In the present study, we elucidate the mechanism of this process by calculating the photoionization transition dipole moments and photoelectron angular distribution using the first-order configuration interaction method and the continuum multiple scattering Xα approximation; these calculations at the S0 equilibrium geometry reproduce the observed anisotropy parameters for D0 ← S2 and D0 ← S1 ionizations, respectively. On the other hand, they do not reproduce the small difference in the photoelectron anisotropy parameters for the D1(π-1) ← S2 and D0 ← S1 ionizations, both of which correspond to removal of an electron from the same π* orbital in the excited states. We show that these ionizations are affected by the kag shape resonance and that the difference between their photoelectron anisotropy parameters originates from the difference in the molecular geometry in D1 ← S2 and D0 ← S1.

  9. Photoelectron spectroscopic studies of polyatomic molecules: Degree of orientation and ionization of rotationally state selected, oriented molecules

    NASA Astrophysics Data System (ADS)

    Chandra, N.; Chakraborty, M.

    1991-11-01

    In this paper we report theoretical studies of angle-resolved photoelectron spectroscopy (ARPES) and of circular dichroism in photoelectron angular distribution (CDAD) for ionization in molecules oriented in a single ‖JKJMJ> rotational eigenstate. These processes have been investigated also as two of the possible alternatives to photodissociation to determine orientational distribution function of rotationally state selected, oriented molecules. Expressions are derived which can be used to calculate ARPES and CDAD for such molecular species from ab initio methods or to analyze these experimentally observed spectra for extracting information about the degree of orientation of the molecular framework. These formulas are put in their simplest possible forms using the transformation properties of the molecular point group to their full advantage. The ionization amplitude is thus shown to decompose into a sum of transitions each involving the final state wave function belonging to an irreducible representation of the point group of the target molecule. It is found that, similar to the case of photodissociation, one can determine the rotational quantum number J purely from experimental photoionization data. Expressions developed herein are used to study ARPES and CDAD for ionization in a1 orbital of those rotationally state selected and oriented spherical top molecules which transform according to the Td point symmetry group. In this case, the detection-integrated cross section, singly differential in molecular orientation, is found to be independent of the photoionization dynamics and directly gives the molecular orientational function. The other ARPES and CDAD formulas are shown to depend upon the dynamics through the integrated partial cross section σ¯, the angularly asymmetry parameter β¯, the phase shift of the continuum waves representing the photoelectron, and the phase of the dipole transition amplitudes. The formulation presented in this paper sets a

  10. Two-electron photoionization of ground-state lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Bray, I.

    2009-12-15

    We apply the convergent close-coupling (CCC) formalism to single-photon two-electron ionization of the lithium atom in its ground state. We treat this reaction as single-electron photon absorption followed by inelastic scattering of the photoelectron on a heliumlike Li{sup +} ion. The latter scattering process can be described accurately within the CCC formalism. We obtain integrated cross sections of single photoionization leading to the ground and various excited states of the Li{sup +} ion as well as double photoionization extending continuously from the threshold to the asymptotic limit of infinite photon energy. Comparison with available experimental and theoretical data validates the CCC model.

  11. Quantum control of molecular tunneling ionization in the spatiotemporal domain

    SciTech Connect

    Ohmura, Hideki; Saito, Naoaki; Morishita, Toru

    2011-06-15

    We report on a method that can control molecular photoionization in both space and time domains. The directionally asymmetric molecular tunneling ionization induced by intense (5.0 x 10{sup 13} W/cm{sup 2}) phase-controlled two-color laser pulses consisting of fundamental and second-harmonic light achieves the selective ionization of asymmetric molecules in the space domain, and manipulates the birth time and direction of photoelectron emission on an attosecond time scale. This method provides a powerful tool for tracking the quantum dynamics of photoelectrons by using phase-dependent oriented molecules as a phase reference in simultaneous ion-electron detection.

  12. Photoionization and Recombination

    NASA Technical Reports Server (NTRS)

    Nahar, Sultana N.

    2000-01-01

    Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.

  13. On the absolute photoionization cross section and dissociative photoionization of cyclopropenylidene.

    PubMed

    Holzmeier, Fabian; Fischer, Ingo; Kiendl, Benjamin; Krueger, Anke; Bodi, Andras; Hemberger, Patrick

    2016-04-01

    We report the determination of the absolute photoionization cross section of cyclopropenylidene, c-C3H2, and the heat of formation of the C3H radical and ion derived by the dissociative ionization of the carbene. Vacuum ultraviolet (VUV) synchrotron radiation as provided by the Swiss Light Source and imaging photoelectron photoion coincidence (iPEPICO) were employed. Cyclopropenylidene was generated by pyrolysis of a quadricyclane precursor in a 1 : 1 ratio with benzene, which enabled us to derive the carbene's near threshold absolute photoionization cross section from the photoionization yield of the two pyrolysis products and the known cross section of benzene. The cross section at 9.5 eV, for example, was determined to be 4.5 ± 1.4 Mb. Upon dissociative ionization the carbene decomposes by hydrogen atom loss to the linear isomer of C3H(+). The appearance energy for this process was determined to be AE(0K)(c-C3H2; l-C3H(+)) = 13.67 ± 0.10 eV. The heat of formation of neutral and cationic C3H was derived from this value via a thermochemical cycle as Δ(f)H(0K)(C3H) = 725 ± 25 kJ mol(-1) and Δ(f)H(0K)(C3H(+)) = 1604 ± 19 kJ mol(-1), using a previously reported ionization energy of C3H. PMID:26975696

  14. Nondipole Photoionization Parameters of Atomic Mercury

    NASA Astrophysics Data System (ADS)

    Banerjee, T.; Manson, S. T.

    2005-05-01

    Over the past few years, photoionization parameters have been found to be affected by nondipole terms at much lower energies than was known earlier [1,2]. The primary motivation for the present investigation is to study the effect of interchannel coupling involving E1 and E2 photoionization channels from subshells with large orbital angular momentum (l>2). In an extension of earlier work [3], the nondipole photoelectron angular distribution asymmetry parameters γandδ from the 6s and 5d subshells of atomic mercury have been obtained in the energy range from the respective thresholds up to 45 au. Relativistic-Random-Phase Approximation (RRPA) theory at various levels of truncation of the RRPA was used which allowed us to pinpoint the effects of interchannel coupling. The role of interchannel coupling between the 6s and 5d photoionization channels and the 4f channels in both the dipole (E1) and the quadrupole (E2) manifolds has been detailed and has been found to be of considerable significance. This work was supported by DST and NSF. [1] A. Derevianko, W. R. Johnson and K. T. Cheng , At. Data Nucl. Data Tables 73, 153 (1999). [2] O. Hemmers, et al, Phys. Rev. Lett. 91, 053002 (2003); 93, 11301 (2004). [3] P. C. Deshmukh, Radiation Phys. and Chem. 70, 515 (2004) and references therein.

  15. Asymmetric photoelectron momentum distribution driven by two-color XUV fields

    NASA Astrophysics Data System (ADS)

    Wu, Wan-Yang; He, Feng

    2016-02-01

    The photoionization of He+ in two-color XUV fields is studied by numerically solving the time-dependent Schrödinger equation. He+ may be ionized by directly absorbing one high-energetic photon or by absorbing two photons sequentially by mediating an excited state. The interference of these two pathways results in either enhancement or suppression of photoionization, depending on the propagating direction of the photoelectron and the relative phase of two pulses. The two-pathway interference also induces the split of photoelectron momenta. This study shows that the participation of intermediate states may substantially change photoionization processes.

  16. Vibrationally resolved molecular-frame angular distribution of O 1s photoelectrons from CO{sub 2} molecules

    SciTech Connect

    Saito, N.; Morishita, Y.; Suzuki, I.H.; Liu, X-J.; Pruemper, G.; Ueda, K.; Machida, M.; Oura, M.; Yamaoka, H.; Tamenori, Y.; Koyano, I.

    2005-10-15

    Vibrationally resolved O 1s photoelectron angular distributions from CO{sub 2} molecules, aligned parallel and perpendicular to the electric vector of the incident light, have been measured in the 5{sigma}{sub g}* shape resonance region, with photon energies up to 2 eV above the O 1s ionization threshold, using multiple-coincidence electron-ion momentum imaging spectroscopy. The angular distributions depend on the vibrational quanta of the antisymmetric vibrations in the O 1s ionized state but do not vary significantly as a function of the photon energy across the 5{sigma}{sub g}* shape resonance.

  17. Molecular photoelectron angular distribution rotations in multi-photon resonant ionization of H{sub 2}{sup +} by circularly polarized ultraviolet laser pulses

    SciTech Connect

    Yuan, Kai-Jun Chelkowski, Szczepan; Bandrauk, André D.

    2015-04-14

    We study effects of pulse durations on molecular photoelectron angular distributions (MPADs) in ultrafast circular polarization ultraviolet resonant ionization processes. Simulations performed on aligned H{sub 2}{sup +} by numerically solving time dependent Schrödinger equations show rotations of MPADs with respect to the molecular symmetry axes. It is found that in multi-photon resonant ionization processes, rotation angles are sensitive to pulse durations, which we attribute to the coherent resonant excitation between the ground state and the intermediate excited electronic state induced by Rabi oscillations. Multi-photon nonresonant and single photon ionization processes are simulated and compared which exhibit a constant rotation angle. An asymmetry parameter is introduced to describe the pulse duration sensitivity by perturbation theory models. Influence of pulse frequency detunings on MPADs is also investigated where oscillations of rotations are absent at long pulse durations due to nonresonance excitation.

  18. The role of multichannel effects in the photoionization of the NO2 molecule: an ab initio R-matrix study

    NASA Astrophysics Data System (ADS)

    Brambila, Danilo S.; Harvey, Alex G.; Mašín, Zdeněk; Gorfinkiel, Jimena D.; Smirnova, Olga

    2015-12-01

    We present the first ab initio photoionization calculations for the NO2 molecule in its equilibrium geometry using the multichannel R-matrix method and a multiconfigurational description of the system. We focus on the role of correlation in NO2 photoionization and find that it plays a key role, both at the level of partial cross sections and asymmetry parameters. For the most sophisticated model used here, we achieve excellent agreement with the experimental data of Baltzer et al (2009 Chem. Phys. 237 451-70) for the asymmetry parameters of angle-resolved photo-electron spectra. We also present and analyse the angle-resolved photoionization dipoles for photon energies up to 90 eV and for the two lowest-energy ionization channels. Our results should advance the analysis of experiments in the field of attosecond spectroscopy, especially high harmonic generation, where angle-resolved photorecombination dipoles become crucial for the interpretation of experiments, even for randomly oriented molecular ensembles, due to coherent addition of signals from different orientations.

  19. Quantum optimal control of photoelectron spectra and angular distributions

    NASA Astrophysics Data System (ADS)

    Goetz, R. Esteban; Karamatskou, Antonia; Santra, Robin; Koch, Christiane P.

    2016-01-01

    Photoelectron spectra and photoelectron angular distributions obtained in photoionization reveal important information on, e.g., charge transfer or hole coherence in the parent ion. Here we show that optimal control of the underlying quantum dynamics can be used to enhance desired features in the photoelectron spectra and angular distributions. To this end, we combine Krotov's method for optimal control theory with the time-dependent configuration interaction singles formalism and a splitting approach to calculate photoelectron spectra and angular distributions. The optimization target can account for specific desired properties in the photoelectron angular distribution alone, in the photoelectron spectrum, or in both. We demonstrate the method for hydrogen and then apply it to argon under strong XUV radiation, maximizing the difference of emission into the upper and lower hemispheres, in order to realize directed electron emission in the XUV regime.

  20. Photoionization by an ultraintense laser field: Response of atomic xenon

    SciTech Connect

    DiChiara, A. D.; Ghebregziabher, I.; Waesche, J. M.; Stanev, T.; Ekanayake, N.; Barclay, L. R.; Wells, S. J.; Watts, A.; Videtto, M.; Mancuso, C. A.; Walker, B. C.

    2010-04-15

    We present energy- and angle-resolved photoionization from Xe in an ultrastrong laser field at 10{sup 19} W/cm{sup 2}. The observed yields are consistent with the tunneling ionization of Xe{sup 9+} to Xe{sup 24+}. However, energy and angle-resolved photoelectron spectra show differences for electrons whose final energies are above or below 0.5 MeV, which is approximately the ponderomotive energy at these intensities. Above 0.5 MeV, the observed photoelectron cutoff energy (between 1 and 1.35 MeV), photoelectron energy spectra, and the angle-resolved photoelectron azimuthal distributions agree with a model using tunneling ionization, multiple charge states, a classical relativistic continuum, and nonparaxial three-dimensional (3D) focused laser field. Below 0.5 MeV the yields and angular distributions observed indicate dynamics not included within a classical, single electron model of the interaction.

  1. Post-collision-interaction distortion of low-energy photoelectron spectra associated with double Auger decay

    SciTech Connect

    Gerchikov, L.; Sheinerman, S.

    2011-08-15

    Atomic inner-shell photoionization followed by double Auger decay is investigated. The focus of our study is the effect of post-collision interaction (PCI) on the photoelectron energy distribution. A semi-classical approach is employed to describe the PCI distortion of the photoelectron line shapes associated with both direct and cascade double Auger decays. This approach is shown to be valid at low photoelectron energies, whereas for large incident photon energies it reduces to the eikonal approximation. The theory is applied to the case of Ar 2p photoionization spectra and good agreement with available experimental data is achieved.

  2. Angular correlation between photoelectrons and auger electrons from K-shell ionization of neon.

    PubMed

    Landers, A L; Robicheaux, F; Jahnke, T; Schöffler, M; Osipov, T; Titze, J; Lee, S Y; Adaniya, H; Hertlein, M; Ranitovic, P; Bocharova, I; Akoury, D; Bhandary, A; Weber, Th; Prior, M H; Cocke, C L; Dörner, R; Belkacem, A

    2009-06-01

    We have used cold target recoil ion momentum spectroscopy to study the continuum correlation between the photoelectron of core-photoionized neon and the subsequent Auger electron. We observe a strong angular correlation between the two electrons. Classical trajectory Monte Carlo calculations agree quite well with the photoelectron energy distribution that is shifted due to the potential change associated with Auger decay. However, a striking discrepancy results in the distribution of the relative angle between Auger and photoelectron. The classical model predicts a shift in photoelectron flux away from the Auger emission direction, and the data strikingly reveal that the flux is lost rather than diverted, indicating that the two-step interpretation of photoionization followed by Auger emission is insufficient to fully describe the core-photoionization process. PMID:19658860

  3. Angular Correlation between Photoelectrons and Auger Electrons from K-Shell Ionization of Neon

    SciTech Connect

    Landers, A. L.; Robicheaux, F.; Bhandary, A.; Jahnke, T.; Schoeffler, M.; Titze, J.; Akoury, D.; Doerner, R.; Osipov, T.; Lee, S. Y.; Adaniya, H.; Hertlein, M.; Weber, Th.; Prior, M. H.; Belkacem, A.; Ranitovic, P.; Bocharova, I.; Cocke, C. L.

    2009-06-05

    We have used cold target recoil ion momentum spectroscopy to study the continuum correlation between the photoelectron of core-photoionized neon and the subsequent Auger electron. We observe a strong angular correlation between the two electrons. Classical trajectory Monte Carlo calculations agree quite well with the photoelectron energy distribution that is shifted due to the potential change associated with Auger decay. However, a striking discrepancy results in the distribution of the relative angle between Auger and photoelectron. The classical model predicts a shift in photoelectron flux away from the Auger emission direction, and the data strikingly reveal that the flux is lost rather than diverted, indicating that the two-step interpretation of photoionization followed by Auger emission is insufficient to fully describe the core-photoionization process.

  4. Energetic photoelectrons and the polar rain

    NASA Technical Reports Server (NTRS)

    Decker, Dwight T.; Jasperse, J. R.; Winningham, J. D.

    1990-01-01

    In the daytime midlatitudes, the Low Altitude Plasma Instrument (LAPI) on board the Dynamics Explorer 2 satellite has observed photoelectrons with energies as high as 850 eV. These energetic photoelectrons are an extension of the 'classical' photoelectrons (less than 60 eV) and result from photoionization of neutrals by soft solar X-rays. Since these photoelectrons are produced wherever the solar flux is incident on the earth's atmosphere, they should be present in sunlit polar cap. But in the polar cap, over these same energies, there is a well-known electron population: the polar rain, a low intensity electron flux of magnetospheric origin. Thus, in the sunlit polar cap, an energetic population of electrons should consist of both an ionospheric (photoelectron) and a magnetospheric (polar rain) component. Using numerical solutions of an electron transport equation with appropriate boundary conditions and sunlit polar cap LAPI data, it is shown that the two populations (photoelectron and polar rain) are indeed present and are both needed to explain polar cap observations.

  5. Is CO Carbon KVV Auger Electron Emission Affected by the Photoelectron?

    SciTech Connect

    Pruemper, G.; Fukuzawa, H.; Sakai, K.; Ueda, K.; Rolles, D.; Prince, K. C.; Harries, J. R.; Tamenori, Y.; Berrah, N.

    2008-12-05

    Angular distributions (ADs) of O{sup +} fragments from C 1s photoexcited CO detected in coincidence with carbon KVV Auger electrons emitted in the horizontal direction were measured at photon energies of 298, 305, 320, and 450 eV. At 450 eV, the ADs are polarization-independent and coincide with the molecular-frame Auger electron angular distribution. All measured ADs can be rationalized as a product of the same molecular-frame Auger electron angular distribution and the axial selectivity in the photoionization process. Thus the interaction between the photoelectron and the Auger electron for the normal Auger decay of CO can be neglected, and the two-step model is a good approximation.

  6. Photoionization of Li2

    NASA Astrophysics Data System (ADS)

    Li, Y.; Pindzola, M. S.; Ballance, C. P.; Colgan, J.

    2014-05-01

    Single and double photoionization cross sections for Li2 are calculated using a time-dependent close-coupling method. The correlation between the outer two electrons of Li2 is obtained by relaxation of the close-coupled equations in imaginary time. Propagation of the close-coupled equations in real time yields single and double photoionization cross sections for Li2. The two active electron cross sections are compared with one active electron distorted-wave and close-coupling results for both Li and Li2. 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.

  7. Photoionization and photodissociation in diffuse interstellar clouds

    SciTech Connect

    Roberge, W.G.; Dalgarno, A.; Flannery, B.P.

    1981-02-01

    An accurate treatment of radiative transfer is used to explore the effects of grain scattering properties on the photoionization and photodissociation efficiencies of atomic and molecular constituents in diffuse clouds and to calculate the rates of heat deposition by photoelectric emission from grains. The observational data on ionization and dissociation are consistent with, but do not establish, a grain scattering model which is highly anisotropic at short wavelengths.

  8. Photoionization of Li

    NASA Astrophysics Data System (ADS)

    Colgan, James

    2011-05-01

    The time-dependent close-coupling approach to multiple photoionization of lithium is presented. Double photoionization of lithium can be treated as a two-electron ejection process where the outgoing electrons move in the field of a ``frozen-core'' Li2+ 1 s state. Recent calculations of this process have resulted in total and triple differential cross sections that are in good agreement with other close-coupling approaches. The time-dependent approach can also be extended to treat the interaction of all three lithium electrons, as is required if triple photoionization is examined, that is, the simultaneous ejection of all three electrons from lithium. The most detailed information about this process is found in the fully angular and energy differential cross sections, which provide information as to how the ionized electrons leave the atom. We present our formulation of the fully differential cross section expression, and provide some convergence studies of the angular distributions. The Los Alamos National Laboratory is operated by Los Alamos National Security, LLC for the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. DE-AC5206NA25396.

  9. X-Ray Photoelectron Spectroscopy Study of GaAs (001) and InP (001) Cleaning Procedures Prior to Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Contour, J. P.; Massies, J.; Saletes, A.

    1985-07-01

    The effect of chemical etching by H2S04/H202/H20 (5/1/1) mixtures and of mechanopolishing by bromine-methanol diluted solution on GaAs (001) and InP (001) substrates for molecular beam epitaxy (MBE) has been studied using X-ray photoelectron spectroscopy (XPS). The final rinse in running deionized water does not produce any passivating oxide layer on the substrate surface. Oxidation observed on GaAs and InP after these cleaning procedures occurs during substrate handling in air. The H2S04/H202/H20 mixture produces arsenic rich surface layers having an atomic ratio As/Ga of 1.15, whereas the bromine-methanol mechanopolishing leads to an arsenic or phosphorus depleted surface with atomic ratios As/Ga=0.7 and P/In=0.65.

  10. Structured photoionization continuum of superheated cesium vapor

    NASA Astrophysics Data System (ADS)

    Pichler, G.; Makdisi, Y.; Kokaj, J.; Thomas, N.; Mathew, J.

    2015-08-01

    We studied the absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the cesium vapor in the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at a temperature of around 450 °C. This enabled the overheating of cesium dimers which greatly reduced its concentration at a temperature of 900 °C, leaving almost pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground state of the Cs2 molecule to the doubly excited Cs2** molecule located above Cs2+ molecular ionization limit. The corresponding potential curves are subjected to mutual interactions and autoionization.

  11. Structured photoionization continuum of cesium vapor

    NASA Astrophysics Data System (ADS)

    Pichler, Goran; Makdisi, Yacoub; Kokaj, Jahja; Thomas, Nicky; Mathew, Joseph; AMIP Team

    2015-05-01

    We studied absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at temperature of about 450 °C. This enabled the overheating of cesium dimers which almost disappeared at a temperature of 900 °C leaving pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground Cs2 molecule to the doubly excited Cs2** molecule located above the molecular ionization limit Cs2+.The corresponding potential curves are subjected to a mutual interactions and autoionization.

  12. Photoabsorption and photoionization of chlorine dioxide

    SciTech Connect

    Flesch, R.; Ruehl, E.; Hottmann, K.; Baumgaertel, H. )

    1993-01-28

    Photoprocesses of chlorine dioxide in the near-UV have become highly important for stratospheric photoprocesses at high latitudes, especially in Antarctica. Chlorine dioxide has been identified among other absorbers because of its specific absorption cross section in the near-UV. Possible contributions of chlorine dioxide photochemistry to polar ozone depletion have been discussed recently. The high-resolution He I photoelectron spectrum and the absolute (vacuum-UV) absorption cross section (6-25 eV) as well as the ionic fragmentation of chlorine dioxide (OCIO) are reported. The photoelectron spectrum is interpreted in terms of exchange splitting effects of the various singlet and triplet cation states as well as by comparison to chemically related molecules. The vacuum-UV absorption spectrum shows different Rydberg series converging to the cation states. These Rydberg series and their vibrational progressions are assigned by term value arguments, dipole selection rules, and comparison with the photoelectron spectrum. Photoionization mass spectrometry is used for measurements of the ionization and fragmentation threshold of OCIO. The major fragment is ClO[sup +] which occurs above 13.4 eV. Thermomechanical data such as heats of formation and bond dissociation energies are derived. No evidence for isomerization of OClO[sup +] is found, as observed for the electronically excited neutral molecule. 54 refs., 6 figs., 7 tabs.

  13. Autoionization of OCS by threshold photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Delwiche, Jacques; Hubin-Franskin, Marie-Jeanne; Guyon, Paul-Marie; Nenner, Irène

    1981-04-01

    Autoionization of carbonyl sulfide between 12 and 16 eV has been investigated by photoionization using the pulsed synchrotron radiation from ACO Orsay's storage ring. The threshold photoelectron spectrum and the total photoionization spectrum of carbonyl sulfide have been recorded at high resolution in the wavelength range between 112.0 and 65.0 nm (11-19 eV). Threshold energy electrons are observed in specific wavelength regions: (i) at excitation energies where the X˜, Ã, B˜, and C˜ ionic states are formed by a direct process; (ii) in the à state region where resonant autoionization to à can be understood classically within the Franck-Condon approximation; (iii) in the ÖX˜ Franck-Condon gap between 90 and 110 nm, where resonant autoionization leads to very sharp electron energy distribution strongly peaked at zero energy. Here the mechanism must be more complex.

  14. Photoionization of Ar2 at high resolution

    SciTech Connect

    Dehmer, Patricia M.

    1982-01-01

    The relative photoionization cross section of Ar2 was determined at a resolution of 0.07 Â in the wavelength region from 800 to 850 Â using a new photoionization mass spectrometer that combines a high intensity helium continuum lamp with a free supersonic molecular beam source. In the region studied, the photoionization cross section is dominated by autoionization of molecular Rydberg states, and the structure is diffuse owing to the combined effects of autoionization and predissociation. The molecular photoionization spectrum is extremely complex and shows little resemblence either to the corresponding atomic spectrum (indicating that the spectrum of the dimer is not simply a perturbed atomic spectrum) or to the molecular absorption spectrum at longer wavelengths. The regular vibrational progressions seen at longer wavelengths are absent above the first ionization potential. Detailed spectroscopic analysis is possible for only a small fraction of the observed features; however, vibrational intervals of 50--100 cm⁻¹ suggest that some of the Rydberg states have B ²Π3/2g ionic cores. A comparison of the absorption and photoionization spectra shows that, at wavelengths shorter than -835 Â, many of the excited states decay via mechanisms other than autoionization

  15. Photoionization and electron-ion recombination of Ti I

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2016-07-01

    Study of the inverse processes of photoionization and electron-ion recombination of (Ti I + h ν ⇋ Ti II + e) using the unified method is reported. The method, based on close coupling (CC) approximation and R-matrix method, subsumes both the radiative recombination (RR) and dielectronic recombination (DR) in a unified manner and provides state-specific and total electron-ion recombination rate coefficients which are self-consistent with the state-specific photoionization cross sections. The present results include state-specific electron-ion recombination rates (αRC(i))and partial photoionization cross sections (σPI(i)) leaving the ion in the ground state of 813 bound states with n ≤ 10 and l ≤ 9 of Ti I. Various features of state-specific and total electron-ion recombination with temperature, and the corresponding photoionization cross sections with energies are discussed with illustrations. Due to closely lying excited states near the ground state of the core, photoionization cross sections show presence of narrow Rydberg resonances in low energy region near the ionization threshold. Many excited states also show broad and enhanced Seaton resonances due to PEC (photo-excitation-of-core) which contribute to the high temperature recombination. The total recombination rate coefficient is found to show a low hump around temperature 280 K and a high dielectronic recombination peak at temperature 25,000 K. Total spectrum of recombination cross sections and rates with photoelectron energy are also presented for experimental observation. Calculations were carried out using a CC wave function expansion of 36 states of the core ion Ti II. The large set of data for recombination rates and partial photoionization cross sections with resonances should provide a complete and accurate modelings of plasmas.

  16. Imaging molecules from within: Ultrafast angstroem-scale structure determination of molecules via photoelectron holography using free-electron lasers

    SciTech Connect

    Krasniqi, F.; Rolles, D.; Najjari, B.; Voitkiv, A.; Strueder, L.; Ullrich, J.

    2010-03-15

    A scheme based on (i) upcoming brilliant x-ray free-electron laser (FEL) sources, (ii) innovative energy and angular-dispersive large-area electron imagers, and (iii) the well-known photoelectron holography is elaborated that provides time-dependent three-dimensional structure determination of small to medium-sized molecules with Angstroem spatial and femtosecond time resolution. Inducing molecular dynamics, wave-packet motion, dissociation, passage through conical intersections, or isomerization by a pump pulse this motion is visualized by the x-ray FEL probe pulse launching keV photoelectrons within a few femtoseconds from specific and well-defined sites, deep core levels of individual atoms, inside the molecule. On their way out, the photoelectrons are diffracted generating a hologram on the detector that encodes the molecular structure at the instant of photoionization, thus providing 'femtosecond snapshot images of the molecule from within'. Detailed calculations in various approximations of increasing sophistication are presented and three-dimensional retrieval of the spatial structure of the molecule with Angstroem spatial resolution is demonstrated. Due to the large photoabsorption cross sections the method extends x-ray-diffraction-based time-dependent structure investigations envisioned at FEL's to new classes of samples that are not accessible by any other method. Among them are dilute samples in the gas phase such as aligned, oriented, or conformer-selected molecules, ultracold ensembles and/or molecular or cluster objects containing mainly light atoms that do not scatter x rays efficiently.

  17. 2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

    SciTech Connect

    Klaus Muller-Dethefs Nancy Ryan GRay

    2009-03-31

    This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.

  18. Photoelectron momentum distributions of molecules in bichromatic circularly polarized attosecond UV laser fields

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Chelkowski, Szczepan; Bandrauk, André D.

    2016-05-01

    We theoretically investigate molecular photoelectron momentum distributions (MPMDs) by bichromatic [frequencies (ω1,ω2)] circularly polarized attosecond UV laser pulses. Simulations performed on aligned single-electron H2+ by numerically solving the corresponding three-dimensional time-dependent Schrödinger equation within a static nucleus frame show that MPMDs exhibit a spiral structure for both co-rotating and counter-rotating schemes. Results are analyzed by attosecond perturbation ionization models. Coherent electron wave packets created, respectively, by the two color pulses in the continuum interfere with each other. Photoionization distributions are functions of the photoelectron momentum p and the ejection angle θ , thus leading to spiral MPMDs. The dependence of spiral MPMDs on the time delay between the bicircular pulses and their relative phases is also presented. The spiral interference patterns are determined by the helicities and frequencies (ω1,ω2 ) of the bicircular fields. It is also found that the spiral patterns are sensitive to the molecular alignment and suppressed by two-center ionization interference, thus offering new tools for imaging molecular geometry.

  19. Photoionization cross sections and oscillator strengths of neutral cesium

    NASA Astrophysics Data System (ADS)

    Haq, S. U.; Nadeem, Ali; Nawaz, M.

    2012-11-01

    The absolute photoionization cross sections from the 6p 2P1/2 excited state of cesium at threshold and above the threshold region have been measured using the saturation absorption technique. The photoionization cross section at the ionization threshold is determined as 22.6±3.6 Mb, whereas in the region above threshold its value ranges from 22 to 20 Mb for photoelectron energies up to 0.1 eV. A comparison of the photoionization cross sections with earlier reported theoretical and experimental data have been presented and are in good agreement within the uncertainty. In addition, the oscillator strengths of the 6p 2P1/2→n d 2D3/2 (21≤n≤60) Rydberg transitions of cesium have been calibrated using the threshold value of the photoionization cross section. A complete picture of the oscillator strengths from the present work and previously reported data from n=5-60 is presented.

  20. In situ synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-2 × 1 surface by supersonic molecular oxygen beams

    SciTech Connect

    Yoshigoe, Akitaka; Teraoka, Yuden; Okada, Ryuta; Yamada, Yoichi; Sasaki, Masahiro

    2014-11-07

    In situ synchrotron radiation photoelectron spectroscopy was performed during the oxidation of the Ge(100)-2 × 1 surface induced by a molecular oxygen beam with various incident energies up to 2.2 eV from the initial to saturation coverage of surface oxides. The saturation coverage of oxygen on the clean Ge(100) surface was much lower than one monolayer and the oxidation state of Ge was +2 at most. This indicates that the Ge(100) surface is so inert toward oxidation that complete oxidation cannot be achieved with only pure oxygen (O{sub 2}) gas, which is in strong contrast to Si surfaces. Two types of dissociative adsorption, trapping-mediated and direct dissociation, were confirmed by oxygen uptake measurements depending on the incident energy of O{sub 2}. The direct adsorption process can be activated by increasing the translational energy, resulting in an increased population of Ge{sup 2+} and a higher final oxygen coverage. We demonstrated that hyperthermal O{sub 2} beams remarkably promote the room-temperature oxidation with novel atomic configurations of oxides at the Ge(100) surface. Our findings will contribute to the fundamental understanding of oxygen adsorption processes at 300 K from the initial stages to saturated oxidation.

  1. Photoionization of Atomic Sc

    NASA Astrophysics Data System (ADS)

    Sossah, A. M.; Zhou, H.-L.; Manson, S. T.; Hibbert, A.

    2009-05-01

    Photoionization cross sections are calculated for the ground ([Mg] 3p^63d4s^2 ^2D^e) state of atomic Sc for photon energies from threshold to 40.0 eV. The discrete Sc^+ orbitals are generated using both the AUTOSTRUCTURE and CIV3 codes, and R-matrix is used to carry out the cross section calculations. The results are compared with each other, then with previous calculations and available experimental data for final-ionic states representing the 3d and 4s main lines and associated satellites (ionization with excitation) in the region of the 3p -> 3d giant resonances [1]. Reasonably good agreement between our non-relativistic results and experiment is obtained. This work is supported by US DOE and NSF [4pt] [1] S. B. Whitfield, K. Kehoe, R. Wehlitz, M. O. Krause, and C. D. Caldwell ->hys. Rev. A 64, 022701 (2001).

  2. Coherent control of photoionization of atomic barium

    NASA Astrophysics Data System (ADS)

    Yamazaki, Rekishu

    We present the results of our study on coherent control of photoionization of atomic barium. Our study focused on the understanding of the controllability, especially due to the effect of the coherent interaction between the atomic system and the laser field. The first half of the study investigates the mechanisms of the control behind the previously observed laser phase-insensitive product state control. The controllability of this excitation scheme, two-color two-photon resonantly enhanced excitation, was analyzed from two aspects, the role of ac Stark shift introduced by the strong laser field and the multi-pathway quantum mechanical interferences. We have analyzed the excitation scheme from the analysis of the photoelectron angular distribution measured using the excitation scheme and the monitoring of the intermediate state population. Analysis of the data as well as the numerical simulation showed clear understanding of the role of two mechanisms in the product state control reported. We also investigated the control of the phase lag during the product state control. We conducted the control of the phase lag in the study of asymmetric photoelectron angular distribution, which arises from the concurrent even-odd parity outgoing electron wave excitation. The phase lag was controlled in full range, 2pi, and the results were analyzed in terms of the role of autoionizing resonance structures as well as the nature of outgoing electron waves at different locations of the autoionizing resonances.

  3. Double Photoionization into Double Core-Hole States in Xe

    SciTech Connect

    Hikosaka, Y.; Kaneyasu, T.; Shigemasa, E.; Lablanquie, P.; Penent, F.; Eland, J. H. D.; Aoto, T.; Ito, K.

    2007-05-04

    Double photoionization (DPI) leading to double core-hole states of Xe{sup 2+} 4d{sup -2} has been studied using a magnetic bottle time-of-flight spectrometer. The assignments of the Xe{sup 2+} 4d{sup -2} states are confirmed by the Auger lines extracted from fourfold coincidences including two photoelectrons and two Auger electrons. It is estimated that the core-core DPI into Xe{sup 2+} 4d{sup -2} at a photon energy of 301.6 eV has a favored cross section of about 0.3 MB. The intense core-core DPI is due to mixing of the 4d{sup -2} continuum with the 4p single photoionization, which is manifested in the relative intensities of the Xe{sup 2+} 4d{sup -2} components.

  4. Double photoionization into double core-hole states in Xe.

    PubMed

    Hikosaka, Y; Lablanquie, P; Penent, F; Kaneyasu, T; Shigemasa, E; Eland, J H D; Aoto, T; Ito, K

    2007-05-01

    Double photoionization (DPI) leading to double core-hole states of Xe2+ 4d(-2) has been studied using a magnetic bottle time-of-flight spectrometer. The assignments of the Xe2+ 4d(-2) states are confirmed by the Auger lines extracted from fourfold coincidences including two photoelectrons and two Auger electrons. It is estimated that the core-core DPI into Xe2+ 4d(-2) at a photon energy of 301.6 eV has a favored cross section of about 0.3 MB. The intense core-core DPI is due to mixing of the 4d(-2) continuum with the 4p single photoionization, which is manifested in the relative intensities of the Xe2+ 4d(-2) components. PMID:17501570

  5. Communication: The influence of vibrational parity in chiral photoionization dynamics

    SciTech Connect

    Powis, Ivan

    2014-03-21

    A pronounced vibrational state dependence of photoelectron angular distributions observed in chiral photoionization experiments is explored using a simple, yet realistic, theoretical model based upon the transiently chiral molecule H{sub 2}O{sub 2}. The adiabatic approximation is used to separate vibrational and electronic wavefunctions. The full ionization matrix elements are obtained as an average of the electronic dipole matrix elements over the vibrational coordinate, weighted by the product of neutral and ion state vibrational wavefunctions. It is found that the parity of the vibrational Hermite polynomials influences not just the amplitude, but also the phase of the transition matrix elements, and the latter is sufficient, even in the absence of resonant enhancements, to account for enhanced vibrational dependencies in the chiral photoionization dynamics.

  6. Photoionization of Endohedral Atoms: Collective, Reflective and Collateral Emissions

    SciTech Connect

    Chakraborty, Himadri S.; McCune, Matthew A.; Hopper, Dale E.; Madjet, Mohamed E.; Manson, Steven T.

    2009-12-03

    The photoionization properties of a fullerene-confined atom differ dramatically from that of an isolated atom. In the low energy region, where the fullerene plasmons are active, the electrons of the confined atom emerge through a collective channel carrying a significant chunk of plasmon with it. The photoelectron angular distribution of the confined atom however shows far lesser impact of the effect. At higher energies, the interference between two single-electron ionization channels, one directly from the atom and another reflected off the fullerene cage, producuces oscillatory cross sections. But for the outermost atomic level, which transfers some electrons to the cage, oscillations are further modulated by the collateral emission from the part of the atomic charge density transferred to the cage. These various modes of emissions are studied for the photoionization of Ar endohedrally confined in C{sub 60}.

  7. Effects of anisotropic electron-ion interactions in atomic photoelectron angular distributions

    NASA Technical Reports Server (NTRS)

    Dill, D.; Starace, A. F.; Manson, S. T.

    1975-01-01

    A summary of the angular momentum transfer formulation of the differential photoionization cross section is presented and photoionization amplitudes in LS coupling are considered. The application of the theoretical concepts and relations developed is illustrated with the aid of an example involving the calculation of the angular distribution of photoelectrons ionized from atomic sulfur according to a certain reaction. The investigation shows that anisotropic electron-ion interactions in atomic sulfur lead to measurable differences between photoelectron angular distribution asymmetry parameters corresponding to alternative ionic term levels.

  8. Size Effects in Angle-Resolved Photoelectron Spectroscopy of Free Rare-Gas Clusters

    SciTech Connect

    Rolles, D.; Zhang, H.; Pesic, Z.D.; Bilodeau, R.C.; Wills, A.; Kukk, E.; Rude, B.S.; Ackerman, G.D.; Bozek, J.D.; Muino, R.D.; de Abajo, F.J.G.; Berrah, N.; /Western Michigan U. /LBNL, ALS /Turku U. /SLAC /Basque U., San Sebastian /Madrid, Inst. Optica

    2007-05-23

    The photoionization of free Xe clusters is investigated by angle-resolved time-of-flight photoelectron spectroscopy. The measurements probe the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. While the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the free atoms, distinct differences in the angular distribution point at cluster-size-dependent effects. Multiple scattering calculations trace their origin to elastic photoelectron scattering.

  9. Absolute photoionization cross-section of the methyl radical.

    SciTech Connect

    Taatjes, C. A.; Osborn, D. L.; Selby, T.; Meloni, G.; Fan, H.; Pratt, S. T.; Chemical Sciences and Engineering Division; SNL

    2008-01-01

    The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH{sub 3} photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; {sigma}{sub CH}(10.2 eV) = (5.7 {+-} 0.9) x 10{sup -18} cm{sup 2} and {sigma}{sub CH{sub 3}}(11.0 eV) = (6.0 {+-} 2.0) x 10{sup -18} cm{sup 2}. The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH{sub 3} and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 {+-} 2.0) x 10{sup -18} cm{sup 2} at 10.460 eV, (5.5 {+-} 2.0) x 10{sup -18} cm{sup 2} at 10.466 eV, and (4.9 {+-} 2.0) x 10{sup -18} cm{sup 2} at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

  10. The combined use of a singly charged ion beam and undulator radiation for photoelectron spectrometry studies on atomic ions

    NASA Astrophysics Data System (ADS)

    Bizau, J. M.; Cubaynes, D.; Richter, M.; Wuilleumier, F.; Obert, J.; Putaux, J. C.

    1992-01-01

    We present the first photoelectron spectrometry experiment on a singly charged ion beam. Taking advantage of the high photon flux emitted in the undulator SU6 of Super-ACO, we have measured photoelectron spectra produced in the resonant photoionization of Ca+ ions at 33.2-eV photon energy. The success of this experiment depended strongly on the photon flux available. We demonstrate the capability of photoelectron spectrometry to precisely calibrate the photon spectrum emitted in the undulator.

  11. FAST TRACK COMMUNICATION: Generalized geometrical model for photoionization of polarized atoms: II. Magnetic dichroism in the 3p photoemission from the K 3p64s 2S1/2 ground state

    NASA Astrophysics Data System (ADS)

    Grum-Grzhimailo, A. N.; Cubaynes, D.; Heinecke, E.; Hoffmann, P.; Zimmermann, P.; Meyer, M.

    2010-10-01

    The generalized geometrical model for photoionization from polarized atoms is extended to include mixing of configurations in the initial atomic and/or the final photoion states. The theoretical results for angle-resolved linear and circular magnetic dichroism are in good agreement with new high-resolution photoelectron data for 3p-1 photoionization of potassium atoms polarized in the K 3p64s 2S1/2 ground state by laser optical pumping.

  12. Confinement resonances in photoionization of Xe@C₆₀+.

    PubMed

    Kilcoyne, A L D; Aguilar, A; Müller, A; Schippers, S; Cisneros, C; Alna'washi, G; Aryal, N B; Baral, K K; Esteves, D A; Thomas, C M; Phaneuf, R A

    2010-11-19

    Experimental evidence is presented for confinement resonances associated with photoabsorption by a Xe atom in a C60 cage. The giant 4d resonance in photoionization of Xe is predicted to be redistributed into four components due to multipath interference of photoelectron waves reflected by the cage. The measurements were made in the photon energy range 60-150 eV by merging a beam of synchrotron radiation with a mass/charge selected Xe@C₆₀+ ion beam. The phenomenon was observed in the Xe@C(58)(3+) product ion channel. [corrected] PMID:21231297

  13. Decoherence in Attosecond Photoionization

    SciTech Connect

    Pabst, Stefan; Santra, Robin; Greenman, Loren; Mazziotti, David A.; Ho, Phay J.

    2011-02-04

    The creation of superpositions of hole states via single-photon ionization using attosecond extreme-ultraviolet pulses is studied with the time-dependent configuration-interaction singles (TDCIS) method. Specifically, the degree of coherence between hole states in atomic xenon is investigated. We find that interchannel coupling not only affects the hole populations, but it also enhances the entanglement between the photoelectron and the remaining ion, thereby reducing the coherence within the ion. As a consequence, even if the spectral bandwidth of the ionizing pulse exceeds the energy splittings among the hole states involved, perfectly coherent hole wave packets cannot be formed. For sufficiently large spectral bandwidth, the coherence can only be increased by increasing the mean photon energy.

  14. Decoherence in attosecond photoionization.

    PubMed

    Pabst, Stefan; Greenman, Loren; Ho, Phay J; Mazziotti, David A; Santra, Robin

    2011-02-01

    The creation of superpositions of hole states via single-photon ionization using attosecond extreme-ultraviolet pulses is studied with the time-dependent configuration-interaction singles (TDCIS) method. Specifically, the degree of coherence between hole states in atomic xenon is investigated. We find that interchannel coupling not only affects the hole populations, but it also enhances the entanglement between the photoelectron and the remaining ion, thereby reducing the coherence within the ion. As a consequence, even if the spectral bandwidth of the ionizing pulse exceeds the energy splittings among the hole states involved, perfectly coherent hole wave packets cannot be formed. For sufficiently large spectral bandwidth, the coherence can only be increased by increasing the mean photon energy. PMID:21405393

  15. Sum rules for the polarization correlations in photoionization and bremsstrahlung

    NASA Astrophysics Data System (ADS)

    Pratt, R. H.; Müller, R. A.; Surzhykov, A.

    2016-05-01

    The polarization correlations in doubly differential cross sections are investigated for photoionization and ordinary bremsstrahlung. These correlations describe the polarization transfer between incident light and ejected photoelectrons as well as between an incoming electron beam and bremsstrahlung light, respectively. They are characterized by a set of seven real parameters Ci j. We show that the squares of these parameters are connected by simple "sum rules." These sum rules can be applied for both one-electron systems and also for atoms, if the latter are described within the independent particle approximation. In particular, they are exact in their simplest form (i) for the photoionization of K -, LI ,I I-, and MI ,I I-atomic shells, as well as (ii) for bremsstrahlung in which the electron is scattered into s1 /2 or p1 /2 states, as in the tip (bremsstrahlung) region. Detailed calculations are performed to verify the derived identities and to discuss their possible applications for the analysis of modern photoionization and bremsstrahlung experiments. In particular, we argue that the sum rules may help to determine the entire set of (significant) polarization correlations in the case when not all Ci j are available for experimental observation.

  16. Time-resolved photoelectron spectroscopy of liquids

    NASA Astrophysics Data System (ADS)

    Buchner, Franziska; Lübcke, Andrea; Heine, Nadja; Schultz, Thomas

    2010-11-01

    We present a novel setup for the investigation of ultrafast dynamic processes in a liquid jet using time-resolved photoelectron spectroscopy. A magnetic-bottle type spectrometer with a high collection efficiency allows the very sensitive detection of photoelectrons emitted from a 10 μm thick liquid jet. This translates into good signal/noise ratio and rapid data acquisition making femtosecond time-resolved experiments feasible. We describe the experimental setup, a detailed spectrometer characterization based on the spectroscopy of nitric oxide in the gas phase, and results from femtosecond time-resolved experiments on sodium iodide solutions. The latter experiments reveal the formation and evolution of the solvated electron and we characterize two distinct spectral components corresponding to initially thermalized and unthermalized solvated electrons. The absence of dark states in photoionization, the direct measurement of electron binding energies, and the ability to resolve dynamic processes on the femtosecond time scale make time-resolved photoelectron spectroscopy from the liquid jet a very promising method for the characterization of photochemical processes in liquids.

  17. Time-resolved photoelectron spectroscopy of liquids.

    PubMed

    Buchner, Franziska; Lübcke, Andrea; Heine, Nadja; Schultz, Thomas

    2010-11-01

    We present a novel setup for the investigation of ultrafast dynamic processes in a liquid jet using time-resolved photoelectron spectroscopy. A magnetic-bottle type spectrometer with a high collection efficiency allows the very sensitive detection of photoelectrons emitted from a 10 μm thick liquid jet. This translates into good signal/noise ratio and rapid data acquisition making femtosecond time-resolved experiments feasible. We describe the experimental setup, a detailed spectrometer characterization based on the spectroscopy of nitric oxide in the gas phase, and results from femtosecond time-resolved experiments on sodium iodide solutions. The latter experiments reveal the formation and evolution of the solvated electron and we characterize two distinct spectral components corresponding to initially thermalized and unthermalized solvated electrons. The absence of dark states in photoionization, the direct measurement of electron binding energies, and the ability to resolve dynamic processes on the femtosecond time scale make time-resolved photoelectron spectroscopy from the liquid jet a very promising method for the characterization of photochemical processes in liquids. PMID:21133461

  18. Laser photoelectron spectroscopy of ions

    SciTech Connect

    Ellison, G.B.

    1992-01-16

    This enterprise uses photoelectron spectroscopy to study the properties of negative ions and radicals. The essence of our experiment is to cross a 0.6 keV mass-selected ion beam (M{sup {minus}}) with the output of a CW laser, {Dirac h}{omega}{sub o}. The resultant detached photoelectrons with kinetic energy, KE, are energy analyzed by means of a set of electrostatic hemispherical analyzers. Analysis of the photoelectron spectra enables us to extract molecular electron affinities, vibrational frequencies and electronic splittings of the final radical, M, as well as the relative molecular geometries of ions (M{sup {minus}}) and radicals (M). We have scrutinized the two simplest nitrenes: methylnitrene (CH{sub 3}N) and phenylnitrene (C{sub 6}H{sub 5}N). By preparing the corresponding anions, CH{sub 3}N{sup {minus}} and C{sub 6}H{sub 5}N{sup {minus}}, we have studied these nitrene biradicals. Singlet methylnitrene is especially interesting since it is formally a transition state.''

  19. Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling

    SciTech Connect

    Grell, Gilbert; Bokarev, Sergey I. Kühn, Oliver; Winter, Bernd; Seidel, Robert; Aziz, Emad F.; Aziz, Saadullah G.

    2015-08-21

    X-ray photoelectron spectra provide a wealth of information on the electronic structure. The extraction of molecular details requires adequate theoretical methods, which in case of transition metal complexes has to account for effects due to the multi-configurational and spin-mixed nature of the many-electron wave function. Here, the restricted active space self-consistent field method including spin-orbit coupling is used to cope with this challenge and to calculate valence- and core-level photoelectron spectra. The intensities are estimated within the frameworks of the Dyson orbital formalism and the sudden approximation. Thereby, we utilize an efficient computational algorithm that is based on a biorthonormal basis transformation. The approach is applied to the valence photoionization of the gas phase water molecule and to the core ionization spectrum of the [Fe(H{sub 2}O){sub 6}]{sup 2+} complex. The results show good agreement with the experimental data obtained in this work, whereas the sudden approximation demonstrates distinct deviations from experiments.

  20. Angle-resolved photoelectron spectroscopy of randomly oriented 3-hydroxytetrahydrofuran enantiomers.

    PubMed

    Giardini, Anna; Catone, Daniele; Stranges, Stefano; Satta, Mauro; Tacconi, Mario; Piccirillo, Susanna; Turchini, Stefano; Zema, Nicola; Contini, Giorgio; Prosperi, Tommaso; Decleva, Pietro; Di Tommaso, Devis; Fronzoni, Giovanna; Stener, Mauro; Filippi, Antonello; Speranza, Maurizio

    2005-06-13

    Circular dichroism in the angular distribution of valence photoelectrons emitted from randomly oriented 3-hydroxytetrahydrofuran enantiomers (ThS and ThR) has been observed in gas-phase experiments using circularly polarized vacuum ultraviolet (VUV) light. The measured dichroism for both ThS and ThR, acquired at the single magic angle theta=234.73 degrees and at photon energies of 22, 19, 16, and 14 eV, points to an asymmetric forward-backward scattering of the photoelectrons from their highest occupied molecular orbitals (HOMO) HOMO-1 and HOMO-2, of up to 5%, depending on the photon energy. The asymmetry reverses on exchange of either the helicity of the radiation or the configuration of Th. The photoionization dichroic D parameters of ThS and ThR have been measured and their values discussed in the light of LCAO B-spline density functional theory (DFT) predictions. While an acceptable agreement is found between the dichroic parameter measured and calculated at the highest photon energy for the HOMO and HOMO-2 orbitals of Th, a significant discrepancy is observed for the HOMO-1 state which is attributed to the floppiness of Th, in particular to the comparatively large sensitivity of the size and shape of its HOMO-1 on nuclear vibrational motion. PMID:15945047

  1. Photoionization of Benzophenone in the Gas Phase: Theory and Experiment.

    PubMed

    Khemiri, Noura; Messaoudi, Sabri; Abderrabba, Manef; Spighi, Gloria; Gaveau, Marc-André; Briant, Marc; Soep, Benoît; Mestdagh, Jean-Michel; Hochlaf, Majdi; Poisson, Lionel

    2015-06-11

    We report on the single photoionization of jet-cooled benzophenone using a tunable source of VUV synchrotron radiation coupled with a photoion/photoelectron coincidence acquisition device. The assignment and the interpretation of the spectra are based on a characterization by ab initio and density functional theory calculations of the geometry and of the electronic states of the cation. The absence of structures in the slow photoelectron spectrum is explained by a congestion of the spectrum due to the dense vibrational progressions of the very low frequency torsional mode in the cation either in pure form or in combination bands. Also a high density of electronic states has been found in the cation. Presently, we estimate the experimental adiabatic and vertical ionization energy of benzophenone at 8.80 ± 0.01 and 8.878 ± 0.005 eV, respectively. The ionization energy as well as the energies of the excited states are compared to the calculated ones. PMID:25866992

  2. Quantum beat oscillations in the two-color-photoionization continuum of neon and their dependence on the intensity of the ionizing laser pulse

    SciTech Connect

    Geiseler, Henning; Rottke, Horst; Steinmeyer, Guenter; Sandner, Wolfgang

    2011-09-15

    We investigate quantum beat oscillations in the photoionization continuum of Ne atoms that are photoionized by absorption of two photons via a group of excited bound states using ultrashort extreme ultraviolet and infrared laser pulses. The extreme ultraviolet pulse starts an excited-state wave packet that is photoionized by a high-intensity infrared pulse after a variable time delay. We analyze the continuum quantum beats from this two-step photoionization process and their dependence on the photoelectron kinetic energy. We find a pronounced dependence of the quantum beat amplitudes on the photoelectron kinetic energy. The dependence changes significantly with the applied infrared laser-pulse intensity. The experimental results are in good qualitative agreement with a model calculation that is adapted to the experimental situation. It accounts for the intensity dependence of the quantum beat structure through the coupling of the excited-state wave packet to other bound Ne states induced by the high-intensity infrared laser pulse.

  3. Computer simulations of photoionization

    NASA Astrophysics Data System (ADS)

    Wassermann, B.; Martin, T. P.

    1989-03-01

    The Energy Distribution of Ionizing Transitions (EDIT) for (Cs2O) n clusters has been calculated using the technique of molecular dynamics. Isomerization, thermal atomic motion and the electronic density of states all contribute to the shape of these curves.

  4. Gas-Phase Photoionization Of A Protein

    NASA Astrophysics Data System (ADS)

    Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

    2010-07-01

    We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; ˜12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

  5. Relativistic effects in the photoionization of hydrogen-like ions with screened Coulomb interaction

    SciTech Connect

    Xie, L. Y.; Wang, J. G.; Janev, R. K.

    2014-06-15

    The relativistic effects in the photoionization of hydrogen-like ion with screened Coulomb interaction of Yukawa type are studied for a broad range of screening lengths and photoelectron energies. The bound and continuum wave functions have been determined by solving the Dirac equation. The study is focused on the relativistic effects manifested in the characteristic features of photoionization cross section for electric dipole nl→ε,l±1 transitions: shape resonances, Cooper minima and cross section enhancements due to near-zero-energy states. It is shown that the main source of relativistic effects in these cross section features is the fine-structure splitting of bound state energy levels. The relativistic effects are studied in the photoionization of Fe{sup 25+} ion, as an example.

  6. Photoionization in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Landi, E.; Lepri, S. T.

    2015-10-01

    In this work we investigate the effects of photoionization on the charge state composition of the solar wind. Using measured solar EUV and X-ray irradiance, the Michigan Ionization Code and a model for the fast and slow solar wind, we calculate the evolution of the charge state distribution of He, C, N, O, Ne, Mg, Si, S, and Fe with and without including photoionization for both types of wind. We find that the solar radiation has significant effects on the charge state distribution of C, N, and O, causing the ionization levels of these elements to be higher than without photoionization; differences are largest for oxygen. The ions commonly observed for elements heavier than O are much less affected, except in ICMEs where Fe ions more ionized than 16+ can also be affected by the solar radiation. We also show that the commonly used O7+/O6+ density ratio is the most sensitive to photoionization; this sensitivity also causes the value of this ratio to depend on the phase of the solar cycle. We show that the O7+/O6+ ratio needs to be used with caution for solar wind classification and coronal temperature estimates, and recommend the C6+/C4+ ratio for these purposes.

  7. Slow photoelectron spectroscopy of 3-hydroxyisoquinoline.

    PubMed

    Pan, Yi; Lau, Kai-Chung; Poisson, Lionel; Garcia, Gustavo A; Nahon, Laurent; Hochlaf, Majdi

    2013-08-29

    We studied the single photon ionization of gas phase 3-hydroxyisoquinoline by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. Near the ionization thresholds of 3-hydroxyisoquinoline, the photoionization is found to occur mainly via a direct process. The spectra are assigned with the help of theoretical calculations on the equilibrium geometries, electronic states patterns, harmonic and anharmonic wavenumbers of the lactim and lactam forms of 3-hydroxyisoquinoline and their cations. The slow photoelectron spectrum (SPES) of this lactim is dominated by vibrational transitions to the X̃ state of the cation. In addition, several weaker and complex bands are observed, corresponding to the population of the vibrational bands (pure or combination) of the à electronically excited state of the cation. The adiabatic ionization energy of 3-hydroxyisoquinoline and the lowest electronic state energetics of the lactim and lactam cationic forms are determined. PMID:23360492

  8. Comparing Laser Desorption Ionization and Atmospheric Pressure Photoionization Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry To Characterize Shale Oils at the Molecular Level

    USGS Publications Warehouse

    Cho, Yunjo; Jin, Jang Mi; Witt, Matthias; Birdwell, Justin E.; Na, Jeong-Geol; Roh, Nam-Sun; Kim, Sunghwan

    2013-01-01

    Laser desorption ionization (LDI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to analyze shale oils. Previous work showed that LDI is a sensitive ionization technique for assessing aromatic nitrogen compounds, and oils generated from Green River Formation oil shales are well-documented as being rich in nitrogen. The data presented here demonstrate that LDI is effective in ionizing high-double-bond-equivalent (DBE) compounds and, therefore, is a suitable method for characterizing compounds with condensed structures. Additionally, LDI generates radical cations and protonated ions concurrently, the distribution of which depends upon the molecular structures and elemental compositions, and the basicity of compounds is closely related to the generation of protonated ions. This study demonstrates that LDI FT-ICR MS is an effective ionization technique for use in the study of shale oils at the molecular level. To the best of our knowledge, this is the first time that LDI FT-ICR MS has been applied to shale oils.

  9. Hartree-Fock calculation of the differential photoionization cross sections of small Li clusters

    NASA Astrophysics Data System (ADS)

    Galitskiy, S. A.; Artemyev, A. N.; Jänkälä, K.; Lagutin, B. M.; Demekhin, Ph. V.

    2015-01-01

    Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li2-8 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 Li2 are in a good agreement with the available theoretical data, whereas those computed for Li3-8 clusters can be considered as theoretical predictions.

  10. Hartree-Fock calculation of the differential photoionization cross sections of small Li clusters.

    PubMed

    Galitskiy, S A; Artemyev, A N; Jänkälä, K; Lagutin, B M; Demekhin, Ph V

    2015-01-21

    Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li2-8 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 Li2 are in a good agreement with the available theoretical data, whereas those computed for Li3-8 clusters can be considered as theoretical predictions. PMID:25612708

  11. FAST TRACK COMMUNICATION: Confinement resonances in the photoionization of endohedral atoms: myth or reality?

    NASA Astrophysics Data System (ADS)

    Korol, A. V.; Solov'yov, A. V.

    2010-10-01

    We demonstrate that the structure of confinement resonances in the photoionization cross section of an endohedral atom is very sensitive to the mean displacement langarang of the atom from the cage centre. The resonances are strongly suppressed if 2langarang exceeds the photoelectron half-wavelength. We explain the results of recent experiments which contradict the earlier theoretical predictions on the existence of confinement resonances in particular endohedral systems.

  12. Photoionization cross sections for atomic chlorine using an open-shell random phase approximation

    NASA Technical Reports Server (NTRS)

    Starace, A. F.; Armstrong, L., Jr.

    1975-01-01

    The use of the Random Phase Approximation with Exchange (RPAE) for calculating partial and total photoionization cross sections and photoelectron angular distributions for open shell atoms is examined for atomic chlorine. Whereas the RPAE corrections in argon (Z=18) are large, it is found that those in chlorine (Z=17) are much smaller due to geometric factors. Hartree-Fock calculations with and without core relaxation are also presented. Sizable deviations from the close coupling results of Conneely are also found.

  13. Double momentum spectrometer for ion-electron vector correlations in dissociative photoionization

    SciTech Connect

    Bomme, C.; Guillemin, R.; Marin, T.; Journel, L.; Marchenko, T.; Pilette, B.; Avila, A.; Ringuenet, H.; Kushawaha, R. K.; Simon, M.; Dowek, D.; Trcera, N.

    2013-10-15

    We have developed a new momentum spectrometer dedicated to momentum vector correlations in the context of deep core photoionization of atomic and molecular species in the gas phase. In this article, we describe the design and operation of the experimental setup. The capabilities of the apparatus are illustrated with a set of measurements done on the sulphur core 1s photoionization of gas-phase CS{sub 2}.

  14. Molecular above-threshold-ionization angular distributions with intense circularly polarized attosecond XUV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2012-05-01

    Photoionization of aligned and fixed nuclei three-dimensional H2+ and two-dimensional H2 by intense circularly polarized attosecond extreme ultraviolet laser pulses is investigated from numerical solutions of the time-dependent Schrödinger equation. Molecular above-threshold-ionization angular distributions are found to be rotated with respect to the two laser perpendicular polarizations or, equivalently the symmetry axes of the molecule. The angle of rotation is critically sensitive to laser wavelength λ, photoelectron energy Een, and molecular internuclear distance R. The correlated interaction of the two electrons in H2 is shown to also influence such angular distribution rotations in different electronic states.

  15. Photoionization indicators of optical mixing of different-parity degenerate Rydberg states

    NASA Astrophysics Data System (ADS)

    Parzyński, R.; Sobczak, M.; Wójcik, A.

    2000-02-01

    We discuss a photoionization version of the photoexcitation model of Corless and Stroud [Phys. Rev. Lett. 79, 637 (1997)]. In the photoexcitation model, a np hydrogenic state of n>>1 was excited from the ground 1s state and the excited population was allowed to migrate to other angular momentum states within the one n only due to strongly nonresonant electric-dipole \\|Δn\\|=0, \\|Δl\\|=1 Rydberg-to-Rydberg couplings. When, as is the essence of the photoexcitation model, the same one n-manifold approximation is made in the model of high-n Rydberg-state photoionization, a number of interesting photoionization effects are obtained. Among them, the most spectacular seems to be the emission of photoelectrons in the ``forbidden'' directions and the suppression of ionization when compared to the Fermi golden rule predictions. However, we show on the basis of an approximate analysis that these photoionization effects can be strongly diminished when additional n manifolds around the selected one are included in the model. Thus, we conclude that the one n-manifold approximation overestimates results when applied to the problem of high-n Rydberg-state photoionization.

  16. Double Potoionization of Molecular Hydrogen

    NASA Astrophysics Data System (ADS)

    Vanroose, Wim

    2006-05-01

    We report a complete numerical solution of the Schr"odinger equation for the double photoionization of H2, a process where a single photon emits two electrons. The results suggest that the distribution of photoelectrons emitted from aligned molecules reflects electron correlation effects that are purely molecular in origin. It confirms recent experimental results in experiments on oriented hydrogen molecules. These experiments observed that the ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as well as the orientation with respect to the polarization of the photon. We give an overview of the numerical methods we used to solve the exact Schrodinger equation for this problem. We also discuss the different molecular effect we observe in our calculations and compare with experimental observations

  17. Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy.

    PubMed

    Weatherup, Robert S; Eren, Baran; Hao, Yibo; Bluhm, Hendrik; Salmeron, Miquel B

    2016-05-01

    Atmospheric pressure X-ray photoelectron spectroscopy (XPS) is demonstrated using single-layer graphene membranes as photoelectron-transparent barriers that sustain pressure differences in excess of 6 orders of magnitude. The graphene serves as a support for catalyst nanoparticles under atmospheric pressure reaction conditions (up to 1.5 bar), where XPS allows the oxidation state of Cu nanoparticles and gas phase species to be simultaneously probed. We thereby observe that the Cu(2+) oxidation state is stable in O2 (1 bar) but is spontaneously reduced under vacuum. We further demonstrate the detection of various gas-phase species (Ar, CO, CO2, N2, O2) in the pressure range 10-1500 mbar including species with low photoionization cross sections (He, H2). Pressure-dependent changes in the apparent binding energies of gas-phase species are observed, attributable to changes in work function of the metal-coated grids supporting the graphene. We expect atmospheric pressure XPS based on this graphene membrane approach to be a valuable tool for studying nanoparticle catalysis. PMID:27082434

  18. Synchrotron-based valence shell photoionization of CH radical.

    PubMed

    Gans, B; Holzmeier, F; Krüger, J; Falvo, C; Röder, A; Lopes, A; Garcia, G A; Fittschen, C; Loison, J-C; Alcaraz, C

    2016-05-28

    We report the first experimental observations of X(+) (1)Σ(+)←X (2)Π and a(+) (3)Π←X (2)Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes. PMID:27250306

  19. Synchrotron-based valence shell photoionization of CH radical

    NASA Astrophysics Data System (ADS)

    Gans, B.; Holzmeier, F.; Krüger, J.; Falvo, C.; Röder, A.; Lopes, A.; Garcia, G. A.; Fittschen, C.; Loison, J.-C.; Alcaraz, C.

    2016-05-01

    We report the first experimental observations of X+ 1Σ+←X 2Π and a+ 3Π←X 2Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.

  20. A novel aerosol mass spectrometric approach - Analysis of the organic molecular signature of PM by coupling of thermal EC/OC-carbon analysis to photo-ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Zimmermann, R.; Grabowski, J.; Streibel, T.; Sklorz, M.; Chow, J.

    2012-12-01

    Carbonaceous material in airborne particulate matter (PM) is of increasing interest e.g. due to its adverse health effects and its potential influence on the climate. Its analytical assessment on a molecular level is still very challenging. Hence, analysis of carbonaceous fractions for many studies is often solely carried out by determining sum parameters such as the overall content of organic carbon (OC) and elemental carbon (EC) as well as the total carbon content, TC (sum of OC and EC). The used thermal procedure, however, allows getting additional interesting information: By defining different thermal OC fractions (i.e. temperature steps) also information on the refractory properties of the carbonaceous material is obtained. In this context it is particularly interesting to investigate the release and formation behaviors of the molecular species responsible for the different OC and EC fractions. Thus after initial promising results of pre-studies [1,2] in the current work an EC/OC carbon analyzer (Model DRI 2000) and a homebuilt photo-ionization time-of-flight mass spectrometer (PI-TOFMS) were hyphenated and applied to investigate individual organic compounds especially from the different OC fractions. The carbon analyzer enables the stepwise heating of PM loaded filter samples and provides the sum values of the "carbon" release ("Improve protocol" [2]: OC1 - 120 °C, OC2 - 250°C, OC3 - 450°C OC4 - 550°C). With the on-line coupled PI-TOFMS evolved organic compounds, as released during the thermal program, are detectable in real time. This is possible by MS with soft photo ionization methods (SPI - single photon ionization and REMPI - resonance-enhanced multi photon ionization). Soft ionization suppresses fragmentation upon the ionization step and generates molecular signatures in the MS. The EC/OC-analyzer-PI-TOFMS instrument was applied to several types of PM samples, such as ambient aerosol, emission samples (gasoline/diesel car, wood combustion) or

  1. A discharge flow-photoionization mass spectrometric study of the FO(X 2 Pi i) radical. Photoionization efficiency spectrum and ionization energy

    NASA Technical Reports Server (NTRS)

    Zhang, Zhengyu; Kuo, Szu-Cherng; Klemm, R. Bruce; Monks, Paul S.; Stief, Louis J.

    1994-01-01

    Photoionization efficiency spectra of FO were measured over the wavelength range 80.0-100.0 nm and in the ionization threshold region, 94.0-100.0 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. FO was generated by the reaction of F2P atoms with NO3 and via a F2O2 discharge. A value of 12.78 +/- 0.03 eV was obtained for the adiabatic ionization energy of FO from photoion thresholds which corresponds to FO(+)(X 3 Sigma -) from FO(X 2 Pi i). These results, which are the first to be obtained by direct Photo-ionization mass spectrometry (PIMS) measurements, corroborate those of a photoelectron spectroscopy (PES) study; however, the ionization energy determined here is free from interferences due to other species which complicated the PES measurement. A value of 109.5 +/- 8.0 kJ/mol for Delta f H 0 298(FO) is computed from the present value of IE(FO) and a previous appearance energy measurement, and a value for the proton affinity of FO is calculated to be 511.5 +/- 10.0 kJ/mol.

  2. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion.

    PubMed

    Winghart, Marc-Oliver; Yang, Ji-Ping; Vonderach, Matthias; Unterreiner, Andreas-Neil; Huang, Dao-Ling; Wang, Lai-Sheng; Kruppa, Sebastian; Riehn, Christoph; Kappes, Manfred M

    2016-02-01

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H](2-) after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet (1)A2u state and concomitant rise in population of the triplet (3)A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet (1)A2u state takes only a few picoseconds, ESETD from the triplet (3)A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H](2-) is the first example of a photoexcited multianion for which ESETD has been observed following ISC. PMID:26851919

  3. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

    NASA Astrophysics Data System (ADS)

    Winghart, Marc-Oliver; Yang, Ji-Ping; Vonderach, Matthias; Unterreiner, Andreas-Neil; Huang, Dao-Ling; Wang, Lai-Sheng; Kruppa, Sebastian; Riehn, Christoph; Kappes, Manfred M.

    2016-02-01

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H]2- after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet 1A2u state and concomitant rise in population of the triplet 3A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet 1A2u state takes only a few picoseconds, ESETD from the triplet 3A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H]2- is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

  4. Valence and inner-valence shell dissociative photoionization of CO in the 26-33 eV range. I. Ion-electron kinetic energy correlation and laboratory frame photoemission.

    PubMed

    Lebech, M; Houver, J C; Dowek, D

    2009-05-21

    The (V(A+), V(e), ê) vector correlation method, combining imaging and time-of-flight resolved electron-ion coincidence techniques, is used to probe dissociative photoionization (DPI) of CO induced by vacuum ultra violet linearly or circularly polarized synchrotron radiation in the 26-33 eV photon excitation energy range. It provides original information about both the photoionization dynamics of the CO molecule and the dissociation dynamics of the CO(+) molecular ions. The explored region corresponds to valence and inner-valence CO(+) ionic states, which involve doubly or multiply excited electronic configurations. In this paper I we identify up to 17 DPI reaction pathways by the position of the intermediate CO(+) molecular states in the Franck-Condon region and the (C(+) + O) or (O(+) + C) dissociation limits to which they correlate. For these processes we report the laboratory frame beta(C+/O+) and beta(e) asymmetry parameters as well as the relative branching ratios in selected binding energy bands. The I(chi,theta(e),phi(e)) molecular frame photoelectron angular distributions for selected PI processes will be reported in a companion paper II and compared with multichannel Schwinger configuration interaction ab initio calculations of these observables. PMID:19466836

  5. Study of Photoionization Processes of 3d Transition Metal Compound CoCl2 Using Synchrotron Radiation

    SciTech Connect

    Goerguelueer, Oe.; Tutay, A.; Al-Hada, M.; Richter, T.; Zimmermann, P.; Martins, M.

    2007-04-23

    In this work, the photoionization processes of 3d transition metal compound CoCl2 have been investigated using monochromatized synchrotron radiation of the storage ring BESSY II and the atomic-molecular beam technique.

  6. Quantum interference in laser-assisted photoionization and analytical methods for the measurement of an attosecond xuv pulse

    SciTech Connect

    Ge Yucheng; He Haiping

    2011-08-15

    Investigations of the quantum interference in laser-assisted photoionization by an attosecond extreme ultraviolet (xuv) pulse shows an approximately constant value for the total photoionizations for different laser intensities. The square of the full width at half maximum of a photoelectron energy spectrum (PES) linearly depends on the laser intensity. By determining the laser-related phase of each streaked electron and using a transfer equation with linear corrections, an analytically quick method is proposed for precisely reconstructing the xuv pulse intensity (chirp) from one (two) measured PES(s) with a theoretical root-mean-square temporal (energy) difference of less than 1 attosecond (0.1 eV).

  7. Circular dichroism in valence photoelectron spectroscopy of free unoriented chiral molecules: Camphor and bromocamphor

    SciTech Connect

    Lischke, T.; Boewering, N.; Schmidtke, B.; Mueller, N.; Khalil, T.; Heinzmann, U.

    2004-08-01

    The circular dichroism in the photoelectron angular distribution was investigated for valence photoionization of randomly oriented pure enantiomers of camphor and bromocamphor molecules using circularly polarized light in the vacuum ultraviolet. The forward-backward electron emission spectra were recorded simultaneously with two spectrometers at several opposite angles relative to the propagation direction of the photon beam and compared for each of the two substances. Measurements were also carried out for reversed light helicity and opposite molecular handedness. For the left- and right-handed enantiomers of both molecules we observed asymmetries of comparable magnitude up to several percent. The measured asymmetry parameters vary strongly for different orbital binding energies and also for the selected photon energies in the valence region. The results for both molecules are compared. They suggest a strong influence of the final states on the asymmetry, depending on the chiral geometry of the molecular electronic structure, as well as a significant dependence on the initial states involved. They also confirm theoretical predictions describing the effect in pure electric-dipole approximation.

  8. Coherence and Intramolecular Scattering in Molecular Photoionization

    NASA Astrophysics Data System (ADS)

    Becker, U.

    2006-11-01

    In something akin to a double-slit experiment, it could be shown for the first time that electrons display characteristics of both waves- and particles at the same time and, with virtually the push of a button, can be switched back and forth between these states. The experiments provides evidence that disruption of the reflective symmetry of these molecules by introducing two different heavy isotopes, in this case N-14 and N-15, leads to a partial loss of coherence. The electrons begin to partially localise on one of the two, now distinguishable, atoms. The results could have implications for the building and control of "artificial molecules", which are made of semiconductor quantum dots and are a possible component of quantum computers.

  9. High-resolution pulsed-field ionization photoelectron spectroscopy using multi-bunch synchrotron radiation

    SciTech Connect

    Hsu, C.W.; Evans, M.; Ng, C.Y.; Heimann, P.

    1997-04-01

    BL9.0.2.2 is the newly constructed experimental End Station 2 at the Chemical Dynamics Beamline 9.0.2 of the Advanced Light Source (ALS). It is dedicated to the high resolution photoionization study of molecules of interest to atmospheric and combustion chemistry. This End Station is equipped with a high resolution scanning monochromator, which has been demonstrated to have a world record resolution of E/{delta}E=70,000. Taking the advantage of the high resolution ALS light, the authors have improved the energy resolution in threshold photoelectron spectroscopy (TPES) to 0.8 meV. The TPES is a popular technique for photoionization experiments at all synchrotron radiation facilities due to its high energy resolution as compared to that of traditional photoelectron spectroscopy (PES). TPES achieves higher energy resolution by preferentially detecting near zero kinetic energy photoelectrons resulting from threshold photoionization. However, the spectra obtained from the TPES technique generally are complicated by the simultaneous detection of electrons with nonzero kinetic energy, which are not fully discriminated against. On the other hand, the spectra obtained from pulsed field ionization photoelectron spectroscopy (PFI-PES) are completely free of the contamination from kinetic electrons. The PFI-PE technique basically involves the detection of the photoelectrons from field ionization of the very high-n Rydberg states, a few cm{sup {minus}1} below the ionization energy (IE), by applying a delayed pulsed electric field. Within a delay of a few microseconds, all the prompt electrons formed from direct ionization will escape from the photoionization region and will not be collected. The authors have recently overcome problems with energy resolution of an electron time-of-flight technique, and incorporated the PFI-PE technique with multi-bunch VUV synchrotron radiation.

  10. Tunable wavelength soft photoionization of ionic liquid vapors

    SciTech Connect

    Strasser, Daniel; Goulay, Fabien; Belau, Leonid; Kostko, Oleg; Koh, Christine; Chambreau, Steven D.; Vaghjiani, Ghanshyam L.; Ahmed, Musahid; Leone, Stephen R.

    2009-11-11

    Combined data of photoelectron spectra and photoionization efficiency curves in the near threshold ionization region of isolated ion-pairs from [emim][Tf2N], [emim][Pf2N]and [dmpim][Tf2N]ionic liquid vapors reveal small shifts in the ionization energies of ion-pair systems due to cation and anion substitutions. Shifts towards higher binding energy following anion substitution are attributed to increased electronegativity of the anion itself, while shifts towards lower binding energies following cation substitution are attributed to an increase in the cation-anion distance that causes a lower Coulombic binding potential. The predominant ionization mechanism in the near threshold photon energy region is identified as dissociative ionization, involving dissociation of the ion-pair and the production of intact cations as the positively charged products.

  11. Biomedical applications of laser photoionization

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaoxiong; Moore, Larry J.; Fassett, John R.; O'Haver, Thomas C.

    1991-07-01

    Trace elements are important for many essential metabolic functions. Zinc is a structural/functional component in more than 200 enzymes active in the biochemistry of cell division and tissue growth, neurology and endocrine control. Calcium is involved in intracellular control mechanisms and in skeletal bone building and resorption processes related to osteoporosis. Sensitive and selective laser photoionization is being developed to understand mechanisms in smaller samples and biological units approaching the cellular domain. Zinc has an ionization potential of 9.4 eV, or 75766.8 cm-1. Several processes are being explored, including two-photon resonant, three- photon ionization utilizing sequential UV transitions, e.g., 4s2 1S0 yields 4s4p 3P1 and 4s4p 3P1 yields 4s5d 3D1. Preliminary zinc stable isotope ratio data obtained by thermal atomization and laser photoionization agree with accepted values within 2 to 5%, except for anomalous 67Zn. Photoionization of calcium is being studied for isotope enrichment and ratio measurement using narrow and medium bandwidth lasers. Several ionization pathways, e.g., 4s2 1S0 - 2hv1 yields 4s10s - hv2 yields Ca+ (4s2S), are being investigated for isotopically selective ionization. Auto-ionization pathways are explored for greater efficiency in isotopic analysis. All studies have utilized a Nd:YAG- pumped laser system with one or two frequency-doubled tunable dye lasers coupled either to a magnetic sector or time-of-flight mass spectrometer.

  12. Photoionization of methanol and formaldehyde

    NASA Technical Reports Server (NTRS)

    Warneck, P.

    1971-01-01

    Photoions produced in methanol and formaldehyde by radiation in the spectral region 450-1150 A were analyzed mass spectrometrically, and their relative yields were determined as a function of wavelength. First ionization potentials were determined, and the ion yield curves were interpreted in terms of ionization processes in conjunction with other data. Fragment ions were detected on mass numbers of 31, 30, 29, 15, and 14 for methanol, and 29, 2, and 1 for formaldehyde. The associated appearance potentials were determined and were used to calculate heats of formation of the ions CH2OH(+) and HCO(+), and the radicals CH3, CH2, and HCO.

  13. Ar2 photoelectron spectroscopy mediated by autoionizing states.

    PubMed

    Briant, Marc; Poisson, Lionel; Hochlaf, Majdi; de Pujo, Patrick; Gaveau, Marc-André; Soep, Benoît

    2012-11-01

    This experimental work focuses on the complex autoionization dynamics of Ar(2) clusters below the first ionization energy of the argon atom. Ar(2) is submitted to vacuum ultraviolet radiation, and the photoelectron spectra are collected in coincidence with the cluster ions. The ionization dynamics is revealed by the dependence on the photon energy. We applied a new experimental method which we developed to analyze the photoelectron signal. Thus, we were able (i) to get the complete vibrational progression of Ar(2)(+) that was never observed up to now, especially identifying the 0-0 transition overcoming the usual Franck-Condon limitations during single photoionization, and (ii) to obtain the projections of the vibrational wave functions of the autoionizing states over the Ar(2)(+) functions. This method provides a powerful tool to test the potential energy curves computed by high level theoretical calculations on Rydberg states. PMID:23215381

  14. Photoionization of the outer electrons in noble gas endohedral atoms

    SciTech Connect

    Amusia, M. Ya. Baltenkov, A. S.; Chernysheva, L. V.

    2008-08-15

    We suggest a prominent modification of the outer shell photoionization cross section in noble gas (NG) endohedral atoms NG-C{sub n} under the action of the electron shell of fullerene C{sub n}. This shell leads to two important effects: a strong enhancement of the cross section due to fullerene shell polarization under the action of the incoming electromagnetic wave and to prominent oscillation of this cross section due to the reflection of a photoelectron from the NG by the fullerene shell. Both factors lead to powerful maxima in the outer shell ionization cross sections of NG-C{sub n}, which we call giant endohedral resonances. The oscillator strength reaches a very large value in the atomic scale, 25. We consider atoms of all noble gases except He. The polarization of the fullerene shell is expressed in terms of the total photoabsorption cross section of the fullerene. The photoelectron reflection is taken into account in the framework of the so-called bubble potential, which is a spherical {delta}-type potential. It is assumed in the derivations that the NG is centrally located in the fullerene. It is also assumed, in accordance with the existing experimental data, that the fullerene radius R{sub C} is much larger than the atomic radius r{sub A} and the thickness {delta}{sub C} of the fullerene shell. As was demonstrated recently, these assumptions allow us to represent the NG-C{sub n} photoionization cross section as a product of the NG cross section and two well-defined calculated factors.

  15. Photoabsorption and photoionization of HD

    SciTech Connect

    Dehmer, Patricia M.; Chupka, William A.

    1983-01-01

    Relative photoabsorption and photoionization cross sections have been measured for HD at a temperature of 78 K in the wavelength region from 735 to 805 Â. The present wavelength resolution of 0.016 Â represents an improvement of more than two orders of magnitude over that of previous photoionization studies of this molecule. Bands of the 3pπ D ¹Πu←X ¹Σg⁺ system are observed to v'=17, and ionization efficiencies are reported for a number of Rydberg states of low principal quantum number. As in the case of H2, the ionization efficiency is close to unity for Rydberg states that can autoionize with Δv= -1, but drops to zero for states that can autoionize only with a large change in vibrational quantum number and that are significantly predissociated (such as the 3pπ D ¹Πu state). The breakdown of (g,u) symmetry in HD and the resulting effects on the absorption spectrum and on the decay paths of the Rydberg states are discussed.

  16. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization

    NASA Astrophysics Data System (ADS)

    Rapp, Markus; Strelnikova, Irina

    2009-03-01

    We present a new design of an in situ detector for the study of meteor smoke particles (MSPs) in the middle atmosphere. This detector combines a classical Faraday cup with a xenon-flashlamp for the active photoionization/photodetachment of MSPs and the subsequent detection of corresponding photoelectrons. This instrument was successfully launched in September 2006 from the Andøya Rocket Range in Northern Norway. A comparison of photocurrents measured during this rocket flight and measurements performed in the laboratory proves that observed signatures are truly due to photoelectrons. In addition, the observed altitude cut-off at 60 km (i.e., no signals were observed below this altitude) is fully understood in terms of the mean free path of the photoelectrons in the ambient atmosphere. This interpretation is also proven by a corresponding laboratory experiment. Consideration of all conceivable species which can be ionized by the photons of the xenon-flashlamp demonstrates that only MSPs can quantitatively explain the measured currents below an altitude of 90 km. Above this altitude, measured photocurrents are most likely due to photoionization of nitric oxide. In conclusion, our results demonstrate that the active photoionization and subsequent detection of photoelectrons provides a promising new tool for the study of MSPs in the middle atmosphere. Importantly, this new technique does not rely on the a priori charge of the particles, neither is the accessible particle size range severely limited by aerodynamical effects. Based on the analysis described in this study, the geophysical interpretation of our measurements is presented in the companion paper by Strelnikova, I., et al. [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. results. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.011].

  17. Angle-resolved X-ray photoelectron spectroscopy of topmost surface for LaNiO 3 thin film grown on SrTiO 3 substrate by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, P.; Xu, S. Y.; Lin, J.; Ong, C. K.; Cui, D. F.

    1999-01-01

    The LaNiO 3 thin film was grown on SrTiO 3 (001) substrate by computer-controlled laser molecular beam epitaxy (laser MBE). In situ monitoring of the growing film surface was performed with a reflection high energy electron diffraction (RHEED). Angle-resolved X-ray photoelectron spectroscopy (ARXPS) indicated that the terminating plane of the LaNiO 3 film was the LaO atomic plane, and the SrTiO 3 (001) surfaces of as-supplied substrate as well as HF-pretreated substrate were predominantly terminated with TiO atomic plane. The structural conversion of the topmost atomic layer from NiO to LaO occurred during the LaNiO 3 epitaxial growth process.

  18. Double photoionization of SO 2 and fragmentation spectroscopy of SO 2++ studied by a photoion-photoion coincidence method

    NASA Astrophysics Data System (ADS)

    Dujardin, Gérald; Leach, Sydney; Dutuit, Odile; Guyon, Paul-Marie; Richard-Viard, Martine

    1984-08-01

    Doubly charged sulphur dioxide cations (SO 2++) are produced by photoionization with synchrotron radiation from ACO in the excitation-energy range 34-54 eV. A new photoion-photoion coincidence (PIPICO) experiment is described in which coincidences between photoion fragments originating from the dissociation of the doubly charged parent cation are counted. This PIPICO method enables us to study the fragmentation of individual electronically excited states of SO 2++ and to determine the corresponding absolute double-photoionization partial cross sections as a function of the excitation energy. A tentative assignment of the three observed α, β and γ SO 2++ states is given. The dissociation processes of the α and β states into the products SO + + O + are found to be non-statistical in nature; the γ state dissociates completely into three atomic fragments S + + O + + O. Three main observed features of the double-photoionization cross-section curves are discussed in the text: appearance potentials, linear threshold laws, and constant double-photoionization cross sections relative to the total ionization cross section at high energies.

  19. Computational study on the molecular structures and photoelectron spectra of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta).

    PubMed

    Chen, Wen-Jie; Zhang, Chang-Fu; Zhang, Xian-Hui; Zhang, Yong-Fan; Huang, Xin

    2013-05-15

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaW2O9(-) cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the W3O9(+) cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity. PMID:23523755

  20. Computational study on the molecular structures and photoelectron spectra of bimetallic oxide clusters MWO9-/0 (M = V, Nb, Ta)

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Jie; Zhang, Chang-Fu; Zhang, Xian-Hui; Zhang, Yong-Fan; Huang, Xin

    2013-05-01

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MWO9-/0 (M = V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaWO9- cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the WO9+ cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity.

  1. Molecular degradation of D35 and K77 sensitizers when exposed to temperatures exceeding 100 °C investigated by photoelectron spectroscopy.

    PubMed

    Oscarsson, Johan; Fredin, Kristofer; Ahmadi, Sareh; Eriksson, Anna I K; Johansson, Erik M J; Rensmo, Håkan

    2016-03-28

    Degradation of the materials in dye-sensitized solar cells at elevated temperatures is critical for use in real applications. Both during fabrication of the solar cell and under real working conditions the solar cells will be exposed to heat. In this work, mesoporous TiO2 electrodes sensitized with the dyes D35 and K77 were subject to heat-treatment and the effects of this were thereafter investigated by photoelectron spectroscopy. For D35 it was found that heat-treatment changes the binding configuration inducing an increased interaction between the sulfur of the linker unit and the TiO2 surface. The interaction resulting from the change in binding configuration also affects the position of the HOMO level, where a shift of +0.2 eV is observed when heated to 200 °C. For K77, parts of the thiocyanate units are detached and the nitrogen atom leaves the electrode whereas sulfur remains on the surface in various forms of sulfurous oxides. The total dye coverage of K77 gets reduced by heat-treatment. The HOMO level gets progressively less pronounced due to a loss of HOMO level electrons as a consequence of the lower dye coverage when heat-treated, which leads to a lower excitation rate and lower efficiency. The results are discussed in the context of performance for dye-sensitized solar cells. PMID:26949128

  2. Photoionization of cold gas phase coronene and its clusters: Autoionization resonances in monomer, dimer, and trimer and electronic structure of monomer cation

    NASA Astrophysics Data System (ADS)

    Bréchignac, Philippe; Garcia, Gustavo A.; Falvo, Cyril; Joblin, Christine; Kokkin, Damian; Bonnamy, Anthony; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Mulas, Giacomo; Nahon, Laurent

    2014-10-01

    Polycyclic aromatic hydrocarbons (PAHs) are key species encountered in a large variety of environments such as the Interstellar Medium (ISM) and in combustion media. Their UV spectroscopy and photodynamics in neutral and cationic forms are important to investigate in order to learn about their structure, formation mechanisms, and reactivity. Here, we report an experimental photoelectron-photoion coincidence study of a prototypical PAH molecule, coronene, and its small clusters, in a molecular beam using the vacuum ultraviolet (VUV) photons provided by the SOLEIL synchrotron facility. Mass-selected high resolution threshold photoelectron (TPES) and total ion yield spectra were obtained and analyzed in detail. Intense series of autoionizing resonances have been characterized as originating from the monomer, dimer, and trimer neutral species, which may be used as spectral fingerprints for their detection in the ISM by VUV absorption spectroscopy. Finally, a full description of the electronic structure of the monomer cation was made and discussed in detail in relation to previous spectroscopic optical absorption data. Tentative vibrational assignments in the near-threshold TPES spectrum of the monomer have been made with the support of a theoretical approach based on density functional theory.

  3. Photoionization of cold gas phase coronene and its clusters: Autoionization resonances in monomer, dimer, and trimer and electronic structure of monomer cation

    SciTech Connect

    Bréchignac, Philippe Falvo, Cyril; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Garcia, Gustavo A.; Nahon, Laurent; Joblin, Christine; Kokkin, Damian; Bonnamy, Anthony; Mulas, Giacomo

    2014-10-28

    Polycyclic aromatic hydrocarbons (PAHs) are key species encountered in a large variety of environments such as the Interstellar Medium (ISM) and in combustion media. Their UV spectroscopy and photodynamics in neutral and cationic forms are important to investigate in order to learn about their structure, formation mechanisms, and reactivity. Here, we report an experimental photoelectron-photoion coincidence study of a prototypical PAH molecule, coronene, and its small clusters, in a molecular beam using the vacuum ultraviolet (VUV) photons provided by the SOLEIL synchrotron facility. Mass-selected high resolution threshold photoelectron (TPES) and total ion yield spectra were obtained and analyzed in detail. Intense series of autoionizing resonances have been characterized as originating from the monomer, dimer, and trimer neutral species, which may be used as spectral fingerprints for their detection in the ISM by VUV absorption spectroscopy. Finally, a full description of the electronic structure of the monomer cation was made and discussed in detail in relation to previous spectroscopic optical absorption data. Tentative vibrational assignments in the near-threshold TPES spectrum of the monomer have been made with the support of a theoretical approach based on density functional theory.

  4. Photoionization of cold gas phase coronene and its clusters: autoionization resonances in monomer, dimer, and trimer and electronic structure of monomer cation.

    PubMed

    Bréchignac, Philippe; Garcia, Gustavo A; Falvo, Cyril; Joblin, Christine; Kokkin, Damian; Bonnamy, Anthony; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Mulas, Giacomo; Nahon, Laurent

    2014-10-28

    Polycyclic aromatic hydrocarbons (PAHs) are key species encountered in a large variety of environments such as the Interstellar Medium (ISM) and in combustion media. Their UV spectroscopy and photodynamics in neutral and cationic forms are important to investigate in order to learn about their structure, formation mechanisms, and reactivity. Here, we report an experimental photoelectron-photoion coincidence study of a prototypical PAH molecule, coronene, and its small clusters, in a molecular beam using the vacuum ultraviolet (VUV) photons provided by the SOLEIL synchrotron facility. Mass-selected high resolution threshold photoelectron (TPES) and total ion yield spectra were obtained and analyzed in detail. Intense series of autoionizing resonances have been characterized as originating from the monomer, dimer, and trimer neutral species, which may be used as spectral fingerprints for their detection in the ISM by VUV absorption spectroscopy. Finally, a full description of the electronic structure of the monomer cation was made and discussed in detail in relation to previous spectroscopic optical absorption data. Tentative vibrational assignments in the near-threshold TPES spectrum of the monomer have been made with the support of a theoretical approach based on density functional theory. PMID:25362317

  5. Spin-Orbit Activated Interchannel Coupling Effect in Dipole and Quadrupole Photoionization

    NASA Astrophysics Data System (ADS)

    Kumar, S. Sunil; Deschmukh, P. C.; Banerjee, T.; Manson, S. T.

    2008-05-01

    Spin-orbit activated interchannel coupling has been found to affect photoelectron parameters in both the dipole and quadrupole manifolds [1-3]. This effect has been reported in the dipole photoionization parameters of 3d subshells of Xe [1], Ba [1, 3] and Cs [1, 3] and quadrupole spin-polarization parameters of Xe 3d [2]. In the present work, dipole and quadrupole photoionization from 4d and 4p subshells of Xe and 5d and 5p subshells of Rn have been investigated. The effect is significant in dipole photoionization of Xe 4d and Rn 5d, and in quadrupole photoionization of Xe 4p and of Rn 5p states. [1] M. Ya. Amusia, L. V. Chernysheva, S. T. Manson, A. M. Msezane, and V. Radojevic, Phys. Rev. Lett. 88 093002 (2002). [2] M. Ya. Amusia, N. A. Cherepkov, L. V. Chernysheva, Z. Felfli and A. Z. Msezane, J. Phys. B 38 1133 (2005). [3] T. Richter, E. Heinecke, P. Zimmermann, K. Godehusen, M. Yalcinkaya, D. Cubaynes, and M. Meyer, Phys. Rev. Lett. 98 143002 (2007).

  6. Dynamics of ultrafast internal conversion processes studied by femtosecond time-delayed photoelectron spectroscopy

    SciTech Connect

    Cyr, D.R.; Hayden, C.C.

    1995-08-01

    The authors have studied the dynamics of ultrafast internal conversion processes using femtosecond time-resolved photoionization and photoelectron spectroscopy. In hexatriene, following femtosecond pulse excitation at 250 nm, they use time-delayed photoionization to observe the formation and decay of an intermediate species on the subpicosecond time scale. With time-resolved photoelectron spectroscopy, the rapid evolution of vibrational excitation in this intermediate is observed, as electronic energy is converted to vibrational energy in the molecule. The photodynamics of cis and trans isomers of hexatriene are compared and found to be surprisingly different on the 2-3 psec time scale. These results are important for understanding the fundamental photochemical processes in linear polyenes, which have served as models for the active chromophores of many biological photosystems.

  7. Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: charge transfer reaction of N2(+)(X 2Σg+; v+ = 0-2; N+ = 0-9) + Ar.

    PubMed

    Chang, Yih Chung; Xu, Yuntao; Lu, Zhou; Xu, Hong; Ng, C Y

    2012-09-14

    We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N(2)(+)(v(+), N(+)) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N(2)(+)(X (2)Σ(g)(+), v(+) = 0-2, N(+) = 0-9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N(2)(+) PFI-PI beam can be formed with a laboratory kinetic energy resolution of ΔE(lab) = ± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E(cm)'s) down to thermal energies. Absolute total rovibrationally selected cross sections σ(v(+) = 0-2, N(+) = 0-9) for the N(2)(+)(X (2)Σ(g)(+); v(+) = 0-2, N(+) = 0-9) + Ar CT reaction have been measured in the E(cm) range of 0.04-10.0 eV, revealing strong vibrational enhancements and E(cm)-dependencies of σ(v(+) = 0-2, N(+) = 0-9). The thermochemical threshold at E(cm) = 0.179 eV for the formation of Ar(+) from N(2)(+)(X; v(+) = 0, N(+)) + Ar was observed by the measured σ(v(+) = 0), confirming the narrow ΔE(cm) spread achieved in the present study. The σ(v(+) = 0-2; N(+)) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions

  8. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics

    NASA Astrophysics Data System (ADS)

    Quan, Wei; Hao, Xiaolei; Chen, Yongju; Yu, Shaogang; Xu, Songpo; Wang, Yanlan; Sun, Renping; Lai, Xuanyang; Wu, Chengyin; Gong, Qihuang; He, Xiantu; Liu, Xiaojun; Chen, Jing

    2016-06-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends.

  9. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics

    PubMed Central

    Quan, Wei; Hao, XiaoLei; Chen, YongJu; Yu, ShaoGang; Xu, SongPo; Wang, YanLan; Sun, RenPing; Lai, XuanYang; Wu, ChengYin; Gong, QiHuang; He, XianTu; Liu, XiaoJun; Chen, Jing

    2016-01-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends. PMID:27256904

  10. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics.

    PubMed

    Quan, Wei; Hao, XiaoLei; Chen, YongJu; Yu, ShaoGang; Xu, SongPo; Wang, YanLan; Sun, RenPing; Lai, XuanYang; Wu, ChengYin; Gong, QiHuang; He, XianTu; Liu, XiaoJun; Chen, Jing

    2016-01-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends. PMID:27256904

  11. Ratios of photoelectron to EUV ionization rates for aeronomic studies

    SciTech Connect

    Richards, P.G.; Torr, D.G. )

    1988-05-01

    This study reveals that the ratios of the photoelectron to EUV ionization rates are not constant but depend on the degree of attenuation of the solar EUV flux and on the transport of photoelectrons. At high altitudes in the absence of photoelectron transport, the O{sup +} and N{sub 2}{sup +} ionization rate ratios are about 0.35, but they increase with increasing optical depth to such an extent that in the vicinity of the ionization peak, photoelectron impact ionization is as important as photoionization for O{sup +} and N{sub 2}{sup +}. The O{sub 2}{sup +} ratio is about half that of O{sup +} at high altitudes adn also increases with increasing optical depth but reaches a peak of about 0.4. The authors present simple formulae which mimic the attenuation behavior of the ionization ratios. Transport effects become important above about 250 km where the ratios vary by a factor of 2 depending on the presence or absence of photoelectrons from the conjugate ionosphere. In addition to the photoelectron to EUV ionization ratios, they present photodissociative branching ratios for O{sub 2} and N{sub 2}. These photodissociative ratios are also a function of the degree of attenuation of the EUV flux. In the region where attenuation is not important, the N{sup +} to N{sub 2}{sup +} ratio is 0.14, and the O{sup +} to O{sub 2}{sup +} ratio is 0.22. There is a factor of 2 uncertainty in our calculated ratios on account of uncertainties in the solar EUV flux spectrum and also uncertainties in the electron impact cross sections.

  12. Cluster beam analysis via photoionization

    SciTech Connect

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

    1991-08-22

    A photoionization method for quantitatively analyzing the neutral products of free jet expansions is described. The basic principle is to measure the yield of an ion characterization of each component cluster at a photon energy just below that at which production of the same ion from larger clusters can be detected. Since there is then no problem with fragmentation, the beam density of each neutral cluster can be measured in the presence of larger clusters. Although these measurements must be done in the test ions' onset regions where their yields are often quite small, the technique is made highly practicable by the large intensities of widely tunable vacuum-ultraviolet synchrotron light now available at electron storage rings. As an example, the method is applied to the analysis of cluster beams collimated from the free jet expansion of a 200:1 ammonia-chlorobenzene mixture.

  13. Single and double photoionization of Li2

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Li, Ye; Colgan, J.

    2015-01-01

    Time-dependent close-coupling methods are used to study the single and double photoionization of Li2. Formulations for both one-active and two-active electron methods make use of Hartree with local exchange potentials for the core electrons. Both the single and double photoionization cross sections for Li2 are found to be larger for linear polarization than for circular polarization, in sharp contrast to that found before for H2. In particular the double photoionization cross sections for Li2 are found to be approximately five times larger than for H2 and thus more easily observed by future experiments.

  14. Complete photoionization experiments via ultrafast coherent control with polarization multiplexing.

    PubMed

    Hockett, P; Wollenhaupt, M; Lux, C; Baumert, T

    2014-06-01

    Photoelectron angular distributions (PADs) obtained from ionization of potassium atoms using moderately intense femtosecond IR fields (∼10^{12}  W cm^{-2}) of various polarization states are shown to provide a route to "complete" photoionization experiments. Ionization occurs by a net three-photon absorption process, driven via the 4s→4p resonance at the one-photon level. A theoretical treatment incorporating the intrapulse electronic dynamics allows for a full set of ionization matrix elements to be extracted from 2D imaging data. 3D PADs generated from the extracted matrix elements are also compared to experimental, tomographically reconstructed, 3D photoelectron distributions, providing a sensitive test of their validity. Finally, application of the determined matrix elements to ionization via more complex, polarization-shaped, pulses is demonstrated, illustrating the utility of this methodology towards detailed understanding of complex ionization control schemes and suggesting the utility of such "multiplexed" intrapulse processes as powerful tools for measurement. PMID:24949763

  15. In situ high-resolution X-ray photoelectron spectroscopy - Fundamental insights in surface reactions

    NASA Astrophysics Data System (ADS)

    Papp, Christian; Steinrück, Hans-Peter

    2013-11-01

    Since the advent of third generation synchrotron light sources optimized for providing soft X-rays up to 2 keV, X-ray photoelectron spectroscopy (XPS) has been developed to be an outstanding tool to study surface properties and surface reactions at an unprecedented level. The high resolution allows identifying various surface species, and for small molecules even the vibrational fine structure can be resolved in the XP spectra. The high photon flux reduces the required measuring time per spectrum to the domain of a few seconds or even less, which enables to follow surface processes in situ. Moreover, it also provides access to very small coverages down to below 0.1% of a monolayer, enabling the investigation of minority species or processes at defect sites. The photon energy can be adjusted according to the requirement of a particular experiment, i.e., to maximize or minimize the surface sensitivity or the photoionization cross-section of the substrate or the adsorbate. For a few instruments worldwide, a next step forward was taken by combining in situ high-resolution spectrometers with supersonic molecular beams. These beams allow to control and vary the kinetic and internal energies of the incident molecules and provide a local pressure of up to ~10-5 mbar, which can be switched on and off in a controllable way, thus offering a well-defined time structure to study adsorption or reaction processes.

  16. Molecular Studies of Surfaces under Reaction Conditions; Sum Frequency Generation Vibrational Spectroscopy, Scanning Tunneling Microscopy and Ambient Pressure X-Ray Photoelectron Spectroscopy

    SciTech Connect

    Somorjai, G.A.

    2009-11-11

    Instruments developed in our laboratory permit the atomic and molecular level study of NPs under reaction conditions (SFG, ambient pressure XPS and high pressure STM). These studies indicate continuous restructuring of the metal substrate and the adsorbate molecules, changes of oxidation states with NP size and surface composition variations of bimetallic NPs with changes of reactant molecules.

  17. 2006 Photoions, Photoionization & Photodetachment held on January 29-February 3, 2006

    SciTech Connect

    Robert Continetti Nancy Ryan Gray

    2006-09-06

    The 4th Gordon Conference on Photoions, Photoionization and Photodetachment will be held January 29-February 3, 2006 at the Santa Ynez Valley Marriott in Buellton, California. This meeting will continue to cover fundamentals and applications of photoionization and photodetachment, including valence and core-level phenomena and applications to reaction dynamics, ultrashort laser pulses and the study of exotic molecules and anions. Further information will be available soon at the Gordon Conference Website, and will be announced.

  18. Shape resonances in the photoionization of CF4

    SciTech Connect

    Stephens, J. A.; Dill, Dan; Dehmer, Joseph L.

    1986-01-01

    Calculations of photoionization cross sections and photoelectron angular distributions have been performed for all occupied orbitals of CF4 using the multiple-scattering model. Results are compared with very recent experiments which employ synchrotron radiation to measure these quantities, namely the measurements of Truesdale e t a l. for the carbonK shell, and measurements of Carlson e t a l. and Novak e t a l. for the five outermost valence levels. The calculations predict intense shape resonances below 3 eV in continua of a1 and t2 final state symmetry. Qualitative agreement is attained on comparing much of the theory with experiment, notably the five outer valence levels, which serves to establish a one-electron picture of the photoionization dynamics of CF4.

  19. Photoelectronic characterization of heterointerfaces.

    SciTech Connect

    Brumbach, Michael Todd

    2012-02-01

    In many devices such as solar cells, light emitting diodes, transistors, etc., the performance relies on the electronic structure at interfaces between materials within the device. The objective of this work was to perform robust characterization of hybrid (organic/inorganic) interfaces by tailoring the interfacial region for photoelectron spectroscopy. Self-assembled monolayers (SAM) were utilized to induce dipoles of various magnitudes at the interface. Additionally, SAMs of molecules with varying dipolar characteristics were mixed into spatially organized structures to systematically vary the apparent work function. Polymer thin films were characterized by depositing films of varying thicknesses on numerous substrates with and without interfacial modifications. Hard X-ray photoelectron spectroscopy (HAXPES) was performed to evaluate a buried interface between indium tin oxide (ITO), treated under various conditions, and poly(3-hexylthiophene) (P3HT). Conducting polymer films were found to be sufficiently conducting such that no significant charge redistribution in the polymer films was observed. Consequently, a further departure from uniform substrates was taken whereby electrically disconnected regions of the substrate presented ideally insulating interfacial contacts. In order to accomplish this novel strategy, interdigitated electrodes were used as the substrate. Conducting fingers of one half of the electrodes were electrically grounded while the other set of electrodes were electronically floating. This allowed for the evaluation of substrate charging on photoelectron spectra (SCOPES) in the presence of overlying semiconducting thin films. Such an experiment has never before been reported. This concept was developed out of the previous experiments on interfacial modification and thin film depositions and presents new opportunities for understanding chemical and electronic changes in a multitude of materials and interfaces.

  20. Imaging molecules from within: Ultrafast angström-scale structure determination of molecules via photoelectron holography using free-electron lasers

    NASA Astrophysics Data System (ADS)

    Krasniqi, F.; Najjari, B.; Strüder, L.; Rolles, D.; Voitkiv, A.; Ullrich, J.

    2010-03-01

    A scheme based on (i) upcoming brilliant x-ray free-electron laser (FEL) sources, (ii) innovative energy and angular-dispersive large-area electron imagers, and (iii) the well-known photoelectron holography is elaborated that provides time-dependent three-dimensional structure determination of small to medium-sized molecules with Ångström spatial and femtosecond time resolution. Inducing molecular dynamics, wave-packet motion, dissociation, passage through conical intersections, or isomerization by a pump pulse this motion is visualized by the x-ray FEL probe pulse launching keV photoelectrons within a few femtoseconds from specific and well-defined sites, deep core levels of individual atoms, inside the molecule. On their way out, the photoelectrons are diffracted generating a hologram on the detector that encodes the molecular structure at the instant of photoionization, thus providing “femtosecond snapshot images of the molecule from within.” Detailed calculations in various approximations of increasing sophistication are presented and three-dimensional retrieval of the spatial structure of the molecule with Ångström spatial resolution is demonstrated. Due to the large photoabsorption cross sections the method extends x-ray-diffraction-based time-dependent structure investigations envisioned at FEL’s to new classes of samples that are not accessible by any other method. Among them are dilute samples in the gas phase such as aligned, oriented, or conformer-selected molecules, ultracold ensembles and/or molecular or cluster objects containing mainly light atoms that do not scatter x rays efficiently.

  1. Off-resonance photoemission dynamics studied by recoil frame F1s and C1s photoelectron angular distributions of CH{sub 3}F

    SciTech Connect

    Stener, M. Decleva, P.; Mizuno, T.; Yagishita, A.; Yoshida, H.

    2014-01-28

    F1s and C1s photoelectron angular distributions are considered for CH{sub 3}F, a molecule which does not support any shape resonance. In spite of the absence of features in the photoionization cross section profile, the recoil frame photoelectron angular distributions (RFPADs) exhibits dramatic changes depending on both the photoelectron energy and polarization geometry. Time-dependent density functional theory calculations are also given to rationalize the photoionization dynamics. The RFPADs have been compared with the theoretical calculations, in order to assess the accuracy of the theoretical method and rationalize the experimental findings. The effect of finite acceptance angles for both ionic fragments and photoelectrons has been included in the calculations, as well as the effect of rotational averaging around the fragmentation axis. Excellent agreement between theory and experiment is obtained, confirming the good quality of the calculated dynamical quantities (dipole moments and phase shifts)

  2. Photoionized astrophysical plasmas in the laboratory

    SciTech Connect

    Hill, Edward; Rose, Steven

    2010-10-15

    The time-dependent collisional-radiative code ALICE [E. G. Hill and S. J. Rose, High Energy Density Phys. 5, 302 (2009)] is used to model the spectrum from a laboratory photoionized silicon plasma [S. Fujioka et al., Nat. Phys. 5, 821 (2009)]. The results show a good agreement with the laboratory spectrum and lend support to the accompanying analytical discussion of photoionized laboratory spectra, their parametrization, and relevance to astrophysics.

  3. Experimental observation of guanine tautomers with VUV photoionization

    SciTech Connect

    Zhou, Jia; Kostko, Oleg; Nicolas, Christophe; Tang, Xiaonan; Belau, Leonid; de Vries, Mattanjah S.; Ahmed, Musahid

    2008-12-01

    Two methods of preparing guanine in the gas phase, thermal vaporization and laser desorption, have been investigated. The guanine generated by each method is entrained in a molecular beam, single photon ionized with tunable VUV synchrotron radiation, and analyzed using reflectron mass spectrometry. The recorded photoionization efficiency (PIE) curves show a dramatic difference for experiments performed via thermal vaporization compared to laser desorption. The calculated vertical and adiabatic ionization energies for the eight lowest lying tautomers of guanine suggest the experimental observations arise from different tautomers being populated in the two different experimental methods.

  4. Photoelectron spectroscopy of natural products: terpenes

    NASA Astrophysics Data System (ADS)

    Novak, Igor; Kovač, Branka

    2005-01-01

    HeI photoelectron spectra of three terpenes: α-pinene, pulegone and cembrene have been measured. The analysis of their electronic structure is based on the comparison of measured spectra with those of related compounds and on the comparison with molecular structures of studied compounds. We discuss changes in ionization energies of C-C double bonds which are situated at different positions along the rings.

  5. Cosmic-ray-induced photodissociation and photoionization rates of interstellar molecules

    SciTech Connect

    Gredel, R.; Lepp, S.; Dalgarno, A.; Herbst, E. Duke Univ., Durham, NC )

    1989-12-01

    In the Prasad-Tarafdar mechanism, ultraviolet photons are created in the interior of dense interstellar clouds by the impact excitation of molecular hydrogen by secondary electrons generated by cosmic-ray ionization. Detailed calculations of the emission spectrum are described, and the resulting photodissociation and photoionization rates of a wide range of interstellar molecules are calculated. 84 refs.

  6. Confinement Resonances in Photoionization of Xe-C{sub 60}{sup +}

    SciTech Connect

    Kilcoyne, A. L. D.; Aguilar, A.; Mueller, A.; Schippers, S.; Cisneros, C.; Alna'Washi, G.; Aryal, N. B.; Baral, K. K.; Esteves, D. A.; Thomas, C. M.; Phaneuf, R. A.

    2010-11-19

    Experimental evidence is presented for confinement resonances associated with photoabsorption by a Xe atom in a C{sub 60} cage. The giant 4d resonance in photoionization of Xe is predicted to be redistributed into four components due to multipath interference of photoelectron waves reflected by the cage. The measurements were made in the photon energy range 60-150 eV by merging a beam of synchrotron radiation with a mass/charge selected Xe-C{sub 60}{sup +} ion beam. The phenomenon was observed in the Xe-C{sub 583}{sup +} product ion channel.

  7. Photoionization of the alkali dimer cations Li+2, Na+2 and LiNa+

    NASA Astrophysics Data System (ADS)

    Dumitriu, Irina; Vanne, Yulian V.; Awasthi, Manohar; Saenz, Alejandro

    2007-05-01

    Photoionization cross sections for the three alkali dimer cations (Li+2, Na+2 and LiNa+) were calculated at the equilibrium internuclear distance for parallel, perpendicular and isotropic orientations of the molecular axis with respect to the field. A model-potential method was used for the description of the cores. The influence of the model-potential parameters on the photoionization spectra was investigated. Two different methods, a time-independent and a time-dependent one, were implemented and used for computing the cross sections.

  8. 2001 Gordon Research Conference on Photoions, Photoionization and Photodetachment. Final progress report [agenda and attendees list

    SciTech Connect

    Johnson, Mark

    2001-07-13

    The Gordon Research Conference on Photoions, Photoionization and Photodetachment was held at Williams College, Williamstown, Massachusetts, July 8-13, 2001. The 72 conference attendees represented the spectrum of endeavor in this field, coming from academia, industry, and government laboratories, and including US and foreign scientists, senior researchers, young investigators, and students. Emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate discussion about the key issues in the field today. Time for formal presentations was limited. Sessions included the following topics: Vibrational structure, Time resolved studies: nuclear wavepackets, Valence photoionization, Clusters and networks, Resonance structures and decay mechanisms, Ultrafast photoionization, Threshold photoionization, Molecule fixed properties, and Collisional phenomena.

  9. The Multiplexed Chemical Kinetic Photoionization Mass Spectrometer: A New Approach To Isomer-resolved Chemical Kinetics

    SciTech Connect

    Osborne, David L.; Zou, Peng; Johnsen, Howard; Hayden, Carl C.; Taatjes, Craig A.; Knyazev, Vadim D.; North, Simon W.; Peterka, Darcy S.; Ahmed, Musahid; Leone, Stephen R.

    2008-08-28

    We have developed a multiplexed time- and photon-energy?resolved photoionizationmass spectrometer for the study of the kinetics and isomeric product branching of gasphase, neutral chemical reactions. The instrument utilizes a side-sampled flow tubereactor, continuously tunable synchrotron radiation for photoionization, a multi-massdouble-focusing mass spectrometer with 100percent duty cycle, and a time- and positionsensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed 3-dimensional data structure (intensity as a function of molecular mass, reaction time, and photoionization energy) provides insights that might not be available in serial acquisition, as well as additional constraints on data interpretation.

  10. Characterization of Reaction Pathways in Low Temperature Oxidation of Tetrahydrofuran with Multiplexed Photoionization Mass Spectrometry Technique

    NASA Astrophysics Data System (ADS)

    Antonov, Ivan; Sheps, Leonid

    2015-06-01

    Tetrahydrofuran (THF) is a prototype biofuel and a common intermediate in combustion of alkanes and alkenes. Photolytic Cl atom-initiated oxidation of THF was studied with multiplexed photoionization mass spectrometry (MPIMS) technique at temperatures 400-650 K and pressures 0.005-2 bar. Photoionization spectra and kinetic time traces were recorded simultaneously for all mass channels. Photoionization spectra, recorded with tunable VUV synchrotron radiation, were used to separate and identify isomers with the same nominal molecular formula, providing mechanistic insight into the the underlying kinetics. Our study suggests that formation of alkylperoxy radicals and their subsequent isomerization to hydroperoxyalkyl radicals plays an important role in low temperature oxidation of THF, while ring opening of THF-H radical (which dominates THF oxidation at T>800 K) is less important at our conditions.

  11. Rotational Doppler effect in x-ray photoionization

    SciTech Connect

    Sun Yuping; Wang Chuankui; Gel'mukhanov, Faris

    2010-11-15

    The energy of the photoelectron experiences a red or blue Doppler shift when the molecule recedes from the detector or approaches him. This results in a broadening of the photoelectron line due to the translational thermal motion. However, the molecules also have rotational degrees of freedom and we show that the translational Doppler effect has its rotational counterpart. This rotational Doppler effect leads to an additional broadening of the spectral line of the same magnitude as the Doppler broadening caused by translational thermal motion. The rotational Doppler broadening as well as the rotational recoil broadening is sensitive to the molecular orbital from which the photoelectron is ejected. This broadening should be taken into account in analysis of x-ray photoemission spectra of super-high resolution and it can be directly observed using x-ray pump-probe spectroscopy.

  12. Satellite structure in the Argon 1s photoelectron spectrum

    SciTech Connect

    Azuma, Y.; LeBrun, T.; MacDonald, M.; Southworth, S.H.

    1995-08-01

    Atomic inner-shell photoelectron spectra typically display several relatively weak {open_quotes}satellite peaks{close_quotes} at higher ionization energy than the primary peak. Such satellite peaks are associated with final-state configurations corresponding to ionization of an inner-shell electron and excitation or ionization of one or more valence electrons. The observation of satellite peaks demonstrates that the independent-electron picture is inadequate to describe atomic structure and the photoionization process. The measured energies and intensities of photoelectron satellites provide sensitive tests of many-electron theoretical models. We recorded the Ar 1s photoelectron spectrum on beam line X-24A at an X-ray energy of 3628 eV. The primary peak at 3206 eV ionization energy was recorded at an observed resolution of 1.8 eV (FWHM). The satellite structure shows remarkable similarity to that recorded in the suprathreshold region of the Ar K photoabsorption cross section, demonstrating the manner in which these techniques complement each other. Surprisingly, while the region just above the K threshold in Ar was the subject of several theoretical studies using multi-configuration calculations, we find good agreement between our results and those of Dyall and collaborators using a shake model.

  13. Laser photoelectron spectroscopy of ions. Progress report

    SciTech Connect

    Ellison, G.B.

    1992-01-16

    This enterprise uses photoelectron spectroscopy to study the properties of negative ions and radicals. The essence of our experiment is to cross a 0.6 keV mass-selected ion beam (M{sup {minus}}) with the output of a CW laser, {Dirac_h}{omega}{sub o}. The resultant detached photoelectrons with kinetic energy, KE, are energy analyzed by means of a set of electrostatic hemispherical analyzers. Analysis of the photoelectron spectra enables us to extract molecular electron affinities, vibrational frequencies and electronic splittings of the final radical, M, as well as the relative molecular geometries of ions (M{sup {minus}}) and radicals (M). We have scrutinized the two simplest nitrenes: methylnitrene (CH{sub 3}N) and phenylnitrene (C{sub 6}H{sub 5}N). By preparing the corresponding anions, CH{sub 3}N{sup {minus}} and C{sub 6}H{sub 5}N{sup {minus}}, we have studied these nitrene biradicals. Singlet methylnitrene is especially interesting since it is formally a ``transition state.``

  14. The 2p photoionization of ground-state sodium in the vicinity of Cooper minima

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobin; Shi, Yinglong; Dong, Chenzhong

    2016-07-01

    The photoionization processes of ground-state sodium have been investigated with the multiconfiguration Dirac–Fock method. The results are in good or at least reasonable agreement with available experimental and theoretical data. In the energy region near the threshold, the cross sections show non-monotonic changes because of Cooper minima, which due to the sign changes of dominant dipole matrix elements and are very sensitive to electron correlations. As the energy increases continuously, the radial wave functions of the photoelectrons will move towards the nucleus. The values of the cross sections, and hence the Cooper minima, mainly depend on the relative positions of the one-electron radial wave functions of the initial bound electrons 2{p}1/{2,3/2} and the continuum photoelectrons.

  15. Modeling photoionization of aqueous DNA and its components.

    PubMed

    Pluhařová, Eva; Slavíček, Petr; Jungwirth, Pavel

    2015-05-19

    Radiation damage to DNA is usually considered in terms of UVA and UVB radiation. These ultraviolet rays, which are part of the solar spectrum, can indeed cause chemical lesions in DNA, triggered by photoexcitation particularly in the UVB range. Damage can, however, be also caused by higher energy radiation, which can ionize directly the DNA or its immediate surroundings, leading to indirect damage. Thanks to absorption in the atmosphere, the intensity of such ionizing radiation is negligible in the solar spectrum at the surface of Earth. Nevertheless, such an ionizing scenario can become dangerously plausible for astronauts or flight personnel, as well as for persons present at nuclear power plant accidents. On the beneficial side, ionizing radiation is employed as means for destroying the DNA of cancer cells during radiation therapy. Quantitative information about ionization of DNA and its components is important not only for DNA radiation damage, but also for understanding redox properties of DNA in redox sensing or labeling, as well as charge migration along the double helix in nanoelectronics applications. Until recently, the vast majority of experimental and computational data on DNA ionization was pertinent to its components in the gas phase, which is far from its native aqueous environment. The situation has, however, changed for the better due to the advent of photoelectron spectroscopy in liquid microjets and its most recent application to photoionization of aqueous nucleosides, nucleotides, and larger DNA fragments. Here, we present a consistent and efficient computational methodology, which allows to accurately evaluate ionization energies and model photoelectron spectra of aqueous DNA and its individual components. After careful benchmarking, the method based on density functional theory and its time-dependent variant with properly chosen hybrid functionals and polarizable continuum solvent model provides ionization energies with accuracy of 0.2-0.3 e

  16. Photoionization cross section for He in the hyperspherical coordinate method

    SciTech Connect

    Miller, D.L.; Starace, A.F.

    1980-01-01

    In order to more fully explore the role of electron correlations in the photoionization process the hyperspherical coordinate method of Macek was employed in calculating photoionization cross sections of He. Results are presented and discussed. (WHK)

  17. Atomic Auger Doppler effects upon emission of fast photoelectrons.

    PubMed

    Simon, Marc; Püttner, Ralph; Marchenko, Tatiana; Guillemin, Renaud; Kushawaha, Rajesh K; Journel, Loïc; Goldsztejn, Gildas; Piancastelli, Maria Novella; Ablett, James M; Rueff, Jean-Pascal; Céolin, Denis

    2014-01-01

    Studies of photoemission processes induced by hard X-rays including production of energetic electrons have become feasible due to recent substantial improvement of instrumentation. Novel dynamical phenomena have become possible to investigate in this new regime. Here we show a significant change in Auger emission following 1s photoionization of neon, which we attribute to the recoil of the Ne ion induced by the emission of a fast photoelectron. Because of the preferential motion of the ionized Ne atoms along two opposite directions, an Auger Doppler shift is revealed, which manifests itself as a gradual broadening and doubling of the Auger spectral features. This Auger Doppler effect should be a general phenomenon in high-energy photoemission of both isolated atoms and molecules, which will have to be taken into account in studies of other recoil effects such as vibrational or rotational recoil in molecules, and may also have consequences in measurements in solids. PMID:24906107

  18. Photodissociation and photoionization of organosulfur radicals

    SciTech Connect

    Hsu, Chia-Wei

    1994-05-27

    The dynamics of S({sup 3}P{sub 2,1,0}, {sup 1}D{sub 2}) production from the 193 nm photodissociation of CH{sub 3}SCH{sub 3}, H{sub 2}S and CH{sub 3}SH have been studied using 2 + 1 resonance-enhanced multiphoton ionization (REMPI) techniques. The 193 nm photodissociation cross sections for the formation of S from CH{sub 3}S and HS initially prepared in the photodissociation of CH{sub 3}SCH{sub 3} and H{sub 2}S are estimated to be 1 {times} 10{sup {minus}18} and 1.1 {times} 10{sup {minus}18} cm{sup 2}, respectively. The dominant product from CH{sub 3}S is S({sup 1}D), while that from SH is S({sup 3}P). Possible potential energy surfaces involved in the 193 nm photodissociation of CH{sub 3}S({tilde X}) and SH(X) have been also examined. Threshold photoelectron (PE) spectra for SH and CH{sub 3}S formed in the ultraviolet photodissociation of H{sub 2}S and CH{sub 3}SH, respectively, have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. The rotationally resolved N2P-PFI-PE spectrum obtained for SH indicates that photoionization dynamics favors the rotational angular momentum change {Delta}N < 0 with the {Delta}N value up to {minus}3, an observation similar to that found in the PFI-PE spectra of OH (OD) and NO. The ionization energies for SH(X{sup 2}{product}{sub 3,2}) and CH{sub 3}S({tilde X}{sup 2}E{sub 3/2}) are determined to be 84,057.5 {plus_minus} 3 cm{sup {minus}1} and 74,726 {plus_minus} 8 cm{sup {minus}1} respectively. The spin-orbit splittings for SH(X{sup 2}{product}{sub 3/2,1/2}) and CH{sub 3}S({tilde X}{sup 2}E{sub 3/2,1/2}) are found to be 377 {plus_minus} 2 and 257 {plus_minus} 5 cm{sup {minus}1}, respectively, in agreement with previous measurements. The C-S stretching frequency for CH{sub 3}S{sup +}({tilde X}{sup 3}A{sub 2}) is 733 {plus_minus} 5 cm{sup {minus}1}. This study illustrates that the PFI-PE detection method can be a sensitive probe for the nascent internal energy distribution of photoproducts.

  19. Decomposition of diazomeldrum's acid: a threshold photoelectron spectroscopy study.

    PubMed

    Lang, Melanie; Holzmeier, Fabian; Fischer, Ingo; Hemberger, Patrick

    2014-11-26

    Derivatives of meldrum's acid are known precursors for a number of reactive intermediates. Therefore, we investigate diazomeldrum's acid (DMA) and its pyrolysis products by photoionization using vacuum ultraviolet (VUV) synchrotron radiation. The threshold photoelectron spectrum of DMA yields an ionization energy (IE) of 9.68 eV. Several channels for dissociative photoionization are observed. The first one is associated with loss of CH3, leading to a daughter ion with m/z = 155. Its appearance energy AE0K was determined to be 10.65 eV by fitting the experimental data using statistical theory. A second parallel channel leads to m/z = 69, corresponding to N2CHCO, with an AE0K of 10.72 eV. Several other channels open up at higher energy, among them the formation of acetone cation, a channel expected to be the result of a Wolff-rearrangement (WR) in the cation. When diazomeldrum's acid is heated in a pyrolysis reactor, three thermal decomposition pathways are observed. The major one is well-known and yields acetone, N2 and CO as consequence of the WR. However, two further channels were identified: The formation of 2-diazoethenone, NNCCO, together with acetone and CO2 as the second channel and E-formylketene (OCCHCHCO), propyne, N2 and O2 as a third one. 2-Diazoethenone and E-formylketene were identified based on their threshold photoelectron spectra and accurate ionization energies could be determined. Ionization energies for several isomers of both molecules were also computed. One of the key findings of this study is that acetone is observed upon decomposition of DMA in the neutral as well as in the ion and both point to a Wolff rearrangement to occur. However, the ion is subject to other decomposition channels favored at lower internal energies. PMID:25369422

  20. Effects of anisotropic electron-ion interactions in atomic photoelectron angular distributions

    NASA Technical Reports Server (NTRS)

    Dill, D.; Starace, A. F.; Manson, S. T.

    1974-01-01

    The photoelectron asymmetry parameter beta in LS-coupling is obtained as an expansion into contributions from alternative angular momentum transfers j sub t. The physical significance of this expansion of beta is shown to be that: (1) the electric dipole interaction transfers to the atom a charcteristic single angular momentum j sub t = sub o, where sub o is the photoelectron's initial orbital momentum; and (2) angular momentum transfers indicate the presence of anisotropic interaction of the outgoing photoelectron with the residual ion. For open shell atoms the photoelectron-ion interaction is generally anisotropic; photoelectron phase shifts and electric dipole matrix elements depend on both the multiplet term of the residual ion and the total orbital momentum of the ion-photoelectron final state channel. Consequently beta depends on the term levels of the residual ion and contains contributions from all allowed values of j sub t. Numerical calculations of the asymmetry parameters and partial cross sections for photoionization of atomic sulfur are presented.

  1. Effect of strongly coupled plasma on photoionization cross section

    NASA Astrophysics Data System (ADS)

    Das, Madhusmita

    2014-01-01

    The effect of strongly coupled plasma on the ground state photoionization cross section is studied. In the non relativistic dipole approximation, cross section is evaluated from bound-free transition matrix element. The bound and free state wave functions are obtained by solving the radial Schrodinger equation with appropriate plasma potential. We have used ion sphere potential (ISP) to incorporate the plasma effects in atomic structure calculation. This potential includes the effect of static plasma screening on nuclear charge as well as the effect of confinement due to the neighbouring ions. With ISP, the radial equation is solved using Shooting method approach for hydrogen like ions (Li+2, C+5, Al+12) and lithium like ions (C+3, O+5). The effect of strong screening and confinement is manifested as confinement resonances near the ionization threshold for both kinds of ions. The confinement resonances are very much dependent on the edge of the confining potential and die out as the plasma density is increased. Plasma effect also results in appearance of Cooper minimum in lithium like ions, which was not present in case of free lithium like ions. With increasing density the position of Cooper minimum shifts towards higher photoelectron energy. The same behaviour is also true for weakly coupled plasma where plasma effect is modelled by Debye-Huckel potential.

  2. Branching ratio deviations from statistical behavior in core photoionization

    NASA Astrophysics Data System (ADS)

    Di Tommaso, Devis; Decleva, Piero

    2005-08-01

    Accurate calculations of carbon 1s photoionization cross sections have been performed at the density functional level with the B-spline linear combination of atomic orbitals approach. The molecules considered are FCCH, FCCCH3, FCCCN, F2CCH2, CF3COOCH2CH3, and C3H5O. The variation of the branching ratios relative to inequivalent C 1s ionizations have been evaluated from threshold to about 100 eV photoelectron kinetic energy. Large deviations from the statistical ratios are observed at low energies, which remain often significant several tens of eV above threshold. The importance of taking into account core branching ratios for peak deconvolution and quantitative analysis, as well as an additional tool for structural information, is pointed out. Strong shape resonant effects are found to largely cancel in branching ratios. Their nature and variation along the series is analyzed in the framework of excitations into σ* valence orbitals.

  3. Valence Auger decay following 3 s photoionization in potassium

    NASA Astrophysics Data System (ADS)

    Palaudoux, J.; Sheinerman, S.; Soronen, J.; Huttula, S.-M.; Huttula, M.; Jänkälä, K.; Andric, L.; Ito, K.; Lablanquie, P.; Penent, F.; Bizau, J.-M.; Guilbaud, S.; Cubaynes, D.

    2015-07-01

    We have studied photoionization in the inner valence 3 s subshell of K and the spectroscopic properties of the two 3 s-1(1S) and (3S) resulting states. Similar to the Rb and Cs cases, the lifetime widths of the (1S) and (3S) states are found to be markedly different, due to the electron correlation effects. The main part of the study deals with the subsequent Auger decay of the 3 s-1 states, which have the particularity to involve low energy (˜5 eV ) Auger electrons. A magnetic bottle spectrometer with a multicoincidence technique has been used to observe and filter the Auger spectra with respect to the K2 + final state. The evolution of these Auger spectra has been investigated near the ionization threshold. They show strong post-collision interaction (PCI) effects, which are well reproduced by semiclassical and eikonal models. They reveal the importance of the photoelectron-Auger-electron interaction associated with these low energy Auger electrons.

  4. Effect of strongly coupled plasma on photoionization cross section

    SciTech Connect

    Das, Madhusmita

    2014-01-15

    The effect of strongly coupled plasma on the ground state photoionization cross section is studied. In the non relativistic dipole approximation, cross section is evaluated from bound-free transition matrix element. The bound and free state wave functions are obtained by solving the radial Schrodinger equation with appropriate plasma potential. We have used ion sphere potential (ISP) to incorporate the plasma effects in atomic structure calculation. This potential includes the effect of static plasma screening on nuclear charge as well as the effect of confinement due to the neighbouring ions. With ISP, the radial equation is solved using Shooting method approach for hydrogen like ions (Li{sup +2}, C{sup +5}, Al{sup +12}) and lithium like ions (C{sup +3}, O{sup +5}). The effect of strong screening and confinement is manifested as confinement resonances near the ionization threshold for both kinds of ions. The confinement resonances are very much dependent on the edge of the confining potential and die out as the plasma density is increased. Plasma effect also results in appearance of Cooper minimum in lithium like ions, which was not present in case of free lithium like ions. With increasing density the position of Cooper minimum shifts towards higher photoelectron energy. The same behaviour is also true for weakly coupled plasma where plasma effect is modelled by Debye-Huckel potential.

  5. The nonresonant two-photon zero kinetic energy photoelectron spectrum from the electronic ground state of H2S

    NASA Astrophysics Data System (ADS)

    Fischer, Ingo; Lochschmidt, Andreas; Strobel, Andreas; Niedner-Schatteburg, Gereon; Mueller-Dethlefs, Klaus; Bondybey, Vladimir E.

    1993-03-01

    Zero kinetic energy photoelectron spectra from the electronic ground state of hydrogen sulfide are obtained via nonresonant two-photon ionization with complete rotational resolution in the ion. The two-photon spectra are compared with those recently obtained via one-photon VUV photoionization. The spectra show a close similarity, but type a transitions in the two-photon spectra are twice as intense.

  6. Absolute partial photoionization cross sections of ozone.

    SciTech Connect

    Berkowitz, J.; Chemistry

    2008-04-01

    Despite the current concerns about ozone, absolute partial photoionization cross sections for this molecule in the vacuum ultraviolet (valence) region have been unavailable. By eclectic re-evaluation of old/new data and plausible assumptions, such cross sections have been assembled to fill this void.

  7. Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of HCl via the F 1Δ2 Rydberg state

    NASA Astrophysics Data System (ADS)

    Wang, Kwanghsi; McKoy, V.

    1991-12-01

    Results of studies of rotational ion distributions in the X 2Π3/2 and X 2Π1/2 spin-orbit states of HCl+ resulting from (2+1') resonance enhanced multiphoton ionization (REMPI) via the S(0) branch of the F 1Δ2 Rydberg state are reported and compared with measured threshold-field-ionization zero-kinetic-energy spectra reported recently [K. S. Haber, Y. Jiang, G. Bryant, H. Lefebvre-Brion, and E. R. Grant, Phys. Rev. A (in press)]. These results show comparable intensities for J+=3/2 of the X 2Π3/2 ion and J+=1/2 of the X 2Π1/2 ion. Both transitions require an angular momentum change of ΔN=-1 upon photoionization. To provide further insight into the near-threshold dynamics of this process, we also show rotationally resolved photoelectron angular distributions, alignment of the ion rotational levels, and rotational distributions for the parity components of the ion rotational levels. About 18% population is predicted to occur in the (+) parity component, which would arise from odd partial-wave contributions to the photoelectron matrix element. This behavior is similar to that in (2+1) REMPI via the S(2) branch of the F 1Δ2 state of HBr and was shown to arise from significant l mixing in the electronic continuum due to the nonspherical molecular ion potential. Rotational ion distributions resulting from (2+1) REMPI via the S(10) branch of the F 1Δ2 state are also shown.

  8. A two-color infrared-vacuum ultraviolet laser pulsed field ionization photoelectron study of NH3.

    PubMed

    Bahng, Mi-Kyung; Xing, Xi; Baek, Sun Jong; Ng, C Y

    2005-08-22

    We have observed fully rotationally resolved transitions of the photoelectron vibrational bands 2(4), 2(5), 1(1)2(1), and 1(1)2(3) for ammonia cation (NH3+) by two-color infrared (IR)-vacuum ultraviolet (VUV)- pulsed field-ionization photoelectron (PFI-PE) measurements. By preparing an intermediate rovibrational state of neutral NH(3) with a known parity by IR excitation followed by VUV-PFI-PE measurements, we show that the photoelectron parity can be determined unambiguously. The IR-VUV-PFI-PE measurement of the 2(4) band clearly reveals the formation of both even and odd l states for the photoelectrons, where l is the orbital angular momentum quantum number. This observation is consistent with the conclusion that the lack of inversion symmetry for NH3 and NH3+ allows odd/even l mixings, rendering the production of both odd and even l states for the photoelectrons. Evidence is also found, indicating that the photoionization transitions with DeltaK=0 are strongly favored compared to that with DeltaK=3. For the 2(5), 1(1)2(1), and 1(1)2(3) bands, only DeltaK=0 transitions for the production of even l photoelectron states from the J'K'=2(0) rotational level of NH3(nu1=1) are observed. The preferential formation of even l photoelectron states for these vibrational bands is attributed to the fact that the DeltaK=0 transitions for the formation of odd l photoelectron states from the 2(0) rotational level of NH3(nu1=1) are suppressed by the constraint of nuclear-spin statistics. In addition to information obtained on the photoionization dynamics of NH3, this experiment also provides a more precise value of 3232+/-10 cm-1 for the nu1+ (N-H stretch) vibrational frequency of NH3+. PMID:16164295

  9. A fresh look at the photoelectron spectrum of bromobenzene: A third-order non-Dyson electron propagator study

    SciTech Connect

    Schneider, M.; Wormit, M.; Dreuw, A.; Soshnikov, D. Yu.; Trofimov, A. B.; Holland, D. M. P.; Powis, I.; Antonsson, E.; Patanen, M.; Nicolas, C.; Miron, C.

    2015-10-14

    The valence-shell ionization spectrum of bromobenzene, as a representative halogen substituted aromatic, was studied using the non-Dyson third-order algebraic-diagrammatic construction [nD-ADC(3)] approximation for the electron propagator. This method, also referred to as IP-ADC(3), was implemented as a part of the Q-Chem program and enables large-scale calculations of the ionization spectra, where the computational effort scales as n{sup 5} with respect to the number of molecular orbitals n. The IP-ADC(3) scheme is ideally suited for investigating low-lying ionization transitions, so fresh insight could be gained into the cationic state manifold of bromobenzene. In particular, the present IP-ADC(3) calculations with the cc-pVTZ basis reveal a whole class of low-lying low-intensity two-hole-one-particle (2h-1p) doublet and quartet states, which are relevant to various photoionization processes. The good qualitative agreement between the theoretical spectral profile for the valence-shell ionization transitions generated with the smaller cc-pVDZ basis set and the experimental photoelectron spectrum measured at a photon energy of 80 eV on the PLÉIADES beamline at the Soleil synchrotron radiation source allowed all the main features to be assigned. Some theoretical aspects of the ionization energy calculations concerning the use of various approximation schemes and basis sets are discussed.

  10. A fresh look at the photoelectron spectrum of bromobenzene: A third-order non-Dyson electron propagator study

    NASA Astrophysics Data System (ADS)

    Schneider, M.; Soshnikov, D. Yu.; Holland, D. M. P.; Powis, I.; Antonsson, E.; Patanen, M.; Nicolas, C.; Miron, C.; Wormit, M.; Dreuw, A.; Trofimov, A. B.

    2015-10-01

    The valence-shell ionization spectrum of bromobenzene, as a representative halogen substituted aromatic, was studied using the non-Dyson third-order algebraic-diagrammatic construction [nD-ADC(3)] approximation for the electron propagator. This method, also referred to as IP-ADC(3), was implemented as a part of the Q-Chem program and enables large-scale calculations of the ionization spectra, where the computational effort scales as n5 with respect to the number of molecular orbitals n. The IP-ADC(3) scheme is ideally suited for investigating low-lying ionization transitions, so fresh insight could be gained into the cationic state manifold of bromobenzene. In particular, the present IP-ADC(3) calculations with the cc-pVTZ basis reveal a whole class of low-lying low-intensity two-hole-one-particle (2h-1p) doublet and quartet states, which are relevant to various photoionization processes. The good qualitative agreement between the theoretical spectral profile for the valence-shell ionization transitions generated with the smaller cc-pVDZ basis set and the experimental photoelectron spectrum measured at a photon energy of 80 eV on the PLÉIADES beamline at the Soleil synchrotron radiation source allowed all the main features to be assigned. Some theoretical aspects of the ionization energy calculations concerning the use of various approximation schemes and basis sets are discussed.

  11. Relative measurement of the photoionization cross section of the 7D5/2 state of cesium

    NASA Astrophysics Data System (ADS)

    Armstrong, D. J.; Westling, L. A.; Smith, S. J.

    1991-06-01

    We have carried out a relative measurement of the total photoionization cross section of the excited 7D5/2 state of cesium for photoelectron energies in the range 0.103-0.127 Ry above the ionization threshold. Separate measurements were made using two different combinations of laser sources to populate and photoionize the 7D5/2 state. The first measurement was made with a cw diode laser and two pulsed dye lasers, while the second was made with three pulsed dye lasers. The measured cross section was found to vary slowly within experimental uncertainty over this energy range but was otherwise featureless. This result disagrees with the cross section predicted by a Hartree-Slater calculation [J. Lahiri and S. T. Manson, Phys. Rev. A 33, 3151 (1986)], which displayed a deep minimum in this spectral region.

  12. Vibrational branching ratios and asymmetry parameters in the photoionization of CO2 in the region between 650 Å and 840 Å

    National Institute of Standards and Technology Data Gateway

    SRD 119 Vibrational branching ratios and asymmetry parameters in the photoionization of CO2 in the region between 650 Å and 840 Å (Web, free access)   CO2 is studied using dispersed synchrotron radiation in the 650 Å to 850 Å spectral region. The vibrationally resolved photoelectron spectra are analyzed to generate relative vibrational transition amplitudes and the angular asymmetry parameters describing the various transitions observed.

  13. Photoionization of endohedral fullerenes using soft x-ray coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Obaid, Razib; Xiong, Hui; Ablikim, Utuq; Augustin, Sven; Schnorr, Kirsten; Battistoni, Andrea; Wolf, Thomas; Carroll, Ann Marie; Bilodeau, Rene; Osipov, Timur; Rolles, Daniel; Berrah, Nora

    2016-05-01

    Endohedral fullerenes are a model system to understand the reorganization dynamics of highly charged molecular systems with delocalized electronic clouds in the multiphoton excitation regime. Previous experiments at the Linac Coherent Light Source (LCLS) using free-electron laser (FEL) and ultrafast IR laser pulses studied this feature in Ho3N@C80. The question remains whether these dynamics can be studied in the site-specific single photo-ionization regime. Ho3N@C80 is particularly interesting since the inner molecule, Ho3N, is unstable in its natural form. The presence of the encapsulating cage, with the charge exchange characteristics of Holmium, stabilizes the whole molecule. In this study, we will present the charge fragmentation dynamics of this species in the single photoionization process of inner shell electrons (4d) of Holmium using the Advanced Light Source (ALS) at LBNL. Photoion-photoion correlation data, alongside with qualitative electron data will be presented. Funded by the DoE-BES, Grant No. DE-SC0012376.

  14. Hydrodynamics of photoionized columns in the Eagle Nebula, M 16

    NASA Astrophysics Data System (ADS)

    Williams, R. J. R.; Ward-Thompson, D.; Whitworth, A. P.

    2001-11-01

    We present hydrodynamical simulations of the formation, structure and evolution of photoionized columns, with parameters based on those observed in the Eagle Nebula. On the basis of these simulations we argue that there is no unequivocal evidence that the dense neutral clumps at heads of the columns were cores in the pre-existing molecular cloud. In our simulations, a variety of initial conditions leads to the formation and maintenance of near-equilibrium columns. Therefore, it is likely that narrow columns will often occur in regions with large-scale inhomogeneities, but that observations of such columns can tell us little about the processes by which they formed. The manner in which the columns in our simulations develop suggests that their evolution may result in extended sequences of radiation-induced star formation.

  15. Versatile cluster based photoelectron spectrometer

    SciTech Connect

    Knappenberger, K. L. Jr.; Jones, C. E. Jr.; Sobhy, M. A.; Castleman, A. W. Jr.

    2006-12-15

    A recently constructed cluster based photoelectron spectrometer is described. This instrumentation is unique in that it enables the kinetic energy analysis of electrons ejected from both anions and neutral clusters. This capability permits the investigation of discrete electronic levels in all charge states (anionic, neutral, and cationic). A laser vaporization plasma reactor cluster source affixed with a sublimation cell is employed to produce a variety of metal clusters, and the resulting cluster distributions are analyzed with time-of-flight mass spectrometry. The corresponding electronic structure is analyzed with a 'magnetic bottle' photoelectron spectrometer. Examples of instrument performance operating in both anion photodetachment and neutral multiphoton ionization (MPI) modes are provided. In the case of neutral MPI, the corresponding product distribution is collected with a Wiley-McLaren [Rev. Sci. Instrum. 26, 1150 (1955)] mass spectrometer mounted perpendicular to the magnetic bottle photoelectron spectrometer.

  16. Calculation of Ar photoelectron satellites in the hard-x-ray region

    NASA Astrophysics Data System (ADS)

    Yarzhemsky, V. G.; Amusia, M. Ya.

    2016-06-01

    The intensities of photoelectron satellite lines, corresponding to the double core hole (DCH) states of Ar 1 s ionization by hard x rays, are calculated using the many-body perturbation theory. Calculations support the interpretation of the most intense lines as the shake-up excitations 2 p →4 p . It is demonstrated that the intensities of the spectrum lines corresponding to 4 s (and 3 d ) excited states in the DCH field can be explained only taking into account the knock-up process 2 p →3 d along with the shake-up process 1 s →4 s that accompanies 2 p photoionization.

  17. Photoelectron angular distributions in negative-ion photodetachment from mixed sp states.

    PubMed

    Grumbling, Emily R; Sanov, Andrei

    2011-10-28

    We describe an approach for constructing analytical models for the energy-dependence of photoelectron angular distributions in the one-electron, non-relativistic approximation. We construct such a model for electron emission from an orbital described as a superposition of s- and p-type functions, using linearly polarized light. In the limits of pure s or pure p electron photodetachment or photoionization, the model correctly reproduces the familiar Cooper-Zare formula. The model predictions are compared to experimental results for strongly solvated H(-) and NH(2)(-), corresponding to predominantly s and predominantly p character parent states, respectively. PMID:22047234

  18. Photoelectron angular distributions in negative-ion photodetachment from mixed sp states

    NASA Astrophysics Data System (ADS)

    Grumbling, Emily R.; Sanov, Andrei

    2011-10-01

    We describe an approach for constructing analytical models for the energy-dependence of photoelectron angular distributions in the one-electron, non-relativistic approximation. We construct such a model for electron emission from an orbital described as a superposition of s- and p-type functions, using linearly polarized light. In the limits of pure s or pure p electron photodetachment or photoionization, the model correctly reproduces the familiar Cooper-Zare formula. The model predictions are compared to experimental results for strongly solvated H- and NH2-, corresponding to predominantly s and predominantly p character parent states, respectively.

  19. Single and double photoionization of lithium

    NASA Astrophysics Data System (ADS)

    Huang, M.-T.; Wehlitz, R.; Azuma, Y.; Pibida, L.; Sellin, I. A.; Cooper, J. W.; Koide, M.; Ishijima, H.; Nagata, T.

    1999-05-01

    The photoion Li2+/Li+ production cross section ratio of ground-state atomic lithium has been measured for photon energies ranging from 80 to 424 eV. The absolute cross sections for the Li2+ and Li+ yield are also derived. In this energy region, the Li2+/Li+ ratio reaches a plateau of about 1.0% before reaching a maximum of about 4.5%, then decreases slowly. Good agreement is found between the measured total photoionization cross sections of lithium and theoretical calculations. The Li2+/Li+ ratio is also compared to the He2+/He+ ratio from excited He(1s2s) for photon energies up to 70 eV above threshold. The branching ratio of Li2+ to total Li ion production is also compared to the single-ionization cross section of electron impact on Li+ ions.

  20. Scheme for multistep resonance photoionization of atoms

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Ning, Xi-Jing

    2001-07-01

    Traditional schemes for multistep resonance photoionization of atoms let every employed laser beam interact with the atoms simultaneously. In such a situation, analyses via time-dependent Schrödinger equation show that high ionization probability requires all the laser beams must be intense enough. In order to decrease laser intensity, we proposed a scheme that the laser beam used to pump the excited atoms (in a higher bound state) into an autoionization state does not interact with the atoms until all the population is transferred by the other lasers from a ground state to the bound state. As an interesting example, we examined three-step photoionization of 235U with our scheme, showing that the intensity of two laser beams can be lowered by two orders of magnitude without losing high ionization probability.

  1. Photoabsorbtion and Photoionization of Diatomic Molecules

    NASA Astrophysics Data System (ADS)

    Saenz, Alejandro; Dumitriu, Irina

    2008-05-01

    The photodissociation spectra of HeH^+ will be presented together with photoionization cross sections of the alkali dimer cations Li^+2, Na^+2, and LiNa^+. The latter have been calculated using two methods: a time-independent perturbative method and a time-dependent non-perturbative one. The photodissociation of HeH^+ which is of interest for astrophysics and the tritium neutrino-mass experiments currently draws special attention because of the newly developed FEL experimental set-up FLASH in Hamburg at which dissociation of HeH^+ by VUV radiation has been investigated [Phys. Rev. Lett. 98, 223202 (2007)]. The alkali dimer cations are presented as a first methodological step to the photoionization of the alkali dimers, but they are also interesting by themselves since no ab initio data were available for the continuum spectra.

  2. A study of the ion-molecule half reactions O+2(ã4Πu, v)ṡṡṡ(O2)m→O+2m+1+O, m = 1, 2, or 3, using the molecular beam photoionization method

    NASA Astrophysics Data System (ADS)

    Linn, S. H.; Ono, Y.; Ng, C. Y.

    1981-03-01

    The photoionization efficiency (PIE) curve for (O2)+2 has been obtained in the region 650-1 080 Å using the molecular beam photoionization method. The ionization energy (IE) for (O2)2 is determined to be 11.66±0.03 eV. From the measured IE for (O2)+2, the known IE for O2, and the estimated dissociation energy (0.01 eV) of (O2)2, the binding energy for (O2)+2 is deduced to be 0.42±0.03 eV. Comparisons of the PIE spectra for O+2 and (O2)+m, where m = 2, 3, and 4 indicate that the excited dimer complexes O*2(n,v)ṡ(O2)m (m = 1, 2, and 3) formed in this wavelength region are almost completely dissociative, and the cluster ions are predominately formed by the direct photoionization processes (O2)m = 2, 3, or 4+hn→(O2)+m = 2, 3, or 4+e. The PIE curves for O+3, O+5, and O+7 are measured in the region 650-780 Å. The appearance energy 16.66±0.03 eV (744±1.5 Å) for O+3 is found to be consistent with a zero activation energy for the ion-molecule reaction O+2(X˜2Rg)+O2→O+3+O. The appearance energy for O+5 is determined to be 16.41±0.06 eV (755.5±3 Å). This value has allowed the determination of a binding energy of 0.26 eV for O+3ṡO2. The nearly structureless PIE spectra observed for O+3, O+5, and O+7 also suggests that these ions originate mainly from (O2)+2, (O2)+3, and (O2)+4 which are formed by direct ionization processes. Using the relative Franck-Condon factors for the O2 ã4Ru←X˜3S-g transitions, the relative reaction probabilities for the ion-molecule half reactions O+2(ã2Ru, v)ṡ(O2)m→O+2m+1+O(m = 1, 2, and 3)—(1)—as a function of the vibrational quantum number v have been determined. The relative intensities of O+3, O+5, O+7, and (O2)+m = 2-4 observed in this experiment support the conclusion that the reaction probabilities of (1) with m = 2 and 3 are substantially larger than those with m = 1.

  3. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1985-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  4. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1982-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  5. The design of double electrostatic-lens optics for resonance enhanced multiphoton ionization and photoelectron imaging experiments

    SciTech Connect

    Qu, Zehua; Li, Chunsheng; Qin, Zhengbo E-mail: xfzheng@mail.ahnu.edu.cn; Zheng, Xianfeng E-mail: xfzheng@mail.ahnu.edu.cn; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2015-06-15

    Compared to single ion/electron-optics for velocity-map imaging, a double-focusing lens assembly designed not only allows for mapping velocity imaging of photoelectrons but also allows for investigating the vibrational structure of the intermediate states of neutral species in resonance enhanced multiphoton ionization (REMPI) spectra. In this presentation, in order to record REMPI and photoelectron spectra separately, we have constructed a compact photoelectron velocity-map imaging (VMI) apparatus combined with an opposite linear Wiley-Mclaren time-of-flight mass spectrometer (TOFMS). A mass resolution (m/Δm) of ∼1300 for TOFMS and electron energy resolution (ΔE/E) of 2.4% for VMI have been achieved upon three-photon ionization of Xe atom at 258.00 nm laser wavelength. As a benchmark, in combination of one-color (1 + 1) REMPI and photoelectron imaging of benzene via 6{sup 1} and 6{sup 1}1{sup 1} vibronic levels in the S{sub 1} state, the vibrational structures of the cation and photoelectron angular anisotropy are unraveled. In addition, two-color (1 + 1′) REMPI and photoelectron imaging of aniline was used to complete the accurate measurement of ionization potential (62 271 ± 3 cm{sup −1}). The results suggest that the apparatus is a powerful tool for studying photoionization dynamics in the photoelectron imaging using vibrational-state selected excitation to the intermediate states of neutrals based on REMPI technique.

  6. The design of double electrostatic-lens optics for resonance enhanced multiphoton ionization and photoelectron imaging experiments

    NASA Astrophysics Data System (ADS)

    Qu, Zehua; Li, Chunsheng; Qin, Zhengbo; Zheng, Xianfeng; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2015-06-01

    Compared to single ion/electron-optics for velocity-map imaging, a double-focusing lens assembly designed not only allows for mapping velocity imaging of photoelectrons but also allows for investigating the vibrational structure of the intermediate states of neutral species in resonance enhanced multiphoton ionization (REMPI) spectra. In this presentation, in order to record REMPI and photoelectron spectra separately, we have constructed a compact photoelectron velocity-map imaging (VMI) apparatus combined with an opposite linear Wiley-Mclaren time-of-flight mass spectrometer (TOFMS). A mass resolution (m/Δm) of ˜1300 for TOFMS and electron energy resolution (ΔE/E) of 2.4% for VMI have been achieved upon three-photon ionization of Xe atom at 258.00 nm laser wavelength. As a benchmark, in combination of one-color (1 + 1) REMPI and photoelectron imaging of benzene via 61 and 6111 vibronic levels in the S1 state, the vibrational structures of the cation and photoelectron angular anisotropy are unraveled. In addition, two-color (1 + 1') REMPI and photoelectron imaging of aniline was used to complete the accurate measurement of ionization potential (62 271 ± 3 cm-1). The results suggest that the apparatus is a powerful tool for studying photoionization dynamics in the photoelectron imaging using vibrational-state selected excitation to the intermediate states of neutrals based on REMPI technique.

  7. The design of double electrostatic-lens optics for resonance enhanced multiphoton ionization and photoelectron imaging experiments.

    PubMed

    Qu, Zehua; Li, Chunsheng; Qin, Zhengbo; Zheng, Xianfeng; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2015-06-01

    Compared to single ion/electron-optics for velocity-map imaging, a double-focusing lens assembly designed not only allows for mapping velocity imaging of photoelectrons but also allows for investigating the vibrational structure of the intermediate states of neutral species in resonance enhanced multiphoton ionization (REMPI) spectra. In this presentation, in order to record REMPI and photoelectron spectra separately, we have constructed a compact photoelectron velocity-map imaging (VMI) apparatus combined with an opposite linear Wiley-Mclaren time-of-flight mass spectrometer (TOFMS). A mass resolution (m/Δm) of ∼1300 for TOFMS and electron energy resolution (ΔE/E) of 2.4% for VMI have been achieved upon three-photon ionization of Xe atom at 258.00 nm laser wavelength. As a benchmark, in combination of one-color (1 + 1) REMPI and photoelectron imaging of benzene via 6(1) and 6(1)1(1) vibronic levels in the S1 state, the vibrational structures of the cation and photoelectron angular anisotropy are unraveled. In addition, two-color (1 + 1') REMPI and photoelectron imaging of aniline was used to complete the accurate measurement of ionization potential (62,271 ± 3 cm(-1)). The results suggest that the apparatus is a powerful tool for studying photoionization dynamics in the photoelectron imaging using vibrational-state selected excitation to the intermediate states of neutrals based on REMPI technique. PMID:26133827

  8. Photoionization models of the CALIFA HII regions

    NASA Astrophysics Data System (ADS)

    Morisset, C.; Delgado-Inglada, G.; Sánchez, S. F.

    2016-06-01

    We present here a short summary of a forthcoming paper on photoionization models based on CALIFA observations of HII regions. For each of the ˜ 20,000 sources of the CALIFA H ii regions catalog, a grid of photoionization models is computed assuming the ionizing SED being described by the underlying stellar population obtained from spectral synthesis modeling. The nebular metallicity (associated to O/H) is defined using the classical strong line method O3N2. The remaining free parameters are the abundance ratio N/O and the ionization parameter U, which are determined by looking for the model fitting [N II]/Hα and [O III]/Hβ. The models are also selected to fit [O II]/Hβ. This process leads to a set of ˜ 3,200 models that reproduce simultaneously the three observations. We determine new relations between the nebular parameters, like the ionization parameter U and the [O II]/[O III] or [S II]/[S III] line ratios. A new relation between N/O and O/H is obtained, mostly compatible with previous empirical determinations (and not with previous results obtained using photoionization models). A new relation between U and O/H is also determined. All the models are publicly available on the Mexican Millions Models database 3MdB.

  9. 2012 ATOMIC AND MOLECULAR INTERACTIONS GORDON RESEARCH CONFERENCE AND GORDON RESEARCH SEMINAR, JULY 15-20, 2012

    SciTech Connect

    Zwier, Timothy

    2012-07-20

    At the 2012 Atomic and Molecular Interactions Gordon Conference, there will be talks in several broadly defined and partially overlapping areas:  Intramolecular and single-collision reaction dynamics;  Photophysics and photochemistry of excited states;  Clusters, aerosols and solvation;  Interactions at interfaces;  Conformations and folding of large molecules;  Interactions under extreme conditions of temperature and pressure. The theme of the Gordon Research Seminar on Atomic & Molecular Interactions, in keeping with the tradition of the Atomic and Molecular Interactions Gordon Research Conference, is far-reaching and involves fundamental research in the gas and condensed phases along with application of these ideas to practical chemical fields. The oral presentations, which will contain a combination of both experiment and theory, will focus on four broad categories:  Ultrafast Phenomena;  Excited States, Photoelectrons, and Photoions;  Chemical Reaction Dynamics;  Biomolecules and Clusters.

  10. Photoionization of atoms and small molecules using synchrotron radiation. [SF/sub 6/, SiF/sub 4/

    SciTech Connect

    Ferrett, T.A.

    1986-11-01

    The combination of synchrotron radiation and time-of-flight electron spectroscopy has been used to study the photoionization dynamics of atoms (Li) and small molecules (SF/sub 6/, SiF/sub 4/, and SO/sub 2/). Partial cross sections and angular distribution asymmetry parameters have been measured for Auger electrons and photoelectrons as functions of photon energy. Emphasis is on the basic understanding of electron correlation and resonant effects as manifested in the photoemission spectra for these systems. 254 refs., 46 figs., 10 tabs.

  11. Measurements of isotope effects in the photoionization of N2 and implications for Titan's atmosphere

    SciTech Connect

    Croteau, Philip; Randazzo, John B.; Kostko, Oleg; Ahmed, Musahid; Liang, Mao-Chang; Yung, Yuk L.; Boering, Kristie A.

    2010-12-30

    Isotope effects in the non-dissociative photoionization of molecular nitrogen (N2 + h nu -> N2+ + e-) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV (65.6-80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross-sections, sigma(14N2)/sigma(15N14N), ranging from 0.4 to 3.5. Convolving the cross-sections with the solar flux and integrating over the energies measured, the ratios of photoionization rate coefficients are J(15N14N)/J(14N2)=1.00+-0.02 and J(15N2)/J(14N2)=1.00+-0.02, suggesting that isotopic fractionation between N2 and N2+ should be small under such conditions. In contrast, in a one-dimensional model of Titan's atmosphere, isotopic self-shielding of 14N2 leads to values of J(15N14N)/J(14N2) as large as ~;;1.17, larger than under optically thin conditions but still much smaller than values as high as ~;;29 predicted for N2 photodissociation. Since modeled photodissociation isotope effects overpredict the HC15N/HC14N ratio in Titan's atmosphere, and since both N atoms and N2+ ions may ultimately lead to the formation of HCN, estimates of the potential of including N2 photoionization to contribute to a more quantitative explanation of 15N/14N for HCN in Titan's atmosphere are explored.

  12. Double and triple photoionization of Li and Be

    SciTech Connect

    Colgan, J.; Pindzola, M.S.; Robicheaux, F.

    2005-08-15

    We present calculations for the double photoionization (with excitation) and the triple photoionization of Li and Be. We extend and more fully discuss the previous calculations made for Li by Colgan et al. [Phys. Rev. Lett. 93, 053201 (2004)] and present calculations for Be. The Be triple photoionization cross sections are compared with previous double shake-off model calculations of Kheifets and Bray [J. Phys. B 36, L211 (2003)], and our calculations are found to be significantly lower.

  13. Double and triple photoionization of Li and Be

    NASA Astrophysics Data System (ADS)

    Colgan, J.; Pindzola, M. S.; Robicheaux, F.

    2005-08-01

    We present calculations for the double photoionization (with excitation) and the triple photoionization of Li and Be. We extend and more fully discuss the previous calculations made for Li by Colgan et al. [Phys. Rev. Lett. 93, 053201 (2004)] and present calculations for Be. The Be triple photoionization cross sections are compared with previous double shake-off model calculations of Kheifets and Bray [J. Phys. B 36, L211 (2003)], and our calculations are found to be significantly lower.

  14. Spin- and angle-resolved spectroscopy of S 2p photoionization in the hydrogen sulfide molecule

    SciTech Connect

    Turri, G.; Snell, G.; Canton, S.E.; Bilodeau, R.C.; Langer, B.; Martins, M.; Kukk, E.; Cherepkov, N.; Bozek, J.D.; Kilcoyne, A.L.; Berrah, N.

    2004-08-01

    Angle- and spin-resolved photoelectron spectroscopy with circularly and linearly polarized synchrotron radiation were used to study the electronic structure of the hydrogen sulfide molecule. A strong effect of the molecular environment appears in the spin-resolved measurements and, although less clearly, in the angular distribution of the sulfur 2p photoelectrons. The anisotropy and spin parameters of the three main spectral components have been obtained. The validity of simple atomic models in explaining the results is discussed.

  15. Rotamers and Migration: Investigating the Dissociative Photoionization of Ethylenediamine.

    PubMed

    Muller, Giel; Voronova, Krisztina; Sztáray, Bálint; Meloni, Giovanni

    2016-06-01

    The unimolecular dissociation of energy-selected ethylenediamine cations was studied by threshold photoelectron photoion coincidence spectroscopy (TPEPICO) in the photon energy range of 8.60-12.50 eV. Modeling the breakdown diagram and time-of-flight distributions with rigid activated complex RRKM theory yielded 0 K appearance energies for eight dissociation channels, leading to NH2CHCH2(+)(•) at 9.120 ± 0.010 eV, CH3C(NH2)2(+) at 9.200 ± 0.012 eV, NH2CHCH3(+) at 9.34 ± 0.08 eV, CH2NH2(+) at 9.449 ± 0.025 eV, CH2NH3(+) at 9.8 ± 0.1 eV, c-C2H4NH2(+) at 10.1 ± 0.1 eV, CH3NHCHCH2(+) at 10.2 ± 0.1 eV, and the reappearance of CH2NH2(+) at 10.2 ± 0.1 eV. The CBS-QB3-calculated pathways highlighted the influence of intramolecular hydrogen attractions on the dissociation processes, presenting novel isomers and low-energy van der Waals intermediates that led to fragments in good agreement with experimental results. While most of the dissociation channels take place through reverse barriers, the 0 K heat of formation of (•)CH2NH2 was determined to be 147.6 ± 3.7 kJ mol(-1), in excellent agreement with literature, and the 0 K heat of formation of CH2NH3(+) at 844 ± 10 kJ mol(-1) is the first experimentally measured value available and is in good agreement with theory. PMID:27177327

  16. Long Duration Directional Drives for Star Formation and Photoionization

    SciTech Connect

    Kane, J. O.; Martinez, D. A.; Pound, M. W.; Heeter, R. F.; Villette, B.; Casner, A.; Mancini, R. C.

    2015-06-18

    This research will; confirm the possibility of studying the structure and evolution of star-forming regions of molecular clouds in the laboratory; test the cometary model for the formation of the pillar structures in molecular clouds; assess the effect of magnetic fields on the evolution of structures in molecular clouds; and develop and demonstrate a new, long-duration (60-100 ns), directional source of x-ray radiation that can be used for the study of deeply nonlinear hydrodynamics, hydrodynamic instabilities that occur in the presence of directional radiation, shock-driven and radiatively-driven collapse of dense cores, and photoionization. Due to the iconic status of the pillars of the Eagle Nebula, this research will bring popular attention to plasma physics, HED laboratory physics, and fundamental science at NIF and other experimental facilities. The result will be to both to bring new perspectives to the studies of hydrodynamics in inertial confinement fusion and HED scenarios in general, and to promote interest in the STEM disciplines.

  17. Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Seidel, Robert; Winter, Bernd; Bradforth, Stephen E.

    2016-05-01

    The valence orbital electron binding energies of water and of embedded solutes are crucial quantities for understanding chemical reactions taking place in aqueous solution, including oxidation/reduction, transition-metal coordination, and radiation chemistry. Their experimental determination based on liquid-photoelectron spectroscopy using soft X-rays is described, and we provide an overview of valence photoelectron spectroscopy studies reported to date. We discuss principal experimental aspects and several theoretical approaches to compute the measured binding energies of the least tightly bound molecular orbitals. Solutes studied are presented chronologically, from simple electrolytes, via transition-metal ion solutions and several organic and inorganic molecules, to biologically relevant molecules, including aqueous nucleotides and their components. In addition to the lowest vertical ionization energies, the measured valence photoelectron spectra also provide information on adiabatic ionization energies and reorganization energies for the oxidation (ionization) half-reaction. For solutes with low solubility, resonantly enhanced ionization provides a promising alternative pathway.

  18. Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy.

    PubMed

    Seidel, Robert; Winter, Bernd; Bradforth, Stephen E

    2016-05-27

    The valence orbital electron binding energies of water and of embedded solutes are crucial quantities for understanding chemical reactions taking place in aqueous solution, including oxidation/reduction, transition-metal coordination, and radiation chemistry. Their experimental determination based on liquid-photoelectron spectroscopy using soft X-rays is described, and we provide an overview of valence photoelectron spectroscopy studies reported to date. We discuss principal experimental aspects and several theoretical approaches to compute the measured binding energies of the least tightly bound molecular orbitals. Solutes studied are presented chronologically, from simple electrolytes, via transition-metal ion solutions and several organic and inorganic molecules, to biologically relevant molecules, including aqueous nucleotides and their components. In addition to the lowest vertical ionization energies, the measured valence photoelectron spectra also provide information on adiabatic ionization energies and reorganization energies for the oxidation (ionization) half-reaction. For solutes with low solubility, resonantly enhanced ionization provides a promising alternative pathway. PMID:27023757

  19. Photoionization of DABCO via high vibrational levels of the S{sub 1} state.

    SciTech Connect

    Pratt, S. T.; Chemistry

    2002-07-10

    The photoelectron spectrum following resonant two-photon ionization of 1,4-diazabicyclo[2.2.2]octane (DABCO) was recorded with the laser tuned to the origin band of the S{sub 2}{l_arrow}S{sub 0} transition. The spectrum is consistent with the rapid radiationless transition from the S2 state into high vibrational levels of the S1 state, as proposed by Smith et al. Features in the double-resonance spectrum of Smith et al. that were previously assigned to photoionization of S(-) 3s(-){sup 1}A'{sub 2} vibrational levels populated by a radiationless transition from the S2 state are reinterpreted, with the conclusion that the S(-) state has yet to be observed.

  20. Photoionization of DABCO via high vibrational levels of the S 1 state

    NASA Astrophysics Data System (ADS)

    Pratt, S. T.

    2002-07-01

    The photoelectron spectrum following resonant two-photon ionization of 1,4-diazabicyclo[2.2.2]octane (DABCO) was recorded with the laser tuned to the origin band of the S 2←S 0 transition. The spectrum is consistent with the rapid radiationless transition from the S 2 state into high vibrational levels of the S 1 state, as proposed by Smith et al. [J. Phys. Chem. 88 (1984) 2250]. Features in the double-resonance spectrum of Smith et al. that were previously assigned to photoionization of S(-) 3s(-) 1A″2 vibrational levels populated by a radiationless transition from the S 2 state are reinterpreted, with the conclusion that the S(-) state has yet to be observed.

  1. Laser excitation combined with 2p photoionization and Auger decay of potassium

    SciTech Connect

    Jaenkaelae, K.; Sankari, R.; Huttula, M.; Calo, A.; Heinaesmaeki, S.; Aksela, S.; Aksela, H.; Schulz, J.; Fritzsche, S.; Rander, T.; Svensson, S.

    2006-02-15

    The 2p photoionization and subsequent L{sub 2,3}M{sub 2,3}M{sub 2,3} Auger decay spectra from free 4s{sub 1/2}{yields}4p{sub 1/2} laser-excited potassium atoms are studied both experimentally and theoretically. The shake-up-structure of the 2p photoelectron spectrum of K is resolved. A direct experimental way for resolving the satellite structure due to conjugate shake-up transitions accompanying the hole creation in the L{sub 2,3}M{sub 2,3}M{sub 2,3} Auger spectrum of nonexcited atoms is presented. Theoretical ab initio computations based on the multiconfiguration Dirac-Fock approach were performed to interpret the experimental findings.

  2. Experimental and theoretical study of 3p photoionization and subsequent Auger decay in atomic chromium

    NASA Astrophysics Data System (ADS)

    Keskinen, J.; Huttula, S.-M.; Mäkinen, A.; Patanen, M.; Huttula, M.

    2015-12-01

    3p photoionization and subsequent low kinetic energy Coster-Kronig and super Coster-Kronig Auger decay have been studied in atomic chromium. The binding energies, line widths, and relative intensities for the transitions seen in the synchrotron radiation excited 3p photoelectron spectrum are determined. The high resolution M2,3 M4,5 M4,5 and M2,3 M4,5 N1 Auger electron spectra following the electron impact excited 3p ionization are presented and the kinetic energies, relative intensities, and identifications are given for the main lines. The experimental findings are compared with the theoretical predictions obtained from Hartree-Fock and multiconfiguration Dirac-Fock approaches.

  3. Attosecond time delay and confinement resonances in photoionization of endohedral atoms: Xe@C60

    NASA Astrophysics Data System (ADS)

    Deshmukh, P. C.; Mandal, A.; Saha, S.; Kheifets, A. S.; Dolmatov, V. K.; Manson, S. T.

    2014-05-01

    A theoretical study of Wigner time delay has been applied to the investigation of confinement resonances that occur generally in the photoionization of confined atoms. Calculations have been performed on the 4d subshell of Xe@C60 where the existence of confinement resonances has recently been verified experimentally. The random phase approximation in both the nonrelativistic and relativistic versions, which include significant initial and final state correlation, have been employed in the study. The influence of the C60 cage on the atom is represented by a spherical annular well, which should be good for inner atomic shells at energies significantly higher than the C60 plasmons. The results show that the confinement resonances exhibit significant time delay, as compared to the free atom, confirming the interpretation in terms of multiple scattering of the photoelectron off the walls of the confining shell.

  4. Double photoionization of Be-like (Be-F5+) ions

    NASA Astrophysics Data System (ADS)

    Abdel Naby, Shahin; Pindzola, Michael; Colgan, James

    2015-04-01

    The time-dependent close-coupling method is used to study the single photon double ionization of Be-like (Be - F5+) ions. Energy and angle differential cross sections are calculated to fully investigate the correlated motion of the two photoelectrons. Symmetric and antisymmetric amplitudes are presented along the isoelectronic sequence for different energy sharing of the emitted electrons. Our total double photoionization cross sections are in good agreement with available theoretical results and experimental measurements along the Be-like ions. This work was supported in part by grants from NSF and US DoE. Computational work was carried out at NERSC in Oakland, California and the National Institute for Computational Sciences in Knoxville, Tennessee.

  5. Angular anisotropy in valence photoionization of Na clusters: theoretical investigation using jellium model

    NASA Astrophysics Data System (ADS)

    Jänkälä, Kari

    2013-03-01

    Calculation of the behaviour of photoelectron angular anisotropy in valence ionization of initially neutral NaX (X = 34-58) clusters is provided. The calculations are carried out for 1p, 1d and 1g jellium orbitals as a function of photon energy. The adapted theoretical framework is spherical jellium model using Woods-Saxon potential, which is modified to account for the long-range Coulomb tail in the final state. We discuss on the observed dramatic variations of the angular anisotropy parameter β as a function incident photon energy. It is shown that the behaviour is connected to the oscillation of the valence photoionization cross sections, that is a specific interference property of such metallic clusters whose valence structure can be described using the jellium model. ISSPIC 16 - 16th International Symposium on Small Particles and Inorganic Clusters, edited by Kristiaan Temst, Margriet J. Van Bael, Ewald Janssens, H.-G. Boyen and Françoise Remacle.

  6. Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

    SciTech Connect

    Zheng, Xianfeng Zhou, Xiaoyu; Cheng, Zaiqi; Jia, Dandan; Qu, Zehua; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2014-10-15

    We present measurements of photoionization cross-sections of the excited states of cobalt using a two-color, two-step resonance ionization technique in conjunction with a molecular beam time of flight (TOF) mass spectrometer. The atoms were produced by the laser vaporization of a cobalt rod, coupled with a supersonic gas jet. The absolute photoionization cross-sections at threshold and near-threshold regions (0-1.2 eV) were measured, and the measured values ranged from 4.2±0.7 Mb to 10.5±1.8 Mb. The lifetimes of four odd parity energy levels are reported for the first time.

  7. He photoionization dominated by doubly excited resonances

    SciTech Connect

    Chang, T.N.; Zhen, M.

    1993-05-01

    We present the theoretical He photoionization, cross sections from the ground and the {sup 1,3}S bound excited states using a B-spline based configuration-interaction procedure for continuum (CIC). The resonant structures associated with selected sp,2n{sup {plus_minus}} and 2pnd {sup 1,3}P autoionization series below the He{sup +} N=2 threshold will be expressed quantitatively in terms of their resonant energies, widths, and peak cross sections. Comparisons with earlier theoretical results and recent experimental measurement will be presented. The nonresonant spectra from the 1s2s {sup 1,3}S metastable states will also be reexamined.

  8. Photoionization mass spectrometric study of HOCl: Photoionization efficiency spectrum and ionization energy

    SciTech Connect

    Thorn, R.P. Jr.; Stief, L.J.

    1999-02-18

    The photoionization efficiency (PIE) spectrum of HOCl was measured over the wavelength range {lambda} = 102--115 nm, using a discharge flow-photoionization mass spectrometer (DF-PIMS) apparatus coupled to a synchrotron radiation source. The PIE spectra displayed steplike behavior near threshold. This study represents the first determination of the HOCl photoionization efficiency spectrum and the photoionization threshold. A value of 11.12{sub 3} {+-} 0.01{sub 8} eV was obtained for the adiabatic ionization energy (IE) of HOCl from analysis of photoion thresholds, corresponding to the HOCl{sup +}(X{sup 2}A{double_prime}) {l_arrow} HOCl(X{sup 1}A{double_prime}) transition. The PIMS result is identical to the only previous experimental measurement and in good agreement with a recent ab initio calculation. From the result for IE(HOCl), a value of 999.4 {+-} 3.6 kJ mol{sup {minus}1} was calculated for {Delta}{sub f}H{degree}{sub 0}(HOCl{sup +}), and from the latter, the proton affinity of ClO at T = 0 K, PA{sub 0}(ClO), was determined to be 629.6 {+-} 3.6 kJ mol{sup {minus}1}. At 298 K, the computed values for {Delta}{sub f}H{degree}{sub 298}(HOCl{sup +}) and PA{sub 298}(ClO) are 996.5 {+-} 3.6 and 635.1 {+-} 3.6 kJ mol{sup {minus}1}, respectively.

  9. Photoelectron spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil

    NASA Astrophysics Data System (ADS)

    Ruckenbauer, Matthias; Mai, Sebastian; Marquetand, Philipp; González, Leticia

    2016-02-01

    Ground- and excited-state UV photoelectron spectra of thiouracils (2-thiouracil, 4-thiouracil, and 2,4-dithiouracil) have been simulated using multireference configuration interaction calculations and Dyson norms as a measure for the photoionization intensity. Except for a constant shift, the calculated spectrum of 2-thiouracil agrees very well with experiment, while no experimental spectra are available for the two other compounds. For all three molecules, the photoelectron spectra show distinct bands due to ionization of the sulphur and oxygen lone pairs and the pyrimidine π system. The excited-state photoelectron spectra of 2-thiouracil show bands at much lower energies than in the ground state spectrum, allowing to monitor the excited-state population in time-resolved UV photoelectron spectroscopy experiments. However, the results also reveal that single-photon ionization probe schemes alone will not allow monitoring all photodynamic processes existing in 2-thiouracil. Especially, due to overlapping bands of singlet and triplet states the clear observation of intersystem crossing will be hampered.

  10. First Principles Study of Double Photoionization of H2 UsingExterior Complex Scaling

    SciTech Connect

    Rescigno, Thomas N.; Vanroose, Wim; Horner, Daniel A.; Martin,Fernando; McCurdy, C. William

    2006-07-21

    Exterior complex scaling provides a practical path forfirst-principles studies of atomic and molecular ionizationproblemssince it avoids explicit enforcement of asymptotic boundary conditionsfor 3-body Coulomb breakup. We have used the method of exterior complexscaling, implemented with both the discrete variable representation andB-splines, to obtain the first-order wave function for molecular hydrogencorresponding to a single photon having been absorbed by a correlatedinitial state. These wave functions are used to construct convergedtriple differential cross sections for double photoionization of alignedH2 molecules.

  11. Double photoionization of helium with synchrotron x-rays: Proceedings

    SciTech Connect

    Not Available

    1994-01-01

    This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.

  12. Assignment of benzodiazepine UV absorption spectra by the use of photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Khvostenko, O. G.; Tzeplin, E. E.; Lomakin, G. S.

    2002-04-01

    Correlations between singlet transition energies and energy gaps of corresponding pairs of occupied and unoccupied molecular orbitals were revealed in a series of benzodiazepines. The occupied orbital energies were taken from the photoelectron spectra of the compound investigated, the unoccupied ones were obtained from MNDO/d calculations, and the singlet energies were taken from the UV absorption spectra. The correspondence of the singlet transitions to certain molecular orbitals was established using MNDO/d calculations and comparing between UV and photoelectron spectra. It has been concluded that photoelectron spectroscopy can be applied for interpretation of UV absorption spectra of various compounds on the basis of similar correlations.

  13. Towards imaging of ultrafast molecular dynamics using FELs

    NASA Astrophysics Data System (ADS)

    Rouzée, A.; Johnsson, P.; Rading, L.; Hundertmark, A.; Siu, W.; Huismans, Y.; Düsterer, S.; Redlin, H.; Tavella, F.; Stojanovic, N.; Al-Shemmary, A.; Lépine, F.; Holland, D. M. P.; Schlatholter, T.; Hoekstra, R.; Fukuzawa, H.; Ueda, K.; Vrakking, M. J. J.

    2013-08-01

    The dissociation dynamics induced by a 100 fs, 400 nm laser pulse in a rotationally cold Br2 sample was characterized by Coulomb explosion imaging (CEI) using a time-delayed extreme ultra-violet (XUV) FEL pulse, obtained from the Free electron LASer in Hamburg (FLASH). The momentum distribution of atomic fragments resulting from the 400 nm-induced dissociation was measured with a velocity map imaging spectrometer and used to monitor the internuclear distance as the molecule dissociated. By employing the simultaneously recorded in-house timing electro-optical sampling data, the time resolution of the final results could be improved to 300 fs, compared to the inherent 500 fs time-jitter of the FEL pulse. Before dissociation, the Br2 molecules were transiently ‘fixed in space’ using laser-induced alignment. In addition, similar alignment techniques were used on CO2 molecules to allow the measurement of the photoelectron angular distribution (PAD) directly in the molecular frame (MF). Our results on MFPADs in aligned CO2 molecules, together with our investigation of the dissociation dynamics of the Br2 molecules with CEI, show that information about the evolving molecular structure and electronic geometry can be retrieved from such experiments, therefore paving the way towards the study of complex non-adiabatic dynamics in molecules through XUV time-resolved photoion and photoelectron spectroscopy.

  14. Infrared Vacuum-Ultraviolet Laser Pulsed Field Ionization-Photoelectron Study of CH₃Br⁺(X˜ 2E3/2)

    SciTech Connect

    Xing, X.; Wang, P.; Reed, Beth; Baek, Sun-Jong; Ng, Cheuk-Yiu

    2008-10-02

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. By preparing methyl bromide (CH₃Br) in selected rotational levels of the CH₃Br(X˜ 1A1; V1 = 1) state with infrared (IR) laser excitation prior to vacuum-ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have observed rotationally resolved photoionization transitions to the CH₃Br⁺(X˜ 2E3/2; V1 + = 1) state, where V1 and V1 + are the symmetric C-H stretching vibrational mode for the neutral and cation, respectively. The VUV-PFI-PE origin band for CH₃Br⁺(X˜ 2E3/2) has also been measured. The simulation of these IR-VUV-PFI-PE and VUV-PFI-PE spectra have allowed the determination of the V1 + vibrational frequency (2901.8 ( 0.5 cm-1) and the ionization energies of the origin band (85 028.3 ( 0.5 cm-1) and the V1 + ) 1 r V1 ) 1 band (84 957.9 ( 0.5 cm-1).

  15. Inner-shell ionization of rotating linear molecules in the presence of spin-dependent interactions: Entanglement between a photoelectron and an auger electron

    NASA Astrophysics Data System (ADS)

    Ghosh, R.; Chandra, N.; Parida, S.

    2009-03-01

    This paper reports results of a theoretical study of angle- and spin-resolved photo-Auger electron coincident spectroscopy in the form of entanglement between these two particles emitted from a linear molecule. First, we develop an expression for a density matrix needed for studying spin-entanglement between a photoelectron and an Auger electron. In order to properly represent the molecular symmetries, nuclear rotation, and the spin-dependent interactions (SDIs), we have used symmetry adapted wavefunctions in Hund’s coupling scheme (a) for all the species participating in this two-step process. This expression shows that spin-entanglement in a photo-Auger electron pair in the presence of SDIs very strongly depends upon, among other things, polarization of the ionizing radia- tion, directions of motion and of spin polarization of two ejected electrons, and the dynamics of photoionization and of Auger decay. We have applied this expression, as an example, to a generic linear molecule in its J0, M0 = 0 state. This model calculation clearly brings out the salient features of the spin-entanglement of a photo-Auger electron pair in the presence of the SDIs.

  16. Vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters

    SciTech Connect

    Ahmed, Musahid; Ahmed, Musahid; Wilson, Kevin R.; Belau, Leonid; Kostko, Oleg

    2008-05-12

    In this work we report on thevacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuumultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH + (n=1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H + (n=2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH +, (CH 3OH)2 +, (CH3OH)nH + (n=1-9), and (CH 3OH)n(H2O)H + (n=2-9 ) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.

  17. Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol-Water Clusters

    SciTech Connect

    Kostko, Oleg; Belau, Leonid; Wilson, Kevin R.; Ahmed, Musahid

    2008-04-24

    In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH+(n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH n(H2O)H+ (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH+, (CH3OH)2+, (CH3OH)nH+ (n = 1-9), and (CH3OH)n(H2O)H+ (n = 2-9) as a function of photon energy. With an increasein the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.

  18. Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Comes, F. J.; Speier, F.; Elzer, A.

    1982-01-01

    An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

  19. Vacuum-Ultraviolet Photoionization and Mass Spectrometric Characterization of Lignin Monomers Coniferyl and Sinapyl Alcohols

    SciTech Connect

    Takahashi, Lynelle K.; Zhou, Jia; Kostko, Oleg; Golan, Amir; Leone, Stephen R.; Ahmed, Musahid

    2011-02-09

    The fragmentation mechanisms of monolignols under various energetic processes are studied with jet-cooled thermal desorption molecular beam (TDMB) mass spectrometry (MS), 25 keV Bi3+ secondary ion MS (SIMS), synchrotron vacuum-ultraviolet secondary neutral MS (VUV-SNMS) and theoretical methods. Experimental and calculated appearance energies of fragments observed in TDMB MS indicate that the coniferyl alcohol photoionization mass spectra contain the molecular parent and several dissociative photoionization products. Similar results obtained for sinapyl alcohol are also discussed briefly. Ionization energies of 7.60 eV ? 0.05 eV for coniferyl alcohol and<7.4 eV for both sinapyl and dihydrosinapyl alcohols are determined. The positive ion SIMS spectrum of coniferyl alcohol shares few characteristic peaks (m/z = 137 and 151) with the TDMB mass spectra, shows extensive fragmentation, and does not exhibit clear molecular parent signals. VUV-SNMS spectra, on the other hand, are dominated by the parent ion and main fragments also present in the TDMB spectra. Molecular fragmentation in VUV-SNMS spectra can be reduced by increasing the extraction delay time. Some features resembling the SIMS spectra are also observed in the desorbed neutral products. The monolignol VUV-SNMS peaks shared with the TDMB mass spectra suggest that dissociative photoionization of ion-sputtered neutral molecules predominate in the VUV-SNMS mass spectra, despite the extra internal energy imparted in the initial ion impact. The potential applications of these results to imaging mass spectrometry of bio-molecules are discussed.

  20. Vacuum-ultraviolet photoionization and mass spectrometric characterization of lignin monomers coniferyl and sinapyl alcohols.

    PubMed

    Takahashi, Lynelle K; Zhou, Jia; Kostko, Oleg; Golan, Amir; Leone, Stephen R; Ahmed, Musahid

    2011-04-21

    The fragmentation mechanisms of monolignols under various energetic processes are studied with jet-cooled thermal desorption molecular beam (TDMB) mass spectrometry (MS), 25 keV Bi(3)(+) secondary ion MS (SIMS), synchrotron vacuum-ultraviolet secondary neutral MS (VUV-SNMS) and theoretical methods. Experimental and calculated appearance energies of fragments observed in TDMB MS indicate that the coniferyl alcohol photoionization mass spectra contain the molecular parent and several dissociative photoionization products. Similar results obtained for sinapyl alcohol are also discussed briefly. Ionization energies of 7.60 eV ± 0.05 eV for coniferyl alcohol and <7.4 eV for both sinapyl and dihydrosinapyl alcohols are determined. The positive ion SIMS spectrum of coniferyl alcohol shares few characteristic peaks (m/z = 137 and 151) with the TDMB mass spectra, shows extensive fragmentation, and does not exhibit clear molecular parent signals. VUV-SNMS spectra, on the other hand, are dominated by the parent ion and main fragments also present in the TDMB spectra. Molecular fragmentation in VUV-SNMS spectra can be reduced by increasing the extraction delay time. Some features resembling the SIMS spectra are also observed in the desorbed neutral products. The monolignol VUV-SNMS peaks shared with the TDMB mass spectra suggest that dissociative photoionization of ion-sputtered neutral molecules predominate in the VUV-SNMS mass spectra, despite the extra internal energy imparted in the initial ion impact. The potential applications of these results to imaging MS of biomolecules are discussed. PMID:21410275

  1. Internal energy selection in vacuum ultraviolet photoionization of ethanol and ethanol dimers

    NASA Astrophysics Data System (ADS)

    Bodi, Andras

    2013-10-01

    Internal energy selected ethanol monomer and ethanol dimer ions were prepared by threshold photoionization of a supersonic molecular beam seeded with ethanol. The dissociative photoionization processes of the monomer, the lowest-energy CH3-loss channel of the dimer, and the fragmentation of larger clusters were found to be disjunct from the ionization onset to about 12 eV, which made it possible to determine the 0 K appearance energy of C-C bond breaking in the H-donor unit of the ethanol dimer cation as 9.719 ± 0.004 eV. This reaction energy is used together with ab initio calculations in a thermochemical cycle to determine the binding energy change from the neutral ethanol dimer to a protonated ethanol-formaldehyde adduct. The cycle also shows general agreement between experiment, theory, and previously published enthalpies of formation. The role of the initial ionization site, or rather the initial photoion state, is also discussed based on the dimer breakdown diagram and excited state calculations. There is no evidence for isolated state behavior, and the ethanol dimer dissociative photoionization processes appear to be governed by statistical theory and the ground electronic state of the ion. In the monomer breakdown diagram, the smoothly changing branching ratio between H and CH3 loss is at odds with rate theory predictions, and shows that none of the currently employed few-parameter rate models, appropriate for experimental rate curve fitting, yields a correct description for this process in the experimental energy range.

  2. Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra

    SciTech Connect

    Bravaya, Ksenia B.; Kostko, Oleg; Dolgikh, Stanislav; Landau, Arie; Ahmed, Musahid; Krylov, Anna I.

    2010-08-02

    We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed using equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the {omega}B97X-D functional. The ionization-induced geometry changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series G > C > A > T, the respective relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 eV for A,T,C and G, respectively) agree well with the onsets of the photoionization efficiency (PIE) curves (8.20 {+-} 0.05, 8.95 {+-} 0.05, 8.60 {+-} 0.05 and 7.75 {+-} 0.05 eV). Vibrational progressions for the S{sub 0}-D{sub 0} vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra.

  3. Photoionization in negative streamers: Fast computations and two propagation modes

    SciTech Connect

    Luque, Alejandro; Ebert, Ute; Montijn, Carolynne; Hundsdorfer, Willem

    2007-02-19

    Streamer discharges play a central role in electric breakdown of matter in pulsed electric fields, both in nature and in technology. Reliable and fast computations of the minimal model for negative streamers in simple gases such as nitrogen have recently been developed. However, photoionization was not included; it is important in air and poses a major numerical challenge. The authors here introduce a fast and reliable method to include photoionization into our numerical scheme with adaptive grids, and they discuss its importance for negative streamers. In particular, they identify different propagation regimes where photoionization does or does not play a role.0.

  4. Absorption spectroscopy of a laboratory photoionized plasma experiment at Z

    SciTech Connect

    Hall, I. M.; Durmaz, T.; Mancini, R. C.; Bailey, J. E.; Rochau, G. A.; Golovkin, I. E.; MacFarlane, J. J.

    2014-03-15

    The Z facility at the Sandia National Laboratories is the most energetic terrestrial source of X-rays and provides an opportunity to produce photoionized plasmas in a relatively well characterised radiation environment. We use detailed atomic-kinetic and spectral simulations to analyze the absorption spectra of a photoionized neon plasma driven by the x-ray flux from a z-pinch. The broadband x-ray flux both photoionizes and backlights the plasma. In particular, we focus on extracting the charge state distribution of the plasma and the characteristics of the radiation field driving the plasma in order to estimate the ionisation parameter.

  5. Interference effect in the dipole and nondipole anisotropy parameters of the Kr 4p photoelectrons in the vicinity of the Kr (3d){sup -1{yields}}np resonant excitations

    SciTech Connect

    Ricz, S.; Ricsoka, T.; Holste, K.; Borovik, A. Jr.; Bernhardt, D.; Schippers, S.; Mueller, A.; Koever, A.; Varga, D.

    2010-04-15

    The angular distribution of the Kr 4p photoelectrons was investigated in the photon energy range of the (3d){sup -1{yields}}np resonant excitations. The experimental dipole ({beta}) and nondipole ({gamma} and {delta}) anisotropy parameters were determined for the spin-orbit components of the Kr 4p shell. A simple theoretical model was developed for the description of the photoionization and excitation processes. An interference effect was observed between the direct photoionization and the resonant excitation participator Auger decay processes in the photon energy dependence of the experimental anisotropy parameters.

  6. Photoionization profiles of metal clusters and the Fowler formula

    NASA Astrophysics Data System (ADS)

    Prem, Abhinav; Kresin, Vitaly V.

    2012-02-01

    Metal-cluster ionization potentials are important characteristics of these “artificial atoms,” but extracting these quantities from cluster photoabsorption spectra, especially in the presence of thermal smearing, remains a big challenge. Here we demonstrate that the classic Fowler theory of surface photoemission does an excellent job of fitting the photoabsorption profile shapes of neutral Inn=3-34 clusters [Wucher , New J. Phys.NJOPFM1367-263010.1088/1367-2630/10/10/103007 10, 103007 (2008)]. The deduced ionization potentials extrapolate precisely to the bulk work function, and the internal cluster temperatures are in close agreement with values expected for an ensemble of freely evaporating clusters. Supplementing an earlier application to potassium clusters, these results suggest that the Fowler formalism, which is straightforward and physical, may be of significant utility in metal-cluster spectroscopy. It is hoped also that the results will encourage a comprehensive theoretical analysis of the applicability of bulk-derived models to cluster photoionization behavior, and of the transition from atomic and molecular-type to surface-type photoemission.

  7. Femtosecond photoelectron point projection microscope

    SciTech Connect

    Quinonez, Erik; Handali, Jonathan; Barwick, Brett

    2013-10-15

    By utilizing a nanometer ultrafast electron source in a point projection microscope we demonstrate that images of nanoparticles with spatial resolutions of the order of 100 nanometers can be obtained. The duration of the emission process of the photoemitted electrons used to make images is shown to be of the order of 100 fs using an autocorrelation technique. The compact geometry of this photoelectron point projection microscope does not preclude its use as a simple ultrafast electron microscope, and we use simple analytic models to estimate temporal resolutions that can be expected when using it as a pump-probe ultrafast electron microscope. These models show a significant increase in temporal resolution when comparing to ultrafast electron microscopes based on conventional designs. We also model the microscopes spectroscopic abilities to capture ultrafast phenomena such as the photon induced near field effect.

  8. Measuring the angle-dependent photoionization cross section of nitrogen using high-harmonic generation

    NASA Astrophysics Data System (ADS)

    Ren, Xiaoming; Makhija, Varun; Le, Anh-Thu; Troß, Jan; Mondal, Sudipta; Jin, Cheng; Kumarappan, Vinod; Trallero-Herrero, Carlos

    2013-10-01

    We exploit the relationship between high harmonic generation (HHG) and the molecular photorecombination dipole to extract the molecular-frame differential photoionization cross section (PICS) in the extreme ultraviolet (XUV) for molecular nitrogen. A shape resonance and a Cooper-type minimum are reflected in the pump-probe time delay measurements of different harmonic orders, where high-order rotational revivals are observed in N2. We observe the energy- and angle-dependent Cooper minimum and shape resonance directly in the laboratory-frame HHG yield by achieving a high degree of alignment, ≥0.8. The interplay between PICS and rotational revivals is confirmed by simulations using the quantitative rescattering theory. Our method of extracting molecular-frame structural information points the way to similar measurements in more complex molecules.

  9. Ionization Correction Factors based on CALIFA photoionization models

    NASA Astrophysics Data System (ADS)

    Delgado-Inglada, G.; Morisset, C.; Sánchez, S.; Califa Collaboration

    2016-06-01

    We use a grid of photoionization models (especially constructed to reproduce the observations of ~5200 H II regions from the CALIFA survey) to explore the ionization correction factors usually adopted to calculate total element abundances.

  10. Photoionization of potassium atoms from the ground and excited states

    SciTech Connect

    Zatsarinny, O.; Tayal, S. S.

    2010-04-15

    The Dirac-based B-spline R-matrix method is used to investigate the photoionization of atomic potassium from the 4s ground and 4p, 5s-7s, 3d-5d excited states. The effect of the core polarization by the outer electron is included through the polarized pseudostates. Besides the dipole core polarization, we also found a noticeable influence of the quadrupole core polarization. We obtained excellent agreement with experiment for cross sections of the 4s photoionization, including accurate description of the near-threshold Cooper-Seaton minimum. We also obtained close agreement with experiment for the 4p photoionization, but there are unexpectedly large discrepancies with available experimental data for photoionization of the 5d and 7s excited states.

  11. Ultrafast internal conversion of aromatic molecules studied by photoelectron spectroscopy using Sub-20 fs laser pulses.

    PubMed

    Suzuki, Toshinori

    2014-01-01

    This article describes our recent experimental studies on internal conversion via a conical intersection using photoelectron spectroscopy. Ultrafast S2(ππ*)-S1(nπ*) internal conversion in pyrazine is observed in real time using sub-20 fs deep ultraviolet pulses (264 and 198 nm). While the photoelectron kinetic energy distribution does not exhibit a clear signature of internal conversion, the photoelectron angular anisotropy unambiguously reveals the sudden change of electron configuration upon internal conversion. An explanation is presented as to why these two observables have different sensitivities to internal conversion. The 198 nm probe photon energy is insufficient for covering the entire Franck-Condon envelopes upon photoionization from S2/S1 to D1/D0. A vacuum ultraviolet free electron laser (SCSS) producing 161 nm radiation is employed to solve this problem, while its pulse-to-pulse timing jitter limits the time resolution to about 1 ps. The S2-S1 internal conversion is revisited using the sub-20 fs 159 nm pulse created by filamentation four-wave mixing. Conical intersections between D1(π-1) and D0(n-1) and also between the Rydberg state with a D1 ion core and that with a D0 ion core of pyrazine are studied by He(I) photoelectron spectroscopy, pulsed field ionization photoelectron spectroscopy and one-color resonance-enhanced multiphoton ionization spectroscopy. Finally, ultrafast S2(ππ*)-S1(ππ*) internal conversion in benzene and toluene are compared with pyrazine. PMID:24566311

  12. Photoionization of noble-gas atoms by ultrashort electromagnetic pulses

    SciTech Connect

    Astapenko, V. A. Svita, S. Yu.

    2014-11-15

    The photoionization of atoms of noble gases (Ar, Kr, and Xe) by ultrashort electromagnetic pulses of a corrected Gaussian shape is studied theoretically. Computations are performed in the context of perturbation theory using a simple expression for the total probability of photoionization of an atom by electromagnetic pulses. The features of this process are revealed and analyzed for various ranges of the parameters of the problem.

  13. Outer-shell double photoionization of CH2Cl2

    NASA Astrophysics Data System (ADS)

    Alcantara, K. F.; Gomes, A. H. A.; Wolff, W.; Sigaud, L.; Santos, A. C. F.

    2014-01-01

    In this work the roles of the shake-off and knockout processes in the double photoionization of the CH2Cl2 molecule have been studied. The probabilities for both mechanisms accompanying valence-shell photoionization have been estimated as a function of incident photon energy using Samson's (1990) [5] and Thomas's (1994) [3] models, respectively. The experimental results are in qualitative accord with the models.

  14. K-shell photoionization of Li-like Ti XX

    NASA Astrophysics Data System (ADS)

    Liang, Liang; Lu, Xu-yang; Zhou, Chao; Qing, Pang

    2015-04-01

    K-shell photoionization of Li-like Ti XX ions from ground state and first excited state has been studied using the R-matrix method. Through the combination of R-matrix and QB methods, we have not only studied the K-shell photoionization cross section between the first and ninth ionization threshold of Ti XX, but also identified the energy levels of K-shell excited state due to the twelve autoionization Rydberg series.

  15. Anion Photoelectron Angular Distributions: Electron Scattering Resonances in Photodetachment

    NASA Astrophysics Data System (ADS)

    Mabbs, Richard

    2012-06-01

    To a large degree the photoelectron angular distributions (PAD) of anionic species represent signatures of the bound parent orbital. However, these angular distributions are also influenced by interaction of the outgoing electron with the neutral (atomic, molecular or cluster) residue. The electron kinetic energy evolution (eKE) of the PAD is presented for a number of different species (from molecular to cluster anion), showing the often striking effect of excitation of temporary excited anionic states. These cases highlight the influence of different types of electron-molecule scattering resonances in photodetachment dynamics. Additionally, the possibility of using the eKE evolution of the PAD for structural elucidation is discussed.

  16. Double photoionization of He and H{sub 2} at unequal energy sharing

    SciTech Connect

    Kheifets, A.S.; Bray, Igor

    2005-08-15

    A recently developed single-center model of double photoionization (DPI) of the H{sub 2} molecule [Kheifets, Phys. Rev. A 71, 022704 (2005)] has been extended to represent the DPI process at unequal energy sharing. The model is applied to describe the shape of the fully-differential cross-section (FDCS) of a randomly oriented hydrogen molecule in the isotopic form of D{sub 2} at the kinematics of recent experiments. Comparison with analogous FDCS for the He atom helps to elucidate the molecular effects.

  17. The Vitamin E Radical Probed by Anion Photoelectron Imaging.

    PubMed

    Anstöter, Cate S; West, Christopher W; Bull, James N; Verlet, Jan R R

    2016-07-28

    The biological antioxidant activity of vitamin E has been related to the stability of the tocopheroxyl radical. Using anion photoelectron imaging and electronic structure calculations, the four tocopheroxyl components of vitamin E have been studied in the gas phase and have yielded the adiabatic electron affinity of the α-, β/γ-, and δ-tocopheroxyl radicals. Using these values, the bond dissociation enthalpy of the O-H bond of tocopherol has been estimated and is consistent with previous studies and with the trends in biological activity. Differences in the photoelectron angular distributions have been interpreted to result from changes in the symmetry of the molecular orbitals from which the electron was detached. PMID:27367260

  18. Vacuum ultraviolet photoionization of carbohydrates and nucleotides.

    PubMed

    Shin, Joong-Won; Bernstein, Elliot R

    2014-01-28

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5(')-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C-C and C-O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results. PMID:25669546

  19. Vacuum ultraviolet photoionization of carbohydrates and nucleotides

    SciTech Connect

    Shin, Joong-Won; Bernstein, Elliot R.

    2014-01-28

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5{sup ′}-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C–C and C–O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

  20. Zero kinetic energy photoelectron spectroscopy of triphenylene

    NASA Astrophysics Data System (ADS)

    Harthcock, Colin; Zhang, Jie; Kong, Wei

    2014-06-01

    We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S1 of the neutral molecule is of A1' symmetry and is therefore electric dipole forbidden in the D3h group. Consequently, there are no observable Franck-Condon allowed totally symmetric a1' vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E' third electronically excited state S3. The assignment of all vibrational bands as e' symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C2v and resulting in two nearly degenerate electronic states of A2 and B1 symmetry. Here we follow a crude treatment by assuming that all e' vibrational modes resolve into b2 and a1 modes in the C2v molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm-1. The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

  1. Identification of combustion intermediates in a low-pressure premixed laminar 2,5-dimethylfuran/oxygen/argon flame with tunable synchrotron photoionization

    SciTech Connect

    Wu, Xuesong; Huang, Zuohua; Wei, Lixia; Yuan, Tao; Zhang, Kuiwen

    2009-07-15

    Low-pressure (4.0 kPa) premixed laminar 2,5-dimethylfuran (DMF)/oxygen/argon flame with an equivalence ratio of 2.0 was studied with tunable vacuum ultraviolet (VUV) synchrotron radiation photoionization and molecular-beam mass spectrometry. Photoionization mass spectra of DMF/O{sub 2}/Ar flame were recorded and the photoionization efficiency curves of the combustion intermediates were measured. Flame species, including isomeric intermediates, are identified by comparing the measured ionization energies with those reported in literatures or those calculated with Gaussian-3 procedure. More than 70 species have been detected, including furan and its derivatives, aromatics, and free radicals. Possible reaction pathways of DMF, 2-methylfuran, and furan are proposed based on the intermediates identified. DMF can be consumed by H-abstraction and pyrolysis reactions. 2-Methylfuran and furan can be consumed by H-abstraction, H-addition and pyrolysis reactions. (author)

  2. Imaging photoelectron circular dichroism of chiral molecules by femtosecond multiphoton coincidence detection

    SciTech Connect

    Lehmann, C. Stefan; Ram, N. Bhargava; Janssen, Maurice H. M.; Powis, Ivan

    2013-12-21

    Here, we provide a detailed account of novel experiments employing electron-ion coincidence imaging to discriminate chiral molecules. The full three-dimensional angular scattering distribution of electrons is measured after photoexcitation with either left or right circular polarized light. The experiment is performed using a simplified photoelectron-photoion coincidence imaging setup employing only a single particle imaging detector. Results are reported applying this technique to enantiomers of the chiral molecule camphor after three-photon ionization by circularly polarized femtosecond laser pulses at 400 nm and 380 nm. The electron-ion coincidence imaging provides the photoelectron spectrum of mass-selected ions that are observed in the time-of-flight mass spectra. The coincident photoelectron spectra of the parent camphor ion and the various fragment ions are the same, so it can be concluded that fragmentation of camphor happens after ionization. We discuss the forward-backward asymmetry in the photoelectron angular distribution which is expressed in Legendre polynomials with moments up to order six. Furthermore, we present a method, similar to one-photon electron circular dichroism, to quantify the strength of the chiral electron asymmetry in a single parameter. The circular dichroism in the photoelectron angular distribution of camphor is measured to be 8% at 400 nm. The electron circular dichroism using femtosecond multiphoton excitation is of opposite sign and about 60% larger than the electron dichroism observed before in near-threshold one-photon ionization with synchrotron excitation. We interpret our multiphoton ionization as being resonant at the two-photon level with the 3s and 3p Rydberg states of camphor. Theoretical calculations are presented that model the photoelectron angular distribution from a prealigned camphor molecule using density functional theory and continuum multiple scattering X alpha photoelectron scattering calculations

  3. Imaging photoelectron circular dichroism of chiral molecules by femtosecond multiphoton coincidence detection

    NASA Astrophysics Data System (ADS)

    Lehmann, C. Stefan; Ram, N. Bhargava; Powis, Ivan; Janssen, Maurice H. M.

    2013-12-01

    Here, we provide a detailed account of novel experiments employing electron-ion coincidence imaging to discriminate chiral molecules. The full three-dimensional angular scattering distribution of electrons is measured after photoexcitation with either left or right circular polarized light. The experiment is performed using a simplified photoelectron-photoion coincidence imaging setup employing only a single particle imaging detector. Results are reported applying this technique to enantiomers of the chiral molecule camphor after three-photon ionization by circularly polarized femtosecond laser pulses at 400 nm and 380 nm. The electron-ion coincidence imaging provides the photoelectron spectrum of mass-selected ions that are observed in the time-of-flight mass spectra. The coincident photoelectron spectra of the parent camphor ion and the various fragment ions are the same, so it can be concluded that fragmentation of camphor happens after ionization. We discuss the forward-backward asymmetry in the photoelectron angular distribution which is expressed in Legendre polynomials with moments up to order six. Furthermore, we present a method, similar to one-photon electron circular dichroism, to quantify the strength of the chiral electron asymmetry in a single parameter. The circular dichroism in the photoelectron angular distribution of camphor is measured to be 8% at 400 nm. The electron circular dichroism using femtosecond multiphoton excitation is of opposite sign and about 60% larger than the electron dichroism observed before in near-threshold one-photon ionization with synchrotron excitation. We interpret our multiphoton ionization as being resonant at the two-photon level with the 3s and 3p Rydberg states of camphor. Theoretical calculations are presented that model the photoelectron angular distribution from a prealigned camphor molecule using density functional theory and continuum multiple scattering X alpha photoelectron scattering calculations

  4. Critical evaluation of attosecond time delays retrieved from photoelectron streaking measurements

    NASA Astrophysics Data System (ADS)

    Wei, Hui; Morishita, Toru; Lin, C. D.

    2016-05-01

    A photoelectron streaking experiment which was conceived as a means to extract the electron wave packet of single-photon ionization has also been employed to retrieve time delays in the fundamental photoemission processes. The discrepancies between the time delays thus measured and those from many sophisticated theoretical calculations have generated a great deal of controversy in recent years. Here we present a careful examination of the methods that were used to retrieve the time delays and demonstrate the difficulty of achieving an accuracy of the retrieved time delays of a few to tens of attoseconds in typical streaking measurements. The difficulty owes more to the lower sensitivity of the streaking spectra to the phase of the photoionization transition dipole than to the spectral phase of the attosecond light pulse in the experiment. The retrieved time delay contains extra errors when the attochirp of the attosecond pulse is large so that the dipole phase becomes negligible compared to it.

  5. Photoelectron angular distributions in bichromatic atomic ionization induced by circularly polarized VUV femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Douguet, Nicolas; Grum-Grzhimailo, Alexei N.; Gryzlova, Elena V.; Staroselskaya, Ekaterina I.; Venzke, Joel; Bartschat, Klaus

    2016-03-01

    We investigate two-pathway interferences between nonresonant one-photon and resonant two-photon ionization of atomic hydrogen. In particular, we analyze in detail the photoionization mediated by the fundamental frequency and the second harmonic of a femtosecond VUV pulse when the fundamental is tuned near an intermediate atomic state. Following our recent study [Phys. Rev. A 91, 063418 (2015), 10.1103/PhysRevA.91.063418] of such effects with linearly polarized light, we analyze a similar situation with circularly polarized radiation. As a consequence of the richer structure in circularly polarized light, characterized by its right-handed or left-handed helicity, we present and discuss various important features associated with the photoelectron angular distribution.

  6. Photoelectron circular dichroism of the randomly oriented chiral molecules glyceraldehyde and lactic acid

    NASA Astrophysics Data System (ADS)

    Powis, Ivan

    2000-01-01

    The differing interaction of left and right circularly polarized light with chiral molecules is shown to lead to different angular distributions of the photoelectrons created by photoionization of a given enantiomer, even when the target molecules are randomly oriented. Numerical calculations are presented to demonstrate the magnitude of this effect for the C3H6O3 structural isomers lactic acid and glyceraldehyde, including two different conformations of the latter. Circular dichroism in the angular distributions (CDAD) of the valence electrons of these biomolecules is most pronounced close to threshold, but tends to vanish as the electron kinetic energy approaches 20 eV and above. CDAD signals are predicted to range, typically, from 10% to 40% and sometimes to more than 60% of the differential cross section.

  7. Photoelectron circular dichroism of bicyclic ketones from multiphoton ionization with femtosecond laser pulses.

    PubMed

    Lux, Christian; Wollenhaupt, Matthias; Sarpe, Cristian; Baumert, Thomas

    2015-01-12

    Photoelectron circular dichroism (PECD) is a CD effect up to the ten-percent regime and shows contributions from higher-order Legendre polynomials when multiphoton ionization is compared to single-photon ionization. We give a full account of our experimental methodology for measuring the multiphoton PECD and derive quantitative measures that we apply on camphor, fenchone and norcamphor. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure. In addition, we study PECD for elliptically polarized light employing tomographic reconstruction methods. Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal. As a perspective, we suggest to make use of our tomographic data as an experimental basis for a complete photoionization experiment and give a prospect of PECD as an analytic tool. PMID:25492564

  8. 2012 MOLECULAR AND IONIC CLUSTERS GORDON RESEARCH CONFERENCE, JANUARY 29 - FEBRUARY 3, 2012

    SciTech Connect

    Anne McCoy

    2012-02-03

    The Gordon Research Conference on 'Molecular and Ionic Clusters' focuses on clusters, which are the initial molecular species found in gases when condensation begins to occur. Condensation can take place solely from molecules interacting with each other, mostly at low temperatures, or when molecules condense around charged particles (electrons, protons, metal cations, molecular ions), producing ion molecule clusters. These clusters provide models for solvation, allow a pristine look at geometric as well as electronic structures of molecular complexes or matter in general, their interaction with radiation, their reactivity, their thermodynamic properties and, in particular, the related dynamics. This conference focuses on new ways to make clusters composed of different kinds of molecules, new experimental techniques to investigate the properties of the clusters and new theoretical methods with which to calculate the structures, dynamical motions and energetics of the clusters. Some of the main experimental methods employed include molecular beams, mass spectrometry, laser spectroscopy (from infrared to XUV; in the frequency as well as the time domain) and photoelectron spectroscopy. Techniques include laser absorption spectroscopy, laser induced fluorescence, resonance enhanced photoionization, mass-selected photodissociation, photofragment imaging, ZEKE photoelectron spectroscopy, etc. From the theoretical side, this conference highlights work on potential surfaces and measurable properties of the clusters. The close ties between experiment, theory and computation have been a hallmark of the Gordon Research Conference on Molecular and Ionic Clusters. In the 2012 meeting, we plan to have sessions that will focus on topics including: (1) The use of cluster studies to probe fundamental phenomena; (2) Finite size effects on structure and thermodynamics; (3) Intermolecular forces and cooperative effects; (4) Molecular clusters as models for solvation; and (5) Studies of

  9. Negative Ion Photoelectron Spectra of Halomethyl Anions

    NASA Astrophysics Data System (ADS)

    Vogelhuber, Kristen M.; Wren, Scott W.; McCoy, Anne B.; Ervin, Kent M.; Lineberger, W. Carl

    2009-06-01

    Halomethyl anions undergo a significant geometry change upon electron photodetachment, resulting in multiple extended vibrational progressions in the photoelectron spectra. The normal mode analysis that successfully models photoelectron spectra when geometry changes are modest is unable to reproduce the experimental data using physically reasonable parameters. A three-dimensional anharmonic coupled-mode analysis was employed to accurately reproduce the observed vibrational structure. We present the 364 nm negative ion photoelectron spectra of the halomethyl anions CHX_2^- and CDX_2^- (X = Cl, Br, I) and report electron affinities, vibrational frequencies, and geometries.

  10. EMISSION SPECTRUM OF HELIUM-LIKE IONS IN PHOTOIONIZED PLASMAS

    SciTech Connect

    Wang, Feilu; Salzmann, David; Zhao, Gang; Takabe, Hideaki

    2012-10-01

    The aim of the present paper is to investigate the influence of inner-shell photoionization and photoexcitation on He{sub {alpha}} and its satellite's spectra in photoionized plasmas. An analysis is carried out on the relative importance of the various atomic processes in photoionized plasmas as a function of the electron temperature and irradiation conditions. In particular, we investigate the influence of K-shell photoionization of Li-like ions on the He{sub {alpha}} spectrum and of Be-like ions on the He{sub {alpha}} satellites. It is found that in photoionized plasmas these inner-shell processes contribute significantly under low radiation temperature and/or intensity, when Li- and Be-like ions are highly abundant but highly ionized H-like ions are rare. A short discussion is presented about the parameter space in which the excited 1s2p state has statistical or non-statistical distributions, and how such distributions affect the emission spectrum.

  11. Photoionization of Highly Charged Argon Ions and Their Diagnostic Lines

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2012-06-01

    %TEXT OF YOUR ABSTRACT Lines of highly charged He-like and Li-like ions in the ultraviolet and X-ray regions provide useful diagnostics for the physical and chemical conditions of the astrophysical as well as fusion plasmas. For example, Ar XVII lines in a Syfert galaxy have been measured by the X-ray space observatory Chandra. Results on photoionization of Ar XVI and Ar XVII obtained from relativistic Breit-Pauli R-matrix method and close-coupling approximation will be presented. Important features for level-specific photoionization for the diagnostic w, x, y, z lines of He-like Ar XVII in the ultraviolet region will be illustrated. Although monotonous decay dominates the low energy photoionization for these ions, strong resonances appear in the high energy region indicating higher recombination, inverse process of photoionization, at high temperature. The spectra of the well known 22 diagnostics dielectronic satellite lines of Li-like Ar XVI will be shown produced from the the KLL resonances in photoionization. Acknowledgement: Partially supported by DOE, NSF; Computational work was carried out at the Ohio Supercomputer Center

  12. Numerical modeling of radiation physics in kinetic plasmas [IV] - Isochoric heating by intense X-ray laser-produced photoelectrons

    NASA Astrophysics Data System (ADS)

    Royle, Ryan; Sentoku, Yasuhiko

    2014-10-01

    An intense, hard X-ray laser such as an XFEL is an attractive light source since it can directly heat solid matter isochorically to a temperature of millions of degrees on a time scale of a few tens of femtoseconds, which is much shorter than the plasma expansion time scale. The X-ray laser interaction with carbon, aluminum, silicon, and copper is studied with a particle-in-cell code that solves the photoionization and X-ray transport self-consistently. Photoionization is the dominant absorption mechanism and non-thermal photoelectrons are produced with energy near the X-ray photon energy. The photoelectrons' stopping range is a few microns and they are quickly thermalized in tens of femtoseconds. As a result, a hot plasma column is formed behind the laser pulse with a temperature of more than 100,000 kelvin (>10 eV) and energy density greater than 1011 J/m3. The heating depth and temperature depend on the material and are also controllable by changing the photon energy of the incident laser light.

  13. Prominent conjugate processes in the PCI recapture of photoelectrons revealed by high resolution Auger electron measurements of Xe

    NASA Astrophysics Data System (ADS)

    Azuma, Yoshiro; Kosugi, Satoshi; Suzuki, Norihiro; Shigemasa, Eiji; Iwayama, Hiroshi; Koike, Fumihiro

    2016-05-01

    The Xe (N5O2 , 3O2 , 3) Auger electron spectrum originating from 4d5/ 2 - 1 photoionization was measured with the photon energy tuned very close above the ionization threshold. As the photon energy approached the 4d5/ 2 - 1 photoionization threshold, Rydberg series structures including several angular momentum components were formed within the Auger profile by the recapture of the photoelectrons into high-lying final ion orbitals. Our spectrum with resolution much narrower than the lifetime width of the corresponding core excited state allowed us to resolve detailed structures due to the orbital angular momenta very clearly. Unexpectedly, conjugate peaks originating from the exchange of angular momentum between the photoelectron and the Auger electron through Post-Collision-Interaction were found to dominate the spectrum. The new assignments were in accord with the quantum defect values obtained for the high Rydberg series for singly charged ionic Xe + 5 p(1S0) ml. This work was supported by Japan Society for the Promotion of Science through Grants-in-Aid for Scientific Research No. 23600009.

  14. Photoelectron fluxes observed by FAST compared with model predictions incorporating SNOE observations of the solar soft X-ray irradiance

    NASA Astrophysics Data System (ADS)

    Bailey, S. M.; Peterson, W. K.; Solomon, S. C.; Carlson, C. W.; McFadden, J. P.

    2001-12-01

    Photoelectrons are those electrons produced when atoms or molecules in the upper atmosphere are photoionized. These electrons carry the excess energy of the photon remaining from the ionization and can have energies up to and greater than 1 keV. Photoelectrons are important in that they play a significant role in the energetics of the upper atmosphere, resulting in ionization, dissociation, and excitation of atoms and molecules. There have been long standing issues with regard to understanding the magnitude of the terrestrial photoelectron flux as models have not been able to reproduce the observations without scaling the solar soft X-ray irradiance by factors of two to four. The Fast Auroral Snapshot (FAST) spacecraft was launched in August of 1996. While its primary goals focus on the study of auroral energetic particles, in January of 1999 it began making low-latitude observations. From measurements by the FAST energetic electron sensor, upward flowing photoelectron fluxes in the energy range of 50 eV to 1 keV have been obtained. These measurements are in agreement with earlier measurements of the terrestrial photoelectron flux. The Student Nitric Oxide Explorer (SNOE) spacecraft was launched in February of 1998. Since then it has been making daily observations of the solar soft X-ray irradiance in bandpasses of 2 - 7, 6 - 19, and 17 - 20 nm. SNOE observes larger values of the solar soft X-ray irradiance than reported by earlier observations or predicted by empirical models; however, the SNOE observations are in agreement with many suggestions of the solar soft X-ray irradiance obtained from geophysical observations such as airglow and electron densities. These irradiance measurements are used in a photoelectron model that includes transport. Observations of photoelectron fluxes for the first solar rotation of 1999 are modeled. The model photoelectron spectra are in good agreement with the observed photoelectron spectra over most of the 50 eV to 1 keV energy

  15. Partial Photoionization Cross Sections and Angular Distributions for Double Excitation of Helium up to the N=13 Threshold

    SciTech Connect

    Czasch, A.; Schoeffler, M.; Hattass, M.; Schoessler, S.; Jahnke, T.; Weber, Th.; Staudte, A.; Titze, J.; Wimmer, C.; Kammer, S.; Weckenbrock, M.; Voss, S.; Grisenti, R.E.; Jagutzki, O.; Schmidt, L.Ph.H.; Schmidt-Boecking, H.; Doerner, R.; Rost, J.M.; Schneider, T.; Liu, C.-N.

    2005-12-09

    Partial photoionization cross sections {sigma}{sub N}(E{sub {gamma}}) and photoelectron angular distributions {beta}{sub N}(E{sub {gamma}}) were measured for the final ionic states He{sup +}(N>4) in the region between the N=8 and N=13 thresholds (E{sub {gamma}}>78.155 eV) using the cold target recoil ion momentum spectroscopy technique (COLTRIMS). Comparison of the experimental data with two independent sets of theoretical predictions reveals disagreement for the branching ratios to the various He{sub N}{sup +} states. The angular distributions just below the double ionization threshold suggest an excitation process for highly excited N states similar to the Wannier mechanism for double ionization.

  16. Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: Charge transfer reaction of N{sub 2}{sup +}(X {sup 2}{Sigma}{sub g}{sup +}; v{sup +}= 0-2; N{sup +}= 0-9) + Ar

    SciTech Connect

    Chang, Yih Chung; Xu Yuntao; Lu Zhou; Xu Hong; Ng, C. Y.

    2012-09-14

    We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N{sub 2}{sup +}(v{sup +}, N{sup +}) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N{sub 2}{sup +}(X {sup 2}{Sigma}{sub g}{sup +}, v{sup +}= 0-2, N{sup +}= 0-9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N{sub 2}{sup +} PFI-PI beam can be formed with a laboratory kinetic energy resolution of {Delta}E{sub lab}={+-} 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E{sub cm}'s) down to thermal energies. Absolute total rovibrationally selected cross sections {sigma}(v{sup +}= 0-2, N{sup +}= 0-9) for the N{sub 2}{sup +}(X {sup 2}{Sigma}{sub g}{sup +}; v{sup +}= 0-2, N{sup +}= 0-9) + Ar CT reaction have been measured in the E{sub cm} range of 0.04-10.0 eV, revealing strong vibrational enhancements and E{sub cm}-dependencies of {sigma}(v{sup +}= 0-2, N{sup +}= 0-9). The thermochemical threshold at E{sub cm}= 0.179 eV for the formation of Ar{sup +} from N{sub 2}{sup +}(X; v{sup +}= 0, N{sup +}) + Ar was observed by the measured {sigma}(v{sup +}= 0), confirming the narrow {Delta}E{sub cm} spread achieved in

  17. Understanding photoexcitation dynamics in a three-step photoionization of atomic uranium and measurement of photoexcitation and photoionization cross sections

    NASA Astrophysics Data System (ADS)

    Mandal, P. K.; Sahoo, A. C.; Das, R. C.; Shah, M. L.; Pulhani, A. K.; Manohar, K. G.; Dev, Vas

    2015-09-01

    Photoexcitation dynamics in a three-step photoionization of atomic uranium has been investigated using time-resolved two-color three-photon and delayed three-color three-photon photoionization signals. Investigations are carried out in an atomic beam of uranium coupled to a high-resolution time-of-flight mass spectrometer using three tunable pulsed dye lasers. Dependence of both the signals on the second-step laser photon fluence is studied. Excited-level-to-excited-level photoexcitation cross section and photoionization cross section from the second excited level are simultaneously determined by analyzing the two-color three-photon and three-color three-photon photoionization signals using population rate equation model. Using this methodology, photoexcitation and photoionization cross sections at seven values of the second-step laser wavelength have been measured. From the measured values of the photoexcitation cross sections, we have obtained excited-level-to-excited-level transition probabilities and compared these with the values reported in the literature.

  18. Efficient photoionization loading of trapped ions with ultrafast pulses

    SciTech Connect

    Deslauriers, L.; Acton, M.; Blinov, B. B.; Brickman, K.-A.; Haljan, P. C.; Hensinger, W. K.; Hucul, D.; Katnik, S.; Kohn, R. N. Jr.; Lee, P. J.; Madsen, M. J.; Maunz, P.; Olmschenk, S.; Moehring, D. L.; Stick, D.; Sterk, J.; Yeo, M.; Younge, K. C.; Monroe, C.

    2006-12-15

    Atomic cadmium ions are loaded into radiofrequency ion traps by photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The photoionization is driven through an intermediate atomic resonance with a frequency-quadrupled mode-locked Ti:sapphire laser that produces pulses of either 100-fs or 1-ps duration at a central wavelength of 229 nm. The large bandwidth of the pulses photoionizes all velocity classes of the Cd vapor, resulting in a high loading efficiency compared to previous ion trap loading techniques. Measured loading rates are compared with a simple theoretical model, and we conclude that this technique can potentially ionize every atom traversing the laser beam within the trapping volume. This may allow the operation of ion traps with lower levels of background pressures and less trap electrode surface contamination. The technique and laser system reported here should be applicable to loading most laser-cooled ion species.

  19. Interchannel coupling effects in the valence photoionization of SF6

    NASA Astrophysics Data System (ADS)

    Jose, Jobin; Lucchese, Robert; Rescigno, Tom

    2014-05-01

    The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1 g, 5t1 u, 1t2 u, 3eg, 1t2 g, 4t1 u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near threshold and to induce resonant features in other channels to which resonances are coupled.

  20. Triggering Excimer Lasers by Photoionization from Corona Discharges

    NASA Astrophysics Data System (ADS)

    Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

    2009-10-01

    High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

  1. Efficient photoionization loading of trapped ions with ultrafast pulses

    NASA Astrophysics Data System (ADS)

    Deslauriers, L.; Acton, M.; Blinov, B. B.; Brickman, K.-A.; Haljan, P. C.; Hensinger, W. K.; Hucul, D.; Katnik, S.; Kohn, R. N., Jr.; Lee, P. J.; Madsen, M. J.; Maunz, P.; Olmschenk, S.; Moehring, D. L.; Stick, D.; Sterk, J.; Yeo, M.; Younge, K. C.; Monroe, C.

    2006-12-01

    Atomic cadmium ions are loaded into radiofrequency ion traps by photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The photoionization is driven through an intermediate atomic resonance with a frequency-quadrupled mode-locked Ti:sapphire laser that produces pulses of either 100-fs or 1-ps duration at a central wavelength of 229nm . The large bandwidth of the pulses photoionizes all velocity classes of the Cd vapor, resulting in a high loading efficiency compared to previous ion trap loading techniques. Measured loading rates are compared with a simple theoretical model, and we conclude that this technique can potentially ionize every atom traversing the laser beam within the trapping volume. This may allow the operation of ion traps with lower levels of background pressures and less trap electrode surface contamination. The technique and laser system reported here should be applicable to loading most laser-cooled ion species.

  2. Photoelectron Spectroscopy of Aluminum Doped Boron Clusters

    NASA Astrophysics Data System (ADS)

    Li, Wei-Li; Romanescu, Constantin; Wang, Lai-Sheng

    2012-06-01

    Anionic boron clusters have been shown to be planar or quasi-planar up to B21- from a series of combined photoelectron spectroscopy and theoretical studies. All these boron clusters consist of a peripheral ring characterized by strong two-center-two-electron (2c-2e) B-B bonds and one or more interior atoms. The propensity for planarity is due to σ - and π -electron delocalizations throughout the molecular plane, giving rise to concepts of σ - and π -aromaticity. The quasi-planarity, on the other hand, can be mechanical in nature - the circumference of the cluster is too small to fit the inner atoms - even for doubly aromatic clusters. Two questions arise: firstly, can isoelectronic substitution by a single aluminum atom on the outer ring enhance the planarity of quasi-planar structures, and, secondly, can the interior boron atoms be replaced by aluminum? A series of aluminum isoelectronic substitution of boron clusters have been investigated ranging from B7- to B12-. Aluminum turns out to avoid the central position in the all these clusters and enhance the planarity of AlB6- and AlB11- clusters by expanding the peripheral ring. References: [1] C. Romanescu, A. P. Sergeeva, W. L. Li, A. I. Boldyrev and L. S. Wang, {J. Am. Chem. Soc}. {133} (22), 8646-8653 (2011) [2] T. R. Galeev, C. Romanescu, W. L. Li, L. S. Wang and A. I. Boldyrev, {J. Chem. Phys.} {135}, (8) 104301 (2011) [3] W. L. Li, C. Romanescu, T. R. Galeev, L. S. Wang and A. I. Boldyrev, {J. Phys. Chem. A} {115} (38), 10391-10397 (2011)

  3. Photoelectron spectroscopic study of the ethyl cyanoacrylate anion

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxing; Tang, Xin; Bowen, Kit

    2013-09-01

    Anion photoelectron spectroscopy and density functional theory have been utilized to study the parent, ethyl cyanoacrylate molecular anion, ECA-. The measured electron affinity (0.9 ± 0.2 eV), vertical detachment energy (1.3 ± 0.1 eV), and anion-to-triplet neutral, photodetachment transition energies (4.0 ± 0.1 eV and 4.5 ± 0.1 eV) all compare well with their calculated values. The relatively high electron affinity of the ECA monomer is responsible for the fact that its “anionic” polymerization mechanism proceeds even with weak nucleophiles, such as water.

  4. Longitudinal photoelectron momentum shifts induced by absorbing a single XUV photon in diatomic molecules

    NASA Astrophysics Data System (ADS)

    Lao, Di; He, Pei-Lun; He, Feng

    2016-06-01

    The photoelectron momentum shifts along the laser propagation are investigated by the time-dependent perturbation theory for diatomic molecules, such as H2+ , N2, and O2. Such longitudinal momentum shifts characterize the photon momentum sharing in atoms and molecules, and oscillate with respect to photon energies, presenting the double-slit interference structure. The atomic and molecular contributions are disentangled analytically, which gives an intuitive picture of how the double-slit interference structure is formed. Calculation results show that the longitudinal photoelectron momentum distribution depends on the internuclear distance, molecular orientation, and photon energy. The current laser technology is ready to verify these theoretical predictions.

  5. Resonant double photoionization of lithium studied with medium energy resolution

    NASA Astrophysics Data System (ADS)

    Wehlitz, R.; Juranić, P. N.

    2006-10-01

    We have measured the relative photoionization cross section for the formation of Li2+ ions between 148 and 161eV photon energy with higher photon-energy resolution than in previous Li2+ studies. This energy region is characterized by double and triple excitations that lead to strong enhancements in the Li2+ cross section. As a result, the double-to-single photoionization ratio shows a dramatic resonance structure not seen before. We have determined the resonance positions and widths using Fano-profile fits to the Li2+ data and compare them to previously published values and a calculated Li2+ cross-section curve.

  6. Strong-Field Photoionization as Excited-State Tunneling.

    PubMed

    Serebryannikov, E E; Zheltikov, A M

    2016-03-25

    We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling. PMID:27058079

  7. Strong-Field Photoionization as Excited-State Tunneling

    NASA Astrophysics Data System (ADS)

    Serebryannikov, E. E.; Zheltikov, A. M.

    2016-03-01

    We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling.

  8. 2010 Atomic & Molecular Interactions Gordon Research Conference

    SciTech Connect

    Todd Martinez

    2010-07-23

    The Atomic and Molecular Interactions Gordon Conferences is justifiably recognized for its broad scope, touching on areas ranging from fundamental gas phase and gas-condensed matter collision dynamics, to laser-molecule interactions, photophysics, and unimolecular decay processes. The meeting has traditionally involved scientists engaged in fundamental research in gas and condensed phases and those who apply these concepts to systems of practical chemical and physical interest. A key tradition in this meeting is the strong mixing of theory and experiment throughout. The program for 2010 conference continues these traditions. At the 2010 AMI GRC, there will be talks in 5 broadly defined and partially overlapping areas of intermolecular interactions and chemical dynamics: (1) Photoionization and Photoelectron Dynamics; (2) Quantum Control and Molecules in Strong Fields; (3) Photochemical Dynamics; (4) Complex Molecules and Condensed Phases; and (5) Clusters and Reaction Dynamics. These areas encompass many of the most productive and exciting areas of chemical physics, including both reactive and nonreactive processes, intermolecular and intramolecular energy transfer, and photodissociation and unimolecular processes. Gas phase dynamics, van der Waals and cluster studies, laser-matter interactions and multiple potential energy surface phenomena will all be discussed.

  9. Inner-Shell Photoionization: Teijo A˚berg's Concept of RRRS

    NASA Astrophysics Data System (ADS)

    Armen, G. Bradley

    2003-01-01

    Teijo Åberg died on December 29, 2000 — and with his passing we have lost a gifted and important member of our community. Over the years Teijo has made many major contributions to the science of x-ray and inner-shell physics. Perhaps the most visionary of these was his idea of radiative and radiationless resonant Raman scattering (RRRRS) [1]. This arose as an outgrowth of his earlier thoughts on Auger [2] and x-ray [3] processes. It is visionary in that it attempts to unify the various aspects of inner-shell photoexcitation and decay as different aspects of the same basic process, i.e. resonant inelastic x-ray scattering. In honor and memory of Teijo, and as a last attempt to promote his ideas, I describe here the theory and some of its consequences. First, RRRRS is outlined in a semi-rigorous form, with emphasis placed on the physical nature of the concepts. Then, using the example of atomic K-shell photoionization, we see how features such as fluorescence and photoelectron lines arise in a natural way as manifestations of resonance scattering.

  10. High-resolution pulsed-field ionization photoelectron study of O{sub 2}

    SciTech Connect

    Hsu, C.W.; Evans, M.; Stimson, S.

    1997-04-01

    There have been numerous photoionization studies of O{sub 2} over the past 10 years. Using the pulsed field ionization (PFI) photoelectron spectroscopy (PES) technique, the electronic ground state of O{sub 2}{sup +} (X{sup 2}{Pi}{sub g}{sup {minus}}) has been well studied on the rotationally resolved level by several groups. However, due to the difficulty of producing photon energies above 18 eV using the tunable lasers, the electronic excited states of O{sub 2}{sup +} have been mostly studied on the vibrationally resolved level using the threshold photoelectron spectroscopy (TPES) and the synchrotron radiation. Recently, the authors developed a new technique for performing the PFI-PE experiments using multi-bunch synchrotron radiation at the Chemical Dynamics Beamline of the Advanced Light Source (ALS). Using the high resolution VUV light from the ALS, they have obtained the PFI-PE spectra of O{sub 2} between 12 and 24 eV. In this abstract, the authors report for the first time the rotationally resolved spectra of O{sub 2}{sup +} (b{sup 4}{Sigma}{sub g}{sup {minus}}, v{sup +}=0).

  11. Ambipolar Electric Field, Photoelectrons, and Their Role in Atmospheric Escape From Hot Jupiters

    NASA Technical Reports Server (NTRS)

    Cohen, O.; Glocer, A.

    2012-01-01

    Atmospheric mass loss from Hot Jupiters can be large due to the close proximity of these planets to their host star and the strong radiation the planetary atmosphere receives. On Earth, a major contribution to the acceleration of atmospheric ions comes from the vertical separation of ions and electrons, and the generation of the ambipolar electric field. This process, known as the "polar wind," is responsible for the transport of ionospheric constituents to Earth's magnetosphere, where they are well observed. The polar wind can also be enhanced by a relatively small fraction of super-thermal electrons (photoelectrons) generated by photoionization.We formulate a simplified calculation of the effect of the ambipolar electric field and the photoelectrons on the ion scale height in a generalized manner. We find that the ion scale height can be increased by a factor of 2-15 due to the polar wind effects. We also estimate a lower limit of an order of magnitude increase of the ion density and the atmospheric mass-loss rate when polar wind effects are included.

  12. Theoretical and Experimental Photoelectron Spectroscopy Characterization of the Ground State of Thymine Cation.

    PubMed

    Majdi, Youssef; Hochlaf, Majdi; Pan, Yi; Lau, Kai-Chung; Poisson, Lionel; Garcia, Gustavo A; Nahon, Laurent; Al-Mogren, Muneerah Mogren; Schwell, Martin

    2015-06-11

    We report on the vibronic structure of the ground state X̃(2)A″ of the thymine cation, which has been measured using a threshold photoelectron photoion coincidence technique and vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum, recorded over ∼0.7 eV above the ionization potential (i.e., covering the whole ground state of the cation) shows rich vibrational structure that has been assigned with the help of calculated anharmonic modes of the ground electronic cation state at the PBE0/aug-cc-pVDZ level of theory. The adiabatic ionization energy has been experimentally determined as AIE = 8.913 ± 0.005 eV, in very good agreement with previous high resolution results. The corresponding theoretical value of AIE = 8.917 eV has been calculated in this work with the explicitly correlated method/basis set (R)CCSD(T)-F12/cc-pVTZ-F12, which validates the theoretical approach and benchmarks its accuracy for future studies of medium-sized biological molecules. PMID:25539153

  13. AMBIPOLAR ELECTRIC FIELD, PHOTOELECTRONS, AND THEIR ROLE IN ATMOSPHERIC ESCAPE FROM HOT JUPITERS

    SciTech Connect

    Cohen, O.; Glocer, A.

    2012-07-01

    Atmospheric mass loss from Hot Jupiters can be large due to the close proximity of these planets to their host star and the strong radiation the planetary atmosphere receives. On Earth, a major contribution to the acceleration of atmospheric ions comes from the vertical separation of ions and electrons, and the generation of the ambipolar electric field. This process, known as the 'polar wind', is responsible for the transport of ionospheric constituents to Earth's magnetosphere, where they are well observed. The polar wind can also be enhanced by a relatively small fraction of super-thermal electrons (photoelectrons) generated by photoionization. We formulate a simplified calculation of the effect of the ambipolar electric field and the photoelectrons on the ion scale height in a generalized manner. We find that the ion scale height can be increased by a factor of 2-15 due to the polar wind effects. We also estimate a lower limit of an order of magnitude increase of the ion density and the atmospheric mass-loss rate when polar wind effects are included.

  14. Nonadiabatic Dynamics May Be Probed through Electronic Coherence in Time-Resolved Photoelectron Spectroscopy.

    PubMed

    Bennett, Kochise; Kowalewski, Markus; Mukamel, Shaul

    2016-02-01

    We present a hierarchy of Fermi golden rules (FGRs) that incorporate strongly coupled electronic/nuclear dynamics in time-resolved photoelectron spectroscopy (TRPES) signals at different levels of theory. Expansion in the joint electronic and nuclear eigenbasis yields the numerically most challenging exact FGR (eFGR). The quasistatic Fermi Golden Rule (qsFGR) neglects nuclear motion during the photoionization process but takes into account electronic coherences as well as populations initially present in the pumped matter as well as those generated internally by coupling between electronic surfaces. The standard semiclassical Fermi Golden Rule (scFGR) neglects the electronic coherences and the nuclear kinetic energy during the ionizing pulse altogether, yielding the classical Condon approximation. The coherence contributions depend on the phase-profile of the ionizing field, allowing coherent control of TRPES signals. The photoelectron spectrum from model systems is simulated using these three levels of theory. The eFGR and the qsFGR show temporal oscillations originating from the electronic or vibrational coherences generated as the nuclear wave packet traverses a conical intersection. These oscillations, which are missed by the scFGR, directly reveal the time-evolving splitting between electronic states of the neutral molecule in the curve-crossing regime. PMID:26691822

  15. Photoionization of furan from the ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nada; Decleva, Piero

    2016-02-01

    Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy.

  16. Radiative recombination and excited-state photoionization of lithium

    SciTech Connect

    Lahiri, J. ); Manson, S.T. )

    1993-11-01

    The radiative-recombination rate coefficients for electrons impinging on Li[sup +], along with the associated excited-state photoionization cross sections for Li, are calculated in the low-energy region. In addition to the totals, the contribution of the recombination of individual excited states to the total is discussed.

  17. The operation of a pressurized ultraviolet photoionization threshold cherenkov counter

    NASA Astrophysics Data System (ADS)

    Harnew, N.; Meyer, D. I.

    We have successfully tested an ultraviolet photoionization Cherenkov counter in a 10 GeV/ c pion beam. The counter has been tested to 11 atm pressure for use as a π-K separator. The design and operation of the counter is described.

  18. Electron scattering from and photoionization of open- shell atoms

    NASA Astrophysics Data System (ADS)

    Lin, Dong

    1999-09-01

    The multiconfiguration Hartree-Fock (MCHF) approach, developed by Dr. H. P. Saha et al, has been proved to be extremely successful in the past few years in reproducing experimental results at a very high level of accuracy. The research projects we are interested consist of two areas. In the first area we performed ab initio calculations on elastic scattering of electrons from open-shell sulfur atoms. In the second area, in order to understand the electronic dynamics in photoionization of atoms, we carried out accurate calculations on valence and K-shell photoionization of three-electron systems from lithium through neon for photon energies from threshold to very high energies; to further identify the autoionization resonances which were observed near threshold and to understand the dynamics, we modifies the MCHF method to include relativistic effects and performed calculation on partial photoionization cross section, resonance structure and effect of spin-orbit interaction in photoionization of atomic bromine. The calculated results obtained in each of these investigations are compared with available experimental and theoretical data and are found to be in very good agreement. The research contribution made for the fulfillment of the degree, we understand, will be a valuable addition towards a better understanding of the open-shell systems.

  19. Radiative properties measurements of photoionized plasmas on Z

    NASA Astrophysics Data System (ADS)

    Loisel, Guillaume; Bailey, Jim; Nagayama, Taisuke; Hansen, Stephanie; Rochau, Greg; Liedahl, Duane; Fontes, Chris; Flaugh, Matt; Koepke, Mark; Lane, Ted; Mancini, Roberto

    2015-11-01

    Physical descriptions of accretion-powered objects such as black holes, x-ray binaries, or AGN are informed through the interpretation of emergent spectra from the photoionized plasmas that surround them. Line formation in photoionized plasmas is dependent on the details of the radiation transport treatment and the so-called Resonant Auger Destruction hypothesis typically required to interpret the relativistically broadened Fe K α emitted from near the black hole event horizon. The Z facility at Sandia National Laboratories can produced such photoionized plasmas producing 1.6MJ of x-rays from the z-pinch dynamic hohlraum. The extended suite of diagnostics allows for a detailed characterization of plasmas conditions through absorption spectroscopy. present accurate and high-resolution emergent intensity observed from a photoionized silicon plasma for a discrete set of column densities that will help us evaluate understanding for radiation transport in accretion powered objects. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

  20. Transport of Photoelectrons in the Nightside Magnetosphere

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Liemohn, M. W.

    2002-01-01

    Kinetic modeling results are analyzed to examine the transport of photoelectrons through the nightside inner magnetosphere. Two sources are considered, those on the dayside from direct solar illumination and those across the nightside from light scattered by the upper atmosphere and geocorona. A natural filter exists on the nightside for the dayside photoelectrons. Coulomb collisions erode the distribution at low energies and low L shells, and magnetospheric convection compresses the electrons as they drift toward dawn. It is shown that for low-activity levels a band of photoelectrons forms between L = 4 and 6 that extends throughout the nightside local times and into the morning sector. For the scattered light photoelectrons the trapped zone throughout the nightside is populated with electrons of E less than 30 eV. At high L shells near dawn, convective compression on the nightside yields an accelerated population with electrons at energies up to twice the ionospheric energy maximum (that is, roughly 1200 eV for dayside photoelectrons and 60 eV for scattered light electrons). Modeled energy and pitch angle distributions are presented to show the features of these populations.

  1. A VUV photoionization measurement and ab-initio calculation of the ionization energy of gas phase SiO2

    SciTech Connect

    Kostko, Oleg; Ahmed, Musahid; Metz, Ricardo B.

    2008-12-05

    In this work we report on the detection and vacuum-ultraviolet (VUV) photoionization of gas phase SiO2 generated in situ via laser ablation of silicon in a CO2 molecular beam. The resulting species are investigated by single photon ionization with tunable VUV synchrotron radiation and mass analyzed using reflectron mass spectrometry. Photoionization efficiency (PIE) curves are recorded for SiO and SiO2 and ionization energy estimates are revealed from such measurements. A state-to-state ionizationenergy of 12.60 (+-0.05) eV is recorded by fitting two prominent peaks in the PIE curve for the following process: 1SUM O-Si-O --> 2PRODg [O-Si-O]+. Electronic structure calculations aid in the interpretation of the photoionization process and allow for identification of the symmetric stretch of 2PRODg [O-Si-O]+ which is observed in the PIE spectrum to be 0.11 eV (890 cm-1) above the ground state of the cation and agrees with the 892 cm-1 symmetric stretch frequency calculated at the CCSD(T)/aug-cc-pVTZ level.

  2. Inner-shell photoionization and core-hole decay of Xe and XeF{sub 2}

    SciTech Connect

    Southworth, Stephen H.; Picón, Antonio; Lehmann, C. Stefan; Wehlitz, Ralf; Cheng, Lan; Stanton, John F.

    2015-06-14

    Photoionization cross sections and partial ion yields of Xe and XeF{sub 2} from Xe 3d{sub 5/2}, Xe 3d{sub 3/2}, and F 1s subshells in the 660–740 eV range are compared to explore effects of the F ligands. The Xe 3d-ϵf continuum shape resonances dominate the photoionization cross sections of both the atom and molecule, but prominent resonances appear in the XeF{sub 2} cross section due to nominal excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Comparisons of the ion products from the atom and molecule following Xe 3d photoionization show that the charge-state distribution of Xe ions is shifted to lower charge states in the molecule along with production of energetic F{sup +} and F{sup 2+} ions. This suggests that, in decay of a Xe 3d core hole, charge is redistributed to the F ligands and the system dissociates due to Coulomb repulsion. The ion products from excitation of the F 1s-LUMO resonance are different and show strong increases in the yields of Xe{sup +} and F{sup +} ions. The subshell ionization thresholds, the LUMO resonance energies, and their oscillator strengths are calculated by relativistic coupled-cluster methods and agree well with measurements.

  3. Photoionization of Fe7+ from the ground and metastable states

    NASA Astrophysics Data System (ADS)

    Tayal, S. S.; Zatsarinny, O.

    2015-01-01

    The B -spline Breit-Pauli R -matrix method is used to investigate the photoionization of Fe7 + from the ground and metastable states in the energy region from ionization thresholds to 172 eV. The present calculations were designed to resolve the large discrepancies between recent measurements and available theoretical results. The multiconfiguration Hartree-Fock method in connection with B -spline expansions is employed for an accurate representation of the initial- and final-state wave functions. The close-coupling expansion includes 99 fine-structure levels of the residual Fe8 + ion in the energy region up to 3 s23 p54 s states. It includes levels of the 3 s23 p6,3 s23 p53 d ,3 s23 p54 s , and 3 s 3 p63 d configurations and some levels of the 3 s23 p43 d2 configuration which lie in the energy region under investigation. The present photoionization cross sections in the length and velocity formulations exhibit excellent agreement. The present photoionization cross sections agree well with the Breit-Pauli R -matrix calculation by Sossah et al. and the TOPbase data in the magnitude of the background nonresonant cross sections but show somewhat richer resonance structures, which qualitatively agree with the measurements. The calculated cross sections, however, are several times lower than the measured cross sections, depending upon the photon energy. The cross sections for photoionization of metastable states were found to have approximately the same magnitude as the cross sections for photoionization of the ground state, thereby the presence of metastable states in the ion beam may not be the reason for the enhancement of the measured cross sections.

  4. Photoionized Plasma and Opacity Experiments on the Z Machine

    NASA Astrophysics Data System (ADS)

    Bailey, James

    2008-04-01

    Laboratory experiments at Z use high energy density to create plasma conditions similar to extreme astrophysical environments, including stellar interiors and accretion powered objects. The importance of radiation unifies these topics, even though the plasmas involved are very different. Understanding stellar interiors requires knowledge of radiation transport in dense, hot, collision-dominated plasma. A Z x-ray source was used to measure iron plasma transmission at 156 eV electron temperature, 2x higher than in prior work. The data provide the first experimental tests of absorption features critical for stellar interior opacity models and may provide insight into whether the present discrepancy between solar models and helioseismology originates in opacity model deficiencies or in some other aspect of the solar model. In contrast, accretion physics requires interpretation of x-ray spectra from lower density photoionization-dominated plasma. Exploiting astrophysical spectra requires a spectral model that connects the observations with a model that describes the overall picture of the astrophysical object. However, photoionized plasma spectral models are largely untested. Z-pinch radiation was used to create photoionized iron and neon plasmas with photoionization parameter 5-25 erg cm /s. Comparisons with the data improve x-ray photoionization models and promote more accurate interpretation of spectra acquired with astrophysical observatories. The prospects for new experiments at the higher radiation powers provided by the recently upgraded Z facility will be described.* In collaboration with scientists from CEA, LANL, LLNL, Oxford, Prism, Queens University, Swarthmore College, U. Nevada Reno, and Sandia ++Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

  5. Anion photoelectron spectroscopy of radicals and clusters

    SciTech Connect

    Travis, Taylor R.

    1999-12-16

    Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying {sup 2}{Sigma} and {sup 2}{Pi} states of C{sub 2n}H (n = 1--4) have been studied. The anion photoelectron spectra yielded electron affinities, term values, and vibrational frequencies for these combustion and astrophysically relevant species. Photoelectron angular distributions allowed the author to correctly assign the electronic symmetry of the ground and first excited states and to assess the degree of vibronic coupling in C{sub 2}H and C{sub 4}H. Other radicals studied include NCN and I{sub 3}. The author was able to observe the low-lying singlet and triplet states of NCN for the first time. Measurement of the electron affinity of I{sub 3} revealed that it has a bound ground state and attachment of an argon atom to this moiety enabled him to resolve the symmetric stretching progression.

  6. Coherent control of photoelectron wavepacket angular interferograms

    NASA Astrophysics Data System (ADS)

    Hockett, P.; Wollenhaupt, M.; Baumert, T.

    2015-11-01

    Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process, where the final (time-integrated) observable coherently samples all instantaneous states of the light-matter interaction. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the coherent control over the resultant photoelectron interferogram is thus explored in detail. Based on this understanding, the use of coherent control with polarization-shaped pulses as a methodology for a highly multiplexed coherent quantum metrology is also investigated, and defined in terms of the information content of the observable.

  7. Selectivity in Ketenimine Cycloadditions. Photoelectron Hel Spectra of Ketenimines

    NASA Astrophysics Data System (ADS)

    Bernardi, Fernando; Bottoni, Andrea; Ballaglia, Arturo; Distefano, Giuseppe; Dondoni, Alessandro

    1980-05-01

    The first few bands in the photoelectron (Hel) spectra of ketenimines R1R2C-C=NR3(R1,R2=H, CH3, C5H6, CH2=CH; R3=alkyl or aryl group) are assigned to the corresponding molecular orbitals. The assignment is based on SCF-MO calculations made at three different levels (CNDO/2, ab-initio STO-3C and 4-31G) coupled with perturbational molecular orbital analyses. The π-orbitals of the unsaturated substituents are found to interact with one of the two perpendicular π-electron systems of the>C=C=N- residue, the critical factor being the position of attack of the substituent. The relevance of these results on the site selectivity observed in cycloaddition reactions of these species is discussed.

  8. Acid generation efficiency: EUV photons versus photoelectrons

    NASA Astrophysics Data System (ADS)

    Goldfarb, Dario L.; Afzali-Ardakani, Ali; Glodde, Martin

    2016-03-01

    EUV photoacid generation efficiency has been described primarily in terms of the EUV photon absorption by the PAG or the resist matrix and the production of low energy photoelectrons, which are reported as being ultimately responsible for the high quantum efficiencies reported in EUV resists (<1). Such observation led to a number of recent studies on PAGs with variable electron affinity (EA) and reduction potential (Ered) presumably conducive to a differential EUV photoelectron harvesting efficiency. However, such studies either did not disclose the PAG chemical structures, replaced the EUV source with an e-beam source, or lacked a fundamental discussion of the underlying physical mechanisms behind EUV PAG decomposition. In this work, we report the EUV photospeed of a methacrylatebased resist formulated with a battery of openly disclosed isostructural sulfonium PAGs covering a wide range of EA's and Ered's, to unveil any preferential photoelectron scavenging effect. In parallel, several iodonium PAGs are also tested in order to compare the direct EUV photon absorption route to the photoelectron-based decomposition path. Contrarily to what has been widely reported, we have found no direct correlation whatsoever between photospeed and the calculated EA's or experimental Ered's for the isostructural sulfonium PAGs studied. Instead, we found that iodonium PAGs make more efficient use of the available EUV power due to their higher photoabsorption cross-section. Additionally, we determined a cation size effect for both PAG groups, which is able to further modulate the acid generation efficiency. Finally, we present a formal explanation for the unselective response towards photoelectron harvesting based on the stabilization of the PAG cation by bulky substituent groups, the spatial and temporal range of the transient photoelectron and the differences in electron transfer processes for the different systems studied.

  9. Photon momentum sharing between an electron and an ion in photoionization: from one-photon (photoelectric effect) to multiphoton absorption.

    PubMed

    Chelkowski, Szczepan; Bandrauk, André D; Corkum, Paul B

    2014-12-31

    We investigate photon-momentum sharing between an electron and an ion following different photoionization regimes. We find very different partitioning of the photon momentum in one-photon ionization (the photoelectric effect) as compared to multiphoton processes. In the photoelectric effect, the electron acquires a momentum that is much greater than the single photon momentum ℏω/c [up to (8/5) ℏω/c] whereas in the strong-field ionization regime, the photoelectron only acquires the momentum corresponding to the photons absorbed above the field-free ionization threshold plus a momentum corresponding to a fraction (3/10) of the ionization potential Ip. In both cases, due to the smallness of the electron-ion mass ratio, the ion takes nearly the entire momentum of all absorbed N photons (via the electron-ion center of mass). Additionally, the ion takes, as a recoil, the photoelectron momentum resulting from mutual electron-ion interaction in the electromagnetic field. Consequently, the momentum partitioning of the photofragments is very different in both regimes. This suggests that there is a rich, unexplored physics to be studied between these two limits which can be generated with current ultrafast laser technology. PMID:25615323

  10. Electronic structure of β-Ga{sub 2}O{sub 3} single crystals investigated by hard X-ray photoelectron spectroscopy

    SciTech Connect

    Li, Guo-Ling; Zhang, Fabi; Guo, Qixin; Cui, Yi-Tao; Oji, Hiroshi; Son, Jin-Young

    2015-07-13

    By combination of hard X-ray photoelectron spectroscopy (HAXPES) and first-principles band structure calculations, the electronic states of β-Ga{sub 2}O{sub 3} were investigated to deepen the understanding of bulk information for this compound. The valence band spectra of HAXPES presented the main contribution from Ga 4sp, which are well represented by photoionization cross section weighted partial density of states. The experimental data complemented with the theoretical study yield a realistic picture of the electronic structure for β-Ga{sub 2}O{sub 3}.

  11. Angle-resolved photoelectron spectroscopy of sequential three-photon triple ionization of neon at 90.5 eV photon energy

    SciTech Connect

    Rouzee, A.; Siu, W.; Huismans, Y.; Johnsson, P.; Gryzlova, E. V.; Fukuzawa, H.; Yamada, A.; Ueda, K.; Louis, E.; Bijkerk, F.; Holland, D. M. P.; Grum-Grzhimailo, A. N.; Kabachnik, N. M.; Vrakking, M. J. J.

    2011-03-15

    Multiple photoionization of neon atoms by a strong 13.7 nm (90.5 eV) laser pulse has been studied at the FLASH free electron laser in Hamburg. A velocity map imaging spectrometer was used to record angle-resolved photoelectron spectra on a single-shot basis. Analysis of the evolution of the spectra with the FEL pulse energy in combination with extensive theoretical calculations allows the ionization pathways that contribute to be assigned, revealing the occurrence of sequential three-photon triple ionization.

  12. Photoelectron spectroscopy of nitromethane anion clusters

    NASA Astrophysics Data System (ADS)

    Pruitt, Carrie Jo M.; Albury, Rachael M.; Goebbert, Daniel J.

    2016-08-01

    Nitromethane anion and nitromethane dimer, trimer, and hydrated cluster anions were studied by photoelectron spectroscopy. Vertical detachment energies, estimated electron affinities, and solvation energies were obtained from the photoelectron spectra. Cluster structures were investigated using theoretical calculations. Predicted detachment energies agreed with experiment. Calculations show water binds to nitromethane anion through two hydrogen bonds. The dimer has a non-linear structure with a single ionic Csbnd H⋯O hydrogen bond. The trimer has two different solvent interactions, but both involve the weak Csbnd H⋯O hydrogen bond.

  13. VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Bellili, A.; Schwell, M.; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.; Hochlaf, M.

    2014-10-01

    The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetyl cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.

  14. VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

    SciTech Connect

    Bellili, A.; Hochlaf, M. E-mail: martin.schwell@lisa.u-pec.fr; Schwell, M. E-mail: martin.schwell@lisa.u-pec.fr; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.

    2014-10-07

    The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetyl cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.

  15. Photoelectron imaging as a probe of the repulsive Coulomb barrier in the photodetachment of antimony tartrate dianions

    NASA Astrophysics Data System (ADS)

    West, Christopher W.; Bull, James N.; Woods, David A.; Verlet, Jan R. R.

    2016-02-01

    A photoelectron imaging study of the text-book antimony tartrate dianion is presented. The vertical and adiabatic detachment energies are determined to be 2.5 ± 0.1 eV and 2.1 ± 0.2 eV, respectively. The photoelectron spectra exhibit a typical cut-off due to the presence of the repulsive Coulomb barrier (RCB) and the photoelectron images are highly anisotropic. Using a simple model for the RCB combined with classical molecular dynamics simulations, the photoelectron images were calculated and compared with experiment. Very good overall agreement between the simulations and experiments was achieved when the photodetachment occurs along a specific molecular axis.

  16. Instrumentation for the Atmospheric Explorer photoelectron spectrometer

    NASA Technical Reports Server (NTRS)

    Peletier, D. P.

    1973-01-01

    The photoelectron spectrometer (PES) is part of the complements of scientific instruments aboard three NASA Atmosphere Explorer (AE) satellites. The PES measures the energy spectrum, angular distribution, and intensity of electrons in the earth's thermosphere. Measurements of energies between 2 and 500 eV are made at altitudes as low as 130 km. The design, characteristics, and performance of the instrument are described.

  17. Photoelectrons in the plume of Enceladus

    NASA Astrophysics Data System (ADS)

    Coates, A. J.; Wellbrock, A.; Jones, G. H.; Young, D. T.; Arridge, C. S.

    2012-09-01

    The E19 encounter on 2 May 2012 executed a sideways trajectory through the Enceladus plume with a closest approach of 65km. The CAPS field of view was oriented well away from the spacecraft ram direction, allowing different populations than cluster ions (Coates et al., 2010) or charged nanograins (Jones et al., 2009, Hill et al., 2012) to be distinguished. During the energetic particle shadow, when particles from Saturn's radiation belts are shielded by Enceladus itself, a low energy magnetospheric electron population was observed with a short reduced density interval very near to closest approach, possibly associated with flow stagnation (Tokar et al., 2009) or with ice grain charging. In addition to this population, a distinctive photoelectron peak was observed, similar to those seen in Saturn's ring environment (Coates et al., 2005 and references therein), at Titan (Coates et al., 2007, 2012, Wellbrock et al., 2012) and in the magnetosphere near Enceladus (Schippers et al., 2009) as well as at Mars and Venus (Coates et al., 2008, 2011 and references therein). We interpret these as photoelectrons from ionization of the gas and dust species in Enceladus' plume ionosphere. We will compare the observations of ionospheric photoelectrons at different locations within the Saturn system, as well as with models for photoelectrons produced in the plume region (Ozak et al., 2012).

  18. Vacuum photoelectronic devices for measuring pulsed radiation

    NASA Astrophysics Data System (ADS)

    Berkovskii, A. G.; Veretennikov, A. I.; Kozlov, O. V.

    The design of these devices is discussed, and data are presented on their characteristics. These vacuum photoelectronic devices comprise photocells, photomultipliers, and electrooptical transducers designed for measuring pulsed radiation of nanosecond and subnanosecond duration. The fluctuation characteristics of the devices are examined, and their use in detectors of pulsed luminous and ionizing radiation is considered.

  19. Photoelectron Spectroscopy in Advanced Placement Chemistry

    ERIC Educational Resources Information Center

    Benigna, James

    2014-01-01

    Photoelectron spectroscopy (PES) is a new addition to the Advanced Placement (AP) Chemistry curriculum. This article explains the rationale for its inclusion, an overview of how the PES instrument records data, how the data can be analyzed, and how to include PES data in the course. Sample assessment items and analysis are included, as well as…

  20. Intense-Field Photoionization of Molecules using Ultrashort Radiation Pulses: Carbon Disulfide and Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Beck, Joshua; Uiterwaal, Cornelis

    2016-05-01

    We experimentally investigate the photoionization and photofragmentation of molecules using intense fields from an 800 nm, femtosecond laser source and an experimental method that eliminates the focal volume effect without the need for data deconvolution. Targets include carbon disulfide and carbon dioxide. We show that ionization is insignificant for intensities that maximize alignment of carbon disulfide, which validates ultrafast electron diffraction experiments from aligned carbon disulfide. For comparison, we also investigate the analogous molecule carbon dioxide. In this molecule the molecular bonding orbitals include the n = 2 atomic orbitals of the oxygen atom, while in carbon disulfide the n = 3 orbitals of the sulfur atom contribute to the bonding. Recent work will be presented. This work supported by U.S. Dept. of Education GAANN Grants Nos. P200A090156 and P200A120188 and National Science Foundation EPSCoR RII Track-2 CA Award No. IIA-1430519 (Cooperative Nebraska-Kansas Grant).

  1. Photoelectron spectroscopy and the dipole approximation

    SciTech Connect

    Hemmers, O.; Hansen, D.L.; Wang, H.

    1997-04-01

    Photoelectron spectroscopy is a powerful technique because it directly probes, via the measurement of photoelectron kinetic energies, orbital and band structure in valence and core levels in a wide variety of samples. The technique becomes even more powerful when it is performed in an angle-resolved mode, where photoelectrons are distinguished not only by their kinetic energy, but by their direction of emission as well. Determining the probability of electron ejection as a function of angle probes the different quantum-mechanical channels available to a photoemission process, because it is sensitive to phase differences among the channels. As a result, angle-resolved photoemission has been used successfully for many years to provide stringent tests of the understanding of basic physical processes underlying gas-phase and solid-state interactions with radiation. One mainstay in the application of angle-resolved photoelectron spectroscopy is the well-known electric-dipole approximation for photon interactions. In this simplification, all higher-order terms, such as those due to electric-quadrupole and magnetic-dipole interactions, are neglected. As the photon energy increases, however, effects beyond the dipole approximation become important. To best determine the range of validity of the dipole approximation, photoemission measurements on a simple atomic system, neon, where extra-atomic effects cannot play a role, were performed at BL 8.0. The measurements show that deviations from {open_quotes}dipole{close_quotes} expectations in angle-resolved valence photoemission are observable for photon energies down to at least 0.25 keV, and are quite significant at energies around 1 keV. From these results, it is clear that non-dipole angular-distribution effects may need to be considered in any application of angle-resolved photoelectron spectroscopy that uses x-ray photons of energies as low as a few hundred eV.

  2. High resolution threshold photoelectron spectroscopy by electron attachment

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Ajello, J. M. (Inventor)

    1979-01-01

    A system is provided for determining the stable energy levels of a species ion, of an atomic, molecular, or radical type, by application of ionizing energy of a predetermined level, such as through photoionization. The system adds a trapping gas to the gaseous species to provide a technique for detection of the energy levels. The electrons emitted from ionized species are captured by the trapping gas, only if the electrons have substantially zero kinetic energy. If the electrons have nearly zero energy, they are absorbed by the trapping gas to produce negative ions of the trapping gas that can be detected by a mass spectrometer. The applied energies (i.e. light frequencies) at which large quantities of trapping gas ions are detected, are the stable energy levels of the positive ion of the species. SF6 and CFCl3 have the narrowest acceptance bands, so that when they are used as the trapping gas, they bind electrons only when the electrons have very close to zero kinetic energy.

  3. Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies.

    PubMed

    Desmazières, Bernard; Legros, Véronique; Giuliani, Alexandre; Buchmann, William

    2014-01-15

    Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8eV up to 10.6eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the ionization energy of the solvent. As commercial APPI sources typically use krypton lamps with energy fixed at 10eV and 10.6eV, the study of the ionization of polymers over a wavelength range allowed to confirm and refine the previously proposed ionization mechanisms. Moreover, the APPI source can efficiently be used as an interface between size exclusion chromatography or reverse phase liquid chromatography and MS for the study of synthetic oligomers. However, the photoionization at fixed wavelength of polymer standards with different molecular weights showed that it was difficult to obtain intact ionized oligomers with molecular weights above a few thousands. PMID:24370106

  4. Attosecond Coherent Control of Single and Double Photoionization in Argon

    NASA Astrophysics Data System (ADS)

    Hogle, C. W.; Tong, X. M.; Martin, L.; Murnane, M. M.; Kapteyn, H. C.; Ranitovic, P.

    2015-10-01

    Ultrafast high harmonic beams provide new opportunities for coherently controlling excitation and ionization processes in atoms, molecules, and materials on attosecond time scales by employing multiphoton two-pathway electron-wave-packet quantum interferences. Here we use spectrally tailored and frequency tuned vacuum and extreme ultraviolet harmonic combs, together with two phase-locked infrared laser fields, to show how the total single and double photoionization yields of argon can be coherently modulated by controlling the relative phases of both optical and electronic-wave-packet quantum interferences. This Letter is the first to apply quantum control techniques to double photoionization, which is a fundamental process where a single, high-energy photon ionizes two electrons simultaneously from an atom.

  5. A non-invasive online photoionization spectrometer for FLASH2.

    PubMed

    Braune, Markus; Brenner, Günter; Dziarzhytski, Siarhei; Juranić, Pavle; Sorokin, Andrey; Tiedtke, Kai

    2016-01-01

    The stochastic nature of the self-amplified spontaneous emission (SASE) process of free-electron lasers (FELs) effects pulse-to-pulse fluctuations of the radiation properties, such as the photon energy, which are determinative for processes of photon-matter interactions. Hence, SASE FEL sources pose a great challenge for scientific investigations, since experimenters need to obtain precise real-time feedback of these properties for each individual photon bunch for interpretation of the experimental data. Furthermore, any device developed to deliver the according information should not significantly interfere with or degrade the FEL beam. Regarding the spectral properties, a device for online monitoring of FEL wavelengths has been developed for FLASH2, which is based on photoionization of gaseous targets and the measurements of the corresponding electron and ion time-of-flight spectra. This paper presents experimental studies and cross-calibration measurements demonstrating the viability of this online photoionization spectrometer. PMID:26698040

  6. Atomic Processes in X-ray Photoionized Gas

    NASA Technical Reports Server (NTRS)

    Kallman, Timothy

    2005-01-01

    It has long been known that photoionization and photoabsorption play a dominant role in determining the state of gas in nebulae surrounding hot stars and in active galaxies. Recent observations of X-ray spectra demonstrate that these processes are also dominant in highly ionized gas near compact objects, and also affect the transmission of X-rays from the majority of astronomical sources. This has led to new insights into the understanding of what is going on in these sources. It has also pointed out the need for a better atomic cross sections for photoionization and absorption, notably for processes involving inner shells. In this talk I will discuss these issues, what is known and where more work is needed.

  7. A non-invasive online photoionization spectrometer for FLASH2

    PubMed Central

    Braune, Markus; Brenner, Günter; Dziarzhytski, Siarhei; Juranić, Pavle; Sorokin, Andrey; Tiedtke, Kai

    2016-01-01

    The stochastic nature of the self-amplified spontaneous emission (SASE) process of free-electron lasers (FELs) effects pulse-to-pulse fluctuations of the radiation properties, such as the photon energy, which are determinative for processes of photon–matter interactions. Hence, SASE FEL sources pose a great challenge for scientific investigations, since experimenters need to obtain precise real-time feedback of these properties for each individual photon bunch for interpretation of the experimental data. Furthermore, any device developed to deliver the according information should not significantly interfere with or degrade the FEL beam. Regarding the spectral properties, a device for online monitoring of FEL wavelengths has been developed for FLASH2, which is based on photoionization of gaseous targets and the measurements of the corresponding electron and ion time-of-flight spectra. This paper presents experimental studies and cross-calibration measurements demonstrating the viability of this online photoionization spectrometer. PMID:26698040

  8. Attosecond Coherent Control of Single and Double Photoionization in Argon.

    PubMed

    Hogle, C W; Tong, X M; Martin, L; Murnane, M M; Kapteyn, H C; Ranitovic, P

    2015-10-23

    Ultrafast high harmonic beams provide new opportunities for coherently controlling excitation and ionization processes in atoms, molecules, and materials on attosecond time scales by employing multiphoton two-pathway electron-wave-packet quantum interferences. Here we use spectrally tailored and frequency tuned vacuum and extreme ultraviolet harmonic combs, together with two phase-locked infrared laser fields, to show how the total single and double photoionization yields of argon can be coherently modulated by controlling the relative phases of both optical and electronic-wave-packet quantum interferences. This Letter is the first to apply quantum control techniques to double photoionization, which is a fundamental process where a single, high-energy photon ionizes two electrons simultaneously from an atom. PMID:26551112

  9. Spatially resolved photoionization of ultracold atoms on an atom chip

    SciTech Connect

    Kraft, S.; Guenther, A.; Fortagh, J.; Zimmermann, C.

    2007-06-15

    We report on photoionization of ultracold magnetically trapped Rb atoms on an atom chip. The atoms are trapped at 5 {mu}K in a strongly anisotropic trap. Through a hole in the chip with a diameter of 150 {mu}m, two laser beams are focused onto a fraction of the atomic cloud. A first laser beam with a wavelength of 778 nm excites the atoms via a two-photon transition to the 5D level. With a fiber laser at 1080 nm the excited atoms are photoionized. Ionization leads to depletion of the atomic density distribution observed by absorption imaging. The resonant ionization spectrum is reported. The setup used in this experiment is suitable not only to investigate mixtures of Bose-Einstein condensates and ions but also for single-atom detection on an atom chip.

  10. Dynamical photoionization observables of the CS molecule: The role of electron correlation

    SciTech Connect

    Ponzi, Aurora; Coriani, Sonia; Decleva, Piero; Angeli, Celestino; Cimiraglia, Renzo

    2014-05-28

    Highly correlated calculations are performed on the primary ionic states and the prominent satellite present in the outer valence photoelectron spectrum of carbon monosulfide (CS). Dyson orbitals are coupled to accurate one particle continuum orbitals to provide a correlated description of energy dependent cross sections, asymmetry parameters, branching ratios, and molecular frame photoelectron angular distributions. The comparison with results obtained at the Hartree-Fock and Density Functional Theory level shows the strong sensitivity of these observables to details of the correlation in the bound states. The behaviour of the well characterized satellite state is analyzed in detail, and shows differences from the relevant primary states, revealing the limitations of a simple intensity borrowing mechanism. The results resolve the intensity disagreement with experiment obtained at the level of the sudden approximation.

  11. Nonperturbative theory of double photoionization of the hydrogen molecule

    SciTech Connect

    Vanroose, W.; Martin, F.; Rescigno, T.N.; McCurdy, C.W.

    2004-10-01

    We present completely ab initio nonperturbative calculations of the integral and single differential cross sections for double photoionization of H2 for photon energies from 53.9 to 75.7 eV. The method of exterior complex scaling, implemented with B-splines, is used to solve the Schrodinger equation for a correlated continuum wave function corresponding to a single photon having been absorbed by a correlated initial state. The results are in good agreement with experimental integral cross sections.

  12. Differential cross sections of double photoionization of lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-08-15

    We extend our previous application of the convergent close-coupling (CCC) and time-dependent close-coupling (TDCC) methods [Phys. Rev. A 81, 023418 (2010)] to describe energy and angular resolved double photoionization (DPI) of lithium at arbitrary energy sharing. By doing so, we are able to evaluate the recoil ion momentum distribution of DPI of Li and make a comparison with recent measurements of Zhu et al. [Phys. Rev. Lett. 103, 103008 (2009)].

  13. Precision measurements on the photoionization of neutral atomic species

    NASA Astrophysics Data System (ADS)

    Stolte, Wayne

    2016-05-01

    In contrast to studies on rare gas atoms, experimental studies of open-shell atoms offers very challenging problems, such as creation of the atom, low signal, purity and stability. Because of this, studies of inner-shell excitations for open shell atoms are limited. In this talk I will discuss precision experimental measurements for photoionization of atomic oxygen, nitrogen, and chlorine over the last two decades on various beamlines at Lawrence Berkeley National Laboratories, Advanced Light Source.

  14. High resolution photoelectron spectroscopy of clusters of Group V elements

    SciTech Connect

    Wang, Lai-sheng; Niu, B.; Lee, Y.T.; Shirley, D.A.

    1989-07-01

    High resolution HeI (580{angstrom}) photoelectron spectra of As{sub 2}, As{sub 4}, and P{sub 4} were obtained with a newly-built high temperature molecular beam source. Vibrational structure was resolved in the photoelectron spectra of the three cluster species. The Jahn-Teller effect is discussed for the {sup 2}E and {sup 2}T{sub 2} states of P{sub 4}{sup +} and As{sub 4}{sup +}. As a result of the Jahn-Teller effect, the {sup 2}E state splits into two bands, and the {sup 2}T{sub 2} state splits into three bands, in combination with the spin-orbit effect. It was observed that the {nu}{sub 2} normal vibrational mode was involved in the vibronic interaction of the {sup 2}E state, while both the {nu}{sub 2} and {nu}{sub 3} modes were active in the {sup 2}T{sub 2} state. 26 refs., 5 figs., 3 tabs.

  15. Capillary photoionization: a high sensitivity ionization method for mass spectrometry.

    PubMed

    Haapala, Markus; Suominen, Tina; Kostiainen, Risto

    2013-06-18

    We present a capillary photoionization (CPI) method for mass spectrometric (MS) analysis of liquid and gaseous samples. CPI utilizes a heated transfer capillary with a vacuum ultraviolet transparent MgF2 window, through which vacuum UV light (10 eV) from an external source enters the capillary. The liquid or gaseous sample, together with dopant, is introduced directly into the heated transfer capillary between the atmosphere and the vacuum of the MS. Since the sample is vaporized and photoionized inside the capillary, ion transmission is maximized, resulting in good overall sensitivity for nonpolar and polar compounds. As in atmospheric pressure photoionization, ionization in CPI occurs either by proton transfer or by charge exchange reactions. The feasibility of CPI was demonstrated with selected nonpolar and polar compounds. A particular advantage of CPI is that it enables the analysis of nonvolatile and nonpolar compounds in liquid samples with high ionization efficiency. This is not possible with existing capillary ionization methods. The performance of CPI as an interface between GC and MS and its applicability for the analysis of steroids in biological samples are also demonstrated. The GC-CPI-MS method shows good chromatographic resolution, linearity (R(2) > 0.993), limits of detection (LOD) in the range of 2-6 pg/mL and repeatability of injection with relative standard deviations of 4-15%. PMID:23713722

  16. Theoretical photoionization processes for aluminum-like P2+

    NASA Astrophysics Data System (ADS)

    Wang, HongBin; Jiang, Gang; Duan, Jie

    2016-05-01

    The theoretical photoionization cross sections for the ground and metastable states of Al-like P2+ are first time investigated in the photon energy range of 30-43.5 eV by the Dirac R-matrix method, and a good agreement between the dipole length and velocity form is achieved. The effects of the partial photoionization on the total PI of ground and metastable states are discussed. Our theoretical results are consistent with the latest experimental measurement, only some discrepancies are found. The channel coupling effects play an important role in the photoionization of Al-like P2+. The resonance energies and quantum defects are obtained, where a comparison between the theoretical and experimental data is made. It is worth noting that the theoretical resonance is as large as 0.28 eV. Our results can serve as a reference to further study the PI of Al-like P2+ in theory and experiment and be regarded as a supplement for Opacity Project TOP base results.

  17. Electron-ion Recombination and Photoionization of P II

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana

    2016-05-01

    Study of the inverse processes of photoionization and electron-ion recombination of P II will be reported. It is a highly reactive ion and has been difficult to detect without detailed information of its interactions. Although a low charged ion, present study shows features in photoionization resulting from relativistic fine structure couplings at low energy region near the ionization threshold of many levels. Unified method under the framework of close coupling approximation and R-matrix method and an extension of Bell and Seaton theory has been used to study the inverse processes. The method gives the level-specific as well as the total recombination rate coefficients which include both the radiative recombination (RR) and dielectronic recombination (DR) in a precise manner. The present results include level specific rates and photoionization cross sections of 475 fine structure levels with n <= 10. Preliminary results on the total recombination rates show considerable interference of RR and DR around 4000 K and a DR peak around 105 K. NSF,DOE,OSC.

  18. Solvent jet desorption capillary photoionization-mass spectrometry.

    PubMed

    Haapala, Markus; Teppo, Jaakko; Ollikainen, Elisa; Kiiski, Iiro; Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2015-03-17

    A new ambient mass spectrometry method, solvent jet desorption capillary photoionization (DCPI), is described. The method uses a solvent jet generated by a coaxial nebulizer operated at ambient conditions with nitrogen as nebulizer gas. The solvent jet is directed onto a sample surface, from which analytes are extracted into the solvent and ejected from the surface in secondary droplets formed in collisions between the jet and the sample surface. The secondary droplets are directed into the heated capillary photoionization (CPI) device, where the droplets are vaporized and the gaseous analytes are ionized by 10 eV photons generated by a vacuum ultraviolet (VUV) krypton discharge lamp. As the CPI device is directly connected to the extended capillary inlet of the MS, high ion transfer efficiency to the vacuum of MS is achieved. The solvent jet DCPI provides several advantages: high sensitivity for nonpolar and polar compounds with limit of detection down to low fmol levels, capability of analyzing small and large molecules, and good spatial resolution (250 μm). Two ionization mechanisms are involved in DCPI: atmospheric pressure photoionization, capable of ionizing polar and nonpolar compounds, and solvent assisted inlet ionization capable of ionizing larger molecules like peptides. The feasibility of DCPI was successfully tested in the analysis of polar and nonpolar compounds in sage leaves and chili pepper. PMID:25715054

  19. Interchannel coupling effects in the valence photoionization of SF6

    NASA Astrophysics Data System (ADS)

    Jose, J.; Lucchese, R. R.; Rescigno, T. N.

    2014-05-01

    The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u61t2g63eg4(5t1u6+1t2u6) 1t1g6 as the most likely ordering.

  20. Photoionization Modeling and the K Lines of Iron

    NASA Technical Reports Server (NTRS)

    Kallman, T. R.; Palmeri, P.; Bautista, M. A.; Mendoza, C.; Krolik, J. H.

    2004-01-01

    We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases, and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of K(alpha) lines, the K(beta) energy, and the ratio of the K(alpha(sub 1)) to K(alpha(sub 2)) components are all diagnostics of the ionization parameter of our model slabs.

  1. Photoionized Mixing Layer Models of the Diffuse Ionized Gas

    NASA Astrophysics Data System (ADS)

    Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe

    2009-04-01

    It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/Hα, [O I]/Hα, [N II]/[S II], and [O III]/Hβ reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.

  2. Absolute photoionization cross-section of the propargyl radical

    SciTech Connect

    Savee, John D.; Welz, Oliver; Taatjes, Craig A.; Osborn, David L.; Soorkia, Satchin; Selby, Talitha M.

    2012-04-07

    Using synchrotron-generated vacuum-ultraviolet radiation and multiplexed time-resolved photoionization mass spectrometry we have measured the absolute photoionization cross-section for the propargyl (C{sub 3}H{sub 3}) radical, {sigma}{sub propargyl}{sup ion}(E), relative to the known absolute cross-section of the methyl (CH{sub 3}) radical. We generated a stoichiometric 1:1 ratio of C{sub 3}H{sub 3} : CH{sub 3} from 193 nm photolysis of two different C{sub 4}H{sub 6} isomers (1-butyne and 1,3-butadiene). Photolysis of 1-butyne yielded values of {sigma}{sub propargyl}{sup ion}(10.213 eV)=(26.1{+-}4.2) Mb and {sigma}{sub propargyl}{sup ion}(10.413 eV)=(23.4{+-}3.2) Mb, whereas photolysis of 1,3-butadiene yielded values of {sigma}{sub propargyl}{sup ion}(10.213 eV)=(23.6{+-}3.6) Mb and {sigma}{sub propargyl}{sup ion}(10.413 eV)=(25.1{+-}3.5) Mb. These measurements place our relative photoionization cross-section spectrum for propargyl on an absolute scale between 8.6 and 10.5 eV. The cross-section derived from our results is approximately a factor of three larger than previous determinations.

  3. Neon Photoionization Experiments Driven By Z-Pinch Radiation

    NASA Astrophysics Data System (ADS)

    Bailey, J. E.; Cohen, D.; Chandler, G. A.; Cuneo, M. E.; Nash, T. J.; Stygar, W. A.; MacFarlane, J. J.; Jobe, D.; Lake, P.; Nielson, D.; Smelser, R.; Foord, M. E.; Heeter, R. F.; Liedahl, D. A.

    2000-10-01

    Present-day Z-pinch experiments generate 2 x 1021 erg/s, 5 nsec duration x-ray bursts that provide new possibilities to study radiation-heated matter. We are using this source to investigate plasmas in which photoionization dominates collisional ionization. Spectroscopic measurements of such plasmas can serve to benchmark photoionized-plasma atomic physics models that will be used to interpret data from the new generation of x-ray satellite spectrographs. This should be useful for understanding accretion-powered objects such as X-ray binaries and active galactic nuclei. These objects are frequently observed, but the interpretation of their spectra is difficult: state-of-the-art models for photoionized plasmas do not always agree on the expected ionization distribution. Our experiments use a 1-cm-scale gas cell to expose various gases to an x-ray flux of approximately 3 x 1019 erg/s/cm2. Thin mylar (1.5 micron) windows allow the radiation to flow into the cell. The ionization is monitored using emission and absorption spectroscopy. In initial experiments we acquired an absorption spectrum from Li- and He-like Ne. Analysis of the measurements and comparison with computer simulations are in progress. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000

  4. Molecular Properties of the Anti-Aromatic Species Cyclopentadienone, C5H5=0

    NASA Astrophysics Data System (ADS)

    Ormond, Thomas; Ellison, Barney; Daily, John W.; Stanton, John F.; Ahmed, Musahid; Zwier, Timothy S.; Hemberger, Patrick

    2015-06-01

    A common intermediate in the high temperature combustion of benzene is cyclopentadienone, C5H4=O. Cyclopentadienone is considered to be an "anti-aromatic" molecule. It is certainly a metastable species; samples persist at LN2 temperatures but dimerize upon warming to -80°C. It is of great interest to physically characterize this "anti-aromatic" species. The microwave spectrum, the infrared spectrum, the ionization energy, and the electron affinity of cyclopentadienone have been measured. Flash pyrolysis of o-phenylene sulfite (C6H4O2SO) provides molecular beams of C5H4=O entrained in a rare gas carrier. The beams are interrogated with time-of-flight photoionization mass spectrometry, confirming the clean, intense production of C5H4=O. a) Chirped-pulse Fourier transform microwave spectroscopy and CCSD(T) electronic structure calculations have combined to determine the re molecular structure of C5H4=O. b) Guided by CCSD(T) electronic structure calculations, the matrix infrared absorbance spectrum of C5H4=O isolated in a 4 K neon matrix has been used to assign 20 of the 24 fundamental vibrational frequencies. c) Imaging photoelectron photoion coincidence (iPEPICO) spectra of cyclopentadienone establishes the ionization energy, IE(C5H4=O), to be 9.41 ± 0.01 eV. d) Prof. A. Sanov's group has reported the electron affinity, EA(C5H4=O), to be 1.06 ± 0.01 eV. Kidwell et al. J. Phys. Chem. Letts. 2201 (2014) Ormond et al. J. Phys. Chem. A 118, 708 (2014) Ormond et al. Mol. Phys. in press (2015) Khuseynov et al. J. Phys. Chem. A 118, 6965 (2014)

  5. Photoelectron sidebands induced by a chirped laser field for shot-by-shot temporal characterization of FEL pulses

    NASA Astrophysics Data System (ADS)

    Liu, Chien-Nan; Morishita, Toru; Fushitani, Mizuho; Hishikawa, Akiyoshi

    2016-02-01

    We theoretically investigate the laser-assisted photoionization of He by an extreme ultra violet (XUV) pulse in the presence of a linearly chirped intense laser pulse by solving the time-dependent Schrödinger equation within the single-active-electron approximation. Analysis based on the time-dependent perturbation theory is also carried out to provide more physical insights. A new scheme is shown to be capable of extracting the arrival time of an XUV free-electron laser (FEL) pulse relative to an external laser pulse as well as the XUV pulse duration from the photoelectron sidebands resulting from XUV ionization in the presence of a chirped laser pulse. This scheme is independent of the energy fluctuation and the timing jittering of the FEL pulse. Therefore it can be implemented in a non-invasive way to characterize FEL pulses on a shot-by-shot basis in time-resolved spectroscopy.

  6. Photoionized Plasmas in the Z Facility and in Astrophysics

    NASA Astrophysics Data System (ADS)

    Mancini, Roberto

    2013-06-01

    Many astrophysical environments such as x-ray binaries, active galactic nuclei, and accretion disks of compact objects have photoionized plasmas. Detailed x-ray spectral observations performed with the Chandra and XMM-Newton orbiting telescopes provide critical information on the state of photoionized plasmas. However, the complexity of the astrophysical environment makes the spectral analysis challenging, and thus laboratory experiments are important for data interpretation and testing of modeling codes. The Z facility at Sandia National Laboratories is a powerful source of x-rays to produce and study in the laboratory photoionized plasmas relevant for astrophysics under well characterized conditions. We discuss an experimental and theory/modeling effort in which the intense x-ray flux emitted at the collapse of a z-pinch implosion conducted at the Z pulsed-power machine is employed to produce a neon photoionized plasma. The broadband x-ray radiation flux from the z-pinch is used to both create the photoionized plasma and provide a source of backlighting photons to study the atomic kinetics through K-shell line absorption spectroscopy. The plasma is contained in a cm-scale gas cell that can be located at different distances from the z-pinch, thus effectively controlling the x-ray flux producing the plasma. Time-integrated and gated transmission spectra are recorded with a spectrometer equipped with two elliptically-bent KAP crystals and a set of slits to record up to six spatially-resolved spectra per crystal in the same shot. The transmission data shows a rich line absorption spectrum that spans over several ionization stages of neon including Be-, Li-, He- and H-like ions. Modeling calculations are used to interpret the transmission spectra recorded in the Z experiments with the goal of extracting the charge- state distribution, electron temperature and the radiation flux driving the plasma, as well as to determine the ionization parameter of the plasma. This

  7. Symmetry adapted cluster-configuration interaction calculation of the photoelectron spectra of famous biological active steroids

    NASA Astrophysics Data System (ADS)

    Abyar, Fatemeh; Farrokhpour, Hossein

    2014-11-01

    The photoelectron spectra of some famous steroids, important in biology, were calculated in the gas phase. The selected steroids were 5α-androstane-3,11,17-trione, 4-androstane-3,11,17-trione, cortisol, cortisone, corticosterone, dexamethasone, estradiol and cholesterol. The calculations were performed employing symmetry-adapted cluster/configuration interaction (SAC-CI) method using the 6-311++G(2df,pd) basis set. The population ratios of conformers of each steroid were calculated and used for simulating the photoelectron spectrum of steroid. It was found that more than one conformer contribute to the photoelectron spectra of some steroids. To confirm the calculated photoelectron spectra, they compared with their corresponding experimental spectra. There were no experimental gas phase Hesbnd I photoelectron spectra for some of the steroids of this work in the literature and their calculated spectra can show a part of intrinsic characteristics of this molecules in the gas phase. The canonical molecular orbitals involved in the ionization of each steroid were calculated at the HF/6-311++g(d,p) level of theory. The spectral bands of each steroid were assigned by natural bonding orbital (NBO) calculations. Knowing the electronic structures of steroids helps us to understand their biological activities and find which sites of steroid become active when a modification is performing under a biological pathway.

  8. Photon-momentum transfer in multiphoton ionization and in time-resolved holography with photoelectrons

    NASA Astrophysics Data System (ADS)

    Chelkowski, Szczepan; Bandrauk, André D.; Corkum, Paul B.

    2015-11-01

    In most models and theoretical calculations describing multiphoton ionization by infrared light, the dipole approximation is used. This is equivalent to setting the very small photon momentum to zero. Using numerical solutions of the two-dimensional (2-D) time-dependent Schrödinger equation for one electron (H-like) systems, we show that, for linear polarization, the radiation pressure on photoelectrons is very sensitive to the details of the ionization mechanism. The directly ionized photoelectrons, those that never recollide with the parent ion, are driven in the direction of the laser photon momentum, whereas a fraction of slower photoelectrons are pushed in the opposite direction, leading to the counterintuitive shifts observed in recent experiments [Phys. Rev. Lett. 113, 243001 (2014), 10.1103/PhysRevLett.113.243001]. This complex response is due to the interplay between the Lorentz force and the Coulomb attraction from the ion. On average, however, the photoelectron momentum is in the direction of the photon momentum as in the case of circular polarization. The influence of the photon momentum is shown to be discernible in the holographic patterns of time-resolved atomic and molecular holography with photoelectrons, thus suggesting a new research subject in multiphoton ionization.

  9. Photoelectron Imaging of Nitroethane, Nitropropane and Nitrobutane

    NASA Astrophysics Data System (ADS)

    Adams, Christopher L.; Knurr, Benjamin J.; Weber, J. Mathias

    2011-06-01

    We will show high resolution, low-energy photoelectron imaging data on nitroethane, nitropropane, 2-nitropropane and nitrobutane. We obtain new values for the adiabatic electron affinities of these nitroalkanes by comparison of the spectra of bare anions with the spectra of Ar solvated anions, where hot bands are strongly suppressed. For nitroethane, we can quantitatively recover the photoelectron spectrum using Franck-Condon calculations and find an adiabatic electron affinity of (192 ± 6) meV. Similar to the case of nitromethane, the main contributions to the Franck-Condon profile come from the vibrational modes involving the nitro group. For nitropropane and nitrobutane, electron affinities are tentatively 223 meV and 238 meV, respectively.

  10. Photoelectron diffraction and holography: Some new directions

    SciTech Connect

    Fadley, C.S. |

    1993-08-01

    Photoelectron diffraction has by now become a versatile and powerful technique for studying surface structures, with special capabilities for resolving chemical and magnetic states of atoms and deriving direct structural information from both forward scattering along bond directions and back-scattering path length differences. Further fitting experiment to theory can lead to structural accuracies in the {plus_minus}0.03 ){Angstrom} range. Holographic inversions of such diffraction data also show considerable promise for deriving local three-dimensional structures around a given emitter with accuracies of {plus_minus}0.2--0.3 {Angstrom}. Resolving the photoelectron spin in some way and using circularly polarized radiation for excitation provide added dimensions for the study of magnetic systems and chiral experimental geometries. Synchrotron radiation with the highest brightness and energy resolution, as well as variable polarization, is crucial to the full exploitation of these techniques.

  11. Fragmentation of doubly charged ammonia cations NH{3/++} studied by the photoion-photoion coincidence (PIPICO) method

    NASA Astrophysics Data System (ADS)

    Winkoun, D.; Dujardin, G.

    1986-03-01

    Doubly charged NH{3/++} cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35 49 eV energy range. The fragmentation of NH{3/++} was studied by the photoion-photoion coincidence (PIPICO) method. NH{3/++} cations were produced in thetilde X^1 A 1 andtilde B^1 electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH{3/++} ions, initially produced in theirtilde X^1 A 1 state, rapidly dissociate (in less than 50 ns), into NH{2/+} + H+. Furthermore, the comparison with results obtained by other methods indicates that NH{3/++} ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in theirtilde X^1 E A 1 electronic state.

  12. Theory of photoelectron production, transport and energy loss

    NASA Technical Reports Server (NTRS)

    Nagy, A. F.

    1974-01-01

    Current understanding of the theory of ionospheric photoelectron production, transport and energy loss is summarized. The various approaches used in the theoretical calculations of photoelectron fluxes appear to be self consistent and sound; improved values for a number of input parameters are needed now in order to achieve significant improvements and more confidence in the results. The major remaining problem in the present day theory of photoelectron transport and energy loss is centered around the calculations of photoelectron transit through the protonosphere.

  13. Photoelectron Spectroscopy of U Oxide at LLNL

    SciTech Connect

    Tobin, J G; Yu, S; Chung, B W; Waddill, G D

    2010-03-02

    In our laboratory at LLNL, an effort is underway to investigate the underlying complexity of 5f electronic structure with spin-resolved photoelectron spectroscopy using chiral photonic excitation, i.e. Fano Spectroscopy. Our previous Fano measurements with Ce indicate the efficacy of this approach and theoretical calculations and spectral simulations suggest that Fano Spectroscopy may resolve the controversy concerning Pu electronic structure and electron correlation. To this end, we have constructed and commissioned a new Fano Spectrometer, testing it with the relativistic 5d system Pt. Here, our preliminary photoelectron spectra of the UO{sub 2} system are presented. X-ray photoelectron spectroscopy has been used to characterize a sample of UO{sub 2} grown on an underlying substrate of Uranium. Both AlK{alpha} (1487 eV) and MgK{alpha} (1254 eV) emission were utilized as the excitation. Using XPS and comparing to reference spectra, it has been shown that our sample is clearly UO{sub 2}.

  14. X-ray Photoelectron Spectroscopy Database (Version 4.1)

    National Institute of Standards and Technology Data Gateway

    SRD 20 X-ray Photoelectron Spectroscopy Database (Version 4.1) (Web, free access)   The NIST XPS Database gives access to energies of many photoelectron and Auger-electron spectral lines. The database contains over 22,000 line positions, chemical shifts, doublet splittings, and energy separations of photoelectron and Auger-electron lines.

  15. Isotope effects and spectroscopic assignments in the non-dissociative photoionization spectrum of N2

    NASA Astrophysics Data System (ADS)

    Randazzo, John B.; Croteau, Philip; Kostko, Oleg; Ahmed, Musahid; Boering, Kristie A.

    2014-05-01

    Photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV were measured using synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory with a resolution of 6 meV, and significant changes in peak energies and intensities upon isotopic substitution were observed. Previously, we reported the isotope shifts and their applications to Titan's atmosphere. Here, we report more extensive experimental details and tabulate the isotope shifts of many transitions in the N2 spectrum, including those for 15N14N, which have not been previously reported. The isotope shifts are used to address several long-standing ambiguities in spectral peak assignments just above the ionization threshold of N2. The feature at 15.677 eV (the so-called second "cathedral" peak) is of particular interest in this respect. The measured isotope shifts for this peak relative to 14N2 are 0.015 ± 0.001 eV for 15N2 and 0.008 ± 0.001 eV for 15N14N, which match most closely with the isotope shifts predicted for transitions to the (A 2Πu v' = 2)4sσg 1Πu state using Herzberg equations for the isotopic differences in harmonic oscillator energy levels plus the first anharmonic correction of 0.0143 eV for 15N2 and 0.0071 eV for 15N14N. More generally, the isotope shifts measured for both 15N2 and 15N14N relative to 14N2 provide new benchmarks for theoretical calculations of interferences between direct and indirect autoionization states which can interact to produce intricate resonant structures in molecular photoionization spectra in regions near ionization thresholds.

  16. Revealing backward rescattering photoelectron interference of molecules in strong infrared laser fields.

    PubMed

    Li, Min; Sun, Xufei; Xie, Xiguo; Shao, Yun; Deng, Yongkai; Wu, Chengyin; Gong, Qihuang; Liu, Yunquan

    2015-01-01

    Photoelectrons ionized from atoms and molecules in a strong laser field are either emitted directly or rescattered by the nucleus, both of which can serve as efficiently useful tools for molecular orbital imaging. We measure the photoelectron angular distributions of molecules (N2, O2 and CO2) ionized by infrared laser pulses (1320 nm, 0.2 ~ 1 × 10(14) W/cm(2)) from multiphoton to tunneling regime and observe an enhancement of interference stripes in the tunneling regime. Using a semiclassical rescattering model with implementing the interference effect, we show that the enhancement arises from the sub-laser-cycle holographic interference of the contributions of the back-rescattering and the non-rescattering electron trajectory. It is shown that the low-energy backscattering photoelectron interference patterns have encoded the structural information of the molecular initial orbitals and attosecond time-resolved dynamics of photoelectron, opening new paths in high-resolution imaging of sub-Ångström and sub-femtosecond structural dynamics in molecules. PMID:25687446

  17. Zero-electron-kinetic-energy photoelectron spectroscopy of transition-metal--ether complexes: Y-O(CH3)2, Y-O(CD3)2, Y-O(CH3)22, and Y-[O(CD3)2]2

    NASA Astrophysics Data System (ADS)

    Rothschopf, Gretchen K.; Li, Shenggang; Yang, Dong-Sheng

    2002-11-01

    The yttrium complexes with one and two dimethyl ethers and their deuterated derivatives are prepared with laser vaporization molecular beam techniques, identified with photoionization time-of-flight mass spectrometry, and investigated with pulsed-field-ionization zero-electronkinetic-energy (ZEKE) photoelectron spectroscopy and ab initio calculations. Adiabatic ionization potentials and yttrium-oxygen stretch and ether-based vibrations are measured for the 1:1 and 1:2 complexes. Fermi interactions are observed from the ZEKE spectra of the 1:1 species. The ground electronic states of the monoligand complexes are determined to be 2A2 for the neutral and 1A1 for the singly charged positive ion, both in C2v symmetry, with yttrium binding to oxygen. The coordination of a second ether forms a diligand complex with a linear oxygen-yttrium-oxygen configuration. This is the first electronic-vibrational spectroscopic study of yttrium-polyatomic molecule complexes and weakly bound metal complexes with two or more polyatomic molecules.

  18. Angular anisotropy of time delay in XUV+IR photoionization of H2+

    NASA Astrophysics Data System (ADS)

    Serov, Vladislav V.; Kheifets, A. S.

    2016-06-01

    We develop a technique for modeling of atomic and molecular ionization in superposition of XUV and IR fields with characteristics typical for attosecond streaking and RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The method is based on solving the time-dependent Schrödinger equation in the coordinate frame expanding along with the photoelectron wave packet. The efficiency of the method is demonstrated by calculating angular anisotropy of photoemission time delay of the H2+ ion in a field configuration of recent RABBITT experiments.

  19. The Photoionized Accretion Disk in Her X-1

    NASA Astrophysics Data System (ADS)

    Ji, L.; Schulz, N.; Nowak, M.; Marshall, H. L.; Kallman, T.

    2009-08-01

    We present an analysis of several high-resolution Chandra grating observations of the X-ray binary pulsar Her X-1. With a total exposure of 170 ks, the observations are separated by years and cover three combinations of orbital and superorbital phases. Our goal is to determine distinct properties of the photoionized emission and its dependence on phase-dependent variations of the continuum. We find that the continua can be described by a partial covering model which above 2 keV is consistent with recent results from Rossi X-Ray Timing Explorer studies and at low energies is consistent with recent XMM-Newton and BeppoSAX studies. Besides a power law with fixed index, an additional thermal blackbody of 114 eV is required to fit wavelengths above 12 Å (~1 keV). We find that likely all the variability is caused by highly variable absorption columns in the range (1-3) × 1023 cm-2. Strong Fe K line fluorescence in almost all observations reveals that dense, cool material is present not only in the outer regions of the disk but interspersed throughout the disk. Most spectra show strong line emission stemming from a photoionized accretion disk corona (ADC). We model the line emission with generic thermal plasma models as well as with the photoionization code XSTAR and investigate changes of the ionization balance with orbital and superorbital phases. Most accretion disk coronal properties such as disk radii, temperatures, and plasma densities are consistent with previous findings for the low state. We find that these properties change negligibly with respect to orbital and superorbital phases. A couple of the higher energy lines exhibit emissivities that are significantly in excess of expectations from a static ADC.

  20. Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene.

    PubMed

    Chen, Jun; Cao, Maoqi; Wei, Bin; Ding, Mengmeng; Shan, Xiaobin; Liu, Fuyi; Sheng, Liusi

    2016-02-01

    In this work, photoionization and dissociation of cyclohexene have been studied by means of coupling a reflectron time-of-flight mass spectrometer with the tunable vacuum ultraviolet (VUV) synchrotron radiation. The adiabatic ionization energy of cyclohexene as well as the appearance energies of its fragment ions C6 H9 (+) , C6 H7 (+) , C5 H7 (+) , C5 H5 (+) , C4 H6 (+) , C4 H5 (+) , C3 H5 (+) and C3 H3 (+) were derived from the onset of the photoionization efficiency (PIE) curves. The optimized structures for the transition states and intermediates on the ground state potential energy surfaces related to photodissociation of cyclohexene were characterized at the ωB97X-D/6-31+g(d,p) level. The coupled cluster method, CCSD(T)/cc-pVTZ, was employed to calculate the corresponding energies with the zero-point energy corrections by the ωB97X-D/6-31+g(d,p) approach. Combining experimental and theoretical results, possible formation pathways of the fragment ions were proposed and discussed in detail. The retro-Cope rearrangement was found to play a crucial role in the formation of C4 H6 (+) , C4 H5 (+) and C3 H5 (+) . Intramolecular hydrogen migrations were observed as dominant processes in most of the fragmentation pathways of cyclohexene. The present research provides a clear picture of the photoionization and dissociation processes of cyclohexene in the 8- to 15.5-eV photon energy region. Copyright © 2016 John Wiley & Sons, Ltd. PMID:26889934

  1. Photoionization of the excited Na 4d state: Possible confirmation of a zero in the l. -->. l-1 channel

    SciTech Connect

    Msezane, A.Z.; Lahiri, J.; Manson, S.T.

    1986-06-01

    Hartree-Fock calculations of the photoionization cross section of the excited Na 4d state have been performed and compared with experiment. The results indicate an experimental confirmation of a zero in an l..-->..l-1 photoionizing transition.

  2. Rotationally resolved state-to-state photoelectron study of niobium carbide radical

    SciTech Connect

    Luo, Zhihong; Huang, Huang; Zhang, Zheng; Chang, Yih-Chung; Ng, C. Y.

    2014-07-14

    By employing the two-color visible (VIS)-ultraviolet (UV) laser photoexcitation scheme and the pulsed field ionization-photoelectron (PFI-PE) detection, we have obtained rovibronically selected and resolved photoelectron spectra for niobium carbide cation (NbC{sup +}). The fully rotationally resolved state-to-state VIS-UV-PFI-PE spectra thus obtained allow the unambiguous assignments of rotational photoionization transitions, indicating that the electronic configuration and term symmetry of NbC{sup +}(X{sup ~}) ground state are …10σ{sup 2} 5π{sup 4} 11σ{sup 2} (X{sup ~1}Σ{sup +}). Furthermore, the rotational analysis of these spectra yields the ionization energy of NbC [IE(NbC)] to be 56 369.2 ± 0.8 cm{sup −1} (6.9889 ± 0.0001 eV) and the rotation constant B{sub 0}{sup +} = 0.5681 ± 0.0007 cm{sup −1}. The latter value allows the determination of the bond distance r{sub 0}{sup +} = 1.671 ± 0.001 Å for NbC{sup +}(X{sup ~1}Σ{sup +}). Based on conservation of energy, the IE(NbC) determined in the present study along with the known IE(Nb) gives the difference of 0 K bond dissociation energies (D{sub 0}’s) for NbC{sup +} and NbC, D{sub 0}(NbC{sup +}) − D{sub 0}(NbC) = −1855.4 ± 0.9 cm{sup −1} (−0.2300 ± 0.0001 eV). The energetic values and the B{sub 0}{sup +} constant determined in this work are valuable for benchmarking state-of-the-art ab initio quantum calculations of 4d transition metal-containing molecules.

  3. Ab initio calculations of the photoionization of diatomic molecules

    NASA Astrophysics Data System (ADS)

    Lefebvre-Brion, Helene; Raşeev, Georges

    2003-01-01

    A review is presented of the calculation of photoionization spectra, particularly in the spectral range where electron autoionization of diatomic molecules takes place. In addition to some interesting results obtained over years that compare favourably with experiment, the emphasis here is put on the relation between the methods developed for the calculation of observables associated with the continuum energy spectrum of the electrons and the Alchemy system of programs. This system of programs serves as a basis for initial and intermediate calculations. The examples presented show that diatomic molecules not only in gas phase but also oriented in space or physisorbed at surfaces may be studied readily.

  4. The photoionization spectrum of neutral aluminium, Al I

    NASA Technical Reports Server (NTRS)

    Roig, R. A.

    1975-01-01

    The absorption spectrum of Al I has been studied for the wavelength range 1160 to 2000 A by the flash pyrolysis technique. Wavelengths and derived energy levels are reported for 70 new lines converging on the 3s3p(3)P(0) limits of Al II. The autoionization parameters of the 3p(2)P(0)-3p(2)(2)S doublet have been measured. Good agreement is obtained with the experiment of Kohl and Parkinson and the recent calculation of Le Dourneuf et al. The relative photoionization cross section has been measured in the wavelength region 1200 A to 2000 A.

  5. Inner-shell photoionized x-ray lasers

    SciTech Connect

    Moon, S.J.

    1998-06-01

    The inner-shell photoionized x-ray lasing scheme is an attractive method for achieving x-ray lasing at short wavelengths, via population inversion following inner-shell photoionization (ISPI). This scheme promises both a short wavelength and a short pulse source of coherent x rays with high average power. In this dissertation a very complete study of the ISPI x-ray laser scheme is done concerning target structure, filter design and lasant medium. An investigation of the rapid rise time of x-ray emission from targets heated by an ultra-short pulse high-intensity optical laser was conducted for use as the x-ray source for ISPI x-ray lasing. Lasing by this approach in C at a wavelength of 45 {angstrom} requires a short pulse (about 50 fsec) driving optical laser with an energy of 1-5 J and traveling wave optics with an accuracy of {approximately} 15 {micro}m. The optical laser is incident on a high-Z target creating a high-density plasma which emits a broadband spectrum of x rays. This x-ray source is passed through a filter to eliminate the low-energy x rays. The remaining high-energy x rays preferentially photoionize inner-shell electrons resulting in a population inversion. Inner-shell photoionized x-ray lasing relies on the large energy of a K-{alpha} transition in the initially neutral lasant. The photo energy required to pump this scheme is only slightly greater than the photon energy of the lasing transition yielding a lasing scheme with high quantum efficiency. However, the overall efficiency is reduced due to low x-ray conversion efficiency and the large probability of Auger decay yielding an overall efficiency of {approximately} 10{sup {minus}7} resulting in an output energy of {micro}J's. They calculate that a driving laser with a pulse duration of 40 fs, a 10{micro}m x 1 cm line focus, and an energy of 1 J gives an effective gain length product (gl) of 10 in C at 45 {angstrom}. At saturation (gl {approximately} 18) they expect an output of {approximately

  6. Packet narrowing and quantum entanglement in photoionization and photodissociation

    SciTech Connect

    Fedorov, M.V.; Efremov, M.A.; Kazakov, A.E.; Chan, K.W.; Eberly, J.H.; Law, C.K.

    2004-05-01

    The narrowing of electron and ion wave packets in the process of photoionization is investigated, with the electron-ion recoil taken fully into account. Packet localization of this type is directly related to entanglement in the joint quantum state of the electron and ion, and to Einstein-Podolsky-Rosen localization. Experimental observation of such packet-narrowing effects is suggested via coincidence registration by two detectors, with a fixed position of one and varying position of the other. A similar effect, typically with an enhanced degree of entanglement, is shown to occur in the case of photodissociation of molecules.

  7. A simple photoionization scheme for characterizing electron and ion spectrometers

    NASA Astrophysics Data System (ADS)

    Wituschek, A.; von Vangerow, J.; Grzesiak, J.; Stienkemeier, F.; Mudrich, M.

    2016-08-01

    We present a simple diode laser-based photoionization scheme for generating electrons and ions with well-defined spatial and energetic (≲2 eV) structures. This scheme can easily be implemented in ion or electron imaging spectrometers for the purpose of off-line characterization and calibration. The low laser power ˜1 mW needed from a passively stabilized diode laser and the low flux of potassium atoms in an effusive beam make our scheme a versatile source of ions and electrons for applications in research and education.

  8. Double K-shell photoionization of atomic beryllium

    SciTech Connect

    Yip, F. L.; Martin, F.; McCurdy, C. W.; Rescigno, T. N.

    2011-11-15

    Double photoionization of the core 1s electrons in atomic beryllium is theoretically studied using a hybrid approach that combines orbital and grid-based representations of the Hamiltonian. The {sup 1} S ground state and {sup 1} P final state contain a double occupancy of the 2s valence shell in all configurations used to represent the correlated wave function. Triply differential cross sections are evaluated, with particular attention focused on a comparison of the effects of scattering the ejected electrons through the spherically symmetric valence shell with similar cross sections for helium, representing a purely two-electron target with an analogous initial-state configuration.

  9. K-shell photoionization of multielectron atomic systems

    NASA Technical Reports Server (NTRS)

    Gould, R. J.

    1980-01-01

    A simplified procedure is proposed for calculating the cross section for photoionization from the K-shell for a general atomic system that contains an arbitrary number of outer-shell electrons. The procedure retains the formalism of the one-electron atom case (pure Coulomb-field problem) by determining the effective nuclear charge reduced from Z by 'screening parameters' associated with the other K-shell electron and the outer-bound electrons. The parameters are determined essentially by fitting the atom's radial electric field to Coulomb form at the distance from the nucleus where the integrand of the dipole radial integral is peaked.

  10. Photoionization and absorption spectrum of formaldehyde in the vacuum ultraviolet.

    NASA Technical Reports Server (NTRS)

    Mentall, J. E.; Gentieu, E. P.; Krauss, M.; Neumann, D.

    1971-01-01

    The measurements have been conducted in the spectral range from 600 to 2000 A. Integrated oscillator strengths were determined for a number of strong Rydberg transitions above 1200 A. From the photoionization curve the first adiabatic ionization potential was found to be 10.87 plus or minus 0.01 eV. As an aid in interpreting the absorption spectrum, theoretical calculations were made using a single-configuration self-consistent field procedure for the Rydberg states and a model which included mixing between the Rydberg and valence states.

  11. Photo-ionization and residual electron effects in guided streamers

    SciTech Connect

    Wu, S.; Lu, X. Liu, D.; Yang, Y.; Pan, Y.; Ostrikov, K.

    2014-10-15

    Complementary experiments and numerical modeling reveal the important role of photo-ionization in the guided streamer propagation in helium-air gas mixtures. It is shown that the minimum electron concentration ∼10{sup 8 }cm{sup −3} is required for the regular, repeated propagation of the plasma bullets, while the streamers propagate in the stochastic mode below this threshold. The stochastic-to-regular mode transition is related to the higher background electron density in front of the propagating streamers. These findings help improving control of guided streamer propagation in applications from health care to nanotechnology and improve understanding of generic pre-breakdown phenomena.

  12. A simple photoionization scheme for characterizing electron and ion spectrometers.

    PubMed

    Wituschek, A; von Vangerow, J; Grzesiak, J; Stienkemeier, F; Mudrich, M

    2016-08-01

    We present a simple diode laser-based photoionization scheme for generating electrons and ions with well-defined spatial and energetic (≲2 eV) structures. This scheme can easily be implemented in ion or electron imaging spectrometers for the purpose of off-line characterization and calibration. The low laser power ∼1 mW needed from a passively stabilized diode laser and the low flux of potassium atoms in an effusive beam make our scheme a versatile source of ions and electrons for applications in research and education. PMID:27587098

  13. Threshold photoelectron spectroscopy of vibrationally excited nitrogen

    NASA Astrophysics Data System (ADS)

    Innocenti, Fabrizio; Eypper, Marie; Stranges, Stefano; West, John B.; King, George C.; Dyke, John M.

    2013-02-01

    Threshold photoelectron spectroscopy (TPES) has been used to study flowing nitrogen subjected to a microwave discharge. The first three photoelectron (PE) bands of nitrogen corresponding to the ionizations N2+ (X2Σ+g) v+ ← N2 (X1Σ+g) v″, N2+ (A2Πu) v+ ← N2 (X1Σ+g) v″ and N2 + (B2Σ+u) v+ ← N2 (X1Σ+g) v″ were investigated. An analysis of the vibrationally resolved threshold photoelectron (TPE) spectra shows evidence of population of the vibrational levels v″ = 0-5 in the N2 X1Σ+g neutral state. By a comparison with the PE spectrum recorded under the same conditions, use of computed Franck-Condon factors for each ionization and evidence from vacuum ultraviolet absorption spectroscopy, the relative intensities of vibrational components in a TPE band can be qualitatively explained using the Franck-Condon factors for each ionization as well as the gain in intensity from autoionization from Rydberg states that are degenerate with an ionization threshold or lie just above a threshold. The enhancement in intensity obtained in the TPE spectra, relative to the intensity in a PE spectrum recorded under the same conditions, was estimated as at least one order of magnitude. The first band of atomic nitrogen was also observed in the discharge-on TPE spectra. The experimental resolution was sufficiently good to allow the three ionizations N+(3P0,1,2) ← N(4S3/2) to be resolved and their relative component intensities were measured as 1: 0.95 ± 0.10: 0.70 ± 0.10. The complementary nature of the TPES and PES techniques has been outlined and the extra information obtained from studying a vibrationally excited small molecule such as N2 with these methods has been demonstrated.

  14. Attosecond angle-resolved photoelectron spectroscopy.

    PubMed

    Aseyev, S A; Ni, Y; Frasinski, L J; Muller, H G; Vrakking, M J J

    2003-11-28

    We report experiments on the characterization of a train of attosecond pulses obtained by high-harmonic generation, using mixed-color (XUV+IR) atomic two-photon ionization and electron detection on a velocity map imaging detector. We demonstrate that the relative phase of the harmonics is encoded both in the photoelectron yield and the angular distribution as a function of XUV-IR time delay, thus making the technique suitable for the detection of single attosecond pulses. The timing of the attosecond pulse with respect to the field oscillation of the driving laser critically depends on the target gas used to generate the harmonics. PMID:14683238

  15. Electronic and Photoelectron Spectroscopy of Toluene

    NASA Astrophysics Data System (ADS)

    Gardner, Adrian M.; Green, Alistair M.; Tame-Reyes, Victor; Wright, Timothy G.

    2012-06-01

    Electronic and photoelectron spectra of toluene are presented and discussed. The utilization of a recently reported scheme for assigning the normal vibrations of substituted benzenes allows these spectra to be compared to those of other molecules with unprecedented clarity. Changes in vibrational activity within a series of substituted benzene molecules will be discussed, specifically the increased rate of intramolecular vibrational energy redistribution observed in molecules where the substituent is a methyl group. A. M. Gardner and T. G. Wright, J. Chem. Phys., 135, 114305 (2011)

  16. Photoionization cross sections for O-like S IX: a Breit-Pauli R-matrix calculation

    NASA Astrophysics Data System (ADS)

    Tyndall, N. B.; Ramsbottom, C. A.; Hibbert, A.; Ferland, G.

    2015-08-01

    In this paper we present photoionization cross sections for the lowest five states of O-like S IX (1s22s22p4 3P0,1,2, 1D2, 1S0). The relativistic Breit-Pauli R-matrix codes were utilized including all terms of the 2s22p3, 2s2p4, 2p5, 2s22p23s, 3p, 3d and 2s2p33s, 3p, 3d configurations in the expansion of the collision wavefunction for S X. It was also found that to achieve convergence of the low-lying energy separations of the target levels, an additional 21 configuration functions needed to be included in the configuration interaction expansion, incorporating two-electron excitations from the 2s and 2p shells to the 3s, 3p and 3d shells. The present work thus constitutes the most sophisticated photoionization evaluation for ground and metastable levels of the S IX ion. Direct comparisons have been made with the only available data found on the OPEN-ADAS database between level resolved contributions of the spectrum. This comparison for the background cross section exhibits excellent agreement at all photon energies for each partial photoionization cross section contribution investigated. Finally, the autoionizing bound states arising from numerous open channels have also been investigated and identified using the QB approach, a procedure for analyzing resonances in atomic and molecular collision theory which exploits the analytic properties of R-matrix theory. Major Rydberg resonance series are also presented and tabulated for the dominant linewidths considered.

  17. Photoionization cross section of atomic cadmium using the multi-configuration Tamm-Dancoff approximation

    NASA Astrophysics Data System (ADS)

    Pradhan, G. B.; Jose, J.; Radojević, V.; Manson, S. T.; Deshmukh, P. C.

    2009-11-01

    The Multiconfiguration Tamm-Dancoff approximation (MCTD) is used to calculate the photoionization cross section of cadmium. Results are compared with available experimental data and also with earlier computations of the cross-section. We find that while earlier computations overestimated the photoionization cross section compared to experiment, the present MCTD computation underestimates the same.

  18. Solar photoionization as a loss mechanism of neutral interstellar hydrogen in interplanetary space

    NASA Technical Reports Server (NTRS)

    Ogawa, H. S.; Wu, C. Y. Robert; Gangopadhyay, P.; Judge, D. L.

    1995-01-01

    Two primary loss mechanisms of interstellar neutral hydrogen in interplanetary space are resonance charge exchange ionization with solar wind protons and photoionization by solar EUV radiation. The later process has often been neglected since the average photoionization rate has been estimated to be as much as 5 to 10 times smaller than the charge exchange rate. These factors are based on ionization rates from early measurements of solar EUV and solar wind fluxes. Using revised solar EUV and solar wind fluxes measured near the ecliptic plane we have reinvestigated the ionization rates of interplanetary hydrogen. The result of our analysis indicates that indeed the photoionization rate during solar minimum can be smaller than charge exchange by a factor of 5; however, during solar maximum conditions when solar EUV fluxes are high, and solar wind fluxes are low, photoionization can be over 60% of the charge exchange rate at Earth orbit. To obtain an accurate estimate of the importance of photoionization relative to charge exchange, we have included photoionization from both the ground and metastable states of hydrogen. We find, however, that the photoionization from the metastable state does not contribute significantly to the overall photoionization rate.

  19. Research on fluorescence from photoionization, photodissociation, and vacuum, along with bending quantrum study

    NASA Technical Reports Server (NTRS)

    Judge, D. L.

    1975-01-01

    Reports of research concerning the fluorescence of CS2 are presented. Fluorescence from fragments of CS2 vapor produced by vacuum ultraviolet radiation, and fluorescence from photoionization of CS2 vapor are discussed along with fluorescence produced by photodissociation of CS2, and fluorescence from photoionization of OCS.

  20. Photoionization of iodine atoms: Angular distributions and relative partial photoionization cross-sections in the energy region 11.0-23.0 eV

    SciTech Connect

    Eypper, Marie; Innocenti, Fabrizio; Morris, Alan; Dyke, John M.; Stranges, Stefano; West, John B.; King, George C.

    2010-08-28

    Relative partial photoionization cross-sections and angular distribution parameters, {beta}, have been measured for the first, I{sup +}({sup 3}P{sub 2})<-I({sup 2}P{sub 3/2}), and fourth, I{sup +}({sup 1}D{sub 2})<-I({sup 2}P{sub 3/2}), (5p){sup -1} photoelectron (PE) bands of atomic iodine, by performing angle-resolved constant-ionic-state (CIS) measurements on these PE bands in the photon energy range 11.0-23.0 eV. Three Rydberg series, two ns and one nd series, which converge to the I{sup +} {sup 3}P{sub 1} limit at 11.33 eV and four Rydberg series, two ns and two nd series, which converge to the I{sup +} {sup 1}D{sub 2} limit at 12.15 eV were observed in the first PE band CIS spectra. The fourth band CIS spectrum showed structure in the 12.9-14.1eV photon energy range, which is also seen in the first band CIS spectra. This structure arises from excitation to ns and nd Rydberg states that are parts of series converging to the I{sup +} {sup 1}S{sub 0} limit we reported on earlier, as well as 5s{yields}5p excitations in the photon energy range 17.5-22.5 eV. These atomic iodine CIS spectra show reasonably good agreement with the equivalent spectra obtained for atomic bromine. The {beta}-plots for the first PE band recorded up to the I{sup +} {sup 3}P{sub 1} and I{sup +} {sup 1}D{sub 2} limits only show resonances corresponding to some of the 5p{yields}nd excitations observed in the first band CIS spectra scanned to the I{sup +} {sup 1}D{sub 2} limit (12.15 eV). These plots are interpreted in terms of an angular momentum transfer model with the positive values of {beta} obtained on resonances corresponding to parity allowed j{sub t}=1 and 3 channels and the off-resonance negative {beta} values corresponding to parity unfavored channels, where j{sub t} is the quantum number for angular momentum transfer between the molecule, and the ion and photoelectron. The {beta}-plots recorded for iodine are significantly different from those obtained for atomic bromine

  1. Pyrolysis of 3-Methoxypyridine. Detection and Characterization of the Pyrrolyl Radical by Threshold Photoelectron Spectroscopy.

    PubMed

    Holzmeier, Fabian; Wagner, Isabella; Fischer, Ingo; Bodi, Andras; Hemberger, Patrick

    2016-07-14

    Pyrolysis of 3-methoxypyridine in a heated pyrolysis reactor was found to be an efficient way to generate the pyrrolyl radical, c-C4H4N, in the gas phase. The threshold photoelectron (TPE) spectrum of this radical was recorded using vacuum ultraviolet synchrotron radiation. The spectrum revealed a singlet ground state at 9.11 ± 0.02 eV (X̃(+ 1)A) and an excited triplet state (ã(+ 3)A) at 9.43 ± 0.05 eV. Vibrational structure was observed for both cationic states and could be assigned to ring deformation modes. Furthermore, (E)- and (Z)-1-cyanoallyl radicals were found to contribute to the TPE spectrum below 8.9 eV. In addition, we have identified two parallel decomposition channels of the pyrrolyl radical, yielding either hydrogen cyanide and propargyl radical or acetylene and cyanomethyl radical. The reaction energy profiles have also been calculated for these reactions. In addition, the dissociative photoionization of the precursor 3-methoxypyridine is reported. PMID:26698131

  2. Role of Conical Intersections in Molecular Spectroscopy and Photoinduced Chemical Dynamics

    NASA Astrophysics Data System (ADS)

    Domcke, Wolfgang; Yarkony, David R.

    2012-05-01

    This review describes how conical intersections affect measured molecular spectra and simple photofragmentation processes. We consider excitations that result in electron ejection, that is, photoionization or photodetachment, as well as photoinduced H-atom elimination. Section 1 presents a brief overview of the history of conical intersections and their rise from an arcane theoretical concept to a major paradigm in nonadiabatic chemistry. In Section 2, the generic properties of conical intersections are discussed, as well as their characterization with modern electronic-structure methods. Section 3 briefly discusses computational tools used to compute the nuclear motion involving conical intersections. Section 4 describes how the ideas of Sections 2 and 3 are combined to simulate molecular spectra impacted by conical intersections. Section 5 describes selected recent experimental and computational studies of photoelectron, photodetachment, and photofragment spectra. Rather than providing an encyclopedic bibliography of the previous and current literature, we illustrate significant problems currently being addressed and describe what can be accomplished with current computational techniques and how these results are achieved. Section 6 suggests future directions in this field.

  3. Role of conical intersections in molecular spectroscopy and photoinduced chemical dynamics.

    PubMed

    Domcke, Wolfgang; Yarkony, David R

    2012-01-01

    This review describes how conical intersections affect measured molecular spectra and simple photofragmentation processes. We consider excitations that result in electron ejection, that is, photoionization or photodetachment, as well as photoinduced H-atom elimination. Section 1 presents a brief overview of the history of conical intersections and their rise from an arcane theoretical concept to a major paradigm in nonadiabatic chemistry. In Section 2, the generic properties of conical intersections are discussed, as well as their characterization with modern electronic-structure methods. Section 3 briefly discusses computational tools used to compute the nuclear motion involving conical intersections. Section 4 describes how the ideas of Sections 2 and 3 are combined to simulate molecular spectra impacted by conical intersections. Section 5 describes selected recent experimental and computational studies of photoelectron, photodetachment, and photofragment spectra. Rather than providing an encyclopedic bibliography of the previous and current literature, we illustrate significant problems currently being addressed and describe what can be accomplished with current computational techniques and how these results are achieved. Section 6 suggests future directions in this field. PMID:22475338

  4. Inner-shell photoionization and core-hole decay of Xe and XeF2

    NASA Astrophysics Data System (ADS)

    Southworth, Stephen; Picón, Antonio; Lehmann, C. Stefan; Wehlitz, Ralf; Cheng, Lan; Stanton, John F.

    2015-03-01

    Molecular effects on inner-shell photoionization and core-hole decay are explored by comparing cross sections and partial ion yields of Xe and XeF2 from Xe 3d and F 1s subshells in the 660-740 eV range. The Xe 3d- ɛf continuum shape resonances dominate the total cross sections, but prominent resonances appear in the XeF2 cross section due to excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Relativistic coupled-cluster calculations were performed to identify the subshell ionization thresholds, the LUMO resonances and their oscillator strengths. Comparison of the Xe charge state distributions of the atom and molecule show a general shift to lower charge states in XeF2. The measurements support a model of core-hole decay in which charge is redistributed from Xe to the F ligands and energetic F ions are produced by Coulombic fragmentation. 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.

  5. Photoionization dynamics of glycine adsorbed on a silicon cluster: ''On-the-fly'' simulations

    SciTech Connect

    Shemesh, Dorit; Baer, Roi; Seideman, Tamar; Gerber, R. Benny

    2005-05-08

    Dynamics of glycine chemisorbed on the surface of a silicon cluster is studied for a process that involves single-photon ionization, followed by recombination with the electron after a selected time delay. The process is studied by ''on-the-fly'' molecular dynamics simulations, using the semiempirical parametric method number 3 (PM3) potential energy surface. The system is taken to be in the ground state prior to photoionization, and time delays from 5 to 50 fs before the recombination are considered. The time evolution is computed over 10 ps. The main findings are (1) the positive charge after ionization is initially mostly distributed on the silicon cluster. (2) After ionization the major structural changes are on the silicon cluster. These include Si-Si bond breaking and formation and hydrogen transfer between different silicon atoms. (3) The transient ionization event gives rise to dynamical behavior that depends sensitively on the ion state lifetime. Subsequent to 45 fs evolution in the charged state, the glycine molecule starts to rotate on the silicon cluster. Implications of the results to various processes that are induced by transient transition to a charged state are discussed. These include inelastic tunneling in molecular devices, photochemistry on conducting surfaces, and electron-molecule scattering.

  6. Photoionization Spectroscopy of Trapping Centers in GaN FETs

    NASA Astrophysics Data System (ADS)

    Klein Freitas, P. B., Jr.; Binari, S. C.; Wickenden, A. E.

    2000-03-01

    Measurements of the spectral and intensity dependences of the optically-induced reversal of current collapse in a GaN metal semiconductor field effect transistor (MESFET) have been compared to the results of modeling the phenomenon assuming a net transfer of charge from the conducting channel to the high-resistivity (HR) region of the device. The reversal was assumed to result from the photoionization of trapped carriers that return to the channel under the influence of a large built-in field at the channel/HR-substrate interface. For a MESFET in which two distinct trapping centers have been spectrally resolved, the experimentally measured dependence upon light intensity was fitted using this model. The two traps were found to have very different photoionization cross-sections (6x10-17 cm^2 and 2.4x10-15cm^2) but comparable concentrations (3x10^11cm-2 and 7x10^11cm-2), suggesting that both traps contribute comparably to the observed current collapse.

  7. Efficient photoheating algorithms in time-dependent photoionization simulations

    NASA Astrophysics Data System (ADS)

    Lee, Kai-Yan; Mellema, Garrelt; Lundqvist, Peter

    2016-02-01

    We present an extension to the time-dependent photoionization code C2-RAY to calculate photoheating in an efficient and accurate way. In C2-RAY, the thermal calculation demands relatively small time-steps for accurate results. We describe two novel methods to reduce the computational cost associated with small time-steps, namely, an adaptive time-step algorithm and an asynchronous evolution approach. The adaptive time-step algorithm determines an optimal time-step for the next computational step. It uses a fast ray-tracing scheme to quickly locate the relevant cells for this determination and only use these cells for the calculation of the time-step. Asynchronous evolution allows different cells to evolve with different time-steps. The asynchronized clocks of the cells are synchronized at the times where outputs are produced. By only evolving cells which may require short time-steps with these short time-steps instead of imposing them to the whole grid, the computational cost of the calculation can be substantially reduced. We show that our methods work well for several cosmologically relevant test problems and validate our results by comparing to the results of another time-dependent photoionization code.

  8. Kr photoionized plasma induced by intense extreme ultraviolet pulses

    NASA Astrophysics Data System (ADS)

    Bartnik, A.; Wachulak, P.; Fiedorowicz, H.; Skrzeczanowski, W.

    2016-04-01

    Irradiation of any gas with an intense EUV (extreme ultraviolet) radiation beam can result in creation of photoionized plasmas. The parameters of such plasmas can be significantly different when compared with those of the laser produced plasmas (LPP) or discharge plasmas. In this work, the photoionized plasmas were created in a krypton gas irradiated using an LPP EUV source operating at a 10 Hz repetition rate. The Kr gas was injected into the vacuum chamber synchronously with the EUV radiation pulses. The EUV beam was focused onto a Kr gas stream using an axisymmetrical ellipsoidal collector. The resulting low temperature Kr plasmas emitted electromagnetic radiation in the wide spectral range. The emission spectra were measured either in the EUV or an optical range. The EUV spectrum was dominated by emission lines originating from Kr III and Kr IV ions, and the UV/VIS spectra were composed from Kr II and Kr I lines. The spectral lines recorded in EUV, UV, and VIS ranges were used for the construction of Boltzmann plots to be used for the estimation of the electron temperature. It was shown that for the lowest Kr III and Kr IV levels, the local thermodynamic equilibrium (LTE) conditions were not fulfilled. The electron temperature was thus estimated based on Kr II and Kr I species where the partial LTE conditions could be expected.

  9. Inner-shell Photoionization Studies of Neutral Atomic Nitrogen

    NASA Astrophysics Data System (ADS)

    Stolte, W. C.; Jonauskas, V.; Lindle, D. W.; Sant'Anna, M. M.; Savin, D. W.

    2016-02-01

    Inner-shell ionization of a 1s electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD), which results as the 1s-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for inner-shell photoionization of neutral atomic nitrogen for photon energies of 403-475 eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N+, {{{N}}}2+, and {{{N}}}3+, and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to {{{N}}}2+ is somewhat reduced, that for N+ is greatly increased, and that to {{{N}}}3+, which was predicted to be zero, grows to ≈ 10% at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for inner-shell ionization and points the way for the improvements needed to more reliably model the role of inner-shell ionization of cosmic plasmas.

  10. A Bipolar Planetary Nebula NGC 6537: Photoionization or Shock Heating?

    NASA Astrophysics Data System (ADS)

    Hyung, Siek

    1999-04-01

    NGC 6537 is an extremely high excitation bipolar planetary nebula. It exhibits a huge range of excitation from lines of [N I] to [Si VI] or [Fe VII], i.e. from neutral atoms to atoms requiring an ionization potential of 167eV. Its kinematical structures are of special interest. We are here primarily concerned with its high resolution spectrum as revealed by the Hamilton Echelle Spectrograph at Lick Observatory (resolution 0.2 A,) and supplemented by UV and near-UV data. Photoionization model reproduces the observed global spectrum of NGC 6537, the absolute H beta flux, and the observed visual or blue magnitude fairly well. The nebulosity of NGC 6537 is likely to be the result of photo-ionization by a very hot star of Teff 180,000 K, although the global nebular morphology and kinematics suggest an effect by strong stellar winds and resulting shock heating. NGC 6537 can be classified as a Peimbert Type I planetary nebula. It is extremely young and it may have originated from a star of about 5 M_sun.

  11. Photoionization of He above the n =2 threshold

    SciTech Connect

    Sanchez, I.; Martriaan, F. )

    1991-12-01

    We report a theoretical study of He(1{ital s}{sup 2})+{ital h}{nu}{r arrow}He{sup +}(1{ital s},2{ital s},2{ital p})+{ital e}{sup {minus}} photoionization processes, for photon energies greater than 65.4 eV. We pay special attention to the energy region 69.0--73.0 eV, where recent synchrotron experiments exhibit clearly resonant structure associated to 3{ital lnl}{prime} doubly excited states of He. Our method is based on a Feshbach partitioning of the total wave function that includes explicitly resonant structure. Total and partial cross sections do not depend on parametrization, although an obvious one can be obtained in a straightforward manner in the vicinity of isolated resonances; this is very useful for the analysis of most of the resonance peaks observed experimentally. An appealing feature of our approach is the use of {ital L}{sup 2}-integrable basis sets to describe the scattering wave functions. Our discretization method provides coupled continuum states with the proper {delta}-function normalization and with the correct asymptotic behavior. With this method, we have calculated partial photoionization cross sections for leaving the ion in the 1{ital s}, 2{ital s}, and 2{ital p} levels, and the results are in good agreement with recently published experimental data. A complete set of parameters describing the first twelve resonances in partial cross sections is also provided.

  12. Laboratory photoionized plasma experiments at Z - Comparison with modeling

    NASA Astrophysics Data System (ADS)

    Mayes, D.; Lockard, T.; Durmaz, T.; Hall, I.; Mancini, R.; Bailey, J.; Rochau, G.; Loisel, G.; Heeter, R.; Liedahl, D.

    2013-10-01

    Photoionized plasmas are common in astrophysical environments, such as x-ray binaries and active galactic nuclei. We discuss an experimental and modeling effort to study the atomic kinetics in plasmas of this type via K-shell line absorption spectroscopy. Results from a first pass thru our 2nd-generation dataset are compared with results of several modeling codes attempting to simulate our experimental conditions. The experiment employs the intense x-ray flux emitted by the collapse of a z-pinch to produce and backlight a Neon photoionized plasma in a cm-scale gas cell at various distances from the z-pinch. The filling pressure is monitored in situ providing the plasma particle number density. High-resolution spectra from a TREX spectrometer are processed with a suite of specially designed IDL tools to produce transmission spectra, which show absorption in several ionization stages of Neon. Analysis independent of atomic kinetics calculations yields the charge state distribution and ion areal densities used to benchmark atomic kinetics codes. In addition, the electron temperature, extracted from a level population ratio, is used to test heating models. This work is sponsored in part by the National Nuclear Security Administration under the High Energy Density Laboratory Plasmas grant program through DOE Grant DE-FG52-09NA29551, and the Z Facility Fundamental Science Program of SNL.

  13. Attosecond delays in photoionization: time and quantum mechanics

    NASA Astrophysics Data System (ADS)

    Maquet, Alfred; Caillat, Jérémie; Taïeb, Richard

    2014-10-01

    This article addresses topics regarding time measurements performed on quantum systems. The motivation is linked to the advent of ‘attophysics’ which makes feasible to follow the motion of electrons in atoms and molecules, with time resolution at the attosecond (1 as = 10-18 s) level, i.e. at the natural scale for electronic processes in these systems. In this context, attosecond ‘time-delays’ have been recently measured in experiments on photoionization and the question arises if such advances could cast a new light on the still active discussion on the status of the time variable in quantum mechanics. One issue still debatable is how to decide whether one can define a quantum time operator with eigenvalues associated to measurable ‘time-delays’, or time is a parameter, as it is implicit in the Newtonian classical mechanics. One objective of this paper is to investigate if the recent attophysics-based measurements could shed light on this parameter-operator conundrum. To this end, we present here the main features of the theory background, followed by an analysis of the experimental schemes that have been used to evidence attosecond ‘time-delays’ in photoionization. Our conclusion is that these results reinforce the view that time is a parameter which cannot be defined without reference to classical mechanics.

  14. Infrared laser ablation atmospheric pressure photoionization mass spectrometry.

    PubMed

    Vaikkinen, Anu; Shrestha, Bindesh; Kauppila, Tiina J; Vertes, Akos; Kostiainen, Risto

    2012-02-01

    In this paper we introduce laser ablation atmospheric pressure photoionization (LAAPPI), a novel atmospheric pressure ion source for mass spectrometry. In LAAPPI the analytes are ablated from water-rich solid samples or from aqueous solutions with an infrared (IR) laser running at 2.94 μm wavelength. Approximately 12 mm above the sample surface, the ablation plume is intercepted with an orthogonal hot solvent (e.g., toluene or anisole) jet, which is generated by a heated nebulizer microchip and directed toward the mass spectrometer inlet. The ablated analytes are desolvated and ionized in the gas-phase by atmospheric pressure photoionization using a 10 eV vacuum ultraviolet krypton discharge lamp. The effect of operational parameters and spray solvent on the performance of LAAPPI is studied. LAAPPI offers ~300 μm lateral resolution comparable to, e.g., matrix-assisted laser desorption ionization. In addition to polar compounds, LAAPPI efficiently ionizes neutral and nonpolar compounds. The bioanalytical application of the method is demonstrated by the direct LAAPPI analysis of rat brain tissue sections and sour orange (Citrus aurantium) leaves. PMID:22242626

  15. Photoionization cross section and angular distribution calculations of carbon tetrafluoride.

    PubMed

    Toffoli, D; Stener, M; Fronzoni, G; Decleva, P

    2006-06-01

    Correlation in the photoionization dynamics of carbon tetrafluoride is studied in the framework of the time-dependent density-functional theory (TDDFT) approach by employing a multicentric basis set expansion of the scattering wave function linear combination of atomic orbitals (LCAO) TDDFT. Results obtained with the statistical average of orbital potentials and LB94 exchange-correlation (xc) potentials are compared with photoabsorption, photoionization, and electron-scattering experiments as well as with past theoretical calculations. Inadequacies in both the V(xc) parametrizations employed have been suggested from the analysis of the intensity plots for the D2A1 ionization. The formation of resonant scattering states in selected continuum channels has been studied through the analysis of the dipole-prepared scattering wave function; our findings are then compared with results of electron-scattering calculations. Overall, the LCAO-TDDFT results highlight the effectiveness of the approach for the calculation of the unbound spectrum of fairly large molecules. PMID:16774413

  16. Photoionization of atomic chlorine above the 1S threshold

    NASA Astrophysics Data System (ADS)

    Shahabi, Siamak; Starace, Anthony F.; Chang, T. N.

    1984-10-01

    The total photoionization cross section of the 3p subshell of atomic chlorine is presented with use of the recently developed open-shell transition-matrix method of Starace and Shahabi. The role of electron correlations is studied by comparison with Hartree-Fock and close-coupling calculations. In contrast to 3p-subshell photoionization of argon, it is shown that, in chlorine, final-state interchannel interactions are very strong while virtual pair excitations have a weak effect on the shape of the cross section, serving mainly to reduce the discrepancy between length and velocity results. Our results are compared in detail with other theoretical results above the 1S threshold as well as with experimental relative-intensity measurements at 584 Å. While our results are lower than the others at the 1S threshold (ℏω=0.6 a.u.), at photon energies ℏω>1 a.u., our geometric mean cross section is in essentially exact agreement with unrelaxed ionic core results of Brown, Carter, and Kelly and of Fielder and Armstrong.

  17. Photoelectron imaging of atomic chlorine and bromine following photolysis of CH{sub 2}BrCl

    SciTech Connect

    Hua Linqiang; Shen Huan; Hu Changjin; Zhang Bing

    2008-12-28

    Photoionization of chlorine and bromine atoms following photodissociation of CH{sub 2}BrCl was studied in the wavelength range of 231-238 nm by photoelectron imaging technique. Final state-specific speed and angular distributions of the photoelectron were recorded. Analysis of relative branching ratios to different levels of Cl{sup +} and Br{sup +} revealed that the final ion level distributions are generally dominated by the preservation of the ion-core configuration of the intermediate resonant state. Some J{sub c} numbers of the intermediate states were newly assigned according to this regulation. The configuration interaction between resonant states and the autoionization in the continuum were also believed to play an important role in the ionization process since some ions that deviate from the regulation mentioned ahead were observed. The angular distributions of the electrons were found to be well characterized by {beta}{sub 2} and {beta}{sub 4}, although the ionization process of chlorine and bromine atoms involves three photons.

  18. Combining ion mobility spectrometry, mass spectrometry, and photoelectron spectroscopy in a high-transmission instrument.

    PubMed

    Vonderach, Matthias; Ehrler, Oli T; Weis, Patrick; Kappes, Manfred M

    2011-02-01

    We have developed a novel instrument that combines ion mobility spectrometry, mass spectro-metry, and photoelectron spectroscopy. The instrument couples an electrospray ion source, a high-transmission ion mobility cell based on ion funnels, a quadrupole mass filter, and a time-of-flight (magnetic bottle) photoelectron spectrometer operated with a pulsed detachment laser. We show that the instrument can resolve highly structured anion arrival time distributions and at the same time provide corresponding photoelectron spectra-using the DNA oligonucleotide ion [dC(6) - 5H](5-) as a test case. For this multianion we find at least four different, noninterconverting isomers (conformers) simultaneously present in the gas phase at room temperature. For each of these we record well-resolved and remarkably different photoelectron spectra at each of three different detachment laser wavelengths. Two-dimensional ion mobility/electron binding energy plots can be acquired with an automated data collection procedure. We expect that this kind of instrument will significantly improve the capabilities for structure determination of (bio)molecular anions in the gas phase. PMID:21214198

  19. An experimental study of low-pressure premixed pyrrole/oxygen/argon flames with tunable synchrotron photoionization

    SciTech Connect

    Tian, Zhenyu; Li, Yuyang; Zhang, Taichang; Qi, Fei; Zhu, Aiguo; Cui, Zhifeng

    2007-10-15

    Two premixed laminar pyrrole/oxygen/argon flames at 3.33 kPa (25 Torr) with equivalence ratios of 0.55 (C/O/N = 1:5.19:0.25) and 1.84 (C/O/N = 1:1.56:0.25) have been investigated using tunable synchrotron photoionization and molecular-beam mass spectrometry techniques. All observed flame species, including some nitrogen-containing intermediates, have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of species including reactants, intermediates, and products have been determined by scanning burner position at some selected photon energies near ionization thresholds, and flame temperature has been measured by a Pt/Pt-13% Rh thermocouple. The results indicate that N{sub 2}, NO, and NO{sub 2} are the major nitrogenous products, while hydrogen cyanide, isocyanic acid, and 2-propenenitrile are the most important nitrogen-containing intermediates in pyrrole flames. Radicals such as methyl, propargyl, allyl, cyanomethyl, n-propyl, isobutyl, cyclopentadienyl, phenyl, cyclohexyl, phenoxy, and 4-methylbenzyl are observed as well. Moreover, ethenol and methylacrylonitrile are also detected. Reaction pathways involving the major species are proposed. The new results will be useful in developing a kinetic model of nitrogenous compound combustion. (author)

  20. Femtosecond pump-probe photoionization-photofragmentation spectroscopy: photoionization-induced twisting and coherent vibrational motion of azobenzene cation.

    PubMed

    Ho, Jr-Wei; Chen, Wei-Kan; Cheng, Po-Yuan

    2009-10-01

    We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale. PMID:19814554