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Sample records for 2p photoelectron spectra

  1. Correlation and relativistic effects in 2p photoelectron spectra of sodium atoms from the initial state 2{p}^{6}3p

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobin; Shi, Yinglong; Xing, Yongzhong; Lu, Feiping; Chen, Zhanbin

    2017-02-01

    We investigate the 2p photoelectron spectra of sodium atoms with the initial state 2{p}63p at a photon energy of 54 eV. The analysis is performed based on the multi-configuration Dirac–Fock method. Special attention is given to the influences of correlation and relativistic effects on the spectra structures. To explore the nature and importance of such influences, calculations were performed based on detailed analyses of the thresholds, relative intensities and corresponding data calculated in the nonrelativistic limit.

  2. 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)

  3. Interatomic scattering in energy dependent photoelectron spectra of Ar clusters

    SciTech Connect

    Patanen, M.; Benkoula, S.; Nicolas, C.; Goel, A.; Antonsson, E.; Neville, J. J.; Miron, C.

    2015-09-28

    Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters’ surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface.

  4. On the Photoelectron Spectra of Li4

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1996-01-01

    The most stable structure for Li4(-) is found to be the rhombus. Electron detachment from this structure does not seem able to fully explain the photoelectron spectra. The computed results are consistent with those Rao, Jena, and Ray who have proposed that the experimental spectra consists of a superposition of detachment from the Li4(-) rhombus and tetrahedron, forming the singlet and triplet states of Li4, respectively.

  5. 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.

  6. X-ray photoelectron spectra of MgH2

    NASA Astrophysics Data System (ADS)

    He, Z. X.; Pong, W.

    1990-06-01

    Measurements of X-ray photoemission from magnesium hydride MgH2 were made in an effort to further the fundamental understanding of the electronic structure of this metal hydride. The polycrystalline MgH2 was compressed onto a metal holder to provide a smooth solid surface in a dry nitrogen box and then transferred into a ESCA system without exposure to air. Measurements were made immediately after the surface was scrapped in the vacuum. The binding energies of the photoelectrons from Mg 2s and 2p states were found to be 88.9 ± 0.2eV, and 50.1 ± 0.2eV, respectively. The valence band spectrum shows an effective base width of approximately 8.8eV, which is in reasonable agreement with the recent band structure calculation for MgH2. The photoelectron spectra also display features that can be identified as volume plasmon energy loss of 14.6 ± 0.2eV. The data can be shown to be useful in calculating the average band gap energy (5.80eV) for MgH2.

  7. Irradiation-induced degradation of PTB7 investigated by valence band and S 2p photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Darlatt, Erik; Muhsin, Burhan; Roesch, Roland; Lupulescu, Cosmin; Roth, Friedrich; Kolbe, Michael; Gottwald, Alexander; Hoppe, Harald; Richter, Mathias

    2016-08-01

    Monochromatic radiation with known absolute radiant power from an undulator at the electron storage ring Metrology Light Source (MLS) was used to irradiate PTB7 (a thieno[3, 4-b]thiophene-alt-benzodithiophene polymer) thin films at wavelengths (photon energies) of 185 nm (6.70 eV), 220 nm (5.64 eV), 300 nm (4.13 eV), 320 nm (3.88 eV), 356 nm (3.48 eV) and 675 nm (1.84 eV) under ultra-high vacuum conditions for the investigation of radiation-induced degradation effects. The characterization of the thin films is focused at ultraviolet photoelectron spectroscopy (UPS) of valence bands and is complemented by S 2p x-ray photoelectron spectroscopy (S 2p XPS) before and after the irradiation procedure. The radiant exposure was determined for each irradiation by means of photodiodes traceably calibrated to the international system of units SI. The valence band spectra show the strongest changes for the shortest wavelengths and no degradation effect at 356 nm and 675 nm even with the highest radiant exposure applied. In the spectral range where the Sun appears bright on the Earth’s surface, no degradation effects are observed.

  8. X-ray photoelectron spectra and electronic structure of rare-earth orthovanadates

    NASA Astrophysics Data System (ADS)

    Ryzhkov, M. V.; Kostikov, S. P.; Ivanov, I. K.; Gubanov, V. A.

    1981-08-01

    Photoelectron spectra of 4 d and valence states in RVO 4 ( R = Y, Nd, Eu, Gd, Tb, Dy, Yb) have been investigated. The experimental spectra are interpreted using the results of the Xα discrete variational method calculations for orthovanadates. Transformations of electronic structure and covalency in the RVO 4 series are discussed. It is shown that lanthanide 4 f orbitals significantly mix with the O 2 pAO's and hybridize with the rare-earths 5 pAO's. The 5 p levels spin-orbital splitting in orthovanadates has been evaluated.

  9. The He(I) photoelectron spectra of lipid phosphatides

    NASA Astrophysics Data System (ADS)

    Ballard, R. E.; Jones, Jimmy; Read, Derek; Inchley, Andrew

    1986-12-01

    Complete layers of some lipids are formed spontaneously on the surfaces of solutions of sufficient concentration in certain solvents, e.g. phosphatidylcholine (egg lecithin) and phosphatidylinositol (wheat germ) dissolved in hydroxypropionitrile. The He(I) photoelectron spectra of phosphatides in such layers contain: (1) a broad band, assigned to alkyl groups, with maximum intensity at about 11 eV, (2) another broad band at about 8 eV, assigned to the PO -4 group with about 1 % of the band area of (1).

  10. On the analysis of photo-electron spectra

    SciTech Connect

    Gao, C.-Z.; Dinh, P.M.; Reinhard, P.-G.; Suraud, E.

    2015-09-15

    We analyze Photo-Electron Spectra (PES) for a variety of excitation mechanisms from a simple mono-frequency laser pulse to involved combination of pulses as used, e.g., in attosecond experiments. In the case of simple pulses, the peaks in PES reflect the occupied single-particle levels in combination with the given laser frequency. This usual, simple rule may badly fail in the case of excitation pulses with mixed frequencies and if resonant modes of the system are significantly excited. We thus develop an extension of the usual rule to cover all possible excitation scenarios, including mixed frequencies in the attosecond regime. We find that the spectral distributions of dipole, monopole and quadrupole power for the given excitation taken together and properly shifted by the single-particle energies provide a pertinent picture of the PES in all situations. This leads to the derivation of a generalized relation allowing to understand photo-electron yields even in complex experimental setups.

  11. Photoelectron spectra with QPROP and t-SURFF

    NASA Astrophysics Data System (ADS)

    Mosert, Volker; Bauer, Dieter

    2016-10-01

    Calculating strong-field, momentum-resolved photoelectron spectra (PES) from numerical solutions of the time-dependent Schrödinger equation (TDSE) is a very demanding task due to the large spatial excursions and drifts of electrons in intense laser fields. The time-dependent surface flux (t-SURFF) method for the calculation of PES [Tao and Scrinzi (2012)] allows to keep the numerical grid much smaller than the space over which the wavefunction would be spread at the end of the laser pulse. We present an implementation of the t-SURFF method in the well established TDSE-solver QPROP [Bauer and Koval (2006)]. QPROP efficiently propagates wavefunctions for single-active electron systems with spherically symmetric binding potentials in classical, linearly (along z) or elliptically (in the xy-plane) polarized laser fields in dipole approximation. Its combination with t-SURFF makes the simulation of PES feasible in cases where it is just too expensive to keep the entire wavefunction on the numerical grid, e.g., in the long-wavelength or long-pulse regime.

  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. Comparison of hard and soft x-ray photoelectron spectra of silicon

    NASA Astrophysics Data System (ADS)

    Offi, F.; Werner, W. S. M.; Sacchi, M.; Torelli, P.; Cautero, M.; Cautero, G.; Fondacaro, A.; Huotari, S.; Monaco, G.; Paolicelli, G.; Smekal, W.; Stefani, G.; Panaccione, G.

    2007-08-01

    A detailed comparison of the surface sensitivity of x-ray photoemission spectroscopy for hard and soft x rays is presented and discussed. Electron scattering parameters and their energy dependence are given for Si and two Si spectra are analyzed: a MgKα (hν=1253.6eV) excited spectrum of the Si2p and 2s lines and a hard x-ray excited spectrum (hν=5925eV) of the Si1s line. The differential inelastic scattering characteristics for Si are extracted from reflection electron energy loss spectra taken at energies of 1500 and 4000eV . Using these scattering characteristics and electron mean free paths from the literature, simulated spectra are compared with experiment. The experimental spectra are deconvoluted to give the true intrinsic line shape corresponding to the theoretical collision statistics when interference effects between intrinsic and extrinsic scattering are neglected. The magnitude of interference effects cannot be assessed by our analysis. Within the (unknown) uncertainty introduced by neglecting interference effects, it is possible to determine the relative intensity of intrinsic and extrinsic excitations. In this way, it is found that in the case of the soft x-ray excited photoelectron spectrum of the shallower electronic shells ( 2p and 2s ), intrinsic plasmon creation is rather weak, and the apparent asymmetric line shape of the spectrum might be interpreted as the fact that electron-hole pair creation dominates the intrinsic loss spectrum, while an alternative explanation in terms of surface core level shifted components is also proposed. For the deeper core electronic shell, probed with hard x rays, the opposite situation is observed: while intrinsic electron-hole pair creation was not observed, a strong contribution of intrinsic plasmon losses of about 30% was seen.

  14. Structural origin of Si-2p core-level shifts from Si(100)-c[4x2] surface: A spectral x-ray photoelectron diffraction study

    SciTech Connect

    Chen, X.; Tonner, B.P.; Denlinger, J.

    1997-04-01

    The authors have performed angle-resolved x-ray photoelectron diffraction (XPD) from a Si(100)-c(4x2) surface to study the structural origin of Si-2p core-level shifts. In the experiment, the highly resolved surface Si-2p core-level spectra were measured as a fine grid of hemisphere and photon energies, using the SpectroMicroscopy Facility {open_quotes}ultraESCA{close_quotes} instrument. By carefully decomposing the spectra into several surface peaks, the authors are able to obtain surface-atom resolved XPD patterns. Using a multiple scattering analysis, they derived a detailed atomic model for the Si(100)-c(4x2) surface. In this model, the asymmetric dimers were found tilted by 11.5 plus/minus 2.0 degrees with bond length of 2.32 plus/minus 0.05{angstrom}. By matching model XPD patterns to experiment, the authors can identify which atoms in the reconstructed surface are responsible for specific photoemission lines in the 2p spectrum.

  15. Photoelectron spectra of Si-substituted (chloromethyl)silanes

    SciTech Connect

    Zykov, B.G.; Khvostenko, V.I.; Voronkov, M.G.; Yur'ev, V.P.; Lomakin, G.S.; Suslova, E.N.

    1981-11-01

    Using photoelectron spectroscopy it has been established that in methylcholorosilanes (and in chlorosilanes) there is an interaction of the atomic 3d-orbitals of silicon with the unshared electron pair of the chlorine atom which influences the ionization potential of the molecule without however changing the order of molecular orbitals in comparison with tetramethylsilane. Using this method, we decided to study the possibility of an analogous interaction in molecules of trisubstituted (chloromethyl)silanes, in which the chlorine and silicon atoms are separated by a methylene group.

  16. 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.

  17. Revealing Deactivation Pathways Hidden in Time-Resolved Photoelectron Spectra

    PubMed Central

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

    2016-01-01

    Time-resolved photoelectron spectroscopy is commonly employed with the intention to monitor electronic excited-state dynamics occurring in a neutral molecule. With the help of theory, we show that when excited-state processes occur on similar time scales the different relaxation pathways are completely obscured in the total photoionization signal recorded in the experiment. Using non-adiabatic molecular dynamics and Dyson norms, we calculate the photoionization signal of cytosine and disentangle the transient contributions originating from the different deactivation pathways of its tautomers. In the simulations, the total signal from the relevant keto and enol tautomers can be decomposed into contributions either from the neutral electronic state populations or from the distinct mechanistic pathways across the multiple potential surfaces. The lifetimes corresponding to these contributions cannot be extracted from the experiment, thereby illustrating that new experimental setups are necessary to unravel the intricate non-adiabatic pathways occurring in polyatomic molecules after irradiation by light. PMID:27762396

  18. Revealing Deactivation Pathways Hidden in Time-Resolved Photoelectron Spectra

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Time-resolved photoelectron spectroscopy is commonly employed with the intention to monitor electronic excited-state dynamics occurring in a neutral molecule. With the help of theory, we show that when excited-state processes occur on similar time scales the different relaxation pathways are completely obscured in the total photoionization signal recorded in the experiment. Using non-adiabatic molecular dynamics and Dyson norms, we calculate the photoionization signal of cytosine and disentangle the transient contributions originating from the different deactivation pathways of its tautomers. In the simulations, the total signal from the relevant keto and enol tautomers can be decomposed into contributions either from the neutral electronic state populations or from the distinct mechanistic pathways across the multiple potential surfaces. The lifetimes corresponding to these contributions cannot be extracted from the experiment, thereby illustrating that new experimental setups are necessary to unravel the intricate non-adiabatic pathways occurring in polyatomic molecules after irradiation by light.

  19. Photoelectron Spectra of Aqueous Solutions from First Principles

    SciTech Connect

    Gaiduk, Alex P.; Govoni, Marco; Seidel, Robert; Skone, Jonathan H.; Winter, Bernd; Galli, Giulia

    2016-06-08

    We present a combined computational and experimental study of the photoelectron spectrum of a simple aqueous solution of NaCl. Measurements were conducted on microjets, and first-principles calculations were performed using hybrid functionals and many-body perturbation theory at the G0W0 level, starting with wave functions computed in ab initio molecular dynamics simulations. We show excellent agreement between theory and experiments for the positions of both the solute and solvent excitation energies on an absolute energy scale and for peak intensities. The best comparison was obtained using wave functions obtained with dielectric-dependent self-consistent and range-separated hybrid functionals. Our computational protocol opens the way to accurate, predictive calculations of the electronic properties of electrolytes, of interest to a variety of energy problems.

  20. Presence of monovalent oxygen anions in oxides demonstrated using X-ray photoelectron spectra

    SciTech Connect

    Wu, L. Q.; Li, Z. Z.; Tang, G. D. Qi, W. H.; Xue, L. C.; Ding, L. L.; Ge, X. S.; Li, S. Q.; Li, Y. C.

    2016-01-11

    The oxygen vacancy model has been used to explain the magnetic and electrical transport properties of dilute magnetic semiconductors and resistive switching. In particular, some authors have claimed that they found a symmetric peak corresponding to the oxygen vacancies in O1s photoelectron spectra. In this paper, using X-ray photoelectron spectra with argon ion etching, it is shown that this symmetric peak may also be interpreted as being related to O{sup 1−} anions, rather than to oxygen vacancies.

  1. Photoelectron spectra of dihalomethyl anions: Testing the limits of normal mode analysis

    NASA Astrophysics Data System (ADS)

    Vogelhuber, Kristen M.; Wren, Scott W.; McCoy, Anne B.; Ervin, Kent M.; Lineberger, W. Carl

    2011-05-01

    We report the 364-nm negative ion photoelectron spectra of CHX2- and CDX2-, where X = Cl, Br, and I. The pyramidal dihalomethyl anions undergo a large geometry change upon electron photodetachment to become nearly planar, 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 qualitatively the experimental data using physically reasonable parameters. Specifically, the harmonic normal mode analysis using Cartesian displacement coordinates results in much more C-H stretch excitation than is observed, leading to a simulated photoelectron spectrum that is much broader than that which is seen experimentally. A (2 + 1)-dimensional anharmonic coupled-mode analysis much better reproduces the observed vibrational structure. We obtain an estimate of the adiabatic electron affinity of each dihalomethyl radical studied. The electron affinity of CHCl2 and CDCl2 is 1.3(2) eV, of CHBr2 and CDBr2 is 1.9(2) eV, and of CHI2 and CDI2 is 1.9(2) eV. Analysis of the experimental spectra illustrates the limits of the conventional normal mode approach and shows the type of analysis required for substantial geometry changes when multiple modes are active upon photodetachment.

  2. High-resolution photoelectron spectra of the pyrimidine-type nucleobases

    NASA Astrophysics Data System (ADS)

    Fulfer, K. D.; Hardy, D.; Aguilar, A. A.; Poliakoff, E. D.

    2015-06-01

    High-resolution photoelectron spectra of the gas phase pyrimidine-type nucleobases, thymine, uracil, and cytosine, were collected using synchrotron radiation over the photon energy range 17 ≤ hν ≤ 150 eV. These data provide the highest resolution photoelectron spectra of thymine, uracil, and cytosine published to date. By comparing integrated regions of the energy dependent photoelectron spectra of thymine, the ionization potentials of the first four ionic states of thymine were estimated to be 8.8, 9.8, 10.3, and 10.8 eV. The thymine data also show evidence for low energy shape resonances in three of the outermost valence electronic states. Comparing the uracil spectrum with the thymine spectrum, the four outermost valence electronic states of uracil likely begin at binding energies 9.3, 9.9, 10.5, and 11.0 eV. High-resolution spectra indicate only one tautomeric form of cytosine contributes significantly to the spectrum with the four outermost valence electronic states beginning at binding energies 8.9, 9.9, 10.4, and 10.85 eV.

  3. High-resolution photoelectron spectra of the pyrimidine-type nucleobases.

    PubMed

    Fulfer, K D; Hardy, D; Aguilar, A A; Poliakoff, E D

    2015-06-14

    High-resolution photoelectron spectra of the gas phase pyrimidine-type nucleobases, thymine, uracil, and cytosine, were collected using synchrotron radiation over the photon energy range 17 ≤ hν ≤ 150 eV. These data provide the highest resolution photoelectron spectra of thymine, uracil, and cytosine published to date. By comparing integrated regions of the energy dependent photoelectron spectra of thymine, the ionization potentials of the first four ionic states of thymine were estimated to be 8.8, 9.8, 10.3, and 10.8 eV. The thymine data also show evidence for low energy shape resonances in three of the outermost valence electronic states. Comparing the uracil spectrum with the thymine spectrum, the four outermost valence electronic states of uracil likely begin at binding energies 9.3, 9.9, 10.5, and 11.0 eV. High-resolution spectra indicate only one tautomeric form of cytosine contributes significantly to the spectrum with the four outermost valence electronic states beginning at binding energies 8.9, 9.9, 10.4, and 10.85 eV.

  4. Temperature dependence of the photoelectron spectra of an evaporated violanthrene a film

    NASA Astrophysics Data System (ADS)

    Sato, N.; Seki, K.; Inokuchi, H.; Harada, Y.; Takahashi, T.

    1982-03-01

    A reversible temperature dependence of ultraviolet photoelectron spectra was observed for a polycrystalline violanthrene A thin film between 255 and 393 K. A decrease in the linewidth of the lowest-energy peak with decreasing temperature was understood in terms of the interaction of the photoinduced molecular cations with low-energy vibrational modes in the solid film just as in the case of cumene studied by Salaneck et al.

  5. Modelling the effect of nuclear motion on the attosecond time-resolved photoelectron spectra of ethylene

    NASA Astrophysics Data System (ADS)

    Crawford-Uranga, A.; De Giovannini, U.; Mowbray, D. J.; Kurth, S.; Rubio, A.

    2014-06-01

    Using time-dependent density functional theory we examine the energy, angular and time-resolved photoelectron spectra (TRPES) of ethylene in a pump-probe setup. To simulate TRPES we expose ethylene to an ultraviolet femtosecond pump pulse, followed by a time delayed extreme ultraviolet probe pulse. Studying the photoemission spectra as a function of this delay provides us direct access to the dynamic evolution of the molecule’s electronic levels. Further, by including the nuclei’s motion, we provide direct chemical insight into the chemical reactivity of ethylene. These results show how angular and energy resolved TRPES could be used to directly probe electron and nucleus dynamics in molecules.

  6. Photoelectron spectra and electronic structure of nitrogen analogues of boron β-diketonates

    NASA Astrophysics Data System (ADS)

    Tikhonov, Sergey A.; Vovna, Vitaliy I.; Borisenko, Aleksandr V.

    2016-07-01

    The electronic structure of the valence levels of seven nitrogen-containing boron complexes was investigated using methods of ultraviolet photoelectron spectroscopy and density functional theory. The ionization energies of π- and σ-levels were obtained from photoelectron spectra. The electronic structure of nitrogen-containing compounds was compared with the electronic structure of β-diketonates. It was shown the influence of various substituents on carbon and nitrogen atoms of six-membered ring on the electronic structure of complexes. The changes in the electronic structure after the substitution of atoms in condensed cycles have been identified. In order to compare the experimental vertical ionization energies IEi with Kohn-Sham orbital energies εi we used the analogue of Koopmans theorem and average amendment to the orbital energy of the electrons (δbari). For 26 electronic levels of seven studied complexes, the calculated values are in good accordance with experimental energy intervals between electron levels.

  7. Ultraviolet photoelectron spectra of Ce2@C80 and La2@C80

    NASA Astrophysics Data System (ADS)

    Miyazaki, Takafumi; Okita, Sosuke; Ohta, Tomona; Yagi, Hajime; Sumii, Ryohei; Okimoto, Haruya; Ito, Yasuhiro; Shinohara, Hisanori; Hino, Shojun

    2015-02-01

    Ultraviolet photoelectron spectra (UPS) of C80-Ih cage endohedral fullerenes, La2@C80 and Ce2@C80 were measured using a synchrotron radiation light source. The spectral onset energy of La2@C80 and Ce2@C80 is around 0.8-0.9 eV, which is smaller than that of empty C80-Ih. The UPS of these endohedral fullerenes are almost identical and are discussed with an aid of density functional theory (DFT) calculation. Simulation spectra calculated with using the results of the DFT calculations on an optimized structure starting from D3d geometry reproduces the UPS of La2@C80 and Ce2@C80 very well, which supports the theoretically proposed structure.

  8. 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.

  9. Is the Separable Propagator Perturbation Approach Accurate in Calculating Angle Resolved Photoelectron Diffraction Spectra?

    NASA Astrophysics Data System (ADS)

    Ng, C. N.; Chu, T. P.; Wu, Huasheng; Tong, S. Y.; Huang, Hong

    1997-03-01

    We compare multiple scattering results of angle-resolved photoelectron diffraction spectra between the exact slab method and the separable propagator perturbation method. In the slab method,footnote C.H. Li, A.R. Lubinsky and S.Y. Tong, Phys. Rev. B17, 3128 (1978). the source wave and multiple scattering within the strong scattering atomic layers are expanded in spherical waves while interlayer scattering is expressed in plane waves. The transformation between spherical waves and plane waves is done exactly. The plane waves are then matched across the solid-vacuum interface to a single outgoing plane wave in the detector's direction. The separable propagator perturbation approach uses two approximations: (i) A separable representation of the Green's function propagator and (ii) A perturbation expansion of multiple scattering terms. Results of c(2x2) S-Ni(001) show that this approximate method fails to converge due to the very slow convergence of the separable representation for scattering angles less than 90^circ. However, this method is accurate in the backscattering regime and may be applied to XAFS calculations.(J.J. Rehr and R.C. Albers, Phys. Rev. B41, 8139 (1990).) The use of this method for angle-resolved photoelectron diffraction spectra is substantially less reliable.

  10. Sample-morphology effects on x-ray photoelectron peak intensities. III. Simulated spectra of model core–shell nanoparticles

    SciTech Connect

    Powell, Cedric J.; Chudzicki, Maksymilian; Werner, Wolfgang S. M.; Smekal, Werner

    2015-09-15

    The National Institute of Standards and Technology database for the simulation of electron spectra for surface analysis has been used to simulate Cu 2p photoelectron spectra for four types of spherical copper–gold nanoparticles (NPs). These simulations were made to extend the work of Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)] and of Powell et al. [J. Vac. Sci. Technol. A 31, 021402 (2013)] who performed similar simulations for four types of planar copper–gold films. The Cu 2p spectra for the NPs were compared and contrasted with analogous results for the planar films and the effects of elastic scattering were investigated. The new simulations were made for a monolayer of three types of Cu/Au core–shell NPs on a Si substrate: (1) an Au shell of variable thickness on a Cu core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; (2) a Cu shell of variable thickness on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; and (3) an Au shell of variable thickness on a 1 nm Cu shell on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. For these three morphologies, the outer-shell thickness was varied until the Cu 2p{sub 3/2} peak intensity was the same (within 2%) as that found in our previous work with planar Cu/Au morphologies. The authors also performed similar simulations for a monolayer of spherical NPs consisting of a CuAu{sub x} alloy (also on a Si substrate) with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. In the latter simulations, the relative Au concentration (x) was varied to give the same Cu 2p{sub 3/2} peak intensity (within 2%) as that found previously. For each morphology, the authors performed simulations with elastic scattering switched on and off. The authors found that elastic-scattering effects were generally strong for the Cu-core/Au-shell and weak for the Au-core/Cu-shell NPs; intermediate elastic-scattering effects were found for the Au-core/Cu-shell/Au-shell NPs. The shell thicknesses required to give

  11. Method for estimating ionicities of oxides using O1s photoelectron spectra

    SciTech Connect

    Wu, L. Q.; Li, Z. Z.; Tang, G. D. Qi, W. H.; Xue, L. C.; Ge, X. S.; Ding, L. L.; Li, Y. C.; Li, S. Q.

    2015-09-15

    The average valence, V{sub alO}, of the oxygen anions in the perovskite oxide BaTiO{sub 3}, was found using O1s photoelectron spectra to be −1.55. This experimental result is close to the theoretical value for BaTiO{sub 3} (−1.63) calculated by Cohen [Nature 358, 136 (1992)] using density functional theory. Using the same approach, we obtained values of V{sub alO} for several monoxides, and investigated the dependence of V{sub alO} and the ionicity on the second ionization energy, V(M{sup 2+}), of the metal cation. We found that the dependence of the ionicity on V(M{sup 2+}) in this work is close to that reported by Phillips [Rev. Mod. Phys. 42, 317 (1970)]. We therefore suggest that O1s photoelectron spectrum measurements should be accepted as a general experimental method for estimating the ionicity and average valence of oxygen anions.

  12. Valence photoelectron spectra of an electron-beam-irradiated C60 film

    NASA Astrophysics Data System (ADS)

    Onoe, Jun; Nakao, Aiko; Hida, Akira

    2004-10-01

    Valence photoelectron spectra of an electron-beam (EB) irradiated C60 film, which exhibited metallic electron-transport properties in air at room temperature, are presented. The electronic structure of the C60 film became closer to that of graphite as the EB-irradiation time increased, and its density of states around the Fermi level was eventually greater than for the graphite. This suggests that the electronic structure of the C60 film changed from a semiconductor to a semimetal and/or metal by EB irradiation. Interestingly, the electronic structure remained metallic even after five days of air exposure, which is the reason for the metallic electron-transport property in our previous report [Appl. Phys. Lett. 82, 595 (2003)].

  13. [Photoelectron Spectra of CCl2-: Ab Initio Calculation and Franck-Condon Analysis].

    PubMed

    Wu, Jun

    2015-12-01

    Geometry optimization and harmonic vibrational frequency calculations were performed on the X¹A₁ state of CCl₂ and X²B₁ state of CCl₂⁻ at the B3LYP, MP2, CCSD levels. Franck-Condon analysis and spectral simulations were carried out on the photoelectron band of CCl₂⁻ including Duschinsky effects. The simulated spectra obtained are in excellent agreement with the experiment. Note that Duschinsky effect between bending vibration and the symmetric stretch modes should be considered in the CCl₂ (X¹A₁)-CCl₂⁻ (X²B₁) photodetachment process. By combining ab initio calculations with Franck-Condon analyses, the assignment of spectrum observed is firmly established to the X¹A₁-X²B₁ photodetachment process of the CCl₂⁻ radical, and the recommended geometric parameters of which in the literature are confirmed again base on ab initio theory and IFCA process.

  14. The delay time dependence of the photoelectron spectra and state populations of three-level ladder K2 molecule

    NASA Astrophysics Data System (ADS)

    Guo, Wei; Lu, Xingqiang; Wang, Xinlin

    2017-02-01

    The delay time dependence of photoelectron spectra and state populations of three-level ladder K2 molecule is investigated by pump-probe pulses via time-dependent wave packet approach. The periodical motion of the wave packet with oscillating period 500 fs results in the periodical variation of photoelectron spectra. The photoelectron spectra show Autler-Townes double splitting at zero delay time, and no splitting at positive delay time. The periodical change of state populations with delay time can be ascribed to the coupling effect between the two pulses. It is found that the selectivity of the state populations may be attained by regulating the delay time. The results can provide some important basis for realizing the optical control of molecules experimentally.

  15. The cyclopropene radical cation: Rovibrational level structure at low energies from high-resolution photoelectron spectra

    SciTech Connect

    Vasilatou, K.; Michaud, J. M.; Baykusheva, D.; Grassi, G.; Merkt, F.

    2014-08-14

    The cyclopropene radical cation (c-C{sub 3}H{sub 4}{sup +}) is an important but poorly characterized three-membered-ring hydrocarbon. We report on a measurement of the high-resolution photoelectron and photoionization spectra of cyclopropene and several deuterated isotopomers, from which we have determined the rovibrational energy level structure of the X{sup ~+} {sup 2}B{sub 2} ground electronic state of c-C{sub 3}H{sub 4}{sup +} at low energies for the first time. The synthesis of the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, so that the photoelectron spectra of deuterated samples are superpositions of the spectra of several isotopomers. The rotationally resolved spectra indicate a C{sub 2v}-symmetric R{sub 0} structure for the ground electronic state of c-C{sub 3}H{sub 4}{sup +}. Two vibrational modes of c-C{sub 3}H{sub 4}{sup +} are found to have vibrational wave numbers below 300 cm{sup −1}, which is surprising for such a small cyclic hydrocarbon. The analysis of the isotopic shifts of the vibrational levels enabled the assignment of the lowest-frequency mode (fundamental wave number of ≈110 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to the CH{sub 2} torsional mode (ν{sub 8}{sup +}, A{sub 2} symmetry) and of the second-lowest-frequency mode (≈210 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to a mode combining a CH out-of-plane with a CH{sub 2} rocking motion (ν{sub 15}{sup +}, B{sub 2} symmetry). The potential energy along the CH{sub 2} torsional coordinate is flat near the equilibrium structure and leads to a pronounced anharmonicity.

  16. Photoelectron spectra of small LaOn- clusters: decreasing electron affinity upon increasing the number of oxygen atoms

    NASA Astrophysics Data System (ADS)

    Klingeler, R.; Lüttgens, G.; Pontius, N.; Rochow, R.; Bechthold, P. S.; Neeb, M.; Eberhardt, W.

    We present mass selected photoelectron spectra of small lanthanum oxide cluster anions LaOn- (n=1-5) which have been generated in a laser vaporization cluster source. The electron affinity of the lanthanum oxide clusters drops continuously with the number of chemisorbed oxygen atoms as revealed from the anion photoelectron spectra. The decreasing electron affinity behaves contrary to several other metal oxide clusters. The geometry of some of the measured clusters are discussed in comparsion with configuration interaction and density functional calculations using a Gaussian94 program package.

  17. Theoretical study of IR and photoelectron spectra of small gallium-arsenide clusters

    SciTech Connect

    Pouchan, Claude; Marchal, Rémi; Hayashi, Shinsuke

    2015-01-22

    Relative stabilities of small Ga{sub n}As{sub m} clusters, as well as their structural electronic and vibrational properties, were computed and analysed using a CCSD(T) reference method since experimental data in this area are sparse or unknown. With the aim of investigating larger clusters, we explored several DFT functionals and basis sets able to mimic the reliable CCSD(T) approach. Among them, the PBE0/SBKJC+sp,d appears as the most efficient to describe the structural and vibrational properties since average differences of about 0.042Å and 5.1cm{sup −1} were obtained for bond lengths and fundamental vibrational frequencies, respectively for the first small clusters [1] of the series found from our GSAM method [2]. As further test, this model is used in order to investigate and revisit an experimental IR spectrum of Ga{sub n}As{sub m} mixture previously published by Li et al. [3]. More complicated is the difficulty which arises in the electronic description due to the presence of numerous low lying electronic states nearly degenerated to correctly describe the electronic structure. The case of Ga{sub 2}As will be discussed and the photoelectron spectra of the Ga{sub 2}As anion reanalyzed on the ground of our calculations [4] comparatively to the experimental spectra obtained by Neumark and co-workers [5].

  18. Self-consistent modelling of X-ray photoelectron spectra from air-exposed polycrystalline TiN thin films

    NASA Astrophysics Data System (ADS)

    Greczynski, G.; Hultman, L.

    2016-11-01

    We present first self-consistent modelling of x-ray photoelectron spectroscopy (XPS) Ti 2p, N 1s, O 1s, and C 1s core level spectra with a cross-peak quantitative agreement for a series of TiN thin films grown by dc magnetron sputtering and oxidized to different extent by varying the venting temperature Tv of the vacuum chamber before removing the deposited samples. So-obtained film series constitute a model case for XPS application studies, where certain degree of atmosphere exposure during sample transfer to the XPS instrument is unavoidable. The challenge is to extract information about surface chemistry without invoking destructive pre-cleaning with noble gas ions. All TiN surfaces are thus analyzed in the as-received state by XPS using monochromatic Al Kα radiation (hν = 1486.6 eV). Details of line shapes and relative peak areas obtained from deconvolution of the reference Ti 2p and N 1 s spectra representative of a native TiN surface serve as an input to model complex core level signals from air-exposed surfaces, where contributions from oxides and oxynitrides make the task very challenging considering the influence of the whole deposition process at hand. The essential part of the presented approach is that the deconvolution process is not only guided by the comparison to the reference binding energy values that often show large spread, but in order to increase reliability of the extracted chemical information the requirement for both qualitative and quantitative self-consistency between component peaks belonging to the same chemical species is imposed across all core-level spectra (including often neglected O 1s and C 1s signals). The relative ratios between contributions from different chemical species vary as a function of Tv presenting a self-consistency check for our model. We propose that the cross-peak self-consistency should be a prerequisite for reliable XPS peak modelling as it enhances credibility of obtained chemical information, while relying

  19. Photoelectron spectra of CeO{sup −} and Ce(OH){sub 2}{sup −}

    SciTech Connect

    Ray, Manisha; Felton, Jeremy A.; Kafader, Jared O.; Topolski, Josey E.; Jarrold, Caroline Chick

    2015-02-14

    The photoelectron spectrum of CeO{sup −} exhibits what appears to be a single predominant electronic transition over an energy range in which numerous close-lying electronic states of CeO neutral are well known. The photoelectron spectrum of Ce(OH){sub 2}{sup −}, a molecule in which the Ce atom shares the same formal oxidation state as the Ce atom in CeO{sup −}, also exhibits what appears to be a single transition. From the spectra, the adiabatic electron affinities of CeO and Ce(OH){sub 2} are determined to be 0.936 ± 0.007 eV and 0.69 ± 0.03 eV, respectively. From the electron affinity of CeO, the CeO{sup −} bond dissociation energy was determined to be 7.7 eV, 0.5 eV lower than the neutral bond dissociation energy. The ground state orbital occupancies of both CeO{sup −} and Ce(OH){sub 2}{sup −} are calculated to have 4f 6s{sup 2} Ce{sup +} superconfigurations, with open-shell states having 4f5d6s superconfiguration predicted to be over 1 eV higher in energy. Low-intensity transitions observed at higher electron binding energies in the spectrum of CeO{sup −} are tentatively assigned to the {sup 1}Σ{sup +} (Ω = 0) state of CeO with the Ce{sup +2}⍰6s{sup 2} superconfiguration.

  20. Ab Initio Determinations of Photoelectron Spectra Including Vibronic Features: An Upper-Level Undergraduate Physical Chemistry Laboratory

    ERIC Educational Resources Information Center

    Lord, Richard L.; Davis, Lisa; Millam, Evan L.; Brown, Eric; Offerman, Chad; Wray, Paul; Green, Susan M. E.

    2008-01-01

    We present a first-principles determination of the photoelectron spectra of water and hypochlorous acid as a laboratory exercise accessible to students in an undergraduate physical chemistry course. This paper demonstrates the robustness and user-friendliness of software developed for the Franck-Condon factor calculation. While the calculator is…

  1. X-ray photoelectron spectra structure and chemical bond nature in NpO2

    NASA Astrophysics Data System (ADS)

    Teterin, Yu. A.; Teterin, A. Yu.; Ivanov, K. E.; Ryzhkov, M. V.; Maslakov, K. I.; Kalmykov, St. N.; Petrov, V. G.; Enina, D. A.

    2014-01-01

    Quantitative analysis was done of the x-ray photoelectron spectra structure in the binding energy (BE) range of 0 to ˜35 eV for neptunium dioxide (NpO2) valence electrons. The BEs and structure of the core electronic shells (˜35-1250 eV) as well as the relativistic discrete variation calculation results for the finite fragment of the NpO2 lattice and the data of other authors were taken into account. The experimental data show that the many-body effects and the multiplet splitting contribute to the spectral structure much less than the effects of formation of the outer (0-˜15 eV) and the inner (˜15-˜35 eV) valence molecular orbitals (OVMO and IVMO, respectively). The filled Np 5f electronic states were shown to form in the NpO2 valence band. The Np 6p electrons participate in formation of both the IVMO and the OVMO (bands). The filled Np 6p3/2 and the O 2s electronic shells were found to take the maximum part in the IVMO formation. The MO composition and the sequence order in the BE range 0-˜35 eV in NpO2 were established. The experimental and theoretical data allowed a quantitative MO scheme for NpO2, which is fundamental for both understanding the chemical bond nature in neptunium dioxide and the interpretation of other x-ray spectra of NpO2.

  2. Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

    SciTech Connect

    Buchta, D.; Stienkemeier, F.; Mudrich, M.; Krishnan, S. R.; Moshammer, R.; Brauer, N. B.; Drabbels, M.; O’Keeffe, P.; Coreno, M.; Devetta, M.; Di Fraia, M.; Callegari, C.; Richter, R.; Prince, K. C.; Ullrich, J.

    2013-08-28

    The ionization dynamics of pure He nanodroplets irradiated by Extreme ultraviolet radiation is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence spectroscopy. We present photoelectron energy spectra and angular distributions measured in coincidence with the most abundant ions He{sup +}, He{sub 2}{sup +}, and He{sub 3}{sup +}. Surprisingly, below the autoionization threshold of He droplets, we find indications for multiple excitation and subsequent ionization of the droplets by a Penning-like process. At high photon energies we observe inelastic collisions of photoelectrons with the surrounding He atoms in the droplets.

  3. Vibrationally high-resolved electronic spectra of MCl2 (M = C, Si, Ge, Sn, Pb) and photoelectron spectra of MCl2-

    NASA Astrophysics Data System (ADS)

    Ran, Yibin; Pang, Min; Shen, Wei; Li, Ming; He, Rongxing

    2016-10-01

    We systematically studied the vibrational-resolved electronic spectra of group IV dichlorides using the Franck-Condon approximation combined with the Duschinsky and Herzberg-Teller effects in harmonic and anharmonic frameworks (only the simulation of absorption spectra includes the anharmonicity). Calculated results showed that the band shapes of simulated spectra are in accordance with those of the corresponding experimental or theoretical ones. We found that the symmetric bend mode in progression of absorption is the most active one, whereas the main contributor in photoelectron spectra is the symmetric stretching mode. Moreover, the Duschinsky and anharmonic effects exert weak influence on the absorption spectra, except for PbCl2 molecule. The theoretical insights presented in this work are significant in understanding the photophysical properties of MCl2 (M = C, Si, Ge, Sn, Pb) and studying the Herzberg-Teller and the anharmonic effects on the absorption spectra of new dichlorides of this main group.

  4. Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories.

    PubMed

    Huang, Yan R; Ning, Chuan G; Deng, Jing K; Deleuze, Michael S

    2008-05-07

    A complete study of the valence electronic structure and related electronic excitation properties of cyclopentene in its C(s) ground state geometry is presented. Ionization spectra obtained from this compound by means of photoelectron spectroscopy (He I and He II) and electron momentum spectroscopy have been analyzed in details up to electron binding energies of 30 eV using one-particle Green's function (1p-GF) theory along with the outer-valence (OVGF) and the third-order algebraic diagrammatic construction [ADC(3)] schemes. The employed geometries derive from DFT/B3LYP calculations in conjunction with the aug-cc-pVTZ basis set, and closely approach the structures inferred from experiments employing microwave spectroscopy or electron diffraction in the gas phase. The 1p-GF/ADC(3) calculations indicate that the orbital picture of ionization breaks down at electron binding energies larger than approximately 17 eV in the inner-valence region, and that the outer-valence 7a' orbital is also subject to a significant dispersion of the ionization intensity over shake-up states. This study confirms further the rule that OVGF pole strengths smaller than 0.85 foretell a breakdown of the orbital picture of ionization at the ADC(3) level. Spherically averaged (e, 2e) electron momentum distributions at an electron impact energy of 1200 eV that were experimentally inferred from an angular analysis of EMS intensities have been interpreted by comparison with accurate simulations employing ADC(3) Dyson orbitals. Very significant discrepancies were observed with momentum distributions obtained from several outer-valence ionization bands using standard Kohn-Sham orbitals.

  5. Band strength in photoelectron spectra and photoionization cross sections of pyrrole and of conformation isomers of 1,1-dimethylhydrazine

    SciTech Connect

    Kiro, Z. A.; Dykhanov, S. M.; Zverev, V. V.

    1988-09-01

    The dependence of partial photoionization cross sections of the 1,1-dimethylhydrazine molecule on the spatial characteristics (bond lengths, valence and dihedral angles) has been studied. The presence of a gauche-conformation isomer in the gaseous phase has been established, as confirmed by a comparison of the photoionization cross section ratios for the corresponding molecular orbitals with the relative band strengths in photoelectron spectra.

  6. Effect of the Content of Ammonium Dichromate in Dichromated Gelatin on Cr 2 P 3 2 X-Ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Xiong, Liang-Wen; Peng, Bi-Xian

    1999-01-01

    The effect of the content of (NH 4 ) 2 Cr 2 O 7 in dichromated gelatin (DCG) on the binding energy of the Cr 2 P 3 2 level was studied with x-ray photoelectron spectroscopy. It was found that the binding energy of the Cr 2 P 3 2 level of chromium in DCG is lower than that of pure ammonium dichromate. When the content of (NH 4 ) 2 Cr 2 O 7 is not greater than 1%, the chromium in DCG has only one state, near 577.5 eV; when this content is between 1% and 20%, the chromium in DCG has two states, near 577.5 and 579.1 eV. The relative contents of these two states change with the content of (NH 4 ) 2 Cr 2 O 7 . As the (NH 4 ) 2 Cr 2 O 7 content increases, the relative content of the state near 577.5 eV decreases almost linearly, but its absolute content first increases, then reaches a maximum at 10% (NH 4 ) 2 Cr 2 O 7 , and finally decreases. In addition, the absolute content of the state near 577.5 eV changes very slowly between 5% and 15% (NH 4 ) 2 Cr 2 O 7 . According to these experimental results and holography data reported in the literature, it is inferred that the chromium of the state near 577.5 eV is the chromium that forms the latent image center after exposure and then forms the hologram after development. As a result the basis for the optimum content of (NH 4 ) 2 Cr 2 O 7 is found, and an approach to increasing sensitivity is suggested through this experiment.

  7. Effect of the content of ammonium dichromate in dichromated gelatin on Cr 2P3/2 X-ray photoelectron spectroscopy.

    PubMed

    Xiong, L W; Peng, B X

    1999-01-10

    The effect of the content of (NH(4))(2)Cr(2)O(7) in dichromated gelatin (DCG) on the binding energy of the Cr 2P(3/2) level was studied with x-ray photoelectron spectroscopy. It was found that the binding energy of the Cr 2P(3/2) level of chromium in DCG is lower than that of pure ammonium dichromate. When the content of (NH(4))(2)Cr(2)O(7) is not greater than 1%, the chromium in DCG has only one state, near 577.5 eV; when this content is between 1% and 20%, the chromium in DCG has two states, near 577.5 and 579.1 eV. The relative contents of these two states change with the content of (NH(4))(2)Cr(2)O(7). As the (NH(4))(2)Cr(2)O(7) content increases, the relative content of the state near 577.5 eV decreases almost linearly, but its absolute content first increases, then reaches a maximum at ~10% (NH(4))(2)Cr(2)O(7), and finally decreases. In addition, the absolute content of the state near 577.5 eV changes very slowly between 5% and 15% (NH(4))(2)Cr(2)O(7). According to these experimental results and holography data reported in the literature, it is inferred that the chromium of the state near 577.5 eV is the chromium that forms the latent image center after exposure and then forms the hologram after development. As a result the basis for the optimum content of (NH(4))(2)Cr(2)O(7) is found, and an approach to increasing sensitivity is suggested through this experiment.

  8. Franck-Condon profiles in photodetachment-photoelectron spectra of ? and ? based on vibrational configuration interaction wavefunctions

    NASA Astrophysics Data System (ADS)

    Huh, Joonsuk; Neff, Michael; Rauhut, Guntram; Berger, Robert

    2010-02-01

    Explicitly electron correlating coupled cluster calculations, CCSD(T)-F12a, were performed to determine three-dimensional potential energy hypersurfaces of disulphanide and disulphanyl in an automated approach. Surfaces for different electronic states were used in a Watson rovibrational Hamiltonian ansatz to obtain the correlated anharmonic vibrational wavefunctions. Subsequently the anharmonic Franck-Condon overlap integrals were evaluated. The computed Franck-Condon profiles were compared to experimental photodetachment-photoelectron spectra and confirm essentially the assignments made previously. The profiles indicate, however, additional weaker, and as of yet unresolved, additional features.

  9. Quantitative x-ray photoelectron spectroscopy: Quadrupole effects, shake-up, Shirley background, and relative sensitivity factors from a database of true x-ray photoelectron spectra

    SciTech Connect

    Seah, M. P.; Gilmore, I. S.

    2006-05-01

    An analysis is provided of the x-ray photoelectron spectroscopy (XPS) intensities measured in the National Physical Laboratory (NPL) XPS database for 46 solid elements. This present analysis does not change our previous conclusions concerning the excellent correlation between experimental intensities, following deconvolving the spectra with angle-averaged reflection electron energy loss data, and the theoretical intensities involving the dipole approximation using Scofield's cross sections. Here, more recent calculations for cross sections by Trzhaskovskaya et al. involving quadrupole terms are evaluated and it is shown that their cross sections diverge from the experimental database results by up to a factor of 5. The quadrupole angular terms lead to small corrections that are close to our measurement limit but do appear to be supported in the present analysis. Measurements of the extent of shake-up for the 46 elements broadly agree with the calculations of Yarzhemsky et al. but not in detail. The predicted constancy in the shake-up contribution by Yarzhemsky et al. implies that the use of the Shirley background will lead to a peak area that is a constant fraction of the true peak area including the shake-up intensities. However, the measured variability of the shake-up contribution makes the Shirley background invalid for quantification except for situations where the sensitivity factors are from reference samples similar to those being analyzed.

  10. X-ray emission and photoelectron spectra of Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3}

    SciTech Connect

    Kurmaev, E.Z.; Korotin, M.A.; Galakhov, V.R.; Finkelstein, L.D.; Zabolotzky, E.I.; Efremova, N.N.; Lobachevskaya, N.I.; Stadler, S.; Ederer, D.L.; Callcott, T.A.; Zhou, L.; Moewes, A.; Bartkowski, S.; Neumann, M.; Matsuno, J.; Mizokawa, T.; Fujimori, A.; Mitchell, J.

    1999-05-01

    The results of measurements of x-ray photoelectron (XPS), x-ray emission (XES), and x-ray absorption spectra and local spin-density approximation band structure (LSDA) calculations of Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} are presented. The excitation energy dependence of Mn L{sub 2,3} and O K{alpha} x-ray emission spectra of Pr{sub 0.5}Sr{sub 0.5}MnO{sub 3} is measured using tunable synchrotron radiation. The XES measurements yielded no photon energy dependence for the O K{alpha} spectra, but the Mn L{sub 2,3} spectra yielded inelastic scattering losses of 2 and 6 eV, corresponding to features in the structure of the occupied part of the valence band. Comparing XPS and XES measurements with LSDA band-structure calculations, one concludes that the electronic structure of the compound consists mainly of Mn 3d and O 2p states. States of 3d character localized at the Mn site predominate near the top of the valence band (VB). Some differences in the Mn 3d distribution in this part of the XPS valence band and Mn L{sub 3} XES with {ital d} symmetry due to spin-selection rules that govern the Mn L{sub 3} XES. In addition, the Mn 3d states distribution is hybridized with the O 2p part of the VB. Mn L{sub 3} XES spectra were determined relative to the Fermi energy by assuming normal x-ray emission begins from the lowest level of the p{sup 5}d{sup n+1}L intermediate state (which is the Mn 2p ionizatation threshold). From the local spin-density approximation, the orbital character of the Mn 3d electrons can be assigned e{sub g} symmetry at the top of the valence band T{sub 2g} in the central part of the VB, and equal contributions of e{sub g} and t{sub 2g} states at the bottom of the valence band. {copyright} {ital 1999} {ital The American Physical Society}

  11. Calculated photoelectron spectra of isotopomers of the propargyl radical (H 2C 3H): An explicitly correlated coupled cluster study

    NASA Astrophysics Data System (ADS)

    Botschwina, Peter; Oswald, Rainer

    2010-12-01

    Explicitly correlated coupled cluster theory at the (U)CCSD(T∗)-F12a level has been employed to study the vibrational structure of the first two bands of the low-temperature photoelectron spectra of four different isotopomers of the propargyl radical with C 2v symmetry (H 2C 3H, H 2C 3D, D 2C 3H, and D 2C 3D). A five-dimensional anharmonic model is employed to calculate the peak positions and relative intensities. While the first band of the PE spectra of all four isotopomers is dominated by the adiabatic peak, the second band shows a progression in the pseudoantisymmetric CC stretching vibration v3 with relative intensities of 100:68:23:5:1 for n = 0-4 in the case of the most abundant isotopomer.

  12. Linear dimerized Se chains in cancrinite nanochannels: X-ray diffraction and photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Poborchii, V. V.; Sato, M.; Shchukarev, A. V.

    1997-09-01

    Cancrinite crystals containing adsorbed selenium in 1-dimensional nanochannels (Can-Se) have been examined by X-ray diffraction, X-ray photoelectron spectroscopy and polarized infrared spectroscopy. It is found that adsorbed selenium forms Se 22- anions substituting OH - groups inside channels. Se 22- dimers are located in the center of the cancrinite channel and oriented along the channel. They interact with Na + cations located in the channels and with each other giving rise to a linear chain incommensurate to the cancrinite matrix. The arrangement of the dimers in the chain has been found to be dependent on the temperature.

  13. Ab initio study of 2p core-level x-ray photoemission spectra in ferromagnetic transition metals

    NASA Astrophysics Data System (ADS)

    Takahashi, Manabu; Igarashi, Jun-Ichi

    2012-02-01

    We study the 2p core-level x-ray photoemission spectra in ferromagnetic transition metals, Fe, Co, and Ni using a recently developed ab initio method. The excited final states are set up by distributing electrons on the one-electron states calculated under the fully screened potential in the presence of the core hole. We evaluate the overlap between these excited states and the ground state by using one-electron wave functions, and obtain the spectral curves as a function of binding energy. The calculated spectra reproduce well the observed spectra displaying interesting dependence on the element and on the spin of the removed core electron. The origin of the spectral shapes is elucidated in terms of the one-electron states screening the core hole. The magnetic splitting of the threshold energy is also estimated by using the coherent potential approximation within the fully screened potential approximation. It decreases more rapidly than the local spin moment with moving from Fe to Ni. It is estimated to be almost zero for Ni despite the definite local moment about 0.6μB, in agreement with the experiment.

  14. Attosecond electronic and nuclear quantum photodynamics of ozone monitored with time and angle resolved photoelectron spectra

    PubMed Central

    Decleva, Piero; Quadri, Nicola; Perveaux, Aurelie; Lauvergnat, David; Gatti, Fabien; Lasorne, Benjamin; Halász, Gábor J.; Vibók, Ágnes

    2016-01-01

    Recently we reported a series of numerical simulations proving that it is possible in principle to create an electronic wave packet and subsequent electronic motion in a neutral molecule photoexcited by a UV pump pulse within a few femtoseconds. We considered the ozone molecule: for this system the electronic wave packet leads to a dissociation process. In the present work, we investigate more specifically the time-resolved photoelectron angular distribution of the ozone molecule that provides a much more detailed description of the evolution of the electronic wave packet. We thus show that this experimental technique should be able to give access to observing in real time the creation of an electronic wave packet in a neutral molecule and its impact on a chemical process. PMID:27819356

  15. Laser fields at flat interfaces: II. Plasmon resonances in aluminium photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Raşeev, G.

    2012-07-01

    Using the model derived in paper I [G. Raşeev, Eur. Phys. J. D 66, 167 (2012)], this work presents calculations of the photoelectron spectrum (PES) of low index aluminium surfaces in the 10-30 eV region. The laser is p or transverse magnetic linearly polarized incident on a flat structureless surface and its fields are modeled in I using the vector potential in the temporal gauge. This model uses a tensor and non-local isotropic (TNLI) susceptibility and solves the classical Ampère-Maxwell equation through the use of the vector potential from the electron density-coupled integro-differential equations (VPED-CIDE). The PE cross sections are the squares of the PE transition moments calculated using the VPED-CIDE vector potential function of the penetration coordinate. The PES is obtained in a one step model using either the Fermi golden rule or the Weisskopf-Wigner (WW) expressions. The WW cross section PES compares favorably with the experimental angle and energy resolved photoelectron yield (AERPY) spectrum of Levinson et al. [Phys. Rev. Lett. 43, 952 (1979)], Levinson and Plummer [Phys. Rev. B 24, 628 (1981)] for Al(001) and of Barman et al. [Phys. Rev. B 58, R4285 (1998)], Barman [Curr. Sci. 88, 54 (2005)] for Al(111) surfaces. As in the experiment, our theoretical AERPY displays the multipole surface plasmon resonance at 11.32/12.75 eV for Al(001)/Al(111), mainly due to the surface contribution |⟨ψf|p·A|ψi⟩|2, the bulk plasmon minimum at 15 eV and the two single particle excitation resonances at about 16 and 22 eV. The nature of the plasmon resonances of the PES is analyzed using the reflectance, the electron density induced by the laser and Feibelman's parameter d⊥ all introduced in paper I.

  16. Photoelectron spectra and structure of the Mn{sub n}{sup −} anions (n = 2–16)

    SciTech Connect

    Gutsev, G. L. Weatherford, C. A.; Ramachandran, B. R.; Gutsev, L. G.; Zheng, W.-J.; Thomas, O. C.; Bowen, Kit H.

    2015-07-28

    Photoelectron spectra of the Mn{sub n}{sup −} anion clusters (n = 2–16) are obtained by anion photoelectron spectroscopy. The electronic and geometrical structures of the anions are computed using density functional theory with generalized gradient approximation and a basis set of triple-ζ quality. The electronic and geometrical structures of the neutral Mn{sub n} clusters have also been computed to estimate the adiabatic electron affinities. The average absolute difference between the computed and experimental vertical detachment energies of an extra electron is about 0.2 eV. Beginning with n = 6, all lowest total energy states of the Mn{sub n}{sup −} anions are ferrimagnetic with the spin multiplicities which do not exceed 8. The computed ionization energies of the neutral Mn{sub n} clusters are in good agreement with previously obtained experimental data. According to the results of our computations, the binding energies of Mn atoms are nearly independent on the cluster charge for n > 6 and possess prominent peaks at Mn{sub 13} and Mn{sub 13}{sup −} in the neutral and anionic series, respectively. The density of states obtained from the results of our computations for the Mn{sub n}{sup −} anion clusters show the metallic character of the anion electronic structures.

  17. Quantum-classical calculations of X-ray photoelectron spectra of polymers-Polymethyl methacrylate revisited.

    PubMed

    Löytynoja, T; Harczuk, I; Jänkälä, K; Vahtras, O; Ågren, H

    2017-03-28

    In this work, we apply quantum mechanics/molecular mechanics (QM/MM) approach to predict core-electron binding energies and chemical shifts of polymers, obtainable via X-ray photoelectron spectroscopy(XPS), using polymethyl methacrylate as a demonstration example. The results indicate that standard parametrizations of the quantum part (basis sets, level of correlation) and the molecular mechanics parts (decomposed charges, polarizabilities, and capping technique) are sufficient for the QM/MM model to be predictive for XPS of polymers. It is found that the polymer environment produces contributions to the XPS binding energies that are close to monotonous with the number of monomer units, totally amounting to approximately an eV decrease in binding energies. In most of the cases, the order of the shifts is maintained, and even the relative size of the differential shifts is largely preserved. The coupling of the internal core-hole relaxation to the polymer environment is found to be weak in each case, amounting only to one or two tenths of an eV. The main polymeric effect is actually well estimated already at the frozen orbital level of theory, which in turn implies a substantial computational simplification. These conclusions are best represented by the cases where the ionized monomer and its immediate surrounding are treated quantum mechanically. If the QM region includes only a single monomer, a couple of anomalies are spotted, which are referred to the QM/MM interface itself and to the neglect of a possible charge transfer.

  18. Understanding Chemical versus Electrostatic Shifts in X-ray Photoelectron Spectra of Organic Self-Assembled Monolayers

    PubMed Central

    2016-01-01

    The focus of the present article is on understanding the insight that X-ray photoelectron spectroscopy (XPS) measurements can provide when studying self-assembled monolayers. Comparing density functional theory calculations to experimental data on deliberately chosen model systems, we show that both the chemical environment and electrostatic effects arising from a superposition of molecular dipoles influence the measured core-level binding energies to a significant degree. The crucial role of the often overlooked electrostatic effects in polar self-assembled monolayers (SAMs) is unambiguously demonstrated by changing the dipole density through varying the SAM coverage. As a consequence of this effect, care has to be taken when extracting chemical information from the XP spectra of ordered organic adsorbate layers. Our results, furthermore, imply that XPS is a powerful tool for probing local variations in the electrostatic energy in nanoscopic systems, especially in SAMs. PMID:26937264

  19. Derivation of dielectric function and inelastic mean free path from photoelectron energy-loss spectra of amorphous carbon surfaces

    NASA Astrophysics Data System (ADS)

    David, Denis; Godet, Christian

    2016-11-01

    Photoelectron Energy Loss Spectroscopy (PEELS) is a highly valuable non destructive tool in applied surface science because it gives access to both chemical composition and electronic properties of surfaces, including the near-surface dielectric function. An algorithm is proposed for real materials to make full use of experimental X-ray photoelectron spectra (XPS). To illustrate the capabilities and limitations of this algorithm, the near-surface dielectric function ε(ℏω) of a wide range of amorphous carbon (a-C) thin films is derived from energy losses measured in XPS, using a dielectric response theory which relates ε(ℏω) and the bulk plasmon (BP) loss distribution. Self-consistent separation of bulk vs surface plasmon excitations, deconvolution of multiple BP losses and evaluation of Bethe-Born sensitivity factors for bulk and surface loss distributions are crucial to obtain several material parameters: (1) energy loss function for BP excitation, (2) dielectric function of the near-surface material (3-5 nm depth sensitivity), (3) inelastic mean free path, λP (E0), for plasmon excitation, (4) surface excitation parameter, (5) effective number NEFF of valence electrons participating in the plasma oscillation. This photoelectron energy loss spectra analysis has been applied to a-C and a-C:H films grown by physical and chemical methods with a wide range of (sp3/sp2 + sp3) hybridization, optical gap and average plasmon energy values. Different methods are assessed to accurately remove the photoemission peak tail at low loss energy (0-10 eV) due to many-body interactions during the photo-ionization process. The σ + π plasmon excitation represents the main energy-loss channel in a-C; as the C atom density decreases, λP (970 eV) increases from 1.22 nm to 1.6 nm, assuming a cutoff plasmon wavenumber given by a free electron model. The π-π* and σ-σ* transitions observed in the retrieved dielectric function are discussed as a function of the average (sp3/sp

  20. Angle-Resolved Photoelectron Spectrometry Studies of the Autoionization of the 2s{sup 2}2p {sup 2}P Triply Excited State of Atomic Lithium: Experimental Results and R -Matrix Calculations

    SciTech Connect

    Diehl, S.; Cubaynes, D.; Zhou, H. L.; VoKy, L.; Wuilleumier, F. J.; Kennedy, E. T.; Bizau, J. M.; Manson, S. T.; Morgan, T. J.; Blancard, C.

    2000-02-21

    We have measured the angle-resolved energy dependence of the electrons emitted over the energy range of the triply excited 2s{sup 2}2p P{sup 2} lithium resonance using synchrotron radiation. We have also calculated the behavior of the angular distribution parameter {beta} using the R -matrix approximation. Experimental and theoretical results are in good agreement and show deep minima in the 1s2p P{sup 1,} {sup 3} ionic channels. The energy at which the minima occur does not coincide with the resonance energy, but is shifted towards higher energy. (c) 2000 The American Physical Society.

  1. Double-slit experiment with a polyatomic molecule: vibrationally resolved C 1s photoelectron spectra of acetylene

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Thomas, T. D.; Plésiat, E.; Liu, X.-J.; Miron, C.; Lischke, T.; Prümper, G.; Sakai, K.; Ouchi, T.; Püttner, R.; Sekushin, V.; Tanaka, T.; Hoshino, M.; Tanaka, H.; Decleva, P.; Ueda, K.; Martín, F.

    2012-03-01

    We report the first evidence for double-slit interferences in a polyatomic molecule, which we have observed in the experimental carbon 1s photoelectron spectra of acetylene (or ethyne). The spectra have been measured over the photon energy range of 310-930 eV and show prominent oscillations in the intensity ratios σg(υ)/σu(υ) for the vibrational quantum numbers υ = 0,1 and for the ratios σs(υ = 1)/σs(υ = 0) for the symmetry s = g,u. The experimental findings are in very good agreement with ab initio density functional theory (DFT) calculations and are compatible with the Cohen-Fano mechanism of coherent emission from two equivalent atomic centers. This interpretation is supported by the qualitative predictions of a simple model in which the effect of nuclear recoil is taken into account to the lowest order. Our results confirm the delocalized character of the core hole created in the primary photoionization event and demonstrate that intramolecular core-hole coherence can survive the decoherent influence associated with the asymmetric nuclear degrees of freedom which are characteristic of polyatomic molecules.

  2. 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.

  3. Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

    NASA Astrophysics Data System (ADS)

    Greczynski, G.; Primetzhofer, D.; Lu, J.; Hultman, L.

    2017-02-01

    We present the first measurements of x-ray photoelectron spectroscopy (XPS) core level binding energies (BE:s) for the widely-applicable group IVb-VIb polycrystalline transition metal nitrides (TMN's) TiN, VN, CrN, ZrN, NbN, MoN, HfN, TaN, and WN as well as AlN and SiN, which are common components in the TMN-based alloy systems. Nitride thin film samples were grown at 400 °C by reactive dc magnetron sputtering from elemental targets in Ar/N2 atmosphere. For XPS measurements, layers are either (i) Ar+ ion-etched to remove surface oxides resulting from the air exposure during sample transfer from the growth chamber into the XPS system, or (ii) in situ capped with a few nm thick Cr or W overlayers in the deposition system prior to air-exposure and loading into the XPS instrument. Film elemental composition and phase content is thoroughly characterized with time-of-flight elastic recoil detection analysis (ToF-E ERDA), Rutherford backscattering spectrometry (RBS), and x-ray diffraction. High energy resolution core level XPS spectra acquired with monochromatic Al Kα radiation on the ISO-calibrated instrument reveal that even mild etching conditions result in the formation of a nitrogen-deficient surface layer that substantially affects the extracted binding energy values. These spectra-modifying effects of Ar+ ion bombardment increase with increasing the metal atom mass due to an increasing nitrogen-to-metal sputter yield ratio. The superior quality of the XPS spectra obtained in a non-destructive way from capped TMN films is evident from that numerous metal peaks, including Ti 2p, V 2p, Zr 3d, and Hf 4f, exhibit pronounced satellite features, in agreement with previously published spectra from layers grown and analyzed in situ. In addition, the N/metal concentration ratios are found to be 25-90% higher than those obtained from the corresponding ion-etched surfaces, and in most cases agree very well with the RBS and ToF-E ERDA values. The N 1 s BE:s extracted from

  4. Structural chemistry of polycyclic heteroaromatic compounds. Part XI. Photoelectron spectra and electronic structures of tetracyclic hetarenes of the triphenylene type

    NASA Astrophysics Data System (ADS)

    Rademacher, Paul; Heinemann, Christoph; Jänsch, Sylvia; Kowski, Klaus; Weiß, Michael E.

    2000-05-01

    The UV photoelectron spectra of several tetracyclic heteroaromatic compounds ( 2- 9) which are π-isoelectronic with triphenylene ( 1) have been recorded and analysed making use of semiempirical AM1 and PM3 as well as ab initio/DFT B3LYP calculations. In one series of compounds ( 2- 7), the peripheral benzene rings of 1 are successively substituted by thiophene rings that are either [b]- or [c]-annellated with the central benzene unit. In 2- 7 only marginal shifts are found for most of the IPs of electrons. In the benzotrithiophenes 5- 7, a systematic variation is displayed by IP( π7). Compared to 1, the π electron system of benzo[c]trithiophene ( 7) is approximately two times as much destabilized as in the isomers 5 and 6 with [b]annellated thiophene rings. The IP[ n(S)] values of the thiophene derivatives 2- 7 indicate that these orbitals are clearly destabilized relative to thiophene. The same holds for the n(O) orbital of the furane derivative 9 in comparison with that of furane. In 9, only the higher π MOs ( π7- π9) are destabilized whereas the lower levels ( π1- π4) are stabilized, and those in between ( π5- π6) remain essentially unshifted. In the pyrrole derivative 8, all π MOs are substantially destabilized by about 0.5-1.6 eV relative to 1.

  5. Site-specific recoil-induced effects on inner-shell photoionization of linear triatomic molecules: N 1 s photoelectron spectra of N2 O

    NASA Astrophysics Data System (ADS)

    Krivosenko, Yu. S.; Pavlychev, A. A.

    2016-11-01

    We investigate hard X-ray ionization of linear triatomic molecules accenting recoil-induced effects on the dynamics of molecular frame. This dynamics is studied within the two-springs and harmonic approximations. The mode-channel relationship connecting the excitations of vibrational, rotational and translational degrees of freedom with the Σ → Σ and Σ → Π photoionization channels is applied to compute the N 1s-1 photoelectron spectra of molecular N2 O for various photon energies. The distinct ionized-site- and molecular-orientation-specific changes in the vibration structure of the 1 s photoelectron lines of terminal and central nitrogen atoms are revealed and discussed.

  6. Spectroscopy of the simplest Criegee intermediate CH2OO: simulation of the first bands in its electronic and photoelectron spectra.

    PubMed

    Lee, Edmond P F; Mok, Daniel K W; Shallcross, Dudley E; Percival, Carl J; Osborn, David L; Taatjes, Craig A; Dyke, John M

    2012-09-24

    CH(2)OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas-phase studies on CH(2)OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH(2)OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH(2)OO. In order to encourage more direct studies on CH(2)OO and other Criegee intermediates, the electronic and photoelectron spectra of CH(2)OO have been simulated using high level electronic structure calculations and Franck-Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH(2)OO were calculated with TDDFT, EOM-CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low-lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH(2) OO corresponds to the B(1)A' ← X(1)A' absorption. It is a broad band in the region 250-450 nm showing extensive structure in vibrational modes involving O-O stretching and C-O-O bending. Evidence is presented to show that the electronic absorption spectrum of CH(2)OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH(2)OO was prepared in this earlier work from the reaction of CH(2)I with O(2) and that the assignment of the observed spectrum solely to CH(2)IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH(2)OO consists of two overlapping vibrationally structured bands corresponding to one-electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense

  7. Interpretation of the photoelectron, ultraviolet, and vacuum ultraviolet photoabsorption spectra of bromobenzene by ab initio configuration interaction and DFT computations

    SciTech Connect

    Palmer, Michael H. Ridley, Trevor E-mail: vronning@phys.au.dk E-mail: marcello.coreno@elettra.eu E-mail: malgorzata.biczysko@sns.it; Hoffmann, Søren Vrønning E-mail: vronning@phys.au.dk E-mail: marcello.coreno@elettra.eu E-mail: malgorzata.biczysko@sns.it Jones, Nykola C. E-mail: vronning@phys.au.dk E-mail: marcello.coreno@elettra.eu E-mail: malgorzata.biczysko@sns.it; Coreno, Marcello E-mail: vronning@phys.au.dk E-mail: marcello.coreno@elettra.eu E-mail: malgorzata.biczysko@sns.it; Grazioli, Cesare; Zhang, Teng; and others

    2015-10-28

    New photoelectron, ultraviolet (UV), and vacuum UV (VUV) spectra have been obtained for bromobenzene by synchrotron study with higher sensitivity and resolution than previous work. This, together with use of ab initio calculations with both configuration interaction and time dependent density functional theoretical methods, has led to major advances in interpretation. The VUV spectrum has led to identification of a considerable number of Rydberg states for the first time. The Franck-Condon (FC) analyses including both hot and cold bands lead to identification of the vibrational structure of both ionic and electronically excited states including two Rydberg states. The UV onset has been interpreted in some detail, and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. In a similar way, the 6 eV absorption band which is poorly resolved is analysed in terms of the presence of two ππ* states of {sup 1}A{sub 1} (higher oscillator strength) and {sup 1}B{sub 2} (lower oscillator strength) symmetries, respectively. The detailed analysis of the vibrational structure of the 2{sup 2}B{sub 1} ionic state is particularly challenging, and the best interpretation is based on equation-of-motion-coupled cluster with singles and doubles computations. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene. The equilibrium structures of the 3b{sub 1}3s and 6b{sub 2}3s (valence shell numbering) Rydberg states have been obtained and compared with the corresponding ionic limit structures.

  8. 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.

  9. Interpretation of the photoelectron, ultraviolet, and vacuum ultraviolet photoabsorption spectra of bromobenzene by ab initio configuration interaction and DFT computations.

    PubMed

    Palmer, Michael H; Ridley, Trevor; Hoffmann, Søren Vrønning; Jones, Nykola C; Coreno, Marcello; de Simone, Monica; Grazioli, Cesare; Zhang, Teng; Biczysko, Malgorzata; Baiardi, Alberto; Peterson, Kirk

    2015-10-28

    New photoelectron, ultraviolet (UV), and vacuum UV (VUV) spectra have been obtained for bromobenzene by synchrotron study with higher sensitivity and resolution than previous work. This, together with use of ab initio calculations with both configuration interaction and time dependent density functional theoretical methods, has led to major advances in interpretation. The VUV spectrum has led to identification of a considerable number of Rydberg states for the first time. The Franck-Condon (FC) analyses including both hot and cold bands lead to identification of the vibrational structure of both ionic and electronically excited states including two Rydberg states. The UV onset has been interpreted in some detail, and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. In a similar way, the 6 eV absorption band which is poorly resolved is analysed in terms of the presence of two ππ* states of (1)A1 (higher oscillator strength) and (1)B2 (lower oscillator strength) symmetries, respectively. The detailed analysis of the vibrational structure of the 2(2)B1 ionic state is particularly challenging, and the best interpretation is based on equation-of-motion-coupled cluster with singles and doubles computations. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene. The equilibrium structures of the 3b13s and 6b23s (valence shell numbering) Rydberg states have been obtained and compared with the corresponding ionic limit structures.

  10. Correlations Between Variations in Solar EUV and Soft X-Ray Irradiance and Photoelectron Energy Spectra Observed on Mars and Earth

    NASA Technical Reports Server (NTRS)

    Peterson, W. K.; Brain, D. A.; Mitchell, D. L.; Bailey, S. M.; Chamberlin, P. C.

    2013-01-01

    Solar extreme ultraviolet (EUV; 10-120 nm) and soft X-ray (XUV; 0-10 nm) radiation are major heat sources for the Mars thermosphere as well as the primary source of ionization that creates the ionosphere. In investigations of Mars thermospheric chemistry and dynamics, solar irradiance models are used to account for variations in this radiation. Because of limited proxies, irradiance models do a poor job of tracking the significant variations in irradiance intensity in the EUV and XUV ranges over solar rotation time scales when the Mars-Sun-Earth angle is large. Recent results from Earth observations show that variations in photoelectron energy spectra are useful monitors of EUV and XUV irradiance variability. Here we investigate photoelectron energy spectra observed by the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and the FAST satellite during the interval in 2005 when Earth, Mars, and the Sun were aligned. The Earth photoelectron data in selected bands correlate well with calculations based on 1 nm resolution observations above 27 nm supplemented by broadband observations and a solar model in the 0-27 nm range. At Mars, we find that instrumental and orbital limitations to the identifications of photoelectron energy spectra in MGS/ER data preclude their use as a monitor of solar EUV and XUV variability. However, observations with higher temporal and energy resolution obtained at lower altitudes on Mars might allow the separation of the solar wind and ionospheric components of electron energy spectra so that they could be used as reliable monitors of variations in solar EUV and XUV irradiance than the time shifted, Earth-based, F(10.7) index currently used.

  11. Correlations between variations in solar EUV and soft X-ray irradiance and photoelectron energy spectra observed on Mars and Earth

    NASA Astrophysics Data System (ADS)

    Peterson, W. K.; Brain, D. A.; Mitchell, D. L.; Bailey, S. M.; Chamberlin, P. C.

    2013-11-01

    extreme ultraviolet (EUV; 10-120 nm) and soft X-ray (XUV; 0-10 nm) radiation are major heat sources for the Mars thermosphere as well as the primary source of ionization that creates the ionosphere. In investigations of Mars thermospheric chemistry and dynamics, solar irradiance models are used to account for variations in this radiation. Because of limited proxies, irradiance models do a poor job of tracking the significant variations in irradiance intensity in the EUV and XUV ranges over solar rotation time scales when the Mars-Sun-Earth angle is large. Recent results from Earth observations show that variations in photoelectron energy spectra are useful monitors of EUV and XUV irradiance variability. Here we investigate photoelectron energy spectra observed by the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and the FAST satellite during the interval in 2005 when Earth, Mars, and the Sun were aligned. The Earth photoelectron data in selected bands correlate well with calculations based on 1 nm resolution observations above 27 nm supplemented by broadband observations and a solar model in the 0-27 nm range. At Mars, we find that instrumental and orbital limitations to the identifications of photoelectron energy spectra in MGS/ER data preclude their use as a monitor of solar EUV and XUV variability. However, observations with higher temporal and energy resolution obtained at lower altitudes on Mars might allow the separation of the solar wind and ionospheric components of electron energy spectra so that they could be used as reliable monitors of variations in solar EUV and XUV irradiance than the time shifted, Earth-based, F10.7 index currently used.

  12. Investigation on the interfacial chemical state and band alignment for the sputtering-deposited CaF2/p-GaN heterojunction by angle-resolved X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiong; Liao, Meiyong; Sumiya, Masatomo; Koide, Yasuo; Sang, Liwen

    2016-11-01

    The interfacial chemical state and the band alignment of the sputtering-deposited CaF2/p-GaN hetero-structure were investigated by angle-resolved X-ray photoelectron spectroscopy. The dependence of Ga 3p core-level positions on the collection angles proves that the downward band bending of p-GaN is reduced from 1.51 to 0.85 eV after the deposition of CaF2, which may be due to the reduction of Mg-Ga-O-related interface states by the oxygen-free deposition of CaF2. The band gap of sputtering-deposited CaF2 is estimated to be about 7.97 eV with a potential gradient of 0.48 eV obtained by the variation of the Ca 2p3/2 position on different collection angles. By taking into account the p-GaN surface band bending and potential gradient in the CaF2 layer, large valence and conduction band offsets of 2.66 ± 0.20 and 1.92 ± 0.20 eV between CaF2 and p-GaN are obtained. These results indicate that CaF2 is a promising gate dielectric layer on the p-GaN for the application of metal-insulator-semiconductor devices.

  13. X-Ray Photoelectron Spectra of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} Processed by EATPAH Technique

    SciTech Connect

    Mishra, D. K.; Dash, S.; Samantray, S.; Pradhan, S. K.; Das, J.; Roul, B. K.; Varma, S.

    2008-10-23

    La{sub 0.67}Ca{sub 0.33}MnO{sub 3}(LCMO) colossal magnetoresistance (CMR) materials were sintered to highly dense products by an extended arc thermal plasma assisted heating (EATPAH) technique within a short sintering time of 2.5 minutes as compared to conventional long range heating schedule (few hours of time). 2.5 minutes plasma sintered LCMO showed enhanced T{sub c}(272 K), which is closed to T{sub IM}(275 K)[1] as compared to the conventional sintered LCMO sample. Specimens are analyzed by X-ray Photoelectron Spectra (XPS) and electron probe microstructure analysis (EPMA) to get idea on elemental distribution and valence spectra of all the elements present in the specimen. The binding energy of La, Ca and Mn are analogous to the conventional sintered LCMO and to the reference spectra [2].

  14. Crystal structure and vibrational spectra of tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na 4Mg 2(H 2P 2O 7) 4·8H 2O

    NASA Astrophysics Data System (ADS)

    Harcharras, M.; Ennaciri, A.; Assaaoudi, H.; Mattei, G.; D'Orazio, V.; Moliterni, A. G. G.; Capitelli, F.

    2003-04-01

    A tetrasodium dimagnesium dihydrogen diphosphate octahydrate Na 4Mg 2(H 2P 2O 7) 4·8H 2O was synthesized. It crystallizes in the monoclinic system, space group P2 1/ m (no. 11), Z=4, and its unit-cell parameters are: a=8.0445(3) Å, b=11.5244(5) Å, c=9.0825(4) Å, β=113.1401(2)°, V=774.28(6) Å 3. The structure was determined by single-crystal X-ray diffractometry and refined to a R index of 0.0294 (w R=0.0727) for 1878 independent reflections with I>2 σ( I). The framework is made by the alternance of layers of MgO 6/NaO 6 octahedra and double tetrahedra PO 4 along b-axis. Such layers are characterized by the presence of strong hydrogen bonds. (H 2P 2O 7) 2- anions exhibit bent eclipsed conformation. Besides, the crystal was analyzed by FT-IR and micro-Raman vibrational spectroscopy. No coincidences of the majority of the Raman and infrared spectra bands of Na 4Mg 2(H 2P 2O 7) 4·8H 2O confirms a centrosymmetric structure of this material. The vibrational spectra confirm the bent POP configuration in this compound.

  15. Fingerprints of the hydrogen bond in the photoemission spectra of croconic acid condensed phase: An x-ray photoelectron spectroscopy and ab-initio study

    SciTech Connect

    Bisti, F.; Stroppa, A.; Picozzi, S.; Ottaviano, L.

    2011-05-07

    The electronic structure of Croconic Acid in the condensed phase has been studied by comparing core level and valence band x-ray photoelectron spectroscopy experiments and first principles density functional theory calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional and the GW approximation. By exploring the photoemission spectra for different deposition thicknesses, we show how the formation of the hydrogen bond network modifies the O 1s core level lineshape. Moreover, the valence band can be explained only if the intermolecular interactions are taken into account in the theoretical approach.

  16. Application of high-resolution photoelectron spectroscopy: Vibrational resolved C 1s and O 1s spectra of CO adsorbed on Ni(100)

    SciTech Connect

    Foehlisch, A.; Nilsson, A.; Martensson, N.

    1997-04-01

    There are various effects which determine the line shape of a core-level electron spectrum. These are due to the finite life-time of the core hole, inelastic scattering of the outgoing photoelectron, electronic shake-up and shake-off processes and vibrational excitations. For free atoms and molecules the different contributions to the observed line shapes can often be well separated. For solids, surfaces and adsorbates the line shapes are in general much broader and it has in the past been assumed that no separation of the various contributions can be made. In the present report the authors will show that this is indeed not the case. Surprisingly, the vibrational fine structure of CO adsorbed on Ni(100) can be resolved in the C 1s and O 1s electron spectra. This was achieved by the combination of highly monochromatized soft X-rays from B18.0 with a high resolution Scienta 200 mm photoelectron spectrometer. X-ray photoelectron spectroscopy (XPS) with tunable excitation energy yields as a core level spectroscopy atomic and site-specific information. The presented measurements allow for a determination of internuclear distances and potential energy curves in corehole ionized adsorbed molecules. The authors analysis of the c(2x2) phase CO/Ni(100) on {open_quotes}top{close_quotes} yielded a vibrational splitting of 217 +/- 2 meV for C 1s ionization. For O 1s ionization a splitting of 173 +/- 8 meV was found.

  17. Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

    SciTech Connect

    Wang, Jing; Liang, Le; Zhang, Lanting E-mail: lmsun@sjtu.edu.cn; Sun, Limin E-mail: lmsun@sjtu.edu.cn; Hirano, Shinichi

    2014-10-28

    Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearly determined to be 0 and −3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ∼11.2 eV and ∼24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.

  18. A four-component Fock-space coupled cluster investigation of the XMn(CO)5, (X = Cl, Br and I) photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Nikoobakht, Behnam; Siebert, Max; Pernpointner, Markus

    2017-01-01

    In this work we readdress the theoretical interpretation of the XMn(CO)5, X = Cl, Br, I photoelectron spectra by applying four-component Fock-space coupled cluster methods for their calculation. The final state characterization was based on group theoretical considerations of the contributing metal and ligand orbitals and the applied electronic structure methods extend earlier studies based on less demanding approaches. Energy level diagrams show the effect of spin-orbit (SO) coupling starting from scalar-relativistic results and especially for the heavy representative IMn(CO)5 a sizeable influence of the iodine p spinors on the spectral features and nonadditivity effects of SO and electron correlation contributions could be observed.

  19. Above-threshold ionization of Mg by linearly and circularly polarized laser fields: Origin of the subpeaks in the photoelectron energy spectra

    SciTech Connect

    Nakajima, Takashi; Buica, Gabriela

    2006-08-15

    We theoretically investigate above-threshold ionization of Mg by linearly and circularly polarized fs laser pulses. We find that the above-threshold ionization peaks are accompanied by small subpeaks for both linearly and circularly polarized pulses. We interpret the physical origin of the subpeaks as above-threshold ionization from the low-lying bound states which are far off-resonantly excited by the spectral wing of the pulse. This interpretation is confirmed by our comparative numerical studies. Furthermore, we provide a clear explanation of why this kind of subpeak in the photoelectron energy spectra has not been reported for smaller photon energies with Mg and other commonly used atoms such as H and rare gas atoms.

  20. Structural investigation on Ge{sub x}Sb{sub 10}Se{sub 90−x} glasses using x-ray photoelectron spectra

    SciTech Connect

    Wei, Wen-Hou; Xiang, Shen; Xu, Si-Wei; Wang, Rong-Ping; Fang, Liang

    2014-05-14

    The structure of Ge{sub x}Sb{sub 10}Se{sub 90−x} glasses (x = 7.5, 10, 15, 20, 25, 27.5, 30, and 32.5 at. %) has been investigated by x-ray photoelectron spectroscopy (XPS). Different structural units have been extracted and characterized by decomposing XPS core level spectra, the evolution of the relative concentration of each structural unit indicates that, the relative contributions of Se-trimers and Se-Se-Ge(Sb) structure decrease with increasing Ge content until they become zero at chemically stoichiometric glasses of Ge{sub 25}Sb{sub 10}Se{sub 65}, and then the homopolar bonds like Ge-Ge and Sb-Sb begin to appear in the spectra. Increase of homopolar bonds will extend band-tails into the gap and narrow the optical band gap. Thus, the glass with a stoichiometric composition generally has fewer defective bonds and larger optical bandgap.

  1. Are carboxyl groups the most acidic sites in amino acids? Gas-phase acidities, photoelectron spectra, and computations on tyrosine, p-hydroxybenzoic acid, and their conjugate bases.

    PubMed

    Tian, Zhixin; Wang, Xue-Bin; Wang, Lai-Sheng; Kass, Steven R

    2009-01-28

    Deprotonation of tyrosine in the gas phase was found to occur preferentially at the phenolic site, and the conjugate base consists of a 70:30 mixture of phenoxide and carboxylate anions at equilibrium. This result was established by developing a chemical probe for differentiating these two isomers, and the presence of both ions was confirmed by photoelectron spectroscopy. Equilibrium acidity measurements on tyrosine indicated that deltaG(acid)(o) = 332.5 +/- 1.5 kcal mol(-1) and deltaH(acid)(o) = 340.7 +/- 1.5 kcal mol(-1). Photoelectron spectra yielded adiabatic electron detachment energies of 2.70 +/- 0.05 and 3.55 +/- 0.10 eV for the phenoxide and carboxylate anions, respectively. The H/D exchange behavior of deprotonated tyrosine was examined using three different alcohols (CF3CH2OD, C6H5CH2OD, and CH3CH2OD), and incorporation of up to three deuterium atoms was observed. Two pathways are proposed to account for these results, and all of the experimental findings are supplemented with B3LYP/aug-cc-pVDZ and G3B3 calculations. In addition, it was found that electrospray ionization of tyrosine from a 3:1 (v/v) CH3OH/H2O solution using a commercial source produces a deprotonated [M-H]- anion with the gas-phase equilibrium composition rather than the structure of the ion that exists in aqueous media. Electrospray ionization from acetonitrile, however, leads largely to the liquid-phase (carboxylate) structure. A control molecule, p-hydroxybenzoic acid, was found to behave in a similar manner. Thus, the electrospray conditions that are employed for the analysis of a compound can alter the isomeric composition of the resulting anion.

  2. Relating the 4s{sigma}{sup -1} inner-valence photoelectron spectrum of HBr with the Br 3d{sup -1}5l{lambda} resonant Auger spectra: An approach to the assignments

    SciTech Connect

    Puettner, R.; Hu, Y. F.; Bancroft, G. M.; Kivimaeki, A.; Jurvansuu, M.; Aksela, H.; Aksela, S.

    2003-09-01

    The high resolution Br 4s{sigma}{sup -1} photoelectron spectrum of HBr is presented together with the resonant Auger spectra resulting from excitations from the 3d core levels to the low-n Rydberg orbitals 5s{sigma}, 5p{sigma}, and 5p{pi}. The very complex spectra can be broadly assigned using two observations. First, the energy splittings of the 4p{pi}{sup -2}5s and 4p{pi}{sup -2}5p states are very similar to the splittings of the 4p{pi}{sup -2}({sup 1}{sigma}{sup +},{sup 1}{delta}, and {sup 3}{sigma}{sup -}) final states seen previously in the normal Auger spectra. Second, the {sup 2}{sigma}{sup +} states, which are the dominant correlation satellites in the complex 4s{sigma}{sup -1} photoelectron spectrum, are often enhanced in the 5s{sigma} resonance Auger spectra. Electron correlation and spin-orbit interaction in the final states are important to understand all of these spectra. Unlike the normal Auger spectra, vibrational excitations play only a minor role in these spectra, showing that the 5s and 5p Rydberg orbitals have some bonding character.

  3. Opacity of iron, nickel, and copper plasmas in the x-ray wavelength range: Theoretical interpretation of 2p-3d absorption spectra

    SciTech Connect

    Blenski, T.; Loisel, G.; Poirier, M.; Thais, F.; Arnault, P.; Caillaud, T.; Fariaut, J.; Gilleron, F.; Pain, J.-C.; Porcherot, Q.; Reverdin, C.; Silvert, V.; Villette, B.; Bastiani-Ceccotti, S.; Turck-Chieze, S.; Foelsner, W.; Gaufridy de Dortan, F. de

    2011-09-15

    This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm{sup 3}. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code sco and with the fine-structure atomic physics codes hullac and fac. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code rcg has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by sco. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code scric. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the {Delta}n=0 absorption in medium-Z plasmas for astrophysical applications.

  4. Experimental electron energy-loss spectra and cross sections for the 4/2/S - 4/2/P transition in Zn II

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Newell, W. R.

    1982-01-01

    Electron energy-loss spectra and differential cross sections are reported for inelastic scattering from Zn II. Measurements were carried out in a crossed electron beam-ion beam apparatus, at incident electron energies of 30, 40, 50, 60, 75, 85, and 100 eV, and at a scattering angle of 14 deg. The present results are the first reported measurements of inelastic electron scattering from an ion.

  5. Theoretical interpretation for 2p - nd absorption spectra of iron, nickel, and copper in X-ray range measured at the LULI2000 facility

    NASA Astrophysics Data System (ADS)

    Poirier, M.; Arnault, P.; Bastiani-Ceccotti, S.; Blenski, T.; de Gaufridy de Dortan, F.; Gilleron, F.; Loisel, G.; Pain, J.-C.; Porcherot, Q.; Reverdin, C.; Silvert, V.; Thais, F.; Turck-Chièze, S.

    2013-11-01

    The 2p - nd absorption structures in medium Z elements present a valuable benchmark for atomic models since they exhibit a complex dependence on temperature and density. For these transitions lying in the X-ray range, one observes a competition between the spin-orbit splitting and the broadening associated to the excitation of complex structures. Detailed opacity codes based on the HULLAC or FAC suites agree with the statistical code SCO; but in iron computations predict higher peak absorption than measured. An addition procedure on opacities calculated with detailed codes is proposed and successfully tested.

  6. Size-induced changes in optical and X-ray photoelectron spectra of GaN nanoparticles deposited at lower substrate temperature.

    PubMed

    Mann, A K; Varandani, D; Mehta, B R; Malhotra, L K; Shivaprasad, S M

    2005-11-01

    This study reports the synthesis of GaN nanoparticles having hexagonal structure by a simple technique of activated reactive evaporation with substrates kept at comparatively lower temperatures than usually reported. By varying the substrate temperature from 30 degrees C to 350 degrees C, it is possible to vary nanoparticle sizes from 5-30 nm. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirm the formation of GaN on quartz and silicon substrates at room temperature. The observed size dependent shift in energy position, large increase in full width at half maximum value of Ga 3d and N 1s X-ray photoelectron spectroscopy peaks and blue shift in the optical absorption edge are related to nanoparticle character.

  7. Photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Fadley, Charles S.

    1987-01-01

    The use of core-level photoelectron diffraction for structural studies of surfaces and epitaxial overlayers is discussed. Photoelectron diffraction is found to provide several direct and rather unique types of structural information, including the sites and positions of adsorbed atoms; the orientations of small molecules or fragments bound to surfaces; the orientations, layer thicknesses, vertical lattice constants, and degrees of short-range order of epitaxial or partially-epitaxial overlayers; and the presence of short-range spin order in magnetic materials. Specific systems considered are the reaction of oxygen with Ni(001), the growth of epitaxial Cu on Ni(001), the well-defined test case S on Ni(001), and short-range spin order in the antiferromagnet KMnF3. A rather straightforward single scattering cluster (SSC) model also proves capable of quantitatively describing such data, particularly for near-surface species and with corrections for spherical-wave scattering effects and correlated vibrational motion. Promising new directions in such studies also include measurements with high angular resolution and the expanded use of synchrotron radiation.

  8. Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol.

    PubMed

    Demircioğlu, Zeynep; Albayrak, Çiğdem; Büyükgüngör, Orhan

    2014-07-15

    A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C15H15N1O2, reveals that the structure is adopted to its E configuration about the azomethine C=N double bond. The compound adopts a enol-imine tautomeric form with a strong intramolecular O-H⋯N hydrogen bond. The single crystal X-ray diffraction analysis at 296K crystallizes in the monoclinic space group P21/c with a = 13.4791(11) Å, b = 6.8251(3) Å, c = 18.3561(15) Å, α = 90°, β = 129.296(5)°, γ = 90° and Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried out by FT-IR and UV-vis spectrometry. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the relocation of the electron density were determined. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties were also investigated. In addition, frontier molecular orbitals analysis have been performed from the optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S), have been investigated.

  9. Quantum mechanics/molecular mechanics modeling of photoelectron spectra: the carbon 1s core-electron binding energies of ethanol-water solutions.

    PubMed

    Löytynoja, T; Niskanen, J; Jänkälä, K; Vahtras, O; Rinkevicius, Z; Ågren, H

    2014-11-20

    Using ethanol-water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute-solvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics model-electrostatic, polarization, and van der Waals-with atom or bond granulation of the corresponding MM charge and polarizability force-fields. The role of extramolecular charge transfer screening of the core-hole and explicit hydrogen bonding is studied by extending the QM core to cover the first solvation shell. The results are compared to those obtained from pure electrostatic and polarizable continuum models. Particularly, the dependence of the carbon 1s binding energies with respect to the ethanol concentration is studied. Our results indicate that QM/MM can be used as an all-encompassing model to study photoelectron binding energies and chemical shifts in solvent environments.

  10. Photoelectron Microscopy

    NASA Astrophysics Data System (ADS)

    King, Paul Lawrence

    1992-01-01

    This thesis describes the theory and first operations of a novel synchrotron-based imaging system allowing photoemission spectroscopy (XPS or ESCA) to be performed at lateral resolutions better than 10 microns. Originally developed in David Turner's group at Oxford, the MicroESCA^ {rm TM} relies on the diverging magnetic field from a 7 Tesla superconducting solenoid to project photoemitted electrons from a sample to an imaging detector located 1.5 meters away. The diverging magnetic field converts off-axis momentum to forward momentum and electrons form a magnified image at the detector while moving nearly parallel to one another. Because of this "parallelization", a planar gridded retarding field analyzer achieves excellent energy resolution with only minor impact on image quality. The thesis begins with an overview of the various techniques by which high lateral resolution photoelectron spectroscopy can be achieved. This is followed by a theoretical treatment of magnetic projection leading to predictions of lateral and energy resolution. Chapter 3 documents resolution tests and known deviations from ideality. Image forming capabilities and energy resolution of the retarding field analyzer are demonstrated at near-theoretical limits. Practical limitations of the microscope are recognized in the form of poor signal to noise ratios of core level images which originate from a combination of the narrow dynamic range of the imaging detector and the large backgrounds inherent in retarding field spectroscopy of solids. Chapter 4 describes an interactive image processing and interpretation scheme that relies on scatter plots and principal component analysis to reduce the dimensionality of retarding field image sets and improve image signal to noise. This procedure is generally applicable to all imaging spectroscopies and an example from SEM-based energy dispersive spectroscopy (EDS) is included. In a final results section, variations in the surface Fermi levels on cleaved

  11. Cation profiling of passive films on stainless steel formed in sulphuric and acetic acid by deconvolution of angle-resolved X-ray photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Högström, Jonas; Fredriksson, Wendy; Edstrom, Kristina; Björefors, Fredrik; Nyholm, Leif; Olsson, Claes-Olof A.

    2013-11-01

    An approach for determining depth gradients of metal-ion concentrations in passive films on stainless steel using angle-resolved X-ray photoelectron spectroscopy (ARXPS) is described. The iterative method, which is based on analyses of the oxidised metal peaks, provides increased precision and hence allows faster ARXPS measurements to be carried out. The method was used to determine the concentration depth profiles for molybdenum, iron and chromium in passive films on 316L/EN 1.4432 stainless steel samples oxidised in 0.5 M H2SO4 and acetic acid diluted with 0.02 M Na2B4O7 · 10H2O and 1 M H2O, respectively. The molybdenum concentration in the film is pin-pointed to the oxide/metal interface and the films also contained an iron-ion-enriched surface layer and a chromium-ion-dominated middle layer. Although films of similar composition and thickness (i.e., about 2 nm) were formed in the two electrolytes, the corrosion currents were found to be three orders of magnitude larger in the acetic acid solution. The differences in the layer composition, found for the two electrolytes as well as different oxidation conditions, can be explained based on the oxidation potentials of the metals and the dissolution rates of the different metal ions.

  12. H2CN+ and H2CNH+: New insight into the structure and dynamics from mass-selected threshold photoelectron spectra

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    In this paper, we reinvestigate the photoionization of nitrogen containing reactive intermediates of the composition H2CN and H2CNH, molecules of importance in astrochemistry and biofuel combustion. In particular, H2CN is also of considerable interest to theory, because of its complicated potential energy surface. The species were generated by flash pyrolysis, ionized with vacuum ultraviolet synchrotron radiation, and studied by mass-selected threshold photoelectron (TPE) spectroscopy. In the mass-selected TPE-spectrum of m/z = 28, contributions of all four isomers of H2CN were identified. The excitation energy to the triplet cation of the methylene amidogen radical H2CN was determined to be 12.32 eV. Considerable activity in the C-N mode of the cation is visible. Furthermore, we derived values for excitation into the triplet cations of 11.72 eV for cis-HCNH, 12.65 eV for trans-HCNH, and 11.21 eV for H2NC. The latter values are probably accurate to within one vibrational quantum. The spectrum features an additional peak at 10.43 eV that corresponds to excitation into the C2v-symmetric H2CN+. As this structure constitutes a saddle point, the peak is assigned to an activated complex on the singlet potential energy surface of the cation, corresponding to a hydrogen atom migration. For methanimine, H2CNH, the adiabatic ionization energy IEad was determined to be 9.99 eV and the vibrational structure of the spectrum was analyzed in detail. The uncertainty of earlier values that simply assigned the signal onset to the IEad is thus considerably reduced. The spectrum is dominated by the H-N-C bending mode ν1+ and the rocking mode ν3+. All experimental data were supported by calculations and Franck-Condon simulations.

  13. 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.

  14. Tunneling Splittings in Vibronic Structure of CH_3F^+ ( X^2E): Studied by High Resolution Photoelectron Spectra and AB Initio Theoretical Method

    NASA Astrophysics Data System (ADS)

    Mo, Yuxiang; Gao, Shuming; Dai, Zuyang; Li, Hua

    2013-06-01

    We report a combined experimental and theoretical study on the vibronic structure of CH_3F^+. The results show that the tunneling splittings of vibrational energy levels occur in CH_3F^+ due to the Jahn-Teller effect. Experimentally, we have measured a high resolution ZEKE spectrum of CH_3F up to 3500 cm^-^1 above the ground state. Theoretically, we performed an ab initio calculation based on the diabatic model. The adiabatic potential energy surfaces (APES) of CH_3F^+ have been calculated at the MRCI/CAS/avq(t)z level and expressed by Taylor expansions with normal coordinates as variables. The energy gradients for the lower and upper APES, the derivative couplings between them and also the energies of the APES have been used to determine the coefficients in the Taylor expansion. The spin-vibronic energy levels have been calculated by accounting all six vibrational modes and their couplings. The experimental ZEKE spectra were assigned based on the theoretical calculations. W. Domcke, D. R. Yarkony, and H. Köpple (Eds.), Conical Intersections: Eletronic Structure, Dynamics and Spectroscopy (World Scientific, Singapore, 2004). M. S. Schuurman, D. E. Weinberg, and D. R. Yarkony, J. Chem. Phys. 127, 104309 (2007).

  15. From photoelectron detachment spectra of BrHBr{sup −}, BrDBr{sup −} and IHI{sup −}, IDI{sup −} to vibrational bonding of BrMuBr and IMuI

    SciTech Connect

    Manz, Jörn; Sato, Kazuma; Takayanagi, Toshiyuki Yoshida, Takahiko

    2015-04-28

    Photoelectron detachment XLX{sup −}(00{sup 0}0) + hν → XLX(vib) + e{sup −} + KER (X = Br or I, L = H or D) at sufficiently low temperatures photoionizes linear dihalogen anions XLX{sup −} in the vibrational ground state (v{sub 1}v{sub 2}{sup l}v{sub 3} = 00{sup 0}0) and prepares the neutral radicals XLX(vib) in vibrational states (vib). At the same time, part of the photon energy (hν) is converted into kinetic energy release (KER) of the electron [R. B. Metz, S. E. Bradforth, and D. M. Neumark, Adv. Chem. Phys. 81, 1 (1992)]. The process may be described approximately in terms of a Franck-Condon type transfer of the vibrational wavefunction representing XLX{sup −}(00{sup 0}0) from the domain close to the minimum of its potential energy surface (PES) to the domain close to the linear transition state of the PES of the neutral XLX. As a consequence, prominent peaks of the photoelectron detachment spectra (pds) correlate with the vibrational energies E{sub XLX,vib} of states XLX(vib) which are centered at linear transition state. The corresponding vibrational quantum numbers may be labeled vib = (v{sub 1}v{sub 2}{sup l}v{sub 3}) = (00{sup 0}v{sub 3}). Accordingly, the related most prominent peaks in the pds are labeled v{sub 3}. We construct a model PES which mimics the “true” PES in the domain of transition state such that it supports vibrational states with energies E{sub XLX,pds,00{sup 0}v{sub 3}} close to the peaks of the pds labeled v{sub 3} = 0, 2, and 4. Subsequently, the same model PES is also used to calculate approximate values of the energies E{sub XMuX,00{sup 0}0} of the isotopomers XMuX(00{sup 0}0). For the heavy isotopomers XHX and XDX, it turns out that all energies E{sub XLX,00{sup 0}v{sub 3}} are above the threshold for dissociation, which means that all heavy XLX(00{sup 0}v{sub 3}) with wavefunctions centered at the transition state are unstable resonances with finite lifetimes. Turning the table, bound states of the heavy XLX are van

  16. Electronic structure, excited states, and photoelectron spectra of uranium, thorium, and zirconium bis(Ketimido) complexes (C5R5)2M[-NCPh2]2 (M = Th, U, Zr; R = H, CH3).

    PubMed

    Clark, Aurora E; Martin, Richard L; Hay, P Jeffrey; Green, Jennifer C; Jantunen, Kimberly C; Kiplinger, Jaqueline L

    2005-06-23

    Organometallic actinide bis(ketimide) complexes (C5Me5)2An[-N=C(Ph)(R)]2 (where R = Ph, Me, and CH2Ph) of thorium(IV) and uranium(IV) have recently been synthesized that exhibit chemical, structural, and spectroscopic (UV-Visible, resonance-enhanced Raman) evidence for unusual actinide-ligand bonding. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682; Jantunen et al., Organometallics, 2004, 23, 4682; Morris et al., Organometallics, 2004, 23, 5142.] Similar evidence has been observed for the group 4 analogue (C5H5)2Zr[-N=CPh2]2. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.] These compounds have important implications for the development of new heavy-element systems that possess novel electronic and magnetic properties. Here, we have investigated M-ketimido bonding (M = Th, U, Zr), as well as the spectroscopic properties of the highly colored bis-ketimido complexes, using density functional theory (DFT). Photoelectron spectroscopy (PES) has been used to experimentally elucidate the ground-state electronic structure of the thorium and uranium systems. Careful examination of the ground-state electronic structure, as well as a detailed modeling of the photoelectron spectra, reveals similar bonding interactions between the thorium and uranium compounds. Using time-dependent DFT (TDDFT), we have assigned the bands in the previously reported UV-Visible spectra for (C5Me5)2Th[-N=CPh2]2, (C5Me5)2U[-N=CPh2]2, and (C5H5)2Zr[-N=CPh2]2. The low-energy transitions are attributed to ligand-localized N p --> C=N pi excitations. These excited states may be either localized on a single ketimido unit or may be of the ligand-ligand charge-transfer type. Higher-energy transitions are cyclopentadienyl pi --> CN pi or cyclopentadienyl pi --> phenyl pi in character. The lowest-energy excitation in the (C5Me5)2U[-N=Ph2]2 compound is attributed to f-f and metal-ligand charge-transfer transitions that are not available in the thorium and zirconium analogues. Geometry optimization and

  17. UHV-MOCVD growth of TiO 2 on SiO x/Si(1 1 1): Interfacial properties reflected in the Si 2p photoemission spectra

    NASA Astrophysics Data System (ADS)

    Karlsson, P. G.; Richter, J. H.; Andersson, M. P.; Blomquist, J.; Siegbahn, H.; Uvdal, P.; Sandell, A.

    2005-04-01

    Metal-organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 °C and flux-limited growth at 500 °C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiO x/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiO x/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO 2) x(SiO 2) y where x and y changes linearly and continuously over the interface. The model quantifies how (TiO 2) x(SiO 2) y mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon.

  18. Theoretical Studies on the Photoelectron and Absorption Spectra of MnO 4 and TcO 4

    SciTech Connect

    Su, Jing; Xu, Wen-Hua; Xu, Chao-Fei; Schwarz, W. H. E.; Li, Jun

    2013-09-03

    The tetraoxo pertechnetate anion (TcO4-) is of great interest for nuclear waste management and radiopharmceuticals. To elucidate its electronic structure and to compare with that of its lighter congener MnO4-, the photoelectron and electronic absorption spectra of MnO4 - and TcO4 - are investigated with density functional theory (DFT) and ab initio wave function theory (WFT). The vertical electron detachment energies (VDEs) of MnO4 - obtained with the CR-EOM-CCSD(T) method are in good agreement with the lowest two experimental VDEs; the differences are less than 0.1 eV, representing a significant improvement over the IP-EOMCCSD(T) result in the literature. Combining our CCSD(T) and CR-EOMCCSD( T) results, the first five VDEs of TcO4 - are estimated between 5 and 10 eV with an estimated accuracy of about ±0.2 eV. The vertical excitation energies are determined by using TD-DFT, CR-EOM-CCSD(T), and RASPT2 methods. The excitation energies and the assignments of the spectra are analyzed and partly improved. They are compared with reported SAC-CI results and available experimental data. Both dynamic and nondynamic electron correlations are important in the ground and excited states of MnO4 - and TcO4 -. Nondynamical correlations are particularly relevant in TcO4 - for reliable prediction of excitation energies. In TcO4 - one Rydberg state interlaces but does not mix with the valence excited states, and it disappears in the condensed phase.

  19. 1,2-Dimethyl-1,2-Disila-Closo-Dodecaborane(12), A silicon analog of an ortho-carborane: Synthesis; x ray crystal structure; NMR, vibrational and photoelectron spectra; bonding

    NASA Astrophysics Data System (ADS)

    Seyferth, Dietmar; Buechner, Klaus D.; Rees, William S., Jr.; Wesemann, Lars; Davis, William M.

    1993-04-01

    The reaction of (CH3)2Si(NMe2)2 with B1OH14 Yields a polymer, B1OH12 (dot) Me2NSi(CH3)2NMe2(sub n), whose pyrolysis in a stream of ammonia gives hexagonal boron nitride containing a little silicon nitride. In contrast, CH3(H)Si(NMe2)2 reacts with B1OH14 to give 1,2-dimethyl- 1,2-disila-closo- dodecaborane(12) (DMSB), an air-sensitive solid, the structure of whose 1:1 benzene solvate was determined by X-ray diffraction. This compound crystallizes in the space group P ccn (56) with a = 10.081(1) A, b = 10.666(8) A, c = 16.130(5) A, V = 1734(2) cu A, and Z = 4. The final R is equal to 0.044 and RW = 0.058. The H-1, C-13, Si-29, and B-11 NMR spectra and mass spectrum of DMSB are reported. Its vibrational spectrum (Raman, 5-3600 /cm; IR, 200-3600 /cm) was measured and compared with that of ortho-carborane. A study of its He(1) photoelectron spectrum led to the conclusion that DMSB is the most electron-rich cluster of type XYB1OH1O with two adjacent main group element centers known.

  20. Theoretical studies on the electronic structures and photoelectron spectra of tri-rhenium oxide clusters: Re3O(n)(-) and Re3O(n) (n=1-6).

    PubMed

    Zhou, Qi; Gong, Wei-Chao; Xie, Lu; Zheng, Cun-Gong; Zhang, Wei; Wang, Bin; Zhang, Yong-Fan; Huang, Xin

    2014-01-03

    Density functional theory (DFT) calculations are performed to study the structural and electronic properties of tri-rhenium oxide clusters Re3On(-/0) (n=1-6). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level are carried out to search for the global minima for both the anions and the neutrals. For the anions, the first two O atoms prefer the same corner position of a Re3 triangle. Whereas, Re3O3(-) possesses a C2v symmetry with one bridging and two terminal O atoms. The next three O atoms (n=4-6) are adding sequentially on the basis of Re3O3(-) motif, i.e., adding one terminal O atom for Re3O4(-), one terminal and one bridging O atoms for Re3O5(-), and one terminal and two bridging O atoms for Re3O6(-), respectively. Their corresponding neutral species are similar to the anions in geometry except Re3O4 and Re3O5. Molecular orbital analyses are employed to investigate the chemical bonding and structural evolution in these tri-rhenium oxide clusters.

  1. X-ray photoelectron spectroscopy characterization of the {omega} phase in water quenched Ti-5553 alloy

    SciTech Connect

    Qin, Dongyang; Lu, Yafeng; Zhang, Kong; Liu, Qian; Zhou, Lian

    2012-11-15

    X-ray photoelectron spectroscopy was used to investigate the {omega} phase in water quenched Ti-5553 alloy with a nominal composition of Ti-5Al-5V-5Mo-3Cr (wt.%), and the {omega} and the {beta} phase were distinguished by deconvoluting the XPS spectra of Al2p, V2p and Cr2p core level regions. In addition, it is found that the binding energy of core level electron of alloying elements shifts comparing with that of pure metals, and the fact was interpreted by charge redistribution model. X-ray photoelectron spectroscopy technique could be used to characterize the nano-scale {omega} phase in {beta} alloys. - Highlights: Black-Right-Pointing-Pointer We characterize the {omega} phase in Ti-5553 alloy by XPS. Black-Right-Pointing-Pointer Binding energy of Al2p, V2p and Cr2p electron are different in the {omega} and {beta} phase. Black-Right-Pointing-Pointer Structural difference leads to the binding energy gap.

  2. Photoelectron spectroscopy of molecular clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Pitts, Jonathan; Zheng, Chaowen; Knee, Joseph L.

    1995-09-01

    High resolution photoelectron spectroscopy is applied to the study of molecular clusters. The primary species studied are fluorene-Arn complexes. Spectroscopy of the neutral S1 state has been performed on clusters as large as n equals 30. In order to study the photoelectron spectra of the clusters size selectively mass analyzed threshold ionization (MATI) is used which is a mass resolved version of the ZEKE technique. MATI spectroscopy has been applied to clusters up to n equals 5. The spectral shifts in the S1 origin and ion threshold are used as a measure of the relative stability of the different clusters. Using previous experimental and theoretical work on related clusters the structures of the clusters are inferred from the observed spectral shifts. In some cases multiple conformations of a particular cluster size are identified.

  3. Negative ion photoelectron spectra of ISO3-, IS2O3-, and IS2O4- intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

    NASA Astrophysics Data System (ADS)

    Qin, Zhengbo; Hou, Gao-Lei; Yang, Zheng; Valiev, Marat; Wang, Xue-Bin

    2016-12-01

    Three short-lived, anionic intermediates, ISO3-, IS2O3-, and IS2O4-, are detected during reactions between ozone and aqueous iodine/sulfur oxide microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO3-, IS2O3-, and IS2O4-, respectively. Vibrational progressions with frequencies assigned to the S-O symmetric stretching modes are discernable in the ground state transition features. Density functional theory calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by the formation of I-S and S-S bonds and can be structurally viewed as SO3 linked with I, IS, and ISO for ISO3-, IS2O3-, and IS2O4-, respectively. The calculated ADEs and vertical detachment energies are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

  4. Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

    NASA Astrophysics Data System (ADS)

    Matsui, Fumihiko; Eguchi, Ritsuko; Nishiyama, Saki; Izumi, Masanari; Uesugi, Eri; Goto, Hidenori; Matsushita, Tomohiro; Sugita, Kenji; Daimon, Hiroshi; Hamamoto, Yuji; Hamada, Ikutaro; Morikawa, Yoshitada; Kubozono, Yoshihiro

    2016-11-01

    From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K)C8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 Å and 5.7 Å above the photoelectron emitter C atom and the stacking structures were determined as AB- and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 × 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K)C8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms.

  5. Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

    PubMed Central

    Matsui, Fumihiko; Eguchi, Ritsuko; Nishiyama, Saki; Izumi, Masanari; Uesugi, Eri; Goto, Hidenori; Matsushita, Tomohiro; Sugita, Kenji; Daimon, Hiroshi; Hamamoto, Yuji; Hamada, Ikutaro; Morikawa, Yoshitada; Kubozono, Yoshihiro

    2016-01-01

    From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K)C8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 Å and 5.7 Å above the photoelectron emitter C atom and the stacking structures were determined as AB- and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 × 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K)C8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms. PMID:27811975

  6. Development of an Apparatus for High-Resolution Auger Photoelectron Coincidence Spectroscopy (APECS) and Electron Ion Coincidence (EICO) Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kakiuchi, Takuhiro; Hashimoto, Shogo; Fujita, Narihiko; Mase, Kazuhiko; Tanaka, Masatoshi; Okusawa, Makoto

    We have developed an electron electron ion coincidence (EEICO) apparatus for high-resolution Auger photoelectron coincidence spectroscopy (APECS) and electron ion coincidence (EICO) spectroscopy. It consists of a coaxially symmetric mirror electron energy analyzer (ASMA), a miniature double-pass cylindrical mirror electron energy analyzer (DP-CMA), a miniature time-of-flight ion mass spectrometer (TOF-MS), a magnetic shield, an xyz stage, a tilt-adjustment mechanism, and a conflat flange with an outer diameter of 203 mm. A sample surface was irradiated by synchrotron radiation, and emitted electrons were energy-analyzed and detected by the ASMA and the DP-CMA, while desorbed ions were mass-analyzed and detected by the TOF-MS. The performance of the new EEICO analyzer was evaluated by measuring Si 2p photoelectron spectra of clean Si(001)-2×1 and Si(111)-7×7, and by measuring Si-L23VV-Si-2p Auger photoelectron coincidence spectra (Si-L23VV-Si-2p APECS) of clean Si(001)-2×1.

  7. 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.

  8. Short-range order in amorphous SiO{sub x} by x ray photoelectron spectroscopy

    SciTech Connect

    Novikov, Yu. N.; Gritsenko, V. A.

    2011-07-01

    The Si 2p x ray photoelectron spectra of SiO{sub x} with a different composition of 0 {<=} x {<=} 2 have been studied experimentally and theoretically. The SiO{sub x} films were prepared by low-pressure chemical vapor deposition from SiH{sub 4} and N{sub 2}O source at 750 deg. C. Neither random bonding nor random mixture models can adequately describe the structure of these compounds. The interpretation of the experimental results is discussed according to a large scale potential fluctuation due to the spatial variation of chemical composition in SiO{sub x}.

  9. Time-resolved photoelectron spectroscopy of the CH{sub 3}I B{sup I}E 6s [2] state.

    SciTech Connect

    Thire, N.; Cireasa, R.; Blanchet, V.; Pratt, S. T.

    2010-01-01

    The predissociation dynamics of the vibrationless level of the 6s (B {sup 2}E) Rydberg state of CH{sub 3}I was studied by femtosecond-resolved velocity map imaging of photoelectrons. By monitoring the decay of the CH{sub 3}I{sup +} produced by photoionizing the B state, the predissociation lifetime was measured to be 1310 {+-} 70 fs. Photoelectron spectra were recorded as a function of the excitation scheme (one or two photons to the B state), and as a function of the ionizing wavelength. All of these photoelectron spectra show a simple time dependence that is consistent with the decay time of the CH{sub 3}I{sup +} ion signal. The photoelectron angular distributions for the ionization of the B state depend on the excitation scheme and the ionizing wavelength, and show a strong dependence on the vibrational modes excited in the resulting CH{sub 3}I{sup +}. At long delays, the photoelectron spectra are characterized by photoionization of the I({sup 2}P{sub 1/2}) fragment formed by predissociation of the B state.

  10. X-ray photoelectron spectroscopic investigation of nanocrystalline calcium silicate hydrates synthesised by reactive milling

    SciTech Connect

    Black, Leon . E-mail: l.black@shu.ac.uk; Garbev, Krassimir; Beuchle, Guenter; Stemmermann, Peter; Schild, Dieter

    2006-06-15

    X-ray photoelectron spectroscopy (XPS) has been used to analyse a series of mechanochemically synthesised, nanocrystalline calcium silicate hydrates (C-S-H). The samples, with Ca/Si ratios of 0.2 to 1.5, showed structural features of C-S-H(I). XPS analysis revealed changes in the extent of silicate polymerisation. Si 2p, Ca 2p and O 1s spectra showed that, unlike for the crystalline calcium silicate hydrate phases studied previously, there was no evidence of silicate sheets (Q{sup 3}) at low Ca/Si ratios. Si 2p and O 1s spectra indicated silicate depolymerisation, expressed by decreasing silicate chain length, with increasing C/S. In all spectra, peak narrowing was observed with increasing Ca/Si, indicating increased structural ordering. The rapid changes of the slope of FWHM of Si 2p, {delta} {sub Ca-Si} and {delta} {sub NBO-BO} as function of C/S ratio indicated a possible miscibility gap in the C-S-H-solid solution series between C/S 5/6 and 1. The modified Auger parameter ({alpha}') of nanocrystalline C-S-H decreased with increasing silicate polymerisation, a trend already observed studying crystalline C-S-H. Absolute values of {alpha}' were shifted about - 0.7 eV with respect to crystalline phases of equal C/S ratio, due to reduced crystallinity.

  11. The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy

    SciTech Connect

    D.W. Lynch

    2004-09-30

    With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals.

  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. Photoelectron spectrometer for attosecond spectroscopy of liquids and gases

    NASA Astrophysics Data System (ADS)

    Jordan, I.; Huppert, M.; Brown, M. A.; van Bokhoven, J. A.; Wörner, H. J.

    2015-12-01

    A new apparatus for attosecond time-resolved photoelectron spectroscopy of liquids and gases is described. It combines a liquid microjet source with a magnetic-bottle photoelectron spectrometer and an actively stabilized attosecond beamline. The photoelectron spectrometer permits venting and pumping of the interaction chamber without affecting the low pressure in the flight tube. This pressure separation has been realized through a sliding skimmer plate, which effectively seals the flight tube in its closed position and functions as a differential pumping stage in its open position. A high-harmonic photon spectrometer, attached to the photoelectron spectrometer, exit port is used to acquire photon spectra for calibration purposes. Attosecond pulse trains have been used to record photoelectron spectra of noble gases, water in the gas and liquid states as well as solvated species. RABBIT scans demonstrate the attosecond resolution of this setup.

  14. Photoelectron spectrometer for attosecond spectroscopy of liquids and gases

    SciTech Connect

    Jordan, I.; Huppert, M.; Wörner, H. J.; Brown, M. A.; Bokhoven, J. A. van

    2015-12-15

    A new apparatus for attosecond time-resolved photoelectron spectroscopy of liquids and gases is described. It combines a liquid microjet source with a magnetic-bottle photoelectron spectrometer and an actively stabilized attosecond beamline. The photoelectron spectrometer permits venting and pumping of the interaction chamber without affecting the low pressure in the flight tube. This pressure separation has been realized through a sliding skimmer plate, which effectively seals the flight tube in its closed position and functions as a differential pumping stage in its open position. A high-harmonic photon spectrometer, attached to the photoelectron spectrometer, exit port is used to acquire photon spectra for calibration purposes. Attosecond pulse trains have been used to record photoelectron spectra of noble gases, water in the gas and liquid states as well as solvated species. RABBIT scans demonstrate the attosecond resolution of this setup.

  15. Compact, Integrated Photoelectron Linacs

    NASA Astrophysics Data System (ADS)

    Yu, David

    2000-12-01

    The innovative compact high energy iniector which has been developed by DULY Research Inc., will have wide scientific industrial and medical applications. The new photoelectron injector integrates the photocathode directly into a multicell linear accelerator with no drift space between the injector and the linac. By focusing the beam with solenoid or permanent magnets, and producing high current with low emittance, extremely high brightness is achieved. In addition to providing a small footprint and improved beam quality in an integrated structure, the compact system considerably simplifies external subsystems required to operate the photoelectron linac, including rf power transport, beam focusing, vacuum and cooling. The photoelectron linac employs an innovative Plane-Wave-Transformer (PWT) design, which provides strong cell-to-cell coupling, relaxes manufacturing tolerance and facilitates the attachment of external ports to the compact structure with minimal field interference. DULY Research Inc. under the support of the DOE Small Business Innovation Research (SBIR) program, has developed, constructed and installed a 20-MeV, S-band compact electron source at UCLA. DULY Research is also presently engaged in the development of an X-band photoelectron linear accelerator in another SBIR project. The higher frequency structure when completed will be approximately three times smaller, and capable of a beam brightness ten times higher than the S-band structure.

  16. 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)

  17. Photoelectron Spectroscopy and Ionic Fragmentation of OSeCl2 and Its Analogue OSCl2 under VUV Irradiation.

    PubMed

    Geronés, Mariana; Rodríguez Pirani, Lucas S; Erben, Mauricio F; Romano, Rosana M; Cavasso Filho, Reinaldo L; Tong, Sheng Rui; Ge, Maofa; Della Védova, Carlos O

    2015-07-23

    The electronic structure and the dissociative ionization of selenium oxychloride, OSeCl2, have been investigated in the valence region by using results from both photoelectron spectroscopy (PES) and synchrotron-based photoelectron photoion coincidence (PEPICO) spectra. The PES is assigned with the help of quantum chemical calculations at the outer-valence Green's function (OVGF) and symmetry adapted cluster/configuration interaction (SAC-CI) levels. The first energy ionization is observed at 11.47 eV assigned to the ionization of electrons formally delocalized over the Se, Cl, and O lone pair orbitals. Irradiation of OSeCl2 with photons in the valence region leads to the formation of OSeCl2(•+), OSeCl(+), SeCl2(•+), SeCl(+), and SeO(•+) ions. Furthermore, the inner shell Se 3p, Cl 2p, and Se 3s electronic regions of OSeCl2 together with S 2p, Cl 2p, and S 2s electronic regions of thionyl chloride, OSCl2, have been studied by using tunable synchrotron radiation. Thus, total ion yield spectra and the fragmentation patterns deduced from PEPICO spectra at the various excitation energies have been studied. Cl(+), O(•+), and Se(•+) ions appear as the most intense fragments in the OSeCl2 PEPICO spectra, like in the sulfur analogue OSCl2, whose photofragmentation is dominated by the Cl(+), O(•+), and S(•+) ions. Fragmentation processes in OSCl2 leading to the formation of the double coincidences involving atomic ions appear as the most intense in the PEPIPICO spectra.

  18. Global nonresonant vibrational-photoelectron coupling in molecular photoionization

    NASA Astrophysics Data System (ADS)

    Poliakoff, Erwin; Das, Aloke; Hardy, David; Bozek, John; Aguilar, Alex; Lucchese, Robert

    2009-05-01

    Using photoelectron spectroscopy and Schwinger variational scattering theory, we have investigated the coupling between vibrational motion and the exiting photoelectron over extended ranges of photoelectron kinetic energy. Photoelectron spectroscopy is performed with vibrational resolution over uncommonly large ranges of energy (ca. 200 eV). We find clear and significant changes in vibrational branching ratios as a function of photon energy, in direct contradiction to predictions of the Franck-Condon principle. While it is well known that resonances lead to coupling between electronic and vibrational degrees of freedom, nonresonant mechanisms that result in such coupling are not expected or well-documented. Photoelectron spectra are presented for several electronic states of N2^+, CO^+, and NO^+, and we find that valence isoelectronic channels behave very differently, which is also surprising. Theoretical results indicate that Cooper minima are the underlying cause of these effects, and we are currently working to understand the reasons for the sensitivity of the Cooper minima on bond length.

  19. New hypodiphosphates of the alkali metals: Synthesis, crystal structure and vibrational spectra of the hypodiphosphates(IV) M{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (M=Rb and Cs)

    SciTech Connect

    Wu, Peng; Wiegand, Thomas; Eckert, Hellmut

    2012-10-15

    The new hypodiphosphates(IV) Rb{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (1) and Cs{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] (2) were synthesized by soft chemistry reactions from aqueous solutions of hypophosphoric acid and the corresponding heavy alkali-metal carbonates. Their crystal structures were determined by single crystal X-ray diffraction. Both compounds crystallize isotypic in the triclinic space group P-1 with one formula unit in the unit cell. The structures are built up by discrete (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) units in staggered conformation for the P{sub 2}O{sub 6} skeleton and the corresponding alkali-metal cations. In the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} ion the hydrogen atoms are in a 'trans-trans' conformation. O{center_dot}H-O hydrogen bonds between the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) groups consolidate the structures into a three-dimensional network. The FT-Raman and {sup 31}P and {sup 1}H and MAS NMR spectra of the title compounds have been recorded and interpreted, especially with respect to their assignment to the (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) groups. Thermogravimetric data of 2 have been interpreted in terms of a thermal decomposition model. - Graphical Abstract: The layered compounds Rb{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] and Cs{sub 2}[(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})] have been synthesized and investigated. Both crystallize isotypic. The structures are built up by discrete (H{sub 2}P{sub 2}O{sub 6}){sup 2-} and (H{sub 4}P{sub 2}O{sub 6}) units and the corresponding alkali-metal cations. Highlights: Black-Right-Pointing-Pointer Synthesis and single-crystal structure of new alkali hypodiphosphates. Black-Right-Pointing-Pointer Structures are characterized by [(H{sub 2}P{sub 2}O{sub 6})(H{sub 4}P{sub 2}O{sub 6})]{sup 2-} units and M{sup +} cations

  20. Bimolecular reaction dynamics from photoelectron spectroscopy of negative ions

    SciTech Connect

    Bradforth, S.E.

    1992-11-01

    The transition state region of a neutral bimolecular reaction may be experimentally investigated by photoelectron spectroscopy of an appropriate negative ion. The photoelectron spectrum provides information on the spectroscopy and dynamics of the short lived transition state and may be used to develop model potential energy surfaces that are semi-quantitative in this important region. The principles of bound {yields} bound negative ion photoelectron spectroscopy are illustrated by way of an example: a full analysis of the photoelectron bands of CN{sup {minus}}, NCO{sup {minus}} and NCS{sup {minus}}. Transition state photoelectron spectra are presented for the following systems Br + HI, Cl + HI, F + HI, F + CH{sub 3}0H,F + C{sub 2}H{sub 5}OH,F + OH and F + H{sub 2}. A time dependent framework for the simulation and interpretation of the bound {yields} free transition state photoelectron spectra is subsequently developed and applied to the hydrogen transfer reactions Br + HI, F + OH {yields} O({sup 3}P, {sup 1}D) + HF and F + H{sub 2}. The theoretical approach for the simulations is a fully quantum-mechanical wave packet propagation on a collinear model reaction potential surface. The connection between the wavepacket time evolution and the photoelectron spectrum is given by the time autocorrelation function. For the benchmark F + H{sub 2} system, comparisons with three-dimensional quantum calculations are made.

  1. Vector potential photoelectron microscopy.

    PubMed

    Browning, R

    2011-10-01

    A new class of electron microscope has been developed for the chemical microanalysis of a wide range of real world samples using photoelectron spectroscopy. Highly structured, three-dimensional samples, such as fiber mats and fracture surfaces can be imaged, as well as insulators and magnetic materials. The new microscope uses the vector potential field from a solenoid magnet as a spatial reference for imaging. A prototype instrument has demonstrated imaging of uncoated silk, magnetic steel wool, and micron-sized single strand tungsten wires.

  2. 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}.

  3. Chemical bonding and electronic structures of microcline, orthoclase and the plagioclase series by X-ray photoelectron spectroscopy.

    PubMed

    Kloprogge, J Theo; Wood, Barry J

    2015-02-25

    A detailed analysis was undertaken of the X-ray photoelectron spectra obtained from microcline, orthoclase and several samples of plagioclase with varying Na/Ca ratio. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each specimen. The spectra for Si 2p and Al 2p vary with the change in symmetry between microcline and orthoclase, while in plagioclase an increase in Al-O-Si linkages results in a small but observable decrease in binding energy. The overall shapes of the O 1s peaks observed in all spectra are similar and show shifts similar to those observed for Si 2p and Al 2p. The lower-VB spectra for microcline and orthoclase are similar intermediate between α-SiO2 and α-Al2O3 in terms of binding energies. In the plagioclase series increasing coupled substitution of Na and Si for Ca and Al results in a change of the overall shape of the spectra, showing a distinct broadening associated with the presence of two separate but overlapping bands similar to the 21 eV band observed for quartz and the 23 eV band observed for corundum. The bonding character for microcline and orthoclase is more covalent than that of α-Al2O3, but less than that of α-SiO2. In contrast, the plagioclase samples show two distinct bonding characters that are comparable with those of α-SiO2 and α-Al2O3.

  4. High Resolution Photoelectron Spectroscopy of Au_2^- and Au_4^- by Photoelectron Imaging

    NASA Astrophysics Data System (ADS)

    Leon, Iker; Yang, Zheng; Wang, Lai-Sheng

    2013-06-01

    We report high resolution photoelectron spectra of Au_2^- and Au_4^- obtained with a newly-built photoelectron imaging apparatus. Gold anions are produced by laser vaporization and the desired specie is mass selected and focused into the collinear velocity-map imaging (VMI) lens assembly. The design of the imaging lens has allowed us to obtain less than 0.9% energy resolution for high kinetic energy electrons ( > 1eV) while maintaining wavenumber resolution for low kinetic energy electrons. Although gold dimer and tetramer have been studied in the past, we present spectroscopic results under high resolution. For Au_2^-, we report high resolution spectra with an accurate determination of the electron affinity together with a complete vibrational assignment, for both the anion and neutral ground states, while for Au_4^-, we are able to resolve a low frequency mode and obtain accurately the adiabatic detachment energy.

  5. Negative ion photoelectron spectroscopic studies of transition metal cluster

    NASA Astrophysics Data System (ADS)

    Marcy, Timothy Paul

    The studies reported in this thesis were performed using a negative ion photoelectron spectrometer consisting of a cold cathode DC discharge ion source, a flowing afterglow ion-molecule reactor, a magnetic sector mass analyzer, an argon ion laser for photodetachment and a hemispherical electron kinetic energy analyzer and microchannel plate detector for photoelectron spectrum generation. The 476.5 nm (2.601 eV), 488.0 nm (2.540 eV) and 514.5 nm (2.410 eV) negative ion photoelectron spectra of VMn are reported and compared to the previously studied spectra of isoelectronic Cr2.1 The photoelectron spectra are remarkably similar to those of Cr2 in electron affinity and vibrational frequencies. The 488.0 nm photoelectron spectra and electron affinities of Nb n- (n = 1 - 9) are reported with discussion of observed vibrational structure. There are transitions to several electronic states of Nb2 in the reported spectra with overlapping vibrational progressions. The spectra of Nb3, Nb4 and Nb6 show partially resolved vibrational structure in the transitions to the lowest observed electronic state of each cluster. There is a single distinct active vibrational mode in the transition to the ground state of Nb8. Spin-orbit energies of Nb- are also reported. The 488.0 nm negative ion photoelectron spectra of Nb3H(D) are reported and compared to those of Nb3. There is a single vibrational mode active in the spectra of Nb3H(D) which is very similar to the most distinct mode active in the spectrum of Nb3. The 488.0 nm photoelectron spectra of the NbxCyH(D) y- (x = 1, 2, 3, y = 2, 4, 6) dehydrogenated products of the reactions of ethylene with niobium cluster anions are reported. Temperature studies of some of these species give evidence for the presence of multiple isomers of each molecule in the ion beam. The spectra of NbC6H(D) 6 are identical to those obtained from the reactions of benzene with niobium clusters and indicate that benzene is being formed from ethylene in the flow

  6. High-resolution threshold photoelectron spectroscopy by electron attachment

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.; Chutjian, A.

    1976-01-01

    A new technique for measuring high-resolution threshold photoelectron spectra of atoms, molecules, and radicals is described. It involves photoionization of a gaseous species, attachment of the threshold, or nearly zero electron to some trapping molecule (here SF6 or CFCl3), and mass detection of the attachment product (SF6/-/ or Cl/-/ respectively). This technique of threshold photoelectron spectroscopy by electron attachment was used to measure the spectra of argon and xenon at 11 meV (FWHM) resolution, and was also applied to CFCl3.

  7. Occupied and unoccupied electronic structures of an L-cysteine film studied by core-absorption and resonant photoelectron spectroscopies

    NASA Astrophysics Data System (ADS)

    Kamada, M.; Hideshima, T.; Azuma, J.; Yamamoto, I.; Imamura, M.; Takahashi, K.

    2016-04-01

    Unoccupied and occupied electronic structures of an L-cysteine film have been studied by absorption and resonant photoelectron spectroscopies. Core absorptions at S-L, C-K, N-K, and O-K levels indicate that the lower unoccupied states are predominantly composed of oxygen-2p, carbon-2p, and sulfur-4s+3d orbitals, while higher unoccupied states may be attributed dominantly to nitrogen-np (n ≥ 3), oxygen-np (n ≥ 3), and sulfur-ns+md (n ≥ 4, m ≥ 3) orbitals. Resonant photoelectron spectra at S-L23 and O-K levels indicate that the highest occupied state is originated from sulfur-3sp orbitals, while oxygen-2sp orbitals contribute to the deeper valence states. The delocalization lifetimes of the oxygen-1s and sulfur-2p excited states are estimated from a core-hole clock method to be about 9 ± 1 and 125 ± 25 fs, respectively.

  8. X-ray photoelectron spectroscopic study on interface bonding between Pt and Zn- and O-terminated ZnO

    SciTech Connect

    Yoshitake, Michiko; Nemsak, Slavomir; Blumentrit, Petr

    2013-03-15

    Interface bonding between Pt and Zn- and O-terminated ZnO surfaces was investigated by precise analysis of x-ray photoelectron spectra. The interfaces were formed by vapor depositing Pt onto the ZnO surfaces in ultrahigh vacuum. The changes in the Zn 2p{sub 3/2}, O 1s, Zn LMM Auger, and Pt 4f{sub 7/2} spectra upon Pt deposition were observed. The changes in the shape of the Zn LMM spectra and the shifts in the binding energy of Zn 2p{sub 3/2} and O 1s revealed that there was a metallic Zn component in the Zn LMM and Zn 2p{sub 3/2} spectra for Zn-terminated ZnO and a Pt-O component in the O 1s spectra for both Zn- and O-terminated ZnO. Peaks were fitted with multiple components accordingly. The binding energy shifts of Zn 2p{sub 3/2} and O 1s for the ZnO component were almost the same, which confirmed that the fitting was reasonable. From the fitting results, the interface bonding was concluded to be O-terminated, i.e., Zn-O-Pt bond formation occurred at the interface for both Zn- and O-terminated ZnO. This clearly demonstrated that the stable interface bonding occurring between Pt and ZnO is Zn-O-Pt bonding whether the ZnO substrate is initially Zn-terminated or O-terminated.

  9. Anion photoelectron spectroscopy of radicals and clusters

    SciTech Connect

    Travis, Taylor R.

    1999-12-01

    Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying 2Σ and 2π states of C2nH (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 C2H and C4H. Other radicals studied include NCN and I3. 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 I3 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.

  10. Energetic (above 60 eV) atmospheric photoelectrons

    NASA Technical Reports Server (NTRS)

    Winningham, J. D.; Decker, D. T.; Kozyra, J. U.; Nagy, A. F.; Jasperse, J. R.

    1989-01-01

    Data from low altitude plasma instrument (LAPI) on Dynamics Explorer 2 document a population of high-energy (up to 800 eV) atmospheric photoelectrons that has not been reported in the published literature. The source of these photoelectrons is postulated to be the soft X-ray portion of the whole sun spectrum. This conclusion is supported by sunrise-sunset characteristics that track those of the classical (below 60 eV) EUV-produced photoelectrons, and theoretical results from two models that incorporate the soft X-ray portion of the solar spectrum. The models include K-shell ionization effects and predict peaks in the photoelectron spectrum due to Auger electrons emitted from oxygen and nitrogen. The peak for nitrogen is observed as predicted, but the peak for oxygen is barely observable. Excellent quantitative agreement is achieved between theory and experiment by using reasonable adjustments to the few published soft X-ray spectra based on solar activity. The upflowing energetic photoelectrons provide a heretofore unknown source of electrons to the magnetosphere. They occur whenever and wherever the sun is up, that is, at all invariant latitudes. Their density is low, but they are steady and ubiquitous. If scattering and trapping occur on closed field lines, then photoelectrons could contribute as a significant particle source and thus represent a new facet of magnetosphere-ionosphere coupling.

  11. Simulation of XenArm Cluster Formation in a Molecular Beam: Comparison with Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Amar, Francois G.; Preston, Thomas J.

    2006-03-01

    We perform direct MD simulations of the formation of mixed XenArm clusters (5002p3/2 (Ar) core hole photoelectron spectra of these clusters and compare them to the experimental spectra of Tchaplyguine et al[1]. The predicted spectra are calculated as the sum of final state energy shifts of the ionized atoms (within the cluster) relative to the isolated gas phase ion using a self-consistent polarization formalism. We use the results of our earlier calculations on pure argon and xenon clusters [2] to determine the appropriate inelastic mean free path value for the signal electrons leaving the mixed clusters. These results allow us to gain a refined understanding of the size, stoichiometry, and core/shell structure of these mixed clusters. [1] M. Tchaplyguine, et al, Phys. Rev A 69, 031201 (2004); [2] F. Amar, et al, JCP 122, 244717 (2005).

  12. 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.

  13. Solvated Electrons in Clusters: Magic Numbers for the Photoelectron Anisotropy.

    PubMed

    West, Adam H C; Yoder, Bruce L; Luckhaus, David; Signorell, Ruth

    2015-12-17

    This paper reports on a curiosity concerning magic numbers in neutral molecular clusters, namely on magic numbers related to the photoelectron anisotropy in angle-resolved photoelectron spectra. With a combination of density functional calculations and experiment, we search for magic numbers in Na(H2O)n, Na(NH3)n, Na(CH3OH)n, and Na(CH3OCH3)n clusters. In clusters of high symmetry, the highest occupied molecular orbital can be delocalized over an extended region, forming a symmetric charge distribution of high s character, which results in a pronounced anisotropy in the photoelectron angular distribution. We find magic numbers at n = 6 and 4 for sodium-doped dimethyl ether and ammonia clusters, respectively, but not for sodium-doped water and methanol clusters, which is likely a consequence of the degree of hydrogen bonding and the number of structural isomers.

  14. Photoelectron circular dichroism of isopropanolamine

    NASA Astrophysics Data System (ADS)

    Catone, D.; Turchini, S.; Contini, G.; Prosperi, T.; Stener, M.; Decleva, P.; Zema, N.

    2017-01-01

    Spectroscopies based on circular polarized light are sensitive to the electronic and structural properties of chiral molecules. Photoelectron circular dichroism (PECD) is a powerful technique that combines the chiral sensitivity of the circular polarized light and the electronic information obtained by photoelectron spectroscopy. An experimental and theoretical PECD study of the outer valence and C 1s core states of 1-amino-2-propanol in the gas phase is presented. The experimental dichroic dispersions in the photoelectron kinetic energy are compared with theoretical calculations employing a multicentric basis set of B-spline functions and a Kohn-Sham Hamiltonian. In order to understand analogies and differences in the dichroism of structural isomers bearing the same functional groups, a comparison with previous PECD study of valence band of 2-amino-1-propanol is carried out.

  15. Photoelectron backscattering in vacuum phototubes

    NASA Astrophysics Data System (ADS)

    Lubsandorzhiev, B. K.; Vasiliev, R. V.; Vyatchin, Y. E.; Shaibonov, B. A. J.

    2006-11-01

    In this article we describe results of studies of a photoelectron backscattering effect in vacuum phototubes: classical photomultipliers (PMT) and hybrid phototubes (PH). Late pulses occurring in PMTs are attributed to the photoelectron backscattering and distinguished from pulses due to an anode glow effect. The late pulses are measured in a number of PMTs and HPs with various photocathode sizes covering 1 50 cm range and different types of the first dynode materials and construction designs. It is shown that the late pulses are a generic feature of all vacuum photodetectors—PMTs and PHs—and they do not deteriorate dramatically amplitude and timing responses of vacuum phototubes.

  16. 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.

  17. On Interpreting the Photoelectron Spectra of MgO

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Arnold, James (Technical Monitor)

    2001-01-01

    The (sup 2)Sigma(+) and (sup 2)Pi states of MgO(-) and the (sup 1)Sigma(+), (sup 1)Pi, and (sup 3)Pi states of MgO are studied using the averaged coupled-pair functional (ACPF) approach. The computed spectroscopic constants are in good agreement with the available experimental data. The computed Franck-Condon factors and photodetachment overlaps are compared with experiment.

  18. Photoelectron spectra and electron structures of some boron. beta. -diketonates

    SciTech Connect

    Borisenko, A.V.; Vovna, V.I.; Gorachakov, V.V.; Korotkikh, O.A.

    1987-07-01

    The authors have recorded PES in the vapor state for F/sub 2/B(AA-H), F/sub 2/B(AA-Br), F/sub 2/B(BAA-H), Bu/sub 2/B(AA-H), (AA = CH/sub 3/COCCOCH/sub 3/, BAA = C/sub 6/H/sub 5/COCCOCH/sub 3/). The bonding character of the MO and the substitution effects were examined from CNDO/2 calculations for the molecules that had been examined by experiment and certain model ones. To simplify the calculations, they did not incorporate the asymmetry in the coordinated unit.

  19. Vibrationally-resolved polyatomic photoelectron spectroscopy: Mode-specific behavior

    NASA Astrophysics Data System (ADS)

    Rathbone, G. J.; Poliakoff, E. D.; Bozek, J. D.; Lucchese, R. R.

    2002-05-01

    We report the first vibrationally-resolved photoelectron spectra for polyatomic molecules performed over a broad spectral range. Such studies elucidate vibrationally mode-specific aspects of the photoelectron scattering dynamics. Three linear triatomic systems (CO_2, N_2O, and CS_2) are studied, and the results exhibit striking differences for alternative modes. For CO_2^+(C^2Σ_g^+), a continuum resonance results in a 15 eV wide dip for the symmetric stretch branching ratio, while strong peaks are observed for vibrational branching ratios associated with the two symmetry forbidden modes. For CS_2^+(B^2Σ_u^+), mode-specific behavior is displayed, as resonance enhancement of a single quantum excitation is weak for the symmetric stretch, but strong for the bending vibration. For N_2O^+(A^2Σ^+), many vibrational excitations are observed and families of vibrational branching ratio spectra emerge.

  20. Photoelectron spectroscopy of carbonyls: saturated normal dicarboxylic acids

    SciTech Connect

    Chattopadhyay, S.; Meeks, J.L.; Findley, G.L.; McGlynn, S.P.

    1981-04-16

    The ultraviolet photoelectron spectra (UPS) of oxalic, malonic, succinic, glutaric, and adipic acids, and various of their simple derivatives, are presented and discussed. The four lowest-energy ionization events, (I(n/sub +/), I(n/sub -), I (..pi../sub +/), I(..pi../sub -/)), are assigned in all cases. Higher ionization events are not assigned because of molecule-limited resolution in the higher-energy UPS region.

  1. Raman and photoelectron spectroscopic investigation of high-purity niobium materials: Oxides, hydrides, and hydrocarbons

    NASA Astrophysics Data System (ADS)

    Singh, Nageshwar; Deo, M. N.; Nand, Mangla; Jha, S. N.; Roy, S. B.

    2016-09-01

    We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ˜300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm-1), hydrides (1277 and 1385 cm-1: ˜80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm-1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectroscopy study. This study reveals the presence of C and O in the Nb samples. Core level spectra of Nb (doublet 3d5/2 and 3d3/2) show peaks near 206.6 and 209.4 eV, which can be attributed to the Nb5+ oxidation state. The core level spectra of C 1 s of the samples are dominated by graphitic carbon (binding energy, 284.6 eV), while the spectra of O 1 s are asymmetrically peaked near binding energy of ˜529 eV, and that indicates the presence of metal-oxide Nb2O5. The valence-band spectra of the Nb samples are dominated by a broad peak similar to O 2p states, but after sputtering (for 10 min) a peak appears at ˜1 eV, which is a feature of the elemental Nb atom.

  2. Photoionization of iodine atoms: Rydberg series which converge to the I{sup +}({sup 1}S{sub 0})<-I({sup 2}P{sub 3/2}) threshold

    SciTech Connect

    Eypper, Marie; Innocenti, Fabrizio; Morris, Alan; Dyke, John M.; Stranges, Stefano; West, John B.; King, George C.

    2010-06-28

    Relative partial photoionization cross sections and angular distribution parameters {beta} have been measured for the first and fourth (5p){sup -1} photoelectron (PE) bands of atomic iodine by performing angle-resolved constant-ionic-state (CIS) measurements on these PE bands between the {sup 1}D{sub 2} and {sup 1}S{sub 0} (5p){sup -1} ionic thresholds in the photon energy region of 12.9-14.1 eV. Rydberg series arising from the 5p{yields}ns and 5p{yields}nd excitations are observed in both the first PE band, I{sup +}({sup 3}P{sub 2})<-I({sup 2}P{sub 3/2}), and the fourth PE band, I{sup +}({sup 1}D{sub 2})<-I({sup 2}P{sub 3/2}), CIS spectra. For each Rydberg state, the resonance energy, quantum defect, linewidth, line shape, and photoelectron angular distribution parameter {beta} have been determined. For the {beta}-plots for each PE band, only resonances corresponding to 5p{yields}nd excitations are observed; no resonances were seen at photon energies corresponding to the 5p{yields}ns resonances in the CIS spectra. The {beta}-plots are interpreted in terms of the parity unfavored channel with j{sub t}=4 being the major contributor at the 5p{yields}nd resonance positions, where j{sub t} is the quantum number for angular momentum transferred between the molecule, and the ion and photoelectron. Comparison of the results obtained with those published for bromine shows reasonably good agreement for the CIS spectra but poor agreement for the {beta}-plots. It appears that parity unfavored channels are playing a greater role in the valence (np){sup -1} ionization of atomic iodine than in the corresponding ionization of atomic bromine.

  3. Photoelectron Imaging of OXIDE.VOC Clusters

    NASA Astrophysics Data System (ADS)

    Patros, Kellyn M.; Mann, Jennifer; Chick Jarrold, Caroline

    2016-06-01

    Perturbations of the bare O2- and O4- electronic structure arising from VOC (VOC = hexane, isoprene, benzene and benzene.D6) interactions are investigated using anion photoelectron imaging at 2.33 and 3.49 eV photon energies. Trends observed from comparing features in the spectra include VOC-identity-dependent electron affinities of the VOC complexes relative to the bare oxide clusters, due to enhance stability in the anion complex relative to the neutral. Autodetachment is observed in all O4-.VOC spectra and only isoprene with O2-. In addition, the intensities of transitions to states correlated with the singlet states of O2 neutral via detachment from the O2-.VOC anion complexes show dramatic VOC-identity variations. Most notably, benzene as a complex partner significantly enhances these transitions relative to O2- and O2-.hexane. A less significant enhancement is also observed in the O2-.isoprene complex. This enhancement may be due to the presence of low-lying triplet states in the complex partners.

  4. Charge transfer in nanocrystalline-Au /ZnO nanorods investigated by x-ray spectroscopy and scanning photoelectron microscopy

    NASA Astrophysics Data System (ADS)

    Chiou, J. W.; Ray, S. C.; Tsai, H. M.; Pao, C. W.; Chien, F. Z.; Pong, W. F.; Tsai, M.-H.; Wu, J. J.; Tseng, C. H.; Chen, C.-H.; Lee, J. F.; Guo, J.-H.

    2007-05-01

    O K- and Zn and Au L3-edge x-ray absorption near-edge structure (XANES), x-ray emission spectroscopy (XES), and scanning photoelectron microscopy (SPEM) are performed to investigate the electronic structure of ZnO nanorods with nanocrystalline (nc)-Au particles grown on the surfaces. The XANES spectra of nc-Au /ZnO nanorods reveal the decrease of the number of both O 2p and Zn 4s/3d unoccupied states with the increase of the nc-Au particle size. The number of Au 6s /5d unoccupied states increases when the size of nc-Au particle decreases, indicating that the deposition of nc-Au particles on the surface of ZnO nanorods promotes charge transfer from the ZnO nanorods to nc-Au particles. Excitation energy dependent XES and SPEM spectra show that the number of electrons in the valence band of O 2p-Zn 4sp hybridized states decreases as the nc-Au particle size increases, revealing that more electrons are excited from the valence band to the conduction band of ZnO nanorods and the storage of electrons in nc-Au particles.

  5. Symmetry rules in magnetic core-level photoelectron spectroscopy from epitaxial ferromagnetic ultrathin films

    NASA Astrophysics Data System (ADS)

    Schellenberg, R.; Meinert, H.; Perez, A.; Kisker, E.

    2001-09-01

    For two x-ray incidence directions onto an epitaxial FeNi(001) film, one to the left and a second one to the right side of the symmetry plane spanned by the magnetization direction and the photoelectron wave vector, we have measured distributions of the emission-angle dependence with respect to the crystallographic axes of the Fe 2p3/2 core-level photoelectron intensity asymmetry occurring upon magnetization reversal. The two angular distributions transform into each other when the signs of the magnetization and of the photoelectron emission angle are inverted, in accordance with the conservation of parity.

  6. Attosecond Time-Resolved Photoelectron Dispersion and Photoemission Time Delays

    NASA Astrophysics Data System (ADS)

    Liao, Q.; Thumm, U.

    2014-01-01

    We compute spectrograms and relative time delays for laser-assisted photoemission by single attosecond extreme ultraviolet pulses from valence band (VB) and 2p core levels (CLs) of a Mg(0001) surface within a quantum-mechanical model. Comparing the time-dependent dispersion of photoelectron (PE) wave packets for VB and CL emission, we find striking differences in their dependence on the (i) electron mean free path (MFP) in the solid, (ii) screening of the streaking laser field, and (iii) chirp of the attosecond pulse. The relative photoemission delay between VB and 2p PEs is shown to be sensitive to the electron MFP and screening of the streaking laser field inside the solid. Our model is able to reproduce a recent attosecond-streaking experiment [S. Neppl et al., Phys. Rev. Lett. 109, 087401 (2012)], which reveals no relative streaking time delay between VB and 2p PEs.

  7. Final-state effect on X-ray photoelectron spectrum of n-doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Posadas, Agham; Demkov, Alexander; Demkov Team

    2015-03-01

    X-ray photoelectron spectroscopy (XPS) is a widely used technique to determine the oxidation states of chemical elements. In stoichiometric SrTiO3, the Ti4+ peak appears at a binding energy of about 459.0 eV for photoelectrons ejected from the Ti 2 p core level. In lightly n-doped SrTiO3, a weak shoulder at a binding energy of about 1.5 eV lower than the Ti4+ peak appears in the XPS spectrum that has been conventionally interpreted as a Ti3+ signal. By taking the final-state effect into account, i.e. by considering the response of the valence electrons in the presence of a core hole, we argue that such a Ti3+ peak does not necessarily imply the existence of spatially localized Ti3+ ions, and explicitly show that a spatially uniform Ti(4 - x) + distribution also leads to the multi-peak structure. Spectra from metallic n-doped SrTiO3 (e.g. La replacing Sr, Nb replacing Ti, or even oxygen vacancy doping) should be interpreted as the latter case. Several experiments based on this interpretation are discussed. Support for this work was provided through Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. DOE, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences under award number DESC0008877.

  8. Negative ion photoelectron spectra of ISO3, IS2O3, and IS2O4 intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

    SciTech Connect

    Qin, Zhengbo; Hou, Gao-Lei; Yang, Zheng; Valiev, Marat; Wang, Xue-Bin

    2016-12-07

    Three short-lived, anionic intermediates, ISO3, IS2O3, and IS2O4, are detected during reactions between ozone and aqueous iodine/sulfur oxides microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab-initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO3, IS2O3, and IS2O4, respectively. Vibrational progressions with frequencies assigned to the S–O symmetric stretching modes are also discernable in the ground state transition features. Density functional theory (DFT) calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by formation of I–S and S–S bonds and can be structurally viewed as SO3 linked with I, IS, and ISO for ISO3, IS2O3, and IS2O4, respectively. The calculated ADEs and vertical detachment energies (VDEs) are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

  9. Electronic structure of fluorinated multiwalled carbon nanotubes studied using x-ray absorption and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Brzhezinskaya, M. M.; Muradyan, V. E.; Vinogradov, N. A.; Preobrajenski, A. B.; Gudat, W.; Vinogradov, A. S.

    2009-04-01

    This paper presents the results of combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes (MWCNTs) with different fluorine contents (10-55wt%) and reference compounds (highly oriented pyrolytic graphite crystals and “white” graphite fluoride) using x-ray absorption and photoelectron spectroscopy at C1s and F1s thresholds. Measurements were performed at BESSY II (Berlin, Germany) and MAX-laboratory (Lund, Sweden). The analysis of the soft x-ray absorption and photoelectron spectra points to the formation of covalent chemical bonding between fluorine and carbon atoms in the fluorinated nanotubes. It was established that within the probing depth (˜15nm) of carbon nanotubes, the process of fluorination runs uniformly and does not depend on the fluorine concentration. In this case, fluorine atoms interact with MWCNTs through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton (phase 1) and this bonding is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp2) to tetrahedral (sp3) hybridization and by a large electron transfer between carbon an fluorine atoms. In the MWCNT near-surface region the second fluorine-carbon phase with weak electron transfer is formed; it is located mainly within two or three upper graphene monolayers, and its contribution becomes much poorer as the probing depth of fluorinated multiwalled carbon nanotubes (F-MWCNTs) increases. The defluorination process of F-MWCNTs on thermal annealing has been investigated. The conclusion has been made that F-MWCNT defluorination without destruction of graphene layers is possible.

  10. Vibrationally resolved anion photoelectron spectroscopy of metal clusters

    NASA Astrophysics Data System (ADS)

    Miller, Stephen R.

    Vibrationally resolved anion photoelectron spectroscopy of metal clusters Vibrationally resolved anion photoelectron spectroscopy (APES) and density functional theory (DFT) are applied to the study of structure and reactivity in small metal containing molecules. The studies described fall into two general categories: the study of bare metal clusters and the study of metal/organic ligand reactions. The current lack of spectroscopic data for small, bare gas-phase metal compounds makes the experimental study of such compounds important for understanding structure and bonding in open-shell metallic species. The heteronuclear diatomic anions MCu- (M = Cr, Mo) were prepared in a flowing afterglow ion-molecule reactor, and studied experimentally with APES. Anion and neutral vibrational frequencies and MCu electron affinities were obtained for both systems. The experiments were supplemented by DFT calculations. The combined use of experiment and theory allows for the assignment of both photoelectron spectra, including a reassignment of the CrCu ground state reported in the literature. Similarly, DFT was used to assign the anionic/neutral electronic states observed in the photoelectron spectra of Al3- and Al3O-. The study of partially ligated organometallic complexes offers a means of examining the interactions between metal atoms and individual ligand molecules. DFT was used to assign electronic states observed in the photoelectron spectra of NbC2H2-, NbC4H4 -NbC6H6- and VC6H 6-. Comparison of the NbnHn - (n = 2, 4, 6) spectra (obtained through the reaction of C2 H4 and Nb) with DFT results provides the first direct spectroscopic evidence of the conversion of ethylene to benzene by a gas phase metal atom. Experiments were used to probe the reactivity of Y with C2H 4 in an effort to examine the generality of the metal induced C 2H4 dehydrogenation/cyclization reactions. Some of the key products in the Y reactions were YC2H-, YC 2H2-, and YC6H5 -. However, the results

  11. Photoelectron energy peaks at Titan: A statistical overview and comparison to Venus and Mars

    NASA Astrophysics Data System (ADS)

    Wellbrock, Anne; Jones, Geraint; Coates, Andrew

    The Cassini CAPS Electron Spectrometer (ELS) has observed discrete energy peaks at 24.1 eV in the electron spectra in Titan's ionosphere. These electrons are believed to be photoelectrons generated due to the ionisation of N2 by the strong solar He II (30.4nm) line. They are generally observed in Titan's dayside ionosphere, because this is where neutral N2 particles can be ionized by solar radiation. Coates et al. (2007) discuss initial observations of these photoelectrons in Titan's distant tail during the Titan encounter 'T9'. Wellbrock et al. (2012) describe three other case studies where these photoelectrons were observed at large distances from Titan. The photoelectrons are unlikely to have originated at these locations because of low neutral N2 densities. The most likely explanation for their existence at these locations is that they travelled along magnetic field lines to the observation sites from the dayside ionosphere, where they were created. Hybrid modelling results support this idea (Wellbrock et al., 2012). In this paper we continue the study of photoelectrons at Titan by performing a statistical overview of photoelectron observation in Titan's ionosphere and exosphere. Similar photoelectron energy peaks are observed at Mars and Venus due to the ionisation of CO2 and O (Frahm et al., 2006, Coates et al., 2008, 2011). We compare the morphology of photoelectron observations at Titan, Mars and Venus and discuss how they can be used to improve our understanding of the complex magnetic environment surrounding unmagnetised bodies with an atmosphere.

  12. Hard X-ray photoelectron spectroscopy of LixNi1-xO epitaxial thin films with a high lithium content

    NASA Astrophysics Data System (ADS)

    Kumara, L. S. R.; Sakata, Osami; Yang, Anli; Yamauchi, Ryosuke; Taguchi, Munetaka; Matsuda, Akifumi; Yoshimoto, Mamoru

    2014-07-01

    The core-level and valence-band electronic structures of LixNi1-xO epitaxial thin films with x = 0, 0.27, and 0.48 were studied by hard X-ray photoelectron spectroscopy. A double peak structure, consisting of a main peak and a shoulder peak, and a satellite structure were observed in the Ni 2p3/2 core-level spectra. The intensity ratio of the shoulder to main peak in this double peak structure increased with increasing lithium content in LixNi1-xO. This lithium doping dependence of the Ni 2p3/2 core-level spectra was investigated using an extended cluster model, which included the Zhang-Rice (ZR) doublet bound states arising from a competition between O 2p - Ni 3d hybridization and the Ni on-site Coulomb interaction. The results indicated that the change in the intensity ratio in the main peak is because of a reduction in the ZR doublet bound states from lithium substitutions. This strongly suggests that holes compensating Li doping in LixNi1-xO are of primarily ZR character.

  13. Evolution of photoelectron vibrational coupling with molecular complexity

    NASA Astrophysics Data System (ADS)

    Poliakoff, E. D.; Lucchese, R. R.

    2006-11-01

    We review how electronic and vibrational degrees of freedom become coupled in molecular photoionization, and describe effects that emerge as the molecular complexity increases. Molecular photoionization is frequently influenced by the temporary trapping of the continuum electron in the field of the target molecules, which is referred to as a shape resonance, as it depends on the shape of the potential experienced by the exiting photoelectron. Such resonances couple electronic and vibrational motion, and the nature of the coupling can vary widely for polyatomic molecules. We show how vibrationally resolved photoelectron spectra acquired as a function of energy can be used to elucidate such coupling. The experiments are analysed using physically realistic and computationally tractable Schwinger variational theory, and the systems studied to date can be well understood using an independent-particle, adiabatic nuclei framework. As a result, simple and intuitive pictures emerge, even when dealing with scattering phenomena involving complex molecular targets and potentials.

  14. Ultrafast molecular orbital imaging based on attosecond photoelectron diffraction.

    PubMed

    Li, Yang; Qin, Meiyan; Zhu, Xiaosong; Zhang, Qingbin; Lan, Pengfei; Lu, Peixiang

    2015-04-20

    We present ab initio numerical study of ultrafast ionization dynamics of H(2)(+) as well as CO(2) and N(2) exposed to linearly polarized attosecond extreme ultraviolet pulses. When the molecules are aligned perpendicular to laser polarization direction, photonionization of these molecules show clear and distinguishing diffraction patterns in molecular attosecond photoelectron momentum distributions. The internuclear distances of the molecules are related to the position of the associated diffraction patterns, which can be determined with high accuracy. Moreover, the relative heights of the diffraction fringes contain fruitful information of the molecular orbital structures. We show that the diffraction spectra can be well produced using the two-center interference model. By adopting a simple inversion algorithm which takes into account the symmetry of the initial molecular orbital, we can retrieve the molecular orbital from which the electron is ionized. Our results offer possibility for imaging of molecular structure and orbitals by performing molecular attosecond photoelectron diffraction.

  15. Investigation of photoelectron spectroscopy. [for obtaining branching ratios

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1973-01-01

    The problem of obtaining true and meaningful branching ratios from the photoelectron spectra is investigated. The problem consists of understanding the transmission of an electron energy analyzer for electrons with different energies, understanding the effects of using partially polarized radiation from different vacuum monochromators, and in understanding the effects of the angular distribution of photoelectrons ejected from different orbitals. An analysis of the degree of polarization of monochromatic radiation and of the problem of varying angular distributions led to the construction of a cylindrical mirror electron energy analyzer set at the special angle of 54 deg 44 min so that no discrimination would occur for electrons of different angular distributions. With the analyzer properly calibrated for transmission of electrons of different energies, data were taken at several wavelengths and for several atmospheric gases.

  16. Structural Investigation of Phosphorus in CaO-SiO2-P2O5 Ternary Glass

    NASA Astrophysics Data System (ADS)

    Wang, Zhanjun; Cai, Shengjia; Zhang, Mei; Guo, Min; Zhang, Zuotai

    2017-02-01

    The system of CaO-SiO2-P2O5 ternary glass is not only among the major constituents of steelmaking slags in iron and steel industry, but also play a significant role in other industrial process, such as chemical engineering and glass industry. In the present study, the structure of CaO-SiO2-P2O5 ternary glass with varying P2O5 content from 0 to 15 wt pct at a fixed CaO/SiO2 = 1.4 was investigated using molecular dynamics (MD) simulation combined with X-ray photoelectron spectroscopy and Raman spectra techniques. The results indicated that P5+ ions have a higher affinity to Ca2+ ions which are then stripped away from the silicate network with the addition of P2O5, resulting in the formation of Ca-O-P and Si-O-Si linkages. In addition, almost all P5+ ions displayed as Q_{P}0 ( Q_{P}n , n is the number of bridging oxygen in one [PO4]-tetrahedra units) and a small fraction of P5+ ions behave as Q_{P}1 (P-O-P) and P-O-Si. The enhanced degree of polymerization can be detected from the increase of X_{Si}3 and X_{P}1 /X_{P}0 (mole fraction of {Q}_{Si}i or {Q}_{P}i ). Furthermore, the ratio of Raman scattering coefficients for Q_{Si}i /Q_{Si}1 and Q_{P}i /Q_{P}1 were determined by combining MD simulated result with Raman spectra, which were considered to be suitable to the present study.

  17. Structural Investigation of Phosphorus in CaO-SiO2-P2O5 Ternary Glass

    NASA Astrophysics Data System (ADS)

    Wang, Zhanjun; Cai, Shengjia; Zhang, Mei; Guo, Min; Zhang, Zuotai

    2017-04-01

    The system of CaO-SiO2-P2O5 ternary glass is not only among the major constituents of steelmaking slags in iron and steel industry, but also play a significant role in other industrial process, such as chemical engineering and glass industry. In the present study, the structure of CaO-SiO2-P2O5 ternary glass with varying P2O5 content from 0 to 15 wt pct at a fixed CaO/SiO2 = 1.4 was investigated using molecular dynamics (MD) simulation combined with X-ray photoelectron spectroscopy and Raman spectra techniques. The results indicated that P5+ ions have a higher affinity to Ca2+ ions which are then stripped away from the silicate network with the addition of P2O5, resulting in the formation of Ca-O-P and Si-O-Si linkages. In addition, almost all P5+ ions displayed as {{Q}}_{{P}}0 ( {{Q}}_{{P}}n , n is the number of bridging oxygen in one [PO4]-tetrahedra units) and a small fraction of P5+ ions behave as {{Q}}_{{P}}1 (P-O-P) and P-O-Si. The enhanced degree of polymerization can be detected from the increase of {{X}}_{{Si}}3 and X_{{P}}1 /X_{{P}}0 (mole fraction of {{Q}}_{{Si}}i or {{Q}}_{{P}}i ). Furthermore, the ratio of Raman scattering coefficients for Q_{{Si}}i /Q_{{Si}}1 and Q_{{P}}i /Q_{{P}}1 were determined by combining MD simulated result with Raman spectra, which were considered to be suitable to the present study.

  18. X-ray absorption and photoelectron spectroscopic study of plasma-nitrided SiO{sub 2} film

    SciTech Connect

    Song, H.J.; Shin, H.J.; Chung, Youngsu; Lee, J.C.; Lee, M.K.

    2005-06-01

    Plasma-nitrided SiO{sub 2} thin film has been analyzed by synchrotron-radiation-based x-ray absorption and photoelectron spectroscopies (XAS and XPS). High-resolution N 1s XAS and N 1s, O 1s, and Si 2p XPS spectral changes were obtained for different annealing temperatures. N 1s XPS and XAS spectra show that at room temperature, besides the main species of N[Si(O-){sub 3-x}]{sub 3}, there exist free moleculelike N{sub 2} and HN[Si(O-){sub 3}]{sub 2}, H{sub 2}NSi(O-){sub 3}, and N-Si{sub 2}O species with surface contaminants. The spectral intensities of the N{sub 2} and the HN[Si(O-){sub 3}]{sub 2}, H{sub 2}NSi(O-){sub 3}, and N-Si{sub 2}O species decrease as the annealing temperature increases, and finally the nitrogen exists dominantly in the form of N[Si(O){sub 3}]{sub 3} species above 820 K, indicating out-diffusion of molecular N{sub 2} and structural reconstruction to form a stable structure upon annealing. The Si 2p and O 1s XPS spectra show that Si{sup >4+} 2p peak and O 1s peak appear at 103.7 and 534.0 eV, respectively, which are higher binding energies than those of thermally grown oxynitride films with lower coverage on silicon. Upon annealing the sample, these peaks shift towards lower binding energy; {approx}0.3 eV for Si{sup >4+} and 0.4 eV for O 1s. The causes of the peaks appearance at relatively higher binding energy and the peak shift upon annealing are discussed.

  19. Hard x-ray photoelectron spectroscopy of chalcopyrite solar cell components

    NASA Astrophysics Data System (ADS)

    Gloskovskii, A.; Jenkins, C. A.; Ouardi, S.; Balke, B.; Fecher, G. H.; Dai, X.-F.; Gruhn, T.; Johnson, B.; Lauermann, I.; Caballero, R.; Kaufmann, C. A.; Felser, C.

    2012-02-01

    Hard x-ray photoelectron spectroscopy is used to examine the partial density of states of Cu(In,Ga)Se2 (CIGSe), a semiconducting component of solar cells. The investigated, thin Cu(In,Ga)Se2 films were produced by multi-stage co-evaporation. Details of the measured core level and valence band spectra are compared to the calculated density of states. The semiconducting type electronic structure of Cu(In,Ga)Se2 is clearly resolved in the hard x-ray photoelectron spectra.

  20. 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.

  1. 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.

  2. Total reflection X-ray photoelectron spectroscopy as a semiconductor lubricant elemental analysis method

    NASA Astrophysics Data System (ADS)

    Alshehabi, Abbas; Sasaki, Nobuharu; Kawai, Jun

    2015-12-01

    Photoelectron spectra from a typical hard disk storage media device (HDD) were measured at total reflection and non-total reflection at unburnished, acetone-cleaned, and argon-sputtered conditions. F, O, N, and C usually making the upper layer of a typical hard disk medium were detected. Enhancement of the photoelectron emission of the fluorocarbon lubricant was observed at total reflection. Pt and Co were only found by non-total X-ray photoelectron spectroscopy (XPS) because they are constituents of a deeper region than the top and interface regions. Argon-sputtered, ultrasonic acetone-cleaned, and unburnished top layers were compared at total and non-total reflection conditions. Total reflection X-ray photoelectron spectroscopy (TRXPS) is demonstrated to be a powerful tool for storage media lubrication layer chemical state analysis, reliable for industrial quality control application , and reproducible.

  3. Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

    PubMed

    Boll, Rebecca; Rouzée, Arnaud; Adolph, Marcus; Anielski, Denis; Aquila, Andrew; Bari, Sadia; Bomme, Cédric; Bostedt, Christoph; Bozek, John D; Chapman, Henry N; Christensen, Lauge; Coffee, Ryan; Coppola, Niccola; De, Sankar; Decleva, Piero; Epp, Sascha W; Erk, Benjamin; Filsinger, Frank; Foucar, Lutz; Gorkhover, Tais; Gumprecht, Lars; Hömke, André; Holmegaard, Lotte; Johnsson, Per; Kienitz, Jens S; Kierspel, Thomas; Krasniqi, Faton; Kühnel, Kai-Uwe; Maurer, Jochen; Messerschmidt, Marc; Moshammer, Robert; Müller, Nele L M; Rudek, Benedikt; Savelyev, Evgeny; Schlichting, Ilme; Schmidt, Carlo; Scholz, Frank; Schorb, Sebastian; Schulz, Joachim; Seltmann, Jörn; Stener, Mauro; Stern, Stephan; Techert, Simone; Thøgersen, Jan; Trippel, Sebastian; Viefhaus, Jens; Vrakking, Marc; Stapelfeldt, Henrik; Küpper, Jochen; Ullrich, Joachim; Rudenko, Artem; Rolles, Daniel

    2014-01-01

    This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

  4. Adsorption and stability of malonic acid on rutile TiO2 (110), studied by near edge X-ray absorption fine structure and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Syres, Karen L.; Thomas, Andrew G.; Graham, Darren M.; Spencer, Ben F.; Flavell, Wendy R.; Jackman, Mark J.; Dhanak, Vinod R.

    2014-08-01

    The adsorption of malonic acid on rutile TiO2 (110) has been studied using photoelectron spectroscopy and C K-edge, near edge X-ray fine structure spectroscopy (NEXAFS). Analysis of the O 1s and Ti 2p spectra suggest that the molecule adsorbs dissociatively in a doubly-bidentate adsorption geometry as malonate. The data are unable to distinguish between a chelating bonding mode with the backbone of the molecule lying along the [001] azimuth or a bridging geometry along the direction. Work carried out on a wiggler beamline suggests that the molecule is unstable under irradiation by high-flux synchrotron radiation from this type of insertion device.

  5. In-situ observation of self-cleansing phenomena during ultra-high vacuum anneal of transition metal nitride thin films: Prospects for non-destructive photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Greczynski, G.; Hultman, L.

    2016-11-01

    Self-cleansing of transition metal nitrides is discovered to take place during ultra-high vacuum annealing of TiN, NbN, and VN thin films. Native oxide layers from air exposure disappear after isothermal anneal at 1000 °C. Also, for TiN, the Ti 2p and N 1s X-ray photoelectron spectra (XPS) recorded after the anneal are identical to those obtained from in-situ grown and analyzed epitaxial TiN(001). These unexpected effects are explained by oxide decomposition in combination with N-replenishing of the nitride during recrystallization. The finding opens up new possibilities for true bonding assignments through non-destructive XPS analyses, thus avoiding artefacts from Ar etching.

  6. 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.

  7. Zero kinetic energy photoelectron spectroscopy of triphenylene

    SciTech Connect

    Harthcock, Colin; Zhang, Jie; Kong, Wei

    2014-06-28

    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 S{sub 1} of the neutral molecule is of A{sub 1}′ symmetry and is therefore electric dipole forbidden in the D{sub 3h} group. Consequently, there are no observable Franck-Condon allowed totally symmetric a{sub 1}′ vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E′ third electronically excited state S{sub 3}. 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 C{sub 2v} and resulting in two nearly degenerate electronic states of A{sub 2} and B{sub 1} symmetry. Here we follow a crude treatment by assuming that all e′ vibrational modes resolve into b{sub 2} and a{sub 1} modes in the C{sub 2v} molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm{sup −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.

  8. Boronyl Mimics Gold: a Photoelectron Spectroscopy Study

    NASA Astrophysics Data System (ADS)

    Jian, Tian; Lopez, Gary; Wang, Lai-Sheng

    2015-06-01

    Previous studies have found that gold atom and boronyl bear similarities in bonding in many gas phase clusters. B10(BO), B12(BO), B3(BO)n (n=1, 2) were found to possess similar bonding and structures to B10Au, B12Au, B3Aun (n=1, 2), respectively. During the recent photoelectron spectroscopy experiments, the spectra of BiBO- and BiAu- clusters are found to exhibit similar patterns, hinting that they possess similar geometric structures. While BiAu- is a linear molecule, BiBO- is also linear. The similarity in bonding between BiBO- and BiAu- is owing to the fact that Au and BO are monovalent σ ligands. The electron affinities are measured to be 1.79±0.04eV for BiBO- and 1.36±0.02eV for BiAu-. The current results provide new examples for the BO/Au isolobal analogy and enrich the chemistry of boronyl and gold. H.-J. Zhai, C.-Q. Miao, S.-D. Li, L.-S. Wang, J. Phys. Chem. A 2010, 114, 12155-1216 Q. Chen, H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, J. Chem. Phys. 2013, 139, 044308 H. Bai, H.-J. Zhai, S.-D. Li, L.-S. Wang, Phys. Chem. Chem. Phys., 2013, 15, 9646-9653 H.-J. Zhai, Q. Chen, H. Bai, S.-D. Li, L.-S. Wang, Acc. Chem. Res. 2014, 47, 2435-2445

  9. 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.

  10. Zero kinetic energy photoelectron spectroscopy of triphenylene.

    PubMed

    Harthcock, Colin; Zhang, Jie; Kong, Wei

    2014-06-28

    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.

  11. X-ray photoelectron spectroscopy studies of the sodium chloride surface after laser exposure

    NASA Astrophysics Data System (ADS)

    Savintsev, A. P.; Gavasheli, Yu O.; Kalazhokov, Z. Kh; Kalazhokov, Kh Kh

    2016-11-01

    The surface of NaCl crystals outside and in the crater was examined using an x-ray photoelectron spectrometer. The comparative analysis of the XPS spectra showed that high- intensity laser irradiation has a significant impact on the state and composition of the surface of the ionic crystal.

  12. Manganese nanoclusters and MnSi{sub {approx}1.7} nanowires formed on Si(110): A comparative x-ray photoelectron spectroscopy study

    SciTech Connect

    Zou Zhiqiang; Shi Gaoming; Liu Xiaoyong; Sun Limin

    2013-01-14

    The growth of Mn on a Si(110) surface at room temperature (RT) and 550 Degree-Sign C has been investigated by scanning tunneling spectroscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM observation shows that the growth at 550 Degree-Sign C results in the formation of nanowires (NWs), while that at RT produces only nanoclusters. The Mn 2p XPS spectra unambiguously reveal that the NWs are composed of MnSi{sub {approx}1.7} and the nanoclusters are composed of Mn. Curve-fitting analysis of the spectra shows that 64.9% of the NWs were oxidized due to atmospheric exposure during sample transfer, while the Mn nanoclusters were completely oxidized under the same conditions. This fact indicates that the MnSi{sub {approx}1.7} NWs have better oxidation resistance than the Mn clusters, which can be attributed to the protection effect of the SiO{sub 2} layer formed on the NWs and the smaller surface to volume ratio of the NWs comparing with the clusters. The binding energy of Mn 2p for the NWs exhibits a negative shift of {approx}0.5 eV with respect to the Mn metallic state, which is similar to the silicide state of earlier transition metals Ti and Cr, but different from that of later transition metals Fe and Ni. This negative shift can be attributed to the contribution of Madelung potential.

  13. Nonadiabatic and Time-Resolved Photoelectron Spectroscopy for Molecular Systems.

    PubMed

    Flick, Johannes; Appel, Heiko; Rubio, Angel

    2014-04-08

    We quantify the nonadiabatic contributions to the vibronic sidebands of equilibrium and explicitly time-resolved nonequilibrium photoelectron spectra for a vibronic model system of trans-polyacetylene. Using exact diagonalization, we directly evaluate the sum-over-states expressions for the linear-response photocurrent. We show that spurious peaks appear in the Born-Oppenheimer approximation for the vibronic spectral function, which are not present in the exact spectral function of the system. The effect can be traced back to the factorized nature of the Born-Oppenheimer initial and final photoemission states and also persists when either only initial or final states are replaced by correlated vibronic states. Only when correlated initial and final vibronic states are taken into account are the spurious spectral weights of the Born-Oppenheimer approximation suppressed. In the nonequilibrium case, we illustrate for an initial Franck-Condon excitation and an explicit pump-pulse excitation how the vibronic wavepacket motion of the system can be traced in the time-resolved photoelectron spectra as a function of the pump-probe delay.

  14. Resonant photoelectron spectroscopy of Au{sub 2}{sup −} via a Feshbach state using high-resolution photoelectron imaging

    SciTech Connect

    León, Iker; Yang, Zheng; Wang, Lai-Sheng

    2013-11-21

    Photodetachment cross sections are measured across the detachment threshold of Au{sub 2}{sup −} between 1.90 and 2.02 eV using a tunable laser. In addition to obtaining a more accurate electron affinity for Au{sub 2} (1.9393 ± 0.0003 eV), we observe eight resonances above the detachment threshold, corresponding to excitations from the vibrational levels of the Au{sub 2}{sup −} ground state (X {sup 2}Σ{sub u}{sup +}) to those of a metastable excited state of Au{sub 2}{sup −} (or Feshbach resonances) at an excitation energy of 1.9717 ± 0.0003 eV and a vibrational frequency of 129.1 ± 1.5 cm{sup −1}. High-resolution photoelectron spectra of Au{sub 2}{sup −} are obtained using photoelectron imaging to follow the autodetachment processes by tuning the detachment laser to all the eight Feshbach resonances. We observe significant non-Franck-Condon behaviors in the resonant photoelectron spectra due to autodetachment from a given vibrational level of the Feshbach state to selective vibrational levels of the neutral final state. Using the spectroscopic data for the ground states of Au{sub 2}{sup −} (X {sup 2}Σ{sub u}{sup +}) and Au{sub 2} (X {sup 1}Σ{sub g}{sup +}), we estimate an equilibrium bond distance of 2.53 ± 0.02 Å for the Feshbach state of Au{sub 2}{sup −} by simulating the Franck-Condon factors for the resonant excitation and autodetachment processes.

  15. Oxidation and deprotonation of synthetic Fe{sup II}-Fe{sup III} (oxy)hydroxycarbonate Green Rust: An X-ray photoelectron study

    SciTech Connect

    Mullet, M. Guillemin, Y.; Ruby, C.

    2008-01-15

    X-ray photoelectron spectroscopy (XPS) was used to investigate chemical bonding and distribution of iron and oxygen species at the surface of Green Rusts (GRs). GRs with variable composition, i.e. Fe{sup II}{sub 6(1-x)}Fe{sup III}{sub 6x}O{sub 12}H{sub 2(7-3x)} CO{sub 3}.3H{sub 2}O where the Fe{sup III} molar fraction of the positively charged hydroxide sheets, x=[Fe(III)]/[Fe(total)] belongs to [1/3, 1], were synthesised under an inert atmosphere. The broadened Fe(2p{sub 3/2}) spectra were fitted using Gupta and Sen multiplets peaks and additional satellite and surface features. The [Fe(III)]/[Fe(total)] surface atomic ratios closely agree with the x ratios expected from the bulk composition, which gives a high degree of confidence on the validity of the proposed fitting procedure. The valence band spectra are also reported and show dependencies on iron speciation. The O(1s) spectra revealed the presence of O{sup 2-}, OH{sup -} species and adsorbed water. The hydroxyl component decreases with increasing x values, i.e. with the amount of ferric iron, while the oxide component increases. This study provides direct spectroscopic evidence of the deprotonation of hydroxyl groups that occurs simultaneously with the oxidation of ferrous iron within the GR structure. - Graphical abstract: X-ray photoelectron spectroscopy (XPS) is used to investigate chemical bonding and distribution of iron and oxygen species at the surface of Green Rust (GR) compounds. First spectroscopic evidence of the deprotonation of hydroxyls groups occurring simultaneously to the oxidation of Fe(II) into Fe(III) species is provided.

  16. Characterization of P2P Systems

    NASA Astrophysics Data System (ADS)

    Stutzbach, Daniel; Rejaie, Reza

    The combination of large scale and geographically distributed nature of P2P system has led to their significant impact on the Internet. It is essential to characterize deployed P2P system for at least three reasons: (1) Accurately assessing their impact on the Internet, (2) identifying any performance bottleneck as well as any opportunity for performance improvement, (3) understanding user-driven dynamics in P2P systems. To characterize a P2P system, one needs to accurately capture snapshots of the resulting P2P overlay. This is challenging because the overlay is often large and dynamic. While the overlay is discovered by a crawler, it is changing which leads to a distorted view of the system. Capturing unbiased view of the traffic in the overlay is equally challenging because it is difficult to show that the captured behavior represent the observed behavior by all peers. In this chapter, we describe some of the fundamental problems in empirical characterization of widely deployed P2P systems. We present several examples to illustrate the effect of ad-hoc measurement/data collection on the resulting analysis/characterization. We then present two sampling techniques as a powerful approach to capture unbiased view of peer properties in a scalable fashion.

  17. Characterization of Photoelectron Emission for SGEMP Analysis.

    DTIC Science & Technology

    1980-05-01

    solar-cell cover glass 17 Normalized photoelectron spectral data from Mylar, 44 Teflon and two thicknesses of Kapton 18 Photoelectron signals from flat...silver, glass, copper, 63 Teflon /Thick Kapton and Mylar/Thin Mylar irradiated by OWL II aluminum-wire spectrum. Uncertainties are discussed in text 27...experiments; these included gold, silver, anodized aluminum, thick Kapton, thick Teflon , white thermal paint and solar cell covers. The other samples were

  18. Forward-backward asymmetries of atomic photoelectrons.

    SciTech Connect

    Biheux, J. C.; Dunford, R. W.; Gemmell, D. S.; Hasegawa, S.; Kanter, E. P.; Krassig, B.; Southworth, S. H.; Young, L.

    1999-01-19

    When atomic photoionization is treated beyond the dipole approximation, photoelectron angular distributions are asymmetric forward and backward with respect to the direction of the photon beam. We have measured forward-backward asymmetries of Ar 1s and Kr 1s and 2s photoelectrons using 2-19 keV x-rays. The measured asymmetries compare well with calculations which include interference between electric-dipole and electric-quadrupole amplitudes within the nonrelativistic, independent-particle approximations.

  19. 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.

  20. X-ray photoelectron spectroscopy study of the skutterudites LaFe4Sb12 , CeFe4Sb12 , CoSb3 , and CoP3

    NASA Astrophysics Data System (ADS)

    Grosvenor, Andrew P.; Cavell, Ronald G.; Mar, Arthur

    2006-09-01

    The electronic structure of the skutterudites CoSb3 , CoP3 , LaFe4Sb12 , and CeFe4Sb12 has been investigated with x-ray photoelectron spectroscopy. The binding energies in the pnicogen and transition metal 2p spectra are shifted to reflect changes in the bonding character of these compounds. The asymmetric line shapes in the metal 2p spectra signal electronic delocalization. A plasmon loss satellite peak occurs in the Co 2p spectra of CoSb3 and CoP3 . The intensity of this peak in these and other Co-containing compounds increases with greater occupancy of the Co 3d band. The presence of trivalent rare earth was confirmed from the La and Ce 3d spectra, both of which contain shake-up satellite peaks. A second satellite peak, attributable to two-core-hole processes, also appears in the La 3d spectrum of LaFe4Sb12 but not in LaFe4P12 , indicating the involvement of La-Sb covalent bonding and the population of La 4f conduction states in the former. This peak is absent in the Ce 3d spectrum of CeFe4Sb12 because a 4f1 state is located below the Fermi edge. Fitting of the valence band spectra for all four compounds led to the formulations (Co3+)(Pn1-)3 and (R3+)(Fe2+)4(Sb1-)12 , with the electron deficiency in the rare-earth containing compounds being represented by a hole in the valence band.

  1. Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O-

    NASA Astrophysics Data System (ADS)

    Oliveira, Allan M.; Lehman, Julia H.; McCoy, Anne B.; Lineberger, W. Carl

    2016-09-01

    We report the negative ion photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O-. The photoelectron spectra show that 3.49 eV photodetachment produces two distinct electronic states of the neutral hydroxymethoxy radical (H2C(OH)Oṡ). The H2C(OH)Oṡ ground state (X ˜ 2A) photoelectron spectrum exhibits a vibrational progression consisting primarily of the OCO symmetric and asymmetric stretches, the OCO bend, as well as combination bands involving these modes with other, lower frequency modes. A high-resolution photoelectron spectrum aids in the assignment of several vibrational frequencies of the neutral H2C(OH)Oṡ radical, including an experimental determination of the H2C(OH)Oṡ 2ν12 overtone of the H-OCO torsional vibration as 220(10) cm-1. The electron affinity of H2C(OH)Oṡ is determined to be 2.220(2) eV. The low-lying A ˜ 2A excited state is also observed, with a spectrum that peaks ˜0.8 eV above the X ˜ 2A state origin. The A ˜ 2A state photoelectron spectrum is a broad, partially resolved band. Quantum chemical calculations and photoelectron simulations aid in the interpretation of the photoelectron spectra. In addition, the gas phase acidity of methanediol is calculated to be 366(2) kcal mol-1, which results in an OH bond dissociation energy, D0(H2C(OH)O-H), of 104(2) kcal mol-1, using the experimentally determined electron affinity of the hydroxymethoxy radical.

  2. 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.

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

    PubMed

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

    2014-01-28

    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 X(2)E of CH3Br(+) is stable, and both A(2)A1 and B(2)E 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((2)P) atom can be clearly observed in fast dissociation of CH3Br(+)(A(2)A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br(+)(B(2)E) ion. With the aid of the re-calculated potential energy curves of CH3Br(+) including spin-orbit coupling, dissociation mechanisms of CH3Br(+) ion in A(2)A1 and B(2)E states along C-Br rupture are revealed. For CH3Br(+)(A(2)A1) ion, the CH3 (+) + Br((2)P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br((2)P3/2) formation is through vibronic coupling to the high vibrational level of X(2)E state followed by rapid dissociation. C-Br bond breaking of CH3Br(+)(B(2)E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

  4. 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.

  5. 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.

  6. Resonant photoelectron imaging of deprotonated uracil anion via vibrational levels of a dipole-bound excited state

    NASA Astrophysics Data System (ADS)

    Huang, Dao-Ling; Liu, Hong-Tao; Ning, Chuan-Gang; Dau, Phuong Diem; Wang, Lai-Sheng

    2017-01-01

    We report both non-resonant and resonant high-resolution photoelectron imaging of cryogenically-cooled deprotonated uracil anions, N1[U-H]-, via vibrational levels of a dipole-bound excited state. Photodetachment spectroscopy of N1[U-H]- was reported previously (Liu et al., 2014), in which forty-six vibrational autodetachment resonances due to the excited dipole-bound state were observed. By tuning the detachment laser to the vibrational levels of the dipole-bound state, we obtained high-resolution resonant photoelectron spectra, which are highly non-Franck-Condon. The resonant photoelectron spectra reveal many Franck-Condon inactive vibrational modes, significantly expanding the capability of photoelectron spectroscopy. A total of twenty one fundamental vibrational frequencies for the N1[U-H]rad radical are obtained, including all eight low-frequency out-of-plane modes, which are forbidden in non-resonant photoelectron spectroscopy. Furthermore, the breakdown of the Δv = -1 propensity rule is observed for autodetachment from many vibrational levels of the dipole-bound state, due to anharmonic effects. In particular, we have observed intramolecular electron rescattering in a number of resonant photoelectron spectra, leading to excitations of low-frequency vibrational modes. Further theoretical study may be warranted, in light of the extensive experimental data and new observations, to provide further insight into the autodetachment dynamics and vibronic coupling in dipole-bound states, as well as electron molecule interactions.

  7. Flexible H2O2 in water: electronic structure from photoelectron spectroscopy and ab initio calculations.

    PubMed

    Thürmer, Stephan; Seidel, Robert; Winter, Bernd; Ončák, Milan; Slavíček, Petr

    2011-06-16

    The effect of hydration on the electronic structure of H(2)O(2) is investigated by liquid-jet photoelectron spectroscopy measurements and ab initio calculations. Experimental valence electron binding energies of the H(2)O(2) orbitals in water are, on average, 1.9 eV red-shifted with respect to the gas-phase molecule. A smaller width of the first peak was observed in the photoelectron spectrum from the solution. Our experiment is complemented by simulated photoelectron spectra, calculated at the ab initio level of theory (with EOM-IP-CCSD and DFT methods), and using path-integral sampling of the ground-state density. The observed shift in ionization energy upon solvation is attributed to a combination of nonspecific electrostatic effects (long-range polarization) and of the specific interactions between H(2)O(2) and H(2)O molecules in the first solvation shell. Changes in peak widths are found to result from merging of the two lowest ionized states of H(2)O(2) in water due to conformational changes upon solvation. Hydration effects on H(2)O(2) are stronger than on the H(2)O molecule. In addition to valence spectra, we report oxygen 1s core-level photoelectron spectra from H(2)O(2)(aq), and observed energies and spectral intensities are discussed qualitatively.

  8. Synchrotron threshold photoelectron photoion coincidence spectroscopy of radicals produced in a pyrolysis source: The methyl radical

    NASA Astrophysics Data System (ADS)

    Zhu, Yupeng; Wu, Xiangkun; Tang, Xiaofeng; Wen, Zuoying; Liu, Fuyi; Zhou, Xiaoguo; Zhang, Weijun

    2016-11-01

    We present here a flash pyrolysis source coupled with a threshold photoelectron photoion coincidence (TPEPICO) spectrometer and vacuum ultraviolet synchrotron radiation to investigate the spectroscopy and photochemistry of free radicals. The radicals are produced from pyrolysis in a heated silicon carbide tube, and the TPEPICO scheme provides a strategy to obtain pure spectra of the radicals without contamination from other byproducts. As a representative example, the methyl radical was studied, and its threshold photoelectron spectrum shows a series of umbrella vibrational transitions. The adiabatic ionization energy of the methyl radical was determined to be 9.84 ± 0.01 eV.

  9. Photoelectron interference fringes by super intense x-ray laser pulses

    NASA Astrophysics Data System (ADS)

    Toyota, Koudai; Tolstikhin, Oleg I.; Morishita, Toru; Watanabe, Shinichi

    2009-09-01

    The photoelectron spectra of H- produced by circularly polarized strong high-frequency laser pulses are theoretically studied. An oscillating substructure in the above-threshold ionization (ATI) peaks is observed, which extends the validity of the earlier findings in the 1D calculations [K. Toyota et al., Phys. Rev. A 76, 043418 (2007)] and 3D calculations for linear polarization [O. I. Tolstikhin, Phys. Rev. A 77, 032712 (2008)]. Its origin is due to an interference between a pair of photoelectron wave packets created in the rising and falling part of the pulse, which appears clearly in the stabilization regime.

  10. Anonymity in P2P Systems

    NASA Astrophysics Data System (ADS)

    Manzanares-Lopez, Pilar; Muñoz-Gea, Juan Pedro; Malgosa-Sanahuja, Josemaria; Sanchez-Aarnoutse, Juan Carlos

    In the last years, the use of peer-to-peer (P2P) applications to share and exchange knowledge among people around the world has experienced an exponential growth. Therefore, it is understandable that, like in any successful communication mechanism used by a lot of humans being, the anonymity can be a desirable characteristic in this scenario. Anonymity in P2P networks can be obtained by means of different methods, although the most significant ones are broadcast protocols, dining-cryptographer (DC) nets and multiple-hop paths. Each of these methods can be tunable in order to build a real anonymity P2P application. In addition, there is a mathematical tool called entropy that can be used in some scenarios to quantify anonymity in communication networks. In some cases, it can be calculated analytically but in others it is necessary to use simulation to obtain the network entropy.

  11. X-ray Photoelectron Spectroscopy of Isolated Nanoparticles.

    PubMed

    Sublemontier, Olivier; Nicolas, Christophe; Aureau, Damien; Patanen, Minna; Kintz, Harold; Liu, Xiaojing; Gaveau, Marc-André; Le Garrec, Jean-Luc; Robert, Emmanuel; Barreda, Flory-Anne; Etcheberry, Arnaud; Reynaud, Cécile; Mitchell, James B; Miron, Catalin

    2014-10-02

    X-ray photoelectron spectroscopy (XPS) is a very efficient and still progressing surface analysis technique. However, when applied to nano-objects, this technique faces drawbacks due to interactions with the substrate and sample charging effects. We present a new experimental approach to XPS based on coupling soft X-ray synchrotron radiation with an in-vacuum beam of free nanoparticles, focused by an aerodynamic lens system. The structure of the Si/SiO2 interface was probed without any substrate interaction or charging effects for silicon nanocrystals previously oxidized in ambient air. Complete characterization of the surface was obtained. The Si 2p core level spectrum reveals a nonabrupt interface.

  12. Threshold photoelectron spectrum of the Argon 3s satellites

    SciTech Connect

    Medhurst, L.J.; Von Wittenau, A.S.; van Zee, R.D.; Zhang, J.S.; Liu, S.H.; Shirley, D.A.; Lindle, D.W.

    1989-07-01

    Lately a variety of techniques have studied the electron correlation satellites with binding energies between the Argon 3s binding energy (29.24 eV) and the 2p/sup /minus/2/ ionization potential (43.38 eV). One of these techniques, Threshold Photoelectron Spectroscopy, with /approximately/90 meV FWHM resolution, revealed at least 25 individual electronic states. All of these could contribute to any other satellite spectrum, and this helped explain some discrepancies between previous measurements. This technique has been applied to the same region with higher resolution (<60 meV at the Ar 3s/sup /minus/1/peak). In this higher resolution spectrum at least 29 individual electronic states are present. In some cases the multiplet splitting is observed. 12 refs., 2 figs.

  13. Photoelectron spectroscopy of pyrene anion clusters: Autodetachment via excited states of anion and intermolecular interactions in anion clusters

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Hyun; Lee, Sang Hak; Song, Jae Kyu

    2009-03-01

    This study examined the anion clusters of pyrene (Py) by mass spectrometry, photoelectron spectroscopy, and theoretical calculations. The photoelectron spectra of Pyn- (n =1-4) were obtained at various photon energies. A change in photodetachment wavelength resulted in a large change in the relative intensities of vibrational progression in the photoelectron spectra. It is proposed that the observed modulation of the Franck-Condon factors by the different photon energies reflects autodetachment via the excited states of anion. The photoelectron spectra of Pyn- at 355 nm showed a broad band structure between the S0 and T1 states, which is also due to the autodetachment via a Feshbach resonance state. The photoelectron spectra of Py2- suggest the presence of a unique dimeric interaction between the two pyrene moieties, whereas the spectral features of Py3- are similar to those of Py1-. The stable structures of Py2- and Py3- obtained by density functional theory calculations support the experimental findings, where different intermolecular interactions govern the stabilization of these two species.

  14. 2p radioactivity studied by tracking technique

    SciTech Connect

    Mukha, Ivan

    2010-06-01

    The recent advance in experimental studies of short-lived exotic nuclei beyond the proton drip line is presented. In particular, in-flight decays of proton-unbound nuclei with picosecond lifetimes can be probed by a novel technique which tracks all decay products precisely, and the decay vertices as well as the angular correlations of the fragments are deduced from the measured trajectories. The corresponding pioneering experiment which identified a previously-unknown isotope {sup 19}Mg and its two-proton (2p) radioactivity as well as studied the reference 2p decay of the known isotope {sup 16}Ne is described. Systematic studies of other 2p precursors beyond the proton drip line are foreseen with this powerful technique whose sensitivity is larger by factor of 30 in comparison with a conventional invariant-mass method. The 2p radioactivity candidates {sup 30}Ar, {sup 34}Ca and {sup 26}S are discussed. Information about the respective one-proton unbound nuclei can be obtained with this technique by evaluating proton-heavy-fragment correlations. Systematic studies of nuclei beyond the proton drip line, e.g., the well-known proton resonances above the 'waiting points' in the astrophysical rp-process, {sup 69}Br and {sup 73}Br are feasible.

  15. 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.

  16. Scanning Photoelectron Microscope (SPEM) with a zone plate generated microprobe

    SciTech Connect

    Ade, H.; Kirz, J.; Hulbert, S.; Johnson, E.; Anderson, E.; Kern, D. . Dept. of Physics; Brookhaven National Lab., Upton, NY; Lawrence Berkeley Lab., CA . Center for X-Ray Optics; International Business Machines Corp., Yorktown Heights, NY . Thomas J. Watson Research Center)

    1989-01-01

    We describe instrumentation of a scanning photoelectron microscope (SPEM), which we are presently developing and commissioning at the X1A beamline of the National Synchrotron Light Source (NSLS). This instrument is designed to use the Soft X-ray Undulator (SXU) at the NSLS as a high brightness source to illuminate a Fresnel zone plate, thus forming a finely focused probe, {le} 0.2{mu}m in size, on the specimen surface. A grating monochromator selects the photon energy in the 400-800 eV range with an energy resolution better than 1 eV. The expected flux in the focus is in the 5 {times} 10{sup 7} {minus} 10{sup 9} photons/s range. A single pass Cylindrical Mirror Analyzer (CMA) is used to record photoemission spectra, or to form an image within a fixed electron energy bandwidth as the specimen is mechanically scanned. As a first test, a 1000 mesh Au grid was successfully imaged with Au 4 f primary photoelectrons, achieving a resolution of about 1{mu}m. 10 refs., 5 figs., 1 tab.

  17. Photoelectron diffraction of magnetic ultrathin films: Fe/Cu(001)

    SciTech Connect

    Tobin, J.G. ); Wagner, M.K. . Dept. of Chemistry); Guo, X.Q.; Tong, S.Y. . Dept. of Physics)

    1991-01-03

    The preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p cross section measurements with multiple scattering calculations indicates that the Fe is in a fourfold hollow site with a spacing of 3.6{Angstrom} between it and the atom directly beneath it, in the third layer. This is consistent with an FCC structure. The possibility of utilizing spin-dependent photoelectron diffraction to investigate magnetic ultrathin films will be demonstrated, using our preliminary spectra of the multiplet-split Fe3s os near-monolayer Fe/Cu(001). 18 refs., 10 figs.

  18. Photoelectron Emission Studies in CsBr at 257 nm

    SciTech Connect

    Maldonado, Juan R.; Liu, Zhi; Sun, Yun; Pianetta, Piero A.; Pease, Fabian W.; /Stanford U., Elect. Eng. Dept. /SLAC, SSRL

    2006-09-28

    CsBr/Cr photocathodes were found [1,2] to meet the requirements of a multi-electron beam lithography system operating with a light energy of 4.8 eV (257nm). The fact that photoemission was observed with a light energy below the reported 7.3 eV band gap for CsBr was not understood. This paper presents experimental results on the presence of intra-band gap absorption sites (IBAS) in CsBr thin film photo electron emitters, and presents a model based on IBAS to explain the observed photoelectron emission behavior at energies below band gap. A fluorescence band centered at 330 nm with a FWHM of about 0.34 eV was observed in CsBr/Cr samples under 257 nm laser illumination which can be attributed to IBAS and agrees well with previously obtained synchrotron photoelectron spectra[1] from the valence band of CsBr films.

  19. 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.

  20. Final-state effect on x-ray photoelectron spectrum of nominally d1 and n -doped d0 transition-metal oxides

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Posadas, Agham; Hadamek, Tobias; Demkov, Alexander A.

    2015-07-01

    We investigate the x-ray photoelectron spectroscopy (XPS) of nominally d1 and n -doped d0 transition-metal oxides including NbO2,SrVO3, and LaTiO3 (nominally d1), as well as n -doped SrTiO3 (nominally d0). In the case of single phase d1 oxides, we find that the XPS spectra (specifically photoelectrons from Nb 3 d , V 2 p , Ti 2 p core levels) all display at least two, and sometimes three distinct components, which can be consistently identified as d0,d1, and d2 oxidation states (with decreasing order in binding energy). Electron doping increases the d2 component but decreases the d0 component, whereas hole doping reverses this trend; a single d1 peak is never observed, and the d0 peak is always present even in phase-pure samples. In the case of n -doped SrTiO3, the d1 component appears as a weak shoulder with respect to the main d0 peak. We argue that these multiple peaks should be understood as being due to the final-state effect and are intrinsic to the materials. Their presence does not necessarily imply the existence of spatially localized ions of different oxidation states nor of separate phases. A simple model is provided to illustrate this interpretation, and several experiments are discussed accordingly. The key parameter to determine the relative importance between the initial-state and final-state effects is also pointed out.

  1. Theory and Application of Auger and Photoelectron Diffraction and Holography

    NASA Astrophysics Data System (ADS)

    Chen, Xiang

    This dissertation addresses the theories and applications of three important surface analysis techniques: Auger electron diffraction (AED), x-ray photoelectron diffraction (XPD), and Auger and photoelectron holography. A full multiple-scattering scheme for the calculations of XPD, AED, and Kikuchi electron diffraction pattern from a surface cluster is described. It is used to simulate 64 eV M_{2,3}VV and 913 eV L_3VV AED patterns from Cu(001) surfaces, in order to test assertions in the literature that they are explicable by a classical "blocking" and channeling model. We find that this contention is not valid, and that only a quantum mechanical multiple-scattering calculation is able to simulate these patterns well. The same multiple scattering simulation scheme is also used to investigate the anomalous phenomena of peak shifts off the forward-scattering directions in photo -electron diffraction patterns of Mg KLL (1180 eV) and O 1s (955 eV) from MgO(001) surfaces. These shifts are explained by calculations assuming a short electron mean free path. Similar simulations of XPD from a CoSi_2(111) surface for Co-3p and Si-2p normal emission agree well with experimental diffraction patterns. A filtering process aimed at eliminating the self -interference effect in photoelectron holography is developed. A better reconstructed image from Si-2p XPD from a Si(001) (2 times 1) surface is seen at atomic resolution. A reconstruction algorithm which corrects for the anisotropic emitter waves as well as the anisotropic atomic scattering factors is used for holographic reconstruction from a Co-3p XPD pattern from a CoSi_2 surface. This new algorithm considerably improves the reconstructed image. Finally, a new reconstruction algorithm called "atomic position recovery by iterative optimization of reconstructed intensities" (APRIORI), which takes account of the self-interference terms omitted by the other holographic algorithms, is developed. Tests on a Ni-C-O chain and Si(111

  2. Observation of spin-polarized photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Sinković, B.; Hermsmeier, B.; Fadley, C. S.

    1985-09-01

    We report the first observation of spin-polarized photoelectron diffraction in core-level emission from anti-ferromagnetic KMnF3. The Mn 3s multiplet splitting provides an internal source of polarized electrons, and spin polarized photoelectron diffraction effects of up to 17% are seen in the 5/ 7S intensity ratio. These effects are found to be very sensitive to both emission direction and temperature. Short-range antiferromagnetic order is found to persist up to approximately three times the Neél temperature.

  3. Photoelectron Emission Spectroscopy of Liquid Water.

    DTIC Science & Technology

    1981-04-01

    correlated to solvation free energies for H2O+(aq) and OH (aq)., DD ,FO*M 1473 EDITIOOF INOV so iS OBSOLETE Unclassified SECURITY CLASSIFICATION OF THIS PAGE...Photoelectron spectroscopy Reorganization free energy Water, liquid 20. ABSTRACT (Chlnw am ef We, aid* it nooe"mr and 1iEru’h hr 190k le 6) The threshold... energy Et a 10.06 eV (0.002 @V standard deviation) is detemined for phot~oelectron emission by litquid water and is correlated with Et a 8.45 eV for

  4. Anion photoelectron imaging spectroscopy of glyoxal

    NASA Astrophysics Data System (ADS)

    Xue, Tian; Dixon, Andrew R.; Sanov, Andrei

    2016-09-01

    We report a photoelectron imaging study of the radical-anion of glyoxal. The 532 nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA = 1.10 ± 0.02 eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE = 1.30 ± 0.04 eV. The reported EA and VDE values are attributed to the most stable (C2h symmetry) isomers of the neutral and the anion.

  5. Characterization of photocatalytic TiO2 powder under varied environments using near ambient pressure X-ray photoelectron spectroscopy

    PubMed Central

    Krishnan, Padmaja; Liu, Minghui; Itty, Pierre A.; Liu, Zhi; Rheinheimer, Vanessa; Zhang, Min-Hong; Monteiro, Paulo J. M.; Yu, Liya E.

    2017-01-01

    Consecutive eight study phases under the successive presence and absence of UV irradiation, water vapor, and oxygen were conducted to characterize surface changes in the photocatalytic TiO2 powder using near-ambient-pressure X-ray photoelectron spectroscopy (XPS). Both Ti 2p and O 1s spectra show hysteresis through the experimental course. Under all the study environments, the bridging hydroxyl (OHbr) and terminal hydroxyl (OHt) are identified at 1.1–1.3 eV and 2.1–2.3 eV above lattice oxygen, respectively. This enables novel and complementary approach to characterize reactivity of TiO2 powder. The dynamic behavior of surface-bound water molecules under each study environment is identified, while maintaining a constant distance of 1.3 eV from the position of water vapor. In the dark, the continual supply of both water vapor and oxygen is the key factor retaining the activated state of the TiO2 powder for a time period. Two new surface peaks at 1.7–1.8 and 4.0–4.2 eV above lattice oxygen are designated as peroxides (OOH/H2O2) and H2O2 dissolved in water, respectively. The persistent peroxides on the powder further explain previously observed prolonged oxidation capability of TiO2 powder without light irradiation. PMID:28240300

  6. Characterization of photocatalytic TiO2 powder under varied environments using near ambient pressure X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Krishnan, Padmaja; Liu, Minghui; Itty, Pierre A.; Liu, Zhi; Rheinheimer, Vanessa; Zhang, Min-Hong; Monteiro, Paulo J. M.; Yu, Liya E.

    2017-02-01

    Consecutive eight study phases under the successive presence and absence of UV irradiation, water vapor, and oxygen were conducted to characterize surface changes in the photocatalytic TiO2 powder using near-ambient-pressure X-ray photoelectron spectroscopy (XPS). Both Ti 2p and O 1s spectra show hysteresis through the experimental course. Under all the study environments, the bridging hydroxyl (OHbr) and terminal hydroxyl (OHt) are identified at 1.1–1.3 eV and 2.1–2.3 eV above lattice oxygen, respectively. This enables novel and complementary approach to characterize reactivity of TiO2 powder. The dynamic behavior of surface-bound water molecules under each study environment is identified, while maintaining a constant distance of 1.3 eV from the position of water vapor. In the dark, the continual supply of both water vapor and oxygen is the key factor retaining the activated state of the TiO2 powder for a time period. Two new surface peaks at 1.7–1.8 and 4.0–4.2 eV above lattice oxygen are designated as peroxides (OOH/H2O2) and H2O2 dissolved in water, respectively. The persistent peroxides on the powder further explain previously observed prolonged oxidation capability of TiO2 powder without light irradiation.

  7. Transitions of the type 2s-2p in oxygenlike Y, Zr, and Nb

    NASA Technical Reports Server (NTRS)

    Behring, W. E.; Brown, C. M.; Feldman, U.; Seely, J. F.; Reader, J.

    1986-01-01

    Transitions of the type 2s-2p in the oxygenlike ions Y XXXII, Zr XXXIII, and Nb XXXIV were identified in spectra recorded at the University of Rochester's Omega laser facility. Solid targets were spherically irradiated by 24 beams of frequency-tripled (351-nm) Nd-glass laser radiation. The spectra were photographed with a 3-m grazing-incidence spectrograph. The identified transitions of the oxygenlike ions are in the range 30 to 73 A. The wavelengths for the magnetic-dipole transitions within the 2s2p4 ground configurations of these ions are predicted from the experimental energy levels.

  8. Data Sharing in P2P Systems

    NASA Astrophysics Data System (ADS)

    Hayek, Rabab; Raschia, Guillaume; Valduriez, Patrick; Mouaddib, Noureddine

    In this chapter, we survey P2P data sharing systems. All along, we focus on the evolution from simple file-sharing systems, with limited functionalities, to Peer Data Management Systems (PDMS) that support advanced applications with more sophisticated data management techniques. Advanced P2P applications are dealing with semantically rich data (e.g., XML documents, relational tables), using a high-level SQL-like query language. We start our survey with an overview over the existing P2P network architectures, and the associated routing protocols. Then, we discuss data indexing techniques based on their distribution degree and the semantics they can capture from the underlying data. We also discuss schema management techniques which allow integrating heterogeneous data. We conclude by discussing the techniques proposed for processing complex queries (e.g., range and join queries). Complex query facilities are necessary for advanced applications which require a high level of search expressiveness. This last part shows the lack of querying techniques that allow for an approximate query answering.

  9. Titan's photoelectron energy peaks: A statistical overview and comparison to Mars and Venus

    NASA Astrophysics Data System (ADS)

    Wellbrock, A.; Coates, A. J.; Jones, G. H.

    2014-04-01

    Cassini's CAPS Electron Spectrometer (ELS) has observed discrete energy peaks at 24.1 eV in the electron spectra in Titan's ionosphere. These electrons are believed to be photoelectrons generated due to the ionisation of N2 by the strong solar He II (30.4nm) line. They are generally observed in Titan's dayside ionosphere, because this is where neutral N2 particles can be ionized by solar radiation. Coates et al. (2007) discuss initial observations of these photoelectrons in Titan's distant tail during the Titan encounter 'T9'. Wellbrock et al. (2012) describe three other case studies where these photoelectrons were observed at large distances from Titan. The photoelectrons are unlikely to have originated at these locations because of low neutral N2 densities. The most likely explanation for their existence at these locations is that they travelled along magnetic field lines to the observation sites from the dayside ionosphere, where they were created. Hybrid modelling results support this idea (Wellbrock et al., 2012). We continue the study of photoelectron energy peaks at Titan here and present results from a statistical overview of observations in Titan's ionosphere and exosphere.Similar photoelectron energy peak observations at Mars and Venus due to the ionisation of CO2 and O have been studied (Frahm et al., 2006, Coates et al., 2008, 2011). We compare our results at Titan to such studies at Mars and Venus, and discuss implications on the ionospheric and exospheric morphology of these unmagnetised objects with an atmosphere. We also investigate how photoelectrons can be used as tracers of magnetic field lines in order to improve our understanding of these complex magnetic environments.

  10. Theoretical and experimental study of valence photoelectron spectrum of D,L-alanine amino acid.

    PubMed

    Farrokhpour, H; Fathi, F; De Brito, A Naves

    2012-07-05

    In this work, the He-I (21.218 eV) photoelectron spectrum of D,L-alanine in the gas phase is revisited experimentally and theoretically. To support the experiment, the high level ab initio calculations were used to calculate and assign the photoelectron spectra of the four most stable conformers of gaseous alanine, carefully. The symmetry adapted cluster/configuration interaction (SAC-CI) method based on single and double excitation operators (SD-R) and its more accurate version, termed general-R, was used to separately calculate the energies and intensities of the ionization bands of the L- and D-alanine conformers. The intensities of ionization bands were calculated based on the monopole approximation. Also, natural bonding orbital (NBO) calculations were employed for better spectral band assignment. The relative electronic energy, Gibbs free energy, and Boltzmann population ratio of the conformers were calculated at the experimental temperature (403 K) using several theoretical methods. The theoretical photoelectron spectrum of alanine was calculated by summing over the spectra of individual D and L conformers weighted by different population ratios. Finally, the population ratio of the four most stable conformers of alanine was estimated from the experimental photoelectron spectrum using theoretical calculations for the first time.

  11. 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.

  12. Enormous yield of photoelectrons from small particles

    NASA Astrophysics Data System (ADS)

    Schmidt-Ott, A.; Schurtenberger, P.; Siegmann, H. C.

    1980-10-01

    The paper reports a large enhancement of the yield of photoelectrons per incident photon if ultrafine particles with radii not greater than 50 A are chosen as photoemitters. The results are obtained with Ag and WO3 by the use of an ac bridge technique making it possible to study very small particles suspended in gases.

  13. 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…

  14. 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.

  15. 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.

  16. Kinetics of oxynitridation of 6H-SiC( 1 1 2¯ 0) and the interface structure analyzed by ion scattering and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Okawa, T.; Fukuyama, R.; Hoshino, Y.; Nishimura, T.; Kido, Y.

    2007-02-01

    Clean and pre-oxidized 6H-SiC( 1 1 2¯ 0) surfaces were annealed in NO at temperatures ranging from 800 to 1000 °C under a pressure of 1 × 10 -3 Torr. The growing surface and interface structures were analyzed in situ by high-resolution medium energy ion scattering (MEIS) and photoelectron spectroscopy using synchrotron-radiation-light. The present result reveals growth of double-layered structure of SiO 2/SiO xN y on SiC for the samples annealed at 1000 °C in NO with and without pre-oxidation in O 2. Oxynitridation takes place only at SiO 2/SiC interfaces. The thickness of growing layers is saturated at ˜0.2 nm of SiO 2 and 0.3-0.4 nm of SiO xN y layers with the elemental compositions unchanged. For the samples pre-oxidized in 18O 2 followed by annealing in N 16O, the exchange reaction between 18O and 16O occurs at the surface and interface. No nitrogen removal was observed by annealing the oxy-nitrided sample in O 2 at 1000 °C and 1 × 10 -3 Torr. We also observed the C 1s, N 1s and Si 2p spectra and identified the N 1s and Si 2p components originating from Si-oxynitride layers.

  17. Photoelectron Spectroscopic Study on Decay Processes of Core-Excited States of NaNO2

    NASA Astrophysics Data System (ADS)

    Kamada, Masao; Azuma, Junpei; Ueda, Yuki; Yamamoto, Isamu; Imamura, Masaki; Takahashi, Kazutoshi

    2015-05-01

    The absorption and resonant photoelectron spectra of NaNO2 films have been measured at Na-L, N-K, and O-K core levels. The complete understanding of the electronic structures of NaNO2 in a wide energy region is proposed in a band scheme. Resonant photoelectron spectra indicate that the lowest excited states of N-K and O-K excitations (NK-LES and OK-LES) decay predominantly through participator and spectator Auger processes, whereas the normal Auger decay process is negligibly small. The decay probabilities of the NK-LES and OK-LES through the participator Auger process are estimated to be about 47 and 54%, respectively. The delocalization lifetimes of the NK-LES and OK-LES are also estimated to be more than 40 and 28 fs, respectively.

  18. High-resolution photoelectron imaging of cryogenically cooled α- and β-furanyl anions

    NASA Astrophysics Data System (ADS)

    DeVine, Jessalyn A.; Weichman, Marissa L.; Lyle, Steven J.; Neumark, Daniel M.

    2017-02-01

    Isomer-specific, high-resolution photoelectron spectra of α- and β-furanyl obtained via slow electron velocity-map imaging of cryogenically cooled anions are reported. The spectra yield electron affinities of 1.8546(4) and 1.6566(4) eV for the α- and β-furanyl neutral radicals, respectively. New vibronic structure is resolved and assigned based on density functional theory and Franck-Condon simulations, providing several vibrational frequencies for the ground electronic state of both neutral isomers. Subtle differences in orbital hybridization resulting from varying proximity of the deprotonated carbon to the heteroatom are inferred from photoelectron angular distributions, and the Cβsbnd H bond dissociation energy is estimated from a combination of experimental and theoretical results to be 119.9(2) kcal mol-1.

  19. Photo-electron momentum distribution and electron localization studies from laser-induced atomic and molecular dissociations

    NASA Astrophysics Data System (ADS)

    Ray, Dipanwita

    The broad objective of ultrafast strong-field studies is to be able to measure and control atomic and molecular dynamics on a femtosecond timescale. This thesis work has two major themes: (1) Study of high-energy photoelectron distributions from atomic targets. (2) Electron localization control in atomic and molecular reactions using shaped laser pulses. The first section focuses on the study of photoelectron diffraction patterns of simple atomic targets to understand the target structure. We measure the full vector momentum spectra of high energy photoelectrons from atomic targets (Xe, Ar and Kr) generated by intense laser pulses. The target dependence of the angular distribution of the highest energy photoelectrons as predicted by Quantitative Rescattering Theory (QRS) is explored. More recent developments show target structure information can be retrieved from photoelectrons over a range of energies, from 4Up up to 10Up, independent of the peak intensity at which the photoelectron spectra have been measured. Controlling the fragmentation pathways by manipulating the pulse shape is another major theme of ultrafast science today. In the second section we study the asymmetry of electron (and ion) emission from atoms (and molecules) by interaction with asymmetric pulses formed by the superposition of two colors (800 & 400 nm). Xe electron momentum spectra obtained as a function of the two-color phase exhibit a pronounced asymmetry. Using QRS theory we can analyze this asymmetric yield of the high energy photoelectrons to determine accurately the laser peak intensity and the absolute phase of the two-color electric field. This can be used as a standard pulse calibration method for all two-color studies. Experiments showing strong left-right asymmetry in D+ ion yield from D2 molecules using two-color pulses is also investigated. The asymmetry effect is found to be very ion-energy dependent.

  20. Composition depth profiles of Bi 3.15Nd 0.85Ti 3O 12 thin films studied by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Z. H.; Zhong, X. L.; Liao, H.; Wang, F.; Wang, J. B.; Zhou, Y. C.

    2011-06-01

    In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi 3.15Nd 0.85Ti 3O 12 (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO 2/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1 s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1 s, Bi 4 f, Nd 3 d, Ti 2 p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar +-ion sputtering changes lots of Bi 3+ ions into Bi 0 due to weak Bi-O bond and high etching energy.

  1. Electronic structure and correlation in β -T i3O5 and λ -T i3O5 studied by hard x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keisuke; Taguchi, Munetaka; Kobata, Masaaki; Tanaka, Kenji; Tokoro, Hiroko; Daimon, Hiroshi; Okane, Tetsuo; Yamagami, Hiroshi; Ikenaga, Eiji; Ohkoshi, Shin-ichi

    2017-02-01

    We have conducted hard x-ray photoelectron spectroscopy investigations of the electronic structure changes and electron correlation phenomena which take place upon the photoinduced reversible phase transition between β- and λ -T i3O . From valence band spectra of β- and λ -T i3O5 , we have identified the bipolaron caused by the σ-type bonding of dx y orbitals in β -T i3O5 and the π stacking between the dx y orbitals between different Ti sites in λ -T i3O5 , previously predicted by ab initio calculations. This indicates that the single electron band picture is valid for the description of photoinduced phase transitions. On the other hand, the Ti 2 p and Ti 1 s core level spectra exhibit nonlocal screening satellite features, which are typical spectroscopic signs of strong electron correlation in the coherent Ti t2 g states. The most striking result we obtain is that correlation in the valence band also manifests to reduce the plasmon energy, which results in an enhancement of the valence electron mass by a factor of 2.7.

  2. Inequality spectra

    NASA Astrophysics Data System (ADS)

    Eliazar, Iddo

    2017-03-01

    Inequality indices are widely applied in economics and in the social sciences as quantitative measures of the socioeconomic inequality of human societies. The application of inequality indices extends to size-distributions at large, where these indices can be used as general gauges of statistical heterogeneity. Moreover, as inequality indices are plentiful, arrays of such indices facilitate high-detail quantification of statistical heterogeneity. In this paper we elevate from arrays of inequality indices to inequality spectra: continuums of inequality indices that are parameterized by a single control parameter. We present a general methodology of constructing Lorenz-based inequality spectra, apply the general methodology to establish four sets of inequality spectra, investigate the properties of these sets, and show how these sets generalize known inequality gauges such as: the Gini index, the extended Gini index, the Rényi index, and hill curves.

  3. Development of a technique to prevent radiation damage of chromate conversion coatings during X-ray photoelectron spectroscopic analysis

    NASA Astrophysics Data System (ADS)

    Chidambaram, Devicharan; Halada, Gary P.; Clayton, Clive R.

    2001-09-01

    Photoreduction of hydrated sodium dichromate in the presence of carbon compounds has been studied by X-ray photoelectron spectroscopy (XPS). XPS results show that sodium dichromate also undergoes thermal breakdown during analysis. The photochemical and thermal reduction appears to be prevented by cooling with liquid nitrogen and using hydrocarbon-free vacuum pumping conditions. A model for the photoreduction of dichromate has been put forward based on an earlier photoreduction model developed by this group. Using the insight gained from this work, chromium spectra obtained from XPS of chromate conversion coatings (CCCs) on AA2024-T3 aluminum alloy have for the first time been fitted with six species of chromium compounds. The Cr 2p spectra have been critically examined for photoreduction of the hexavalent species: tetravalent and trivalent decomposition products have been identified. To explain the observed photochemical breakdown in CCCs even when performed under clean pumping conditions and liquid nitrogen cooling, its has been verified that the reduction is partly due to the cyanide species present in the CCCs. Cooling with liquid nitrogen prevents the adsorbed water on the coating from reacting with Cr(IV) to form trivalent species as the water molecules are immobilized and kinetics are slowed. As the Cr(VI)/Cr(III) ratio is critical to the performance of the CCC, and its accurate determination by XPS has not formerly been possible due to the photoreduction of Cr(VI) to Cr(III), we present a reliable method by which XPS can be used in characterization of chromate conversion coatings.

  4. Electronic structure of AlCrN films investigated using various photoelectron spectroscopies and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Tatemizo, N.; Imada, S.; Miura, Y.; Yamane, H.; Tanaka, K.

    2017-03-01

    The valence band (VB) structures of wurtzite AlCrN (Cr concentration: 0-17.1%), which show optical absorption in the ultraviolet-visible-infrared light region, were investigated via photoelectron yield spectroscopy (PYS), x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), and ab initio density of states (DOS) calculations. An obvious photoelectron emission threshold was observed ~5.3 eV from the vacuum level for AlCrN, whereas no emission was observed for AlN in the PYS spectra. Comparisons of XPS and UPS VB spectra and the calculated DOS imply that Cr 3d states are formed both at the top of the VB and in the AlN gap. These data suggest that Cr doping could be a viable option to produce new materials with relevant energy band structures for solar photoelectric conversion.

  5. Photoelectron spectroscopy of liquid water, some alcohols, and pure nonane in free micro jets

    NASA Astrophysics Data System (ADS)

    Faubel, Manfred; Steiner, Björn; Toennies, J. Peter

    1997-06-01

    The recently developed technique of accessing volatile liquids in a high vacuum environment by using a very thin liquid jet is implemented to carry out the first measurements of photoelectron spectra of pure liquid water, methanol, ethanol, 1-propanol, 1-butanol, and benzyl alcohol as well as of liquid n-nonane. The apparatus, which consists of a commercial hemispherical (10 cm mean radius) electron analyzer and a hollow cathode discharge He I light source is described in detail and the problems of the sampling of the photoelectrons in such an environment are discussed. For water and most of the alcohols up to six different electronic bands could be resolved. The spectra of 1-butanol and n-nonane show two weakly discernable peaks from which the threshold ionization potential could be determined. A deconvolution of the photoelectron spectra is used to extract ionization potentials of individual molecular bands of molecules near the surface of the liquid and shifts of the order of 1 eV compared to the gas phase are observed. A molecular orientation for water molecules at the surface of liquid water is inferred from a comparison of the relative band strengths with the gas phase. Similar effects are also observed for some of the alcohols. The results are discussed in terms of a simple "Born-solvation" model.

  6. Shake-off of loosely bound electrons in Auger decays of Kr 2p core hole states

    SciTech Connect

    Morishita, Y.; Suzuki, I.H.; Ibuki, T.

    2005-10-15

    Multicharged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. It has been found that a charge-state distribution of Kr ions being coincident with satellite peaks of Kr 2p{sub 3/2} photoelectron is slightly different from that for the main line. Resonant Auger peaks for 2p{sup -1}nl{yields}{sup 1}G{sub 4} nl transitions generated essentially Kr{sup 4+} only, which differs from the charge-state distribution for the normal Auger peak. These findings suggest that loosely bound electrons in high Rydberg orbitals are easily shaken-off in electron emission processes.

  7. Photoelectron circular dichroism in different ionization regimes

    NASA Astrophysics Data System (ADS)

    Wollenhaupt, Matthias

    2016-12-01

    Photoelectron circular dichroism (PECD) describes an asymmetry in the photoelectron angular distribution (PAD) from photoionization of randomly oriented enantiomers with circularly polarized light. Baulieu et al present a comprehensive set of measured PADs from multiphoton ionization of limonene and fenchone in different ionization regimes (multiphoton and tunneling) and analyze the resulting PECD (Baulieu et al 2016 New J. Phys. 18 102002). From their observations the authors conclude that the PECD is universal in the sense that the molecular chirality is encoded in the PAD independent of the ionization regime. The analysis is supplemented by a classical model based on electron scattering in a chiral potential. The paper presents beautiful data and is an important step towards a more complete physical picture of PECD. The results and their interpretation stimulate the ongoing vivid debate on the role of resonances in multiphoton PECD.

  8. Electronic structure of (Ge{sub 2}Sb{sub 2}Te{sub 5}){sub 1-x}(In{sub 3}SbTe{sub 2}){sub x} investigated by x-ray photoelectron spectroscopy

    SciTech Connect

    Benayad, Anass; Kim, Kihong; Lee, JaeCheol; Kang, YounSeon; Suh, Dong-Seok; Kim, KiJoon; Kim, CheolKyu; Lee, Tae-Yon; Noh, Jin-Seo; Khang, YoonHo; Shin, Hyun-Joon

    2009-08-15

    We have investigated the core levels and the valence band of (Ge{sub 2}Sb{sub 2}Te{sub 5}){sub 1-x}(In{sub 3}Sb{sub 1}Te{sub 2}){sub x} quaternary phase system (IGST) by means of x-ray photoelectron spectroscopy. A systematic shift of Sb 3d and Ge 2p core-level peaks toward lower binding energies side was observed with increasing indium amount, whereas the In 3d and Te 3d core peaks showed less change. The Sb 3d and Ge 2p core-level shift is attributed to an increase in the electronic charge of p-electrons dependent of indium amount. The valence band spectra show a distinct change in the sp configuration with indium concentration change. The change in the local bonding as the indium amount increase has a profound impact on both local atomic arrangement and amorphous-to-crystalline transformation temperature. The difference in the photoemission spectra have been discussed according to a simple structural model suggesting that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.

  9. Photoelectron Spectroscopy for Identification of Chemical States

    NASA Technical Reports Server (NTRS)

    Novakov, T.

    1971-01-01

    The technique of X-ray photoelectron spectroscopy and the fundamental electronic interactions constituting the basis of the method will be discussed. The method provides information about chemical states ("oxidation states") of atoms in molecules. In addition, quantitative elemental analysis can be performed using the same method. On the basis of this information identification of chemical species is possible. Examples of applications are discussed with particular references to the study of smog particulate matter.

  10. 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.

  11. 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.

  12. Electronic dynamics in helium nanodroplets studied via femtosecond XUV pump / UV probe photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Ziemkiewicz, Michael; Bacellar, Camila; Leone, Stephen; Neumark, Daniel; Gessner, Oliver

    2014-05-01

    Superfluid helium nanodroplets consisting of ~ 2 × 106 atoms are examined using femtosecond time-resolved photoelectron imaging. The droplets are excited by a 23.6(2) eV extreme ultraviolet (XUV) pulse in resonance with an electronically excited band associated largely with the 1s3p Rydberg level of free He atoms. Relaxation dynamics are monitored by ionizing transient states with a 3.2 eV probe pulse and measuring the time-dependent photoelectron kinetic energy distributions using velocity map imaging (VMI). A broad, intense signal associated with the initially excited 1s3p band (Ekin ~ 2.5 eV) appears within the experimental time resolution and decays within 190(70) fs. Concomitantly, a second photoelectron feature with kinetic energies ranging from 0 to 0.5 eV appears on a time scale of ~ 200 fs. The new feature is identified as originating from the 1s2p droplet Rydberg band, indicating the direct observation of a previously suggested interband relaxation within the droplet. This feature also decays within ~ 200 fs, likely due to intraband relaxation within the 1s2p/1s2s manifold to states which are too deeply bound to be ionized by the 3.2 eV probe pulse.

  13. Determination of the 1s2{\\ell }2{{\\ell }}^{\\prime } state production ratios {{}^{4}P}^{o}/{}^{2}P, {}^{2}D/{}^{2}P and {{}^{2}P}_{+}/{{}^{2}P}_{-} from fast (1{s}^{2},1s2s\\,{}^{3}S) mixed-state He-like ion beams in collisions with H2 targets

    NASA Astrophysics Data System (ADS)

    Benis, E. P.; Zouros, T. J. M.

    2016-12-01

    New results are presented on the ratio {R}m={σ }{T2p}( {}4P)/{σ }{T2p}({}2P) concerning the production cross sections of Li-like 1s2s2p quartet and doublet P states formed in energetic ion-atom collisions by single 2p electron transfer to the metastable 1s2s {}3S component of the He-like ion beam. Spin statistics predict a value of R m = 2 independent of the collision system in disagreement with most reported measurements of {R}m≃ 1{--}9. A new experimental approach is presented for the evaluation of R m having some practical advantages over earlier approaches. It also allows for the determination of the separate contributions of ground- and metastable-state beam components to the measured spectra. Applying our technique to zero-degree Auger projectile spectra from 4.5 MeV {{{B}}}3+ (Benis et al 2002 Phys. Rev. A 65 064701) and 25.3 MeV {{{F}}}7+ (Zamkov et al 2002 Phys. Rev. A 65 062706) mixed state (1{s}2 {}1S,1s2s {}3S) He-like ion collisions with H2 targets, we report new values of {R}m=3.5+/- 0.4 for boron and {R}m=1.8+/- 0.3 for fluorine. In addition, the ratios of {}2D/{}2P and {{}2P}+/{{}2P}- populations from either the metastable and/or ground state beam component, also relevant to this analysis, are evaluated and compared to previously reported results for carbon collisions on helium (Strohschein et al 2008 Phys. Rev. A 77 022706) including a critical comparison to theory.

  14. High-resolution threshold photoelectron study of the propargyl radical by the vacuum ultraviolet laser velocity-map imaging method.

    PubMed

    Gao, Hong; Xu, Yuntao; Yang, Lei; Lam, Chow-Shing; Wang, Hailing; Zhou, Jingang; Ng, C Y

    2011-12-14

    By employing the vacuum ultraviolet (VUV) laser velocity-map imaging (VMI) photoelectron scheme to discriminate energetic photoelectrons, we have measured the VUV-VMI-threshold photoelectrons (VUV-VMI-TPE) spectra of propargyl radical [C(3)H(3)(X̃(2)B(1))] near its ionization threshold at photoelectron energy bandwidths of 3 and 7 cm(-1) (full-width at half-maximum, FWHM). The simulation of the VUV-VMI-TPE spectra thus obtained, along with the Stark shift correction, has allowed the determination of a precise value 70 156 ± 4 cm(-1) (8.6982 ± 0.0005 eV) for the ionization energy (IE) of C(3)H(3). In the present VMI-TPE experiment, the Stark shift correction is determined by comparing the VUV-VMI-TPE and VUV laser pulsed field ionization-photoelectron (VUV-PFI-PE) spectra for the origin band of the photoelectron spectrum of the X̃(+)-X̃ transition of chlorobenzene. The fact that the FWHMs for this origin band observed using the VUV-VMI-TPE and VUV-PFI-PE methods are nearly the same indicates that the energy resolutions achieved in the VUV-VMI-TPE and VUV-PFI-PE measurements are comparable. The IE(C(3)H(3)) value obtained based on the VUV-VMI-TPE measurement is consistent with the value determined by the VUV laser PIE spectrum of supersonically cooled C(3)H(3)(X̃(2)B(1)) radicals, which is also reported in this article.

  15. Lunar photoelectron sheath and levitation of dust

    NASA Astrophysics Data System (ADS)

    Sodha, M. S.; Mishra, S. K.

    2014-09-01

    The decision to launch Luna Glob and Luna Resus satellites, carrying instrumentation to investigate the structure of photoelectron sheath and levitation of dust particles in the sheath, adjacent to the surface of the moon has intensified interest in this exciting area. The present analysis incorporates the following novel features: (i) In contrast to intuitive half Maxwellian (M) distribution of velocities of the photoelectrons, emitted from the surface of the moon, which corresponds to an arbitrary temperature, a well-established half Fermi Dirac (F-D) distribution [R. H. Fowler, Phys. Rev. 38, 45 (1931)] has been used, (ii) the profiles for electric potential, electric field, and electron density have been derived (not a priori assumed), (iii) an expression for the rate of electron accretion on a positively charged dust particle, which takes account of the anisotropic flux of electrons has been derived and used in the analysis, and (iv) a derived (rather than intuitive) expression for the rate of photoelectron emission from a positively charged dust particle has been used for the first time in such analyses. The profiles of the electric potential, electric field, and electron density in the photoelectric sheath have been evaluated for typical lunar environment and used to obtain the profile of the radius of a dust particle for levitation. The dependence of the electric potential on the surface of the moon on the parameters of the solar wind and photo-efficiency of the material of moon's surface has also been discussed. It is seen that the results based on half F-D distribution are significantly different from those obtained on the basis of M-distribution.

  16. Theory of spin polarized photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Sinković, B.; Friedman, D. J.; Fadley, C. S.

    1991-01-01

    We discuss several aspects of the theory of spin-polarized photoelectron diffraction (SPPD). This method makes use of multiplet splittings of core-level binding energies to produce photoelectron peaks with high spin polarization (for example, the two principal peaks associated with Mn 3s emission from Mn 2+). We consider three possible mechanisms for spin-dependent photoelectron scattering and diffraction: exchange scattering by valence electrons (3d 5 for Mn 2+), spin-orbit scattering (which is not expected to yield large effects if the sample does not have a net magnetization), and spin-dependent inelastic scattering (which cannot yet be dealt with in a fully quantitative way, but is estimated to be less important than the other two). The fact that SPPD involves internal sources of polarized electrons references to their respective emitters implies that it can be employed to study magnetic order in both anti-ferromagnets and ferromagnets and at temperatures above their respective Néel or Curie points. The effects of exchange scattering on Mn 3s emission from Mn 2+ in KMnF 3 have been incorporated into a single-scattering cluster model of the diffraction process via either the Dirac-Hara or Kohn-Sham local density approximations. This model is applied to several cases: a single Mn 2+ scatterer, small clusters of Mn 2+ scatterers, and full clusters appropriate to the (110) surface of KMnF 3, with all atoms included. These calculations demonstrate that SPPD should be a short-range probe of magnetic order, a result consistent with conclusions reached in several prior studies of photoelectron diffraction without spin resolution. They also illustrate the perturbative nature of these effects, which are only about ca. 5-15% of the total intensity; this in turn leads to several possible simplifications in the theory. We have in addition phenomenologically modelled the decreases of short-range order with increasing temperature by using a Gaussian modulation of spins; this

  17. Photoelectron emission as an alternative electron impact ionization source for ion trap mass spectrometry.

    PubMed

    Gamez, Gerardo; Zhu, Liang; Schmitz, Thomas A; Zenobi, Renato

    2008-09-01

    Electron impact ionization has several known advantages; however, heated filament electron sources have pressure limitations and their power consumption can be significant for certain applications, such as in field-portable instruments. Herein, we evaluate a VUV krypton lamp as an alternative source for ionization inside the ion trap of a mass spectrometer. The observed fragmentation patterns are more characteristic of electron impact ionization than photoionization. In addition, mass spectra of analytes with ionization potentials higher than the lamp's photon energy (10.6 eV) can be easily obtained. A photoelectron impact ionization mechanism is suggested by the observed data allowed by the work function of the ion trap electrodes (4.5 eV), which is well within the lamp's photon energy. In this case, the photoelectrons emitted at the surface of the ion trap end-cap electrode are accelerated by the applied rf field to the ring electrode. This allows the photoelectrons to gain sufficient energy to ionize compounds with high ionization potentials to yield mass spectra characteristic of electron impact. In this manner, electron impact ionization can be used in ion trap mass spectrometers at low powers and without the limitations imposed by elevated pressures on heated filaments.

  18. Explaining the MoVO4- photoelectron spectrum: Rationalization of geometric and electronic structure

    NASA Astrophysics Data System (ADS)

    Thompson, Lee M.; Jarrold, Caroline C.; Hratchian, Hrant P.

    2017-03-01

    Attempts to reconcile simulated photoelectron spectra of MoVO4- clusters are complicated by the presence of very low energy barriers in the potential energy surfaces (PESs) of the lowest energy spin states and isomers. Transition state structures associated with the inversion of terminal oxygen ligands are found to lie below, or close to, the zero point energy of associated modes, which themselves are found to be of low frequency and thus likely to be significantly populated in the experimental characterization. Our simulations make use of Boltzmann averaging over low-energy coordinates and full mapping of the PES to obtain simulations in good agreement with experimental spectra. Furthermore, molecular orbital analysis of accessible final spin states reveals the existence of low energy two-electron transitions in which the final state is obtained from a finite excitation of an electron along with the main photodetachment event. Two-electron transitions are then used to justify the large difference in intensity between different bands present in the photoelectron spectrum. Owing to the general presence of terminal ligands in metal oxide clusters, this study identifies and proposes a solution to issues that are generally encountered when attempting to simulate transition metal cluster photoelectron spectroscopy.

  19. Unexpectedly broad photoelectron spectrum as a signature of ultrafast electronic relaxation of Rydberg states of carbon dioxide

    NASA Astrophysics Data System (ADS)

    Adachi, Shunsuke; Sato, Motoki; Suzuki, Toshinori; Grebenshchikov, Sergy Yu.

    2017-03-01

    The dynamics of CO2 excited into Rydberg states lying 0.2 eV below the ionization threshold is studied by means of time resolved photoelectron imaging. Over 3 eV broad photoelectron spectra are measured for all pump-probe delay times. Quantum mechanical calculations demonstrate that the spectral broadening is due to ultrafast electronic relaxation of Rydberg states and identify the likely relaxation pathways. Experiment and theory bracket the relaxation time between 15 and 65 fs. A weak time independent ionization signal is attributed to CO2 trapped in near-threshold triplet states.

  20. 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.

  1. Ab initio oscillator strengths and transition probabilities of transitions from 2s{sup 2}2p{sup 2}3l and 2s2p{sup 3}3l in S X

    SciTech Connect

    Karpuskiene, R. . E-mail: karra@itpa.lt; Bogdanovich, P.; Udris, A.

    2005-01-01

    Ab initio energy spectra of the ground configuration 2s{sup 2}2p{sup 3} and the excited configurations 2s2p{sup 4}, 2p{sup 5}, 2s{sup 2}2p{sup 2}3s, 2s{sup 2}2p{sup 2}3p, 2s{sup 2}2p{sup 2}3d, 2s2p{sup 3}3s, 2s2p{sup 3}3p, and 2s2p{sup 3}3d of nitrogen-like sulphur S X have been calculated using the configuration interaction method. The wavelengths, oscillator strengths, and the emission transition probabilities from configurations 2s{sup 2}2p{sup 2}3l and 2s2p{sup 3}3l are obtained. The calculated results are compared with the recent experimental data.

  2. Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy.

    PubMed

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

    2016-05-05

    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.

  3. 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.

  4. FAST TRACK COMMUNICATION: Attosecond photoelectron interference in the separable Coulomb Volkov continuum

    NASA Astrophysics Data System (ADS)

    Yudin, G. L.; Patchkovskii, S.; Corkum, P. B.; Bandrauk, A. D.

    2007-03-01

    We develop a description of laser-assisted x-ray photoionization based on a sudden approximation approach. By splitting the system evolution into three time stages we find necessary and sufficient conditions for spatial and temporal separation of Coulomb and Volkov continuum solutions. Using the separable Coulomb-Volkov wavefunction we present an analytical non-relativistic quantum theory of attosecond photoionization. It applies for arbitrary x-ray parameters, with both Coulomb continuum and laser field treated non-perturbatively. The theory provides a firm basis for characterizing photoelectron phase and atomic and molecular wavefunctions, by extracting them from experimental data. Using the molecular hydrogen ion as a test case, we display a variety of photoelectron interference sources in energy- and angular-resolved spectra for different pulse durations, chirps and delay times between x-ray pulse replicas.

  5. Photoelectron momentum distributions of the hydrogen molecular ion driven by multicycle near-infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Murakami, Mitsuko; Chu, Shih-I.

    2016-10-01

    The photoelectron momentum distributions (PMDs) of the hydrogen molecular ion H2+ driven by strong near-infrared laser pulses are studied based on the ab initio numerical solution of the time-dependent Schrödinger equation and the Volkov wave propagation. Both linear and circular polarization are considered, in accordance with the recent experiment by M. Odenweller et al. [Phys. Rev. A 89, 013424 (2014), 10.1103/PhysRevA.89.013424]. We will discuss the difference between the molecular (diatomic) and the atomic PMDs and the effect of molecular potential to the photoelectron energy. In particular, we demonstrate that the above-threshold ionization spectra of H2+ could upshift their energy when driven by a linearly polarized laser field parallel to the molecular axis.

  6. VUV photodissociation of thiazole molecule investigated by TOF-MS and photoelectron photoion coincidence spectroscopy.

    PubMed

    Lago, A F; Januário, R D; Simon, M; Dávalos, J Z

    2014-11-01

    Photoelectron photoion coincidence measurements have been performed for the thiazole (C3H3NS) molecule in gas phase, using time-of-flight mass spectrometry in the electron-ion coincidence mode and vacuum ultraviolet synchrotron radiation. photoelectron photoion coincidence spectra have been recorded as a function of the photon energy covering the valence range from 10 to 21 eV. The resulting photoionization products as well as the dissociation pathways leading to the ionic species were proposed and discussed. We have also performed density functional theory and ab initio calculations for the neutral molecule, its cation and the ion fragments produced in order to determine their electronic and structural parameters.

  7. 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.

  8. Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds.

    PubMed

    Boulanger, Anne-Marie; Rennie, Emma E; Holland, David M P; Shaw, David A; Mayer, Paul M

    2006-07-13

    The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.

  9. 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.

  10. Photoelectron Spectroscopy of Hexachloroplatinate-Nucleobase Complexes: Nucleobase Excited State Decay Observed via Delayed Electron Emission

    SciTech Connect

    Sen, Ananya; Matthews, Edward M.; Hou, Gao-Lei; Wang, Xue B.; Dessent, Caroline

    2015-11-14

    We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ~1.7 eV, values that are lower than the RCB of the uncomplexed PtCl6 2- dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl6 2-∙thymine and PtCl6 2-∙adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN)4 2-∙nucleobase complexes [Sen et al, J. Phys. Chem. B, 119, 11626, 2015]. The observation of delayed electron emission bands in the PtCl6 2-∙nucleobase spectra obtained in this work, as for the previously studied Pt(CN)4 2-∙nucleobase complexes, is attributed to onephoton excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a “dynamic tag” which has the propensity to emit electrons when the attached nucleobase decays over a timescale long enough to allow autodetachment.

  11. Pu electronic structure and photoelectron spectroscopy

    SciTech Connect

    Joyce, John J; Durakiewicz, Tomasz; Graham, Kevin S; Bauer, Eric D; Moore, David P; Mitchell, Jeremy N; Kennison, John A; Martin, Richard L; Roy, Lindsay E; Scuseria, G. E.

    2010-01-01

    The electronic structure of PuCoGa{sub 5}, Pu metal, and PuO{sub 2} is explored using photoelectron spectroscopy. Ground state electronic properties are inferred from temperature dependent photoemission near the Fermi energy for Pu metal. Angle-resolved photoemission details the energy vs. crystaJ momentum landscape near the Fermi energy for PuCoGa{sub 5} which shows significant dispersion in the quasiparticle peak near the Fermi energy. For the Mott insulators AnO{sub 2}(An = U, Pu) the photoemission results are compared against hybrid functional calculations and the model prediction of a cross over from ionic to covalent bonding is found to be reasonable.

  12. Isomer-selected photoelectron spectroscopy of isolated DNA oligonucleotides: phosphate and nucleobase deprotonation at high negative charge states.

    PubMed

    Vonderach, Matthias; Ehrler, Oli T; Matheis, Katerina; Weis, Patrick; Kappes, Manfred M

    2012-05-09

    Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3-, 4-, and 5-, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A(5-x)T(x)](4-) and [GT(4)](4-) pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral).

  13. Bimolecular reaction dynamics from photoelectron spectroscopy of negative ions

    SciTech Connect

    Bradforth, S.E.

    1992-11-01

    The transition state region of a neutral bimolecular reaction may be experimentally investigated by photoelectron spectroscopy of an appropriate negative ion. The photoelectron spectrum provides information on the spectroscopy and dynamics of the short lived transition state and may be used to develop model potential energy surfaces that are semi-quantitative in this important region. The principles of bound [yields] bound negative ion photoelectron spectroscopy are illustrated by way of an example: a full analysis of the photoelectron bands of CN[sup [minus

  14. Time statistics of the photoelectron emission process in scintillation counters

    NASA Astrophysics Data System (ADS)

    Ranucci, Gioacchino

    1993-10-01

    In this work the statistical time properties of the photoelectron emission process in scintillation counters are evaluated assuming that the total number of emitted photoelectrons is distributed according to a generic random distribution. Under this general assumption, the probability density function of the time of emission of the ith photoelectron is computed; it is also demonstrated that if the number of emitted photoelectrons is Poisson distributed, this probability density function reduces to the expression already published for this particular case. Finally the procedure adopted is extended to give the expressions predicting the performances of organic scintillators for the pulse shape discrimination of particles of different type.

  15. Direct observation of up-conversion via femtosecond photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Liu, Yuzhu; Knopp, Gregor; Gerber, Thomas

    2015-10-01

    Ultrafast relaxation dynamics in 2-methylfuran has been investigated by time-resolved photoelectron imaging. An "up" internal conversion from a low-lying state into a higher-lying one has been observed experimentally. Temporal photoelectron kinetic-energy distributions and angular distributions of the photoelectrons are analyzed. In the up-conversion process, the vibrational energy in the initial state is converted to the electronic energy of the final state during the energy transfer. And the time scale for the up-conversion process is estimated by the observed onset delay for the corresponding photoelectron bands.

  16. Born in weak fields: below-threshold photoelectron dynamics

    NASA Astrophysics Data System (ADS)

    Williams, J. B.; Saalmann, U.; Trinter, F.; Schöffler, M. S.; Weller, M.; Burzynski, P.; Goihl, C.; Henrichs, K.; Janke, C.; Griffin, B.; Kastirke, G.; Neff, J.; Pitzer, M.; Waitz, M.; Yang, Y.; Schiwietz, G.; Zeller, S.; Jahnke, T.; Dörner, R.

    2017-02-01

    We investigate the dynamics of ultra-low kinetic energy photoelectrons. Many experimental techniques employed for the detection of photoelectrons require the presence of (more or less) weak electric extraction fields in order to perform the measurement. Our studies show that ultra-low energy photoelectrons exhibit a characteristic shift in their apparent measured momentum when the target system is exposed to such static electric fields. Already fields as weak as 1 V cm-1 have an observable influence on the detected electron momentum. This apparent shift is demonstrated by an experiment on zero energy photoelectrons emitted from He and explained through theoretical model calculations.

  17. 2P/Encke, the Taurid complex NEOs and the Maribo and Sutter's Mill meteorites

    NASA Astrophysics Data System (ADS)

    Tubiana, C.; Snodgrass, C.; Michelsen, R.; Haack, H.; Böhnhardt, H.; Fitzsimmons, A.; Williams, I. P.

    2015-12-01

    Aims: 2P/Encke is a short period comet that was discovered in 1786 and has been extensively observed and studied for more than 200 years. The Taurid meteoroid stream has long been linked with 2P/Encke owing to a good match of their orbital elements, even though the comet's activity is not strong enough to explain the number of observed meteors. Various small near-Earth objects (NEOs) have been discovered with orbits that can be linked to 2P/Encke and the Taurid meteoroid stream. Maribo and Sutter's Mill are CM type carbonaceous chondrite that fell in Denmark on January 17, 2009 and April 22, 2012, respectively. Their pre-atmospheric orbits place them in the middle of the Taurid meteoroid stream, which raises the intriguing possibility that comet 2P/Encke could be the parent body of CM chondrites. Methods: To investigate whether a relationship between comet 2P/Encke, the Taurid complex associated NEOs, and CM chondrites exists, we performed photometric and spectroscopic studies of these objects in the visible wavelength range. We observed 2P/Encke and 10 NEOs on August 2, 2011 with the FORS instrument at the 8.2 m Very Large Telescope on Cerro Paranal (Chile). Results: Images in the R filter, used to investigate the possible presence of cometary activity around the nucleus of 2P/Encke and the NEOs, show that no resolved coma is present. None of the FORS spectra show the 700 nm absorption feature due to hydrated minerals that is seen in the CM chondrite meteorites. All objects show featureless spectra with moderate reddening slopes at λ< 800 nm. Apart for 2003 QC10 and 1999 VT25, which show a flatter spectrum, the spectral slope of the observed NEOs is compatible with that of 2P/Encke. However, most of the NEOs show evidence of a silicate absorption in lower S/N data at λ> 800 nm, which is not seen in 2P/Encke, which suggests that they are not related. Conclusions: Despite similar orbits, we find no spectroscopic evidence for a link between 2P/Encke, the Taurid

  18. Prediction and identification of some transitions associated with 2p/k/ and 2p/k-1/3l configurations in six-, seven- and eight-electron ions. [spectroscopic analysis using superstructure computer program

    NASA Technical Reports Server (NTRS)

    Kastner, S. O.; Bhatia, A. K.; Cohen, L.

    1977-01-01

    Calculations of fine structure and transition probabilities, using the superstructure program developed at University College London, have been carried out for the 2p(k) and 2p(k-1)3l configurations of ions with six, seven, or eight electrons. The predicted line patterns are compared with existing observations for silicon, sulfur, argon, and calcium to yield some new identifications in laboratory and solar spectra and to indicate some transitions, as yet unobserved, that may be of observational importance.

  19. Probing the electronic and vibrational structure of Au{sub 2}Al{sub 2}{sup −} and Au{sub 2}Al{sub 2} using photoelectron spectroscopy and high resolution photoelectron imaging

    SciTech Connect

    Lopez, Gary V.; Czekner, Joseph; Jian, Tian; Li, Wei-Li; Yang, Zheng; Wang, Lai-Sheng

    2014-12-14

    The electronic and vibrational structures of Au{sub 2}Al{sub 2}{sup −} and Au{sub 2}Al{sub 2} have been investigated using photoelectron spectroscopy (PES), high-resolution photoelectron imaging, and theoretical calculations. Photoelectron spectra taken at high photon energies with a magnetic-bottle apparatus reveal numerous detachment transitions and a large energy gap for the neutral Au{sub 2}Al{sub 2}. Vibrationally resolved PE spectra are obtained using high-resolution photoelectron imaging for the ground state detachment transition of Au{sub 2}Al{sub 2}{sup −} at various photon energies (670.55−843.03 nm). An accurate electron affinity of 1.4438(8) eV is obtained for the Au{sub 2}Al{sub 2} neutral cluster, as well as two vibrational frequencies at 57 ± 8 and 305 ± 13 cm{sup −1}. Hot bands transitions yield two vibrational frequencies for Au{sub 2}Al{sub 2}{sup −} at 57 ± 10 and 144 ± 12 cm{sup −1}. The obtained vibrational and electronic structure information is compared with density functional calculations, unequivocally confirming that both Au{sub 2}Al{sub 2}{sup −} and Au{sub 2}Al{sub 2} possess C{sub 2v} tetrahedral structures.

  20. Characterisation of crystalline C-S-H phases by X-ray photoelectron spectroscopy

    SciTech Connect

    Black, Leon; Garbev, Krassimir; Stemmermann, Peter; Hallam, Keith R.; Allen, Geoffrey C

    2003-06-01

    We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium-silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and {alpha}-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium-silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO) and nonbridging oxygen (NBO) moieties. Finally, the modified Auger parameter has proved particularly useful in determining the extent of silicate anion polymerisation. Of note also are the apparently unusual spectra for 11 A tobermorite. The silicon and oxygen photoelectron spectra indicate a phase with a lower degree of silicate polymerisation than predicted from its composition. The main contributing factor is the intrinsic disorder within the tobermorite structure. This study has shown how XPS may be used to obtain valuable structural information from C-S-H phases, and our analysis of the crystalline phases is the first step towards the analysis of real C-S-H-based cement systems.

  1. Investigations on surface chemical analysis using X-ray photoelectron spectroscopy and optical properties of Dy3+-doped LiNa3P2O7 phosphor

    NASA Astrophysics Data System (ADS)

    Munirathnam, K.; Dillip, G. R.; Chaurasia, Shivanand; Joo, S. W.; Deva Prasad Raju, B.; John Sushma, N.

    2016-08-01

    Near white-light emitting LiNa3P2O7:Dy3+ phosphors were prepared by a conventional solid-state reaction method. The orthorhombic crystal structure of the phosphors was confirmed using X-ray diffraction (XRD), and the valence states of the surface elements were determined from the binding energies of Li 1s, O 1s, Na 1s, P 2p, and Dy 3d by X-ray photoelectron spectroscopy (XPS). Attenuated total reflectance (ATR) - Fourier transform infrared (FT-IR) spectroscopy was employed to identify the pyrophosphate groups in the phosphors. Diffuse reflectance spectra (DRS) show the absorption bands of the Dy3+ ions in the host material. Intense blue (481 nm) and yellow (575 nm) emissions were obtained at an excitation wavelength of 351 nm and are attributed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. The combination of these two intense bands generates light emission in the near-white region of the chromaticity diagram.

  2. In situ investigations of laser and thermally modified As{sub 2}S{sub 3} nanolayers: Synchrotron radiation photoelectron spectroscopy and density functional theory calculations

    SciTech Connect

    Kondrat, O. Holomb, R.; Popovich, N.; Mitsa, V.; Veres, M.; Csik, A.; Feher, A.; Tsud, N.; Matolín, V.; Vondráček, M.; Prince, K. C.

    2015-12-14

    As-deposited, annealed, and in situ As{sub 2}S{sub 3} nanolayers, illuminated by blue (405 nm) and red (650 nm) laser light, were studied using synchrotron radiation photoelectron spectroscopy and DFT electronic structure calculations. Changes in composition and local atomic coordination occurring in the irradiated region of As{sub 2}S{sub 3} films were monitored by analysis of As 3d and S 2p core levels. These studies show that both the thermal treatment and the red laser illumination of As{sub 2}S{sub 3} nanolayers decrease the concentration of homopolar (As-As and S-S) bonds. From the other hand, an increasing concentration of As-rich structural units (s.u.) with a homopolar As-As bond was observed under in situ blue laser illumination of As{sub 2}S{sub 3} nanolayers. Molecular orbital energies were calculated for different As- and S-centered s.u. and used for the interpretation of the core levels and valence band spectra. The surface local structure of the As{sub 2}S{sub 3} nanolayers and its photoinduced transformation are discussed in detail.

  3. Photoelectron Spectroscopy of Rare-Gas Solvated Nucleobase Anions

    NASA Astrophysics Data System (ADS)

    Buonaugurio, Angela M.; Chen, Jing; Bowen, Kit H.

    2012-06-01

    Gas-phase polar molecular anions [uracil (U^-), thymine (T^-), 1-3 dimethyluracil (DMU^-)] solvated by rare gas atoms were studied by means of negative ion photoelectron spectroscopy. The photoelectron spectrum (PES) of U^-, T^-, and DMU^- each exhibit a distinctive dipole-bound (DB) spectral signature. The spectra of U^-, U^- (Ar)_1,2 and U^- (Kr)_1 also only displayed the DB anion feature. Upon the solvation of more rare gas atoms, the spectra of U^- (Ar)_3, U^- (Kr)_2, and U^- (Xe)1-3 not only retained the DB signature but also exhibited the valence anion features. Moreover, the DB and the valence features shifted together to higher electron binding energies (EBEs) with increasing numbers of rare gas solvent atoms. Therefore, the co-existing DB and the valence anions appeared to be strongly coupled with each other, i.e. they effectively form a single state that is a superposition of both DB and valence anion states. For both U^- and T^- series, the ``onset size" of the Xe, Kr, and Ar solvents for the co-existing of the two anionic states was 1, 2, and 3 respectively. In addition, a minimum of 2 methane (CH_4) molecules or 1 ethane (C_2H_6) molecule were required to induce the coupling between the two states in the T^- series. Thus, the nucleobase anion interaction with non-polar solvent atoms tracks as the sum of the solvent polarizabilities. However for the DMU- series, the DB and the valence anions of DMU^-(Xe)_1, DMU^-(Kr)_2, and DMU^-(Ar)_3 were completely absent in both the mass spectra and the PES. Beyond these ``holes", their PES displayed the similar behaviors to the U^- and T^- series. Extrapolated EA values for these missing species were at or very close to zero, which may explain why they were not seen. However, why this was the case is not clear. With better Franck-Condon overlap between the origins of the NB^- (Rg)_n valence anion and the neutral NB(Rg)n than between those of the NB^- (H2O)n valence anion and the neutral NB(H2O)n, extrapolation of

  4. Scanned-energy mode photoelectron diffraction measurements at beamline 7.0.1

    SciTech Connect

    Toomes, R.; Booth, N.A.; Woodruff, D.P.

    1997-04-01

    This report covers the results of the authors first experimental run, in May 1996, conducted to explore the advantages offered by the high spectral resolution available at the SpectroMicroscopy Facility on beam line 7.0 to conduct scanned-energy mode photoelectron diffraction (PhD). This technique is now a well-established method for the determination of local structure of atomic and molecular adsorbates on well-characterised surfaces. The directly-emitted component of an adsorbate core-level photoelectron wavefield interferes coherently with components of the same wavefield elastically scattered by surrounding atoms, leading to a modulation in the photoemission intensity as a function of kinetic energy in any specific emission direction. A series of such PhD modulation spectra, each typically covering energies from 50-500 eV, for a series of different emission directions, provides the basis for a quantitative structure determination of the emitter-scatterer geometry. Within the last years the authors have developed an integrated approach to extract the structural information from these photoelectron diffraction (PhD) spectra in a quantitative way. A direct data inversion technique (the so-called Projection method) provides a first-order estimate of the local adsorbate geometry in the form of an `image` of the scatterer atoms which are nearest neighbours to the emitter. This information is then used as a starting model for optimisation of the structural parameters by comparing the experimental PhD spectra with the results of multiple scattering simulations using a code developed by Fritzsche. The optimisation uses an automated trial-and-error procedure by minimising a reliability factor which provides an objective measure of the quality of agreement between experiment and theory. The authors have successfully applied this approach to the structure determination of about 30 adsorption systems.

  5. Providing VoD Streaming Using P2P Networks

    NASA Astrophysics Data System (ADS)

    Pedro Muñoz-Gea, Juan; Malgosa-Sanahuja, Josemaria; Manzanares-Lopez, Pilar; Carlos Sanchez-Aarnoutse, Juan

    Overlays and P2P systems, initially developed to support IP multicast and file-sharing, have moved beyond that functionality. They are also proving to be key technologies for the delivery of video streaming. Recently, there have been a number of successful deployments for "live" P2P streaming. However, the question remains open whether similar P2P technologies can be used to provide VoD (Video-On-Demand) services. A P2P VoD service is more challenging to design than a P2P live streaming system because the system should allow users arriving at arbitrary times to watch (arbitrary parts of) the video.

  6. Probing molecular frame photoelectron angular distributions via high-order harmonic generation from aligned molecules

    NASA Astrophysics Data System (ADS)

    Lin, C. D.; Jin, Cheng; Le, Anh-Thu; Lucchese, R. R.

    2012-10-01

    We analyse the theory of single photoionization (PI) and high-order harmonic generation (HHG) by intense lasers from aligned molecules. We show that molecular-frame photoelectron angular distributions can be extracted from these measurements. We also show that, under favourable conditions, the phase of PI transition dipole matrix elements can be extracted from the HHG spectra. Furthermore, by varying the polarization axis of the HHG generating laser with respect to the polarization axis of the aligning laser, it is possible to extract angle-dependent tunnelling ionization rates for different subshells of the molecules.

  7. Electronic structure effects in liquid water studied by photoelectron spectroscopy and density functional theory

    SciTech Connect

    Nordlund, Dennis; Odelius, Michael; Bluhm, Hendrik; Ogasawara, Hirohito; Pettersson, Lars G.M.; Nilsson, Anders

    2008-04-29

    We present valence photoelectron emission spectra of liquid water in comparison with gas-phase water, ice close to the melting point, low temperature amorphous and crystalline ice. All aggregation states have major electronic structure changes relative to the free molecule, with rehybridization and development of bonding and anti-bonding states accompanying the hydrogen bond formation. Sensitivity to the local structural order, most prominent in the shape and splitting of the occupied 3a{sub 1} orbital, is understood from the electronic structure averaging over various geometrical structures, and reflects the local nature of the orbital interaction.

  8. Raman spectroscopic study of (Ph 2P) 2CCH 2 and [(Ph 2P) 2CCH 2]W(CO) 4

    NASA Astrophysics Data System (ADS)

    Fickert, C.; Posset, U.; Kiefer, W.

    1997-06-01

    The Raman and IR spectra of 1,1-bis[diphenylphosphino]ethene (Ph 2P) 2CCH 2 (vdpp) and the tetracarbonyl tungsten complex (vdpp)W(CO) 4 have been recorded. Vibrational assignments are proposed based on local symmetry considerations. For the vinylidene stretching mode a coordination shift is observed from 1588 cm -1 in polycrystalline vdpp to 1581 cm -1 in its tetracarbonyl tungsten complex. From a comparison of the v(CO) splitting pattern with those of related complexes monoclinic structure with factor group C2h and four formula units per unit cell is concluded.

  9. Storm Spectra

    NASA Technical Reports Server (NTRS)

    2007-01-01

    portion is defined by the day/night boundary (known as the terminator).

    These two images illustrate only a small fraction of the information contained in a single LEISA scan, highlighting just one aspect of the power of infrared spectra for atmospheric studies.

  10. Electron-impact core excitation of SF6. I. S 2p, S 2s, and F 1s spectroscopy

    NASA Astrophysics Data System (ADS)

    Francis, James T.; Turci, Cássia C.; Tyliszczak, Tolek; de Souza, G. Gerson B.; Kosugi, Nobuhiro; Hitchcock, Adam P.

    1995-12-01

    Electron energy-loss spectra (EELS) of SF6 have been recorded in the region of S 2p, S 2s, and F 1s excitation, using both dipole and nondipole electron-scattering conditions. Impact energies between 700 and 3200 eV and scattering angles between 0° and 30° were used. Relative to dipole EELS or photoabsorption, there are large intensity redistributions in both the S 2p and S 2s spectra under nondipole conditions. In contrast, the F 1s spectrum is essentially the same in near-dipole and nondipole scattering regimes. A higher-order electric multiple S 2p spectra feature is observed at 181 eV. It has an unusual multipeaked line shape whose components are more closely spaced than the typical 1.15-eV S 2p spin-orbit splitting. It is attributed to the overlap of several quadrupole-coupled states, which are likely associated with the [S 2p(t1u)-1,t1u] configuration. Ab initio self-consistent field calculations for various open-shell S 2p excited states are used to assist spectral assignments.

  11. Spectroscopy of transient neutral species via negative ion photoelectron spectroscopy

    SciTech Connect

    Weaver, A.

    1991-12-01

    Negative ion photoelectron spectroscopy has been used to study two types of transient neutral species: bound free radicals (NO{sub 2} and NO{sub 3}) and unstable neutral species ([IHI] and [FH{sub 2}]). The negative ion time-of-flight photoelectron spectrometer used for these experiments is described in detail.

  12. Spectroscopy of transient neutral species via negative ion photoelectron spectroscopy

    SciTech Connect

    Weaver, A.

    1991-12-01

    Negative ion photoelectron spectroscopy has been used to study two types of transient neutral species: bound free radicals (NO{sub 2} and NO{sub 3}) and unstable neutral species ((IHI) and (FH{sub 2})). The negative ion time-of-flight photoelectron spectrometer used for these experiments is described in detail.

  13. Photoelectron Imaging as a Quantum Chemistry Visualization Tool

    ERIC Educational Resources Information Center

    Grumbling, Emily R.; Pichugin, Kostyantyn; Mabbs, Richard; Sanov, Andrei

    2011-01-01

    An overview and simple example of photoelectron imaging is presented, highlighting its efficacy as a pedagogical tool for visualizing quantum phenomena. Specifically, photoelectron imaging of H[superscript -] (the simplest negative ion) is used to demonstrate several quantum mechanical principles. This example could be incorporated into an…

  14. 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.

  15. 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.

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

    DOE PAGES

    Garcia, Gustavo A.; Tang, Xiaofeng; Gil, Jean -Francois; ...

    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

  17. Study of selected benzyl azides by UV photoelectron spectroscopy and mass spectrometry

    NASA Astrophysics Data System (ADS)

    Pinto, R. M.; Olariu, R. I.; Lameiras, J.; Martins, F. T.; Dias, A. A.; Langley, G. J.; Rodrigues, P.; Maycock, C. D.; Santos, J. P.; Duarte, M. F.; Fernandez, M. T.; Costa, M. L.

    2010-09-01

    Benzyl azide and the three methylbenzyl azides were synthesized and characterized by mass spectrometry (MS) and ultraviolet photoelectron spectroscopy (UVPES). The electron ionization fragmentation mechanisms for benzyl azide and their methyl derivatives were studied by accurate mass measurements and linked scans at constant B/ E. For benzyl azide, in order to clarify the fragmentation mechanism, labelling experiments were performed. From the mass analysis of methylbenzyl azides isomers it was possible to differentiate the isomers ortho, meta and para. The abundance and nature of the ions resulting from the molecular ion fragmentation, for the three distinct isomers of substituted benzyl azides, were rationalized in terms of the electronic properties of the substituent. Concerning the para-isomer, IRC calculations were performed at UHF/6-31G(d) level. The photoionization study of benzyl azide, with He(I) radiation, revealed five bands in the 8-21 eV ionization energies region. From every photoelectron spectrum of methylbenzyl azides isomers it has been identified seven bands, on the same range as the benzyl azide. Interpretation of the photoelectron spectra was accomplished applying Koopmans' theorem to the SCF orbital energies obtained at HF/6-311++G(d, p) level.

  18. 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.

  19. Al capping layers for nondestructive x-ray photoelectron spectroscopy analyses of transition-metal nitride thin films

    SciTech Connect

    Greczynski, Grzegorz Hultman, Lars; Petrov, Ivan; Greene, J. E.

    2015-09-15

    X-ray photoelectron spectroscopy (XPS) compositional analyses of materials that have been air exposed typically require ion etching in order to remove contaminated surface layers. However, the etching step can lead to changes in sample surface and near-surface compositions due to preferential elemental sputter ejection and forward recoil implantation; this is a particular problem for metal/gas compounds and alloys such as nitrides and oxides. Here, the authors use TiN as a model system and compare XPS analysis results from three sets of polycrystalline TiN/Si(001) films deposited by reactive magnetron sputtering in a separate vacuum chamber. The films are either (1) air-exposed for ≤10 min prior to insertion into the ultrahigh-vacuum (UHV) XPS system; (2) air-exposed and subject to ion etching, using different ion energies and beam incidence angles, in the XPS chamber prior to analysis; or (3) Al-capped in-situ in the deposition system prior to air-exposure and loading into the XPS instrument. The authors show that thin, 1.5–6.0 nm, Al capping layers provide effective barriers to oxidation and contamination of TiN surfaces, thus allowing nondestructive acquisition of high-resolution core-level spectra representative of clean samples, and, hence, correct bonding assignments. The Ti 2p and N 1s satellite features, which are sensitive to ion bombardment, exhibit high intensities comparable to those obtained from single-crystal TiN/MgO(001) films grown and analyzed in-situ in a UHV XPS system and there is no indication of Al/TiN interfacial reactions. XPS-determined N/Ti concentrations acquired from Al/TiN samples agree very well with Rutherford backscattering and elastic recoil analysis results while ion-etched air-exposed samples exhibit strong N loss due to preferential resputtering. The intensities and shapes of the Ti 2p and N 1s core level signals from Al/TiN/Si(001) samples do not change following long-term (up to 70 days) exposure to ambient conditions

  20. Intramolecular photoelectron diffraction in the gas phase

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Miron, C.; Plésiat, E.; Argenti, L.; Patanen, M.; Kooser, K.; Ayuso, D.; Mondal, S.; Kimura, M.; Sakai, K.; Travnikova, O.; Palacios, A.; Decleva, P.; Kukk, E.; Martín, F.

    2013-09-01

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  1. Intramolecular photoelectron diffraction in the gas phase.

    PubMed

    Ueda, K; Miron, C; Plésiat, E; Argenti, L; Patanen, M; Kooser, K; Ayuso, D; Mondal, S; Kimura, M; Sakai, K; Travnikova, O; Palacios, A; Decleva, P; Kukk, E; Martín, F

    2013-09-28

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  2. Spherical-wave effects in photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Sagurton, M.; Bullock, E. L.; Saiki, R.; Kaduwela, A.; Brundle, C. R.; Fadley, C. S.; Rehr, J. J.

    1986-02-01

    The influence of spherical-wave (SW) effects on the analysis of photoelectron diffraction (PD) data is considered by comparing full SW single-scattering calculations with similar calculations based upon the plane-wave (PW) approximation and a new approximation for including SW effects (SW(1)) due to Rehr, Albers, Natoli, and Stern, as well as with experimental data involving both scanned-energy and scanned-angle measurements. In general, SW effects are found to be much more important in forward scattering and to explain prior empirical adjustments of PW x-ray PD scattering amplitudes at higher energies of >~500 eV. The more easily used SW(1) approximation is also seen to allow very well for SW effects. Not all PD data are expected to be equally sensitive to SW corrections. For example, scanned-energy data for S/Ni(001) emphasizing backscattering events are about equally well described by the PW and SW models, whereas higher-energy azimuthal-scan data for O/Ni(001) in which forward scattering is dominant require SW corrections to describe some, but not all, directions of emission quantitatively.

  3. Photoelectron spectroscopic studies of 5-halouracil anions

    SciTech Connect

    Radisic, Dunja; Ko, Yeon Jae; Nilles, John M.; Stokes, Sarah T.; Bowen, Kit H.; Sevilla, Michael D.; Rak, Janusz

    2011-01-07

    The parent negative ions of 5-chlorouracil, UCl{sup -} and 5-fluorouracil, UF{sup -} have been studied using anion photoelectron spectroscopy in order to investigate the electrophilic properties of their corresponding neutral halouracils. The vertical detachment energies (VDE) of these anions and the adiabatic electron affinities (EA) of their neutral molecular counterparts are reported. These results are in good agreement with the results of previously published theoretical calculations. The VDE values for both UCl{sup -} and UF{sup -} and the EA values for their neutral molecular counterparts are much greater than the corresponding values for both anionic and neutral forms of canonical uracil and thymine. These results are consistent with the observation that DNA is more sensitive to radiation damage when thymine is replaced by halouracil. While we also attempted to prepare the parent anion of 5-bromouracil, UBr{sup -}, we did not observe it, the mass spectrum exhibiting only Br{sup -} fragments, i.e., 5-bromouracil apparently underwent dissociative electron attachment. This observation is consistent with a previous assessment, suggesting that 5-bromouracil is the best radio-sensitizer among these three halo-nucleobases.

  4. Photoelectron spectroscopic studies of 5-halouracil anions

    NASA Astrophysics Data System (ADS)

    Radisic, Dunja; Ko, Yeon Jae; Nilles, John M.; Stokes, Sarah T.; Sevilla, Michael D.; Rak, Janusz; Bowen, Kit H.

    2011-01-01

    The parent negative ions of 5-chlorouracil, UCl- and 5-fluorouracil, UF- have been studied using anion photoelectron spectroscopy in order to investigate the electrophilic properties of their corresponding neutral halouracils. The vertical detachment energies (VDE) of these anions and the adiabatic electron affinities (EA) of their neutral molecular counterparts are reported. These results are in good agreement with the results of previously published theoretical calculations. The VDE values for both UCl- and UF- and the EA values for their neutral molecular counterparts are much greater than the corresponding values for both anionic and neutral forms of canonical uracil and thymine. These results are consistent with the observation that DNA is more sensitive to radiation damage when thymine is replaced by halouracil. While we also attempted to prepare the parent anion of 5-bromouracil, UBr-, we did not observe it, the mass spectrum exhibiting only Br- fragments, i.e., 5-bromouracil apparently underwent dissociative electron attachment. This observation is consistent with a previous assessment, suggesting that 5-bromouracil is the best radio-sensitizer among these three halo-nucleobases.

  5. Effects of rare-earth substitution in the oxyarsenides REFeAsO (RE=Ce, Pr, Nd, Sm, Gd) and CeNiAsO by X-ray photoelectron and absorption spectroscopy

    SciTech Connect

    Blanchard, Peter E.R.; Cavell, Ronald G.; Mar, Arthur

    2010-08-16

    X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structure of the rare-earth transition-metal oxyarsenides REFeAsO (RE=Ce, Pr, Nd, Sm, Gd) and CeNiAsO. Within the metal-arsenic layer [MAs], the bonding character is predominantly covalent and the As atoms are anionic, as implied by the small energy shifts in the M 2p and As 3d XPS spectra. Within the rare-earth-oxygen layer [REO], the bonding character is predominantly ionic, as implied by the similarity of the O 1s binding energies to those in highly ionic oxides. Substitution with a smaller RE element increases the O 1s binding energy, a result of an enhanced Madelung potential. The Ce 3d XPS and Ce L{sub 3}-edge XANES spectra have lineshapes and energies that confirm the presence of trivalent cerium in CeFeAsO and CeNiAsO. A population analysis of the valence band spectrum of CeNiAsO supports the formal charge assignment [Ce{sup 3+}O{sup 2-}][Ni{sup 2+}As{sup 3-}].

  6. Photoelectron trapping in N2O 7σ-->kσ resonant ionization

    NASA Astrophysics Data System (ADS)

    Rathbone, G. J.; Poliakoff, E. D.; Bozek, John D.; Toffoli, Daniele; Lucchese, R. R.

    2005-07-01

    Vibrationally resolved photoelectron spectroscopy of the N2O+(AΣ+2) state is used to compare the dependence of the photoelectron dynamics on molecular geometry for two shape resonances in the same ionization channel. Spectra are acquired over the photon energy range of 18⩽hν⩽55eV. There are three single-channel resonances in this range, two in the 7σ→kσ channel and one in the 7σ→kπ channel. Vibrational branching ratio curves are determined by measuring vibrationally resolved photoelectron spectra as a function of photon energy, and theoretical branching ratio curves are generated via Schwinger variational scattering calculations. In the region 30⩽hν⩽40eV, there are two shape resonances (kσ and kπ). The kσ ionization resonance is clearly visible in vibrationally resolved measurements at hν =35eV, even though the total cross section in this channel is dwarfed by the cross section in the degenerate, more slowly varying 7σ→kπ channel. This kσ resonance is manifested in non-Franck-Condon behavior in the approximately antisymmetric ν3 stretching mode, but it is not visible in the branching ratio curve for the approximately symmetric ν1 stretch. The behavior of the 35-eV kσ resonance is compared to a previously studied N2O 7σ →kσ shape resonance at lower energy. The mode sensitivity of the 35-eV kσ resonance is the opposite of what was observed for the lower-energy resonance. The contrasting mode-specific behavior observed for the high- and low-energy 7σ →kσ resonances can be explained on the basis of the "approximate" symmetry of the quasibound photoelectron resonant wave function, and the contrasting behavior reflects differences in the continuum electron trapping. An examination of the geometry dependence of the photoelectron dipole matrix elements shows that the kσ resonances have qualitatively different dependences on the individual bond lengths. The low-energy resonance is influenced only by changes in the end-to-end length

  7. Synthesis, characterization and photocatalytic performance of PbS/Ni2P flowers

    NASA Astrophysics Data System (ADS)

    Liu, Shuling; Han, Lefang; Liu, Hui

    2016-11-01

    Flower-like PbS/Ni2P composites were synthesized by a facile two-step chemical route. The morphology and structure of the resulting composites were investigated by SEM and TEM images and XRD spectra, respectively. The results showed that the as-obtained composites were composed of the cubic PbS flowers and hexagonal Ni2P nanoparticles, and Ni2P nanoparticles coated on the surfaces of flower-like PbS microstructure. It was found that changing the molar ratio to 3:1, flower-like PbS/Ni2P composites have been successfully synthesized by using cationic cetyltrimethylammonium bromide(CTAB) and anionic sodium dodecyl sulfate (SDS) as template. Furthermore, using methylene blue(MB) as a model organic pollutant, the photocatalytic degradation experiments indicated that the as-prepared composites showed enhanced photocatalytic degradation activity for methylene blue(75%) which is as higher as that of the only flower-like PbS (16.6%) and only Ni2P nanoparticles (44.8%) at the same time. This work may be expected to find its potential application in water pollution treatment.

  8. Photoelectron momentum spectra for multiphoton ionization of Hydrogen atoms by intense laser pulses

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, Serge; Macek, Joseph

    2007-06-01

    Full three-dimensional electron momentum distribution for multiphoton ionization of Hydrogen atoms by intense laser pulses are calculated by solving the time-dependent solutions of Schr"odinger equation on a three-dimensional lattice in a scaled coordinate representation (CSLTDSE). This approach allows one to circumvent many difficulties related to the propagation of wave function to macroscopic distances.

  9. Are 2P/Encke, the Taurid complex NEOs and CM chondrites related?

    NASA Astrophysics Data System (ADS)

    Tubiana, C.; Snodgrass, C.; Michelsen, R.; Haack, H.; Fitzsimmons, A.; Williams, I.; Boehnhardt, H.

    2013-09-01

    Comet 2P/Encke is a short-period comet that was discovered in 1786 and has been extensively observed and studied for more than 200 years. It has an orbital period of 3.3 years and its orbit is dynamically decoupled from Jupiter's control due to gravitational interaction with terrestrial planets [6]. It is the only comet known on such an orbit, making it unique. Capture from the outer solar system onto its current orbit is very unlikely and even a continuous smooth dynamical evolution has a low probability as this requires a continuous period when it is dormant in order to avoid the volatiles from the nucleus becoming exhausted and making the current observed activity impossible. An origin in the asteroid belt is a possibility especially in view of the recently discovered main belt comets. The nucleus of 2P/Encke is dark (geometric albedo of 0.047 ± 0.023 [3]), has an effective radius of 2.4 ± 0.3 km [3] and it has polarimetric properties that are unique compared to other measured types of solar system objects, such as asteroids, TNOs, cometary dust, Centaurs [2]. The colors of 2P/Encke's nucleus are typical for comets, but no spectra of the nucleus in the visible wavelength range exist so far. The Taurid meteoroid stream has long been linked with 2P/Encke, but the activity of the comet is not strong enough to explain the number of observed meteors. It has been suggested that the meteoroid stream was caused by the break up of a larger parent body, which left comet 2P/Encke and other various small bodies along with a stream of dust. Various small near-Earth objects (NEOs) have been discovered with orbits that can be linked with 2P/Encke and the Taurid meteoroid stream [1]. Though many of the associations are spurious due to the low inclination of 2P/Encke's orbit, many NEO's have evolved in a similar way to 2P/Encke overa period of 5000 years [8] suggesting some relationship. In addition to dynamical properties, common taxonomic properties can also provide an

  10. A Scalable P2P Video Streaming Framework

    NASA Astrophysics Data System (ADS)

    Lee, Ivan

    Peer-to-peer (P2P) networking technique represents a vast potential to overcome many constraints in the conventional content distribution networks, especially for the real-time applications such as P2P streaming. In this chapter, a P2P streaming system is examined, and the proposed system combines multiple-description source coding technique and a scalable streaming infrastructure. The proposed system aims to gradually offload congested traffic from a centralized bottleneck to the under-utilized P2P networks and hence, provides seamless transitions from client/server streaming to centralized P2P streaming and to decentralized P2P streaming. The performance of the proposed framework is evaluated in terms of video frame loss rate, which reflects the probability of freeze video frames.

  11. Supporting Collaboration and Creativity Through Mobile P2P Computing

    NASA Astrophysics Data System (ADS)

    Wierzbicki, Adam; Datta, Anwitaman; Żaczek, Łukasz; Rzadca, Krzysztof

    Among many potential applications of mobile P2P systems, collaboration applications are among the most prominent. Examples of applications such as Groove (although not intended for mobile networks), collaboration tools for disaster recovery (the WORKPAD project), and Skype's collaboration extensions, all demonstrate the potential of P2P collaborative applications. Yet, the development of such applications for mobile P2P systems is still difficult because of the lack of middleware.

  12. Time-resolved IR laser-assisted XUV photoelectron spectroscopy of metal surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, C.-H.; Thumm, U.

    2009-11-01

    Photoemission of localized and delocalized electrons from an (adsorbate-covered) metal surface by an XUV pulse of length τX into the field of a delayed IR laser pulse with carrier period TL allows for the time-resolved observation of surface and adsorbate electronic processes. For τX ≪ TL, the energy of the emitted photoelectrons (PEs) oscillates with period TL as a function of the XUV-IR pulse delay, leading to streaked PE spectra. In contrast, for τX ≳ TL, the PE spectrum is characterized by a satellite structure of sideband peaks located at integer multiples of the IR photon energy from the main photoemission peak. We present a theoretical model that allows us to discuss both, streaked and sideband photoemission spectra in comparison with recent experiments.

  13. X-ray photoelectron spectroscopy study of chemically-etched Nd-Ce-Cu-O surfaces

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Gupta, A.; Kussmaul, A.

    1991-01-01

    Acetic acid, Br2, and HCl solutions are investigated for removing insulating species from Nd(1.85)Ce(0.15)CuO(4-delta) (NCCO) thin film surfaces. X-ray photoelectron spectroscopy (XPS) shows that the HCl etch is most effective, yielding O 1s spectra comparable to those obtained from samples cleaned in vacuum and a clear Fermi edge in the valence band region. Reduction and oxidation reversibly induces and eliminates, respectively, Fermi level states for undoped samples, but has no clearly observable effect on the XPS spectra for doped samples. Reactivity to air is much less for NCCO compared to hole superconductors, which is attributed to the lack of reactive alkaline earth elements in NCCO.

  14. Photoelectron spectroscopic study of the negative ions of 4-thiouracil and 2,4-dithiouracil

    NASA Astrophysics Data System (ADS)

    Li, Xiang; Chen, Jing; Bowen, Kit H.

    2011-02-01

    We report the photoelectron spectra of the negative ions of 4-thiouracil (4-TU)- and 2,4-dithiouracil (2,4-DTU)-. Both of these spectra are indicative of valence anions, and they are each dominated by a single broad band with vertical detachment energies of 1.05 and 1.4 eV, respectively. Complementary calculations by Dolgounitcheva, Zakrzewski, and Ortiz (see companion paper) are in accord with our experimental results and conclude that the (4-TU)- and (2,4-DTU)- anions, reported herein, are valence anions of canonical 4-thiouracil and canonical dithiouracil. Comparisons among the anions and corresponding neutrals of 4-thiouracil, 2,4-dithiouracil, 5-chlorouracil, 5-fluorouracil, and uracil itself show that both sulfur and halogen modifications of uracil give rise to significant changes in the electronic structure. The electron affinities of the first four are all substantially larger than that of the canonical uracil.

  15. Photoelectron spectrum of PrO-

    NASA Astrophysics Data System (ADS)

    Kafader, Jared O.; Ray, Manisha; Jarrold, Caroline Chick

    2015-08-01

    The photoelectron (PE) spectrum of PrO- exhibits a short 835 ± 20 cm-1 vibrational progression of doublets (210 ± 30 cm-1 splitting) assigned to transitions from the 4f2 [3H4] σ6s2 Ω = 4 anion ground state to the 4f2 [3H4] σ6s Ω = 3.5 and 4.5 neutral states. This assignment is analogous to that of the recently reported PE spectrum of CeO-, though the 82 cm-1 splitting between the 4f [2F2.5] σ6s Ω = 2 and Ω = 3 CeO neutral states could not be resolved [Ray et al., J. Chem. Phys. 142, 064305 (2015)]. The origin of the transition to the Ω = 3.5 neutral ground state is 0.96 ± 0.01 eV, which is the adiabatic electron affinity of PrO. Density functional theory calculations on the anion and neutral molecules support the assignment. The appearance of multiple, irregularly spaced and low-intensity features observed ca. 1 eV above the ground state cannot be reconciled with low-lying electronic states of PrO that are accessible via one-electron detachment. However, neutral states correlated with the 4f2 [3H4] 5d superconfiguration are predicted to be approximately 1 eV above the 4f2 [3H4] σ6s Ω = 3.5 neutral ground state, leading to the assignment of these features to shake-up transitions to the excited neutral states. Based on tentative hot band transition assignments, the term energy of the previously unobserved 4f2 [3H4] σ6s Ω = 2.5 neutral state is determined to be 1840 ± 110 cm-1.

  16. Attosecond photoelectron microscopy of H2+

    NASA Astrophysics Data System (ADS)

    Hu, S. X.; Collins, L. A.; Schneider, B. I.

    2009-08-01

    We present a numerical study of the ultrafast ionization dynamics of H2+ exposed to attosecond extreme ultraviolet (xuv) pulses that goes beyond the Born-Openheimer approximation. The four-dimensional, time-dependent Schrödinger equation was solved using a generalization of the finite-element discrete-variable-representation/real-space-product technique used in our previous calculations to include the dynamical motion of the nuclei. This has enabled us to expose the target to any polarized light at arbitrary angles with respect to the molecular axis. Calculations have been performed at different angles and photon energies ( ℏω=50eV up to 630 eV) to investigate the energy and orientation dependence of the photoionization probability. A strong orientation dependence of the photoionization probability of H2+ was found at a photon energy of ℏω=50eV . At this energy, we found that the ionization probability is three times larger in the perpendicular polarization than in the parallel case. These observations are explained by the different geometric “cross sections” seen by the photoejected electron as it leaves the molecule. This ionization anisotropy vanishes at the higher-photon energy of ℏω≥170eV . When these higher-energy xuv pulses are polarized perpendicular to the internuclear axis, a “double-slit-like” interference pattern is observed. However, we find that the diffraction angle only approaches the classical formula ϕn=sin-1(nλe/R0) , where n is the diffraction order, λe is the released electron wavelength, and R0 is the internuclear distance, when nλe becomes less than 65% of R0 . These results illustrate the possibility of employing attosecond pulses to perform photoelectron microscopy of molecules.

  17. Zero kinetic energy photoelectron spectroscopy of pyrene.

    PubMed

    Zhang, Jie; Han, Fangyuan; Kong, Wei

    2010-10-28

    We report zero kinetic energy photoelectron (ZEKE) spectroscopy of pyrene via resonantly enhanced multiphoton ionization. Our analysis centers on the symmetry of the first electronically excited state (S(1)), its vibrational modes, and the vibration of the ground cationic state (D(0)). From comparisons between the observed vibrational frequencies and those from ab initio calculations at the configuration interaction singles level using the 6-311G (d,p) basis set, and based on other previous experimental and theoretical reports, we confirm the (1)B(2u) symmetry for the S(1) state. This assignment represents a reversal in the energy order of the two closely spaced electronically excited states from our theoretical calculation, and extensive configuration interactions are attributed to this result. Among the observed vibrational levels of the S(1) state, three are results of vibronic coupling due to the nearby second electronically excited state. The ZEKE spectroscopy obtained via the vibronic levels of the S(1) state reveals similar modes for the cation as those of the intermediate state. Although we believe that the ground ionic state can be considered a single electron configuration, the agreement between theoretical and experimental frequencies for the cation is limited. This result is somewhat surprising based on our previous work on cata-condensed polycyclic aromatic hydrocarbons and small substituted aromatic compounds. Although a relatively small molecule, pyrene demonstrates its nonrigidity via several out-of-plane bending modes corresponding to corrugation of the molecular plane. The adiabatic ionization potential of neutral pyrene is determined to be 59 888 ± 7 cm(-1).

  18. 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)

  19. 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.

  20. Photoelectron spectroscopy of chlorine dioxide and its negative ion: A quantum dynamical study

    NASA Astrophysics Data System (ADS)

    Mahapatra, Susanta; Krishnan, Gireesh M.

    2001-10-01

    The photoelectron spectra of ClO2 and its negative ion are investigated theoretically by a time-dependent wave-packet method. The near equilibrium MRCI potential energy surfaces of Peterson and Werner [J. Chem. Phys. 99, 302 (1993)] are employed in the nuclear dynamical simulations. The theoretical findings are in good agreement with the experimental results. In the experimental recording, excitations along the symmetric stretching and bending vibrational modes of ClO2 were observed. The excitation along the asymmetric stretching vibrational mode is absent in the experimental results. Considering these observations, and utilizing the available electronic structure results, we in our dynamical study focused on the C2v nuclear arrangements of the system. The relevant intial wave function to describe the photoelectron transition is prepared in both ways by the Hamiltonian matrix diagonalization using the ab initio potential energy surface of the ground electronic state, as well as in terms of the dimensionless normal coordinates of the electronic ground state of ClO2. The stick vibronic spectra are calculated by solving the time-independent Schrödinger equation employing a basis set expansion approach and the Lanczos algorithm. The resulting vibrational eigenvalues are compared with the experimental results and are discussed. The inclusion of the asymmetric stretching vibration and the possible role of the nonadiabatic couplings in the nuclear dynamics are also emphasized.

  1. Monte Carlo simulation of photoelectron energization in parallel electric fields: Electroglow on Uranus

    SciTech Connect

    Singhal, R.P.; Bhardwaj, A. )

    1991-09-01

    A Monte Carlo simulation of photoelectron energization and energy degradation in H{sub 2} gas in the presence of parallel electric fields has been carried out. Numerical yield spectra which contain information about the electron energy degradation process and can be used to calculate the yield for any inelastic event are obtained. The variation of yield spectra with incident electron energy, electric field, pitch angle, and cutoff limit has been studied. The yield function is employed to determine the photoelectron fluxes. H{sub 2} Lyman and Werner band excitation rates and integrated column intensity are computed for three different electric field profiles taking various low-energy cutoff limits. It is found that an electric field profile with peak value of 4 mV/m at neutral number density of 3{times}10{sup 10} cm{sup {minus}3} produces enhanced volume emission rates of H{sub 2} bands ({lambda} < 1100 {angstrom}) explaining about 20% of the observed electroglow emission on Uranus. The effect of solar zenith angle and solar cycle variation on peak excitation rate is discussed.

  2. Perspective: Electrospray photoelectron spectroscopy: From multiply-charged anions to ultracold anions

    NASA Astrophysics Data System (ADS)

    Wang, Lai-Sheng

    2015-07-01

    Electrospray ionization (ESI) has become an essential tool in chemical physics and physical chemistry for the production of novel molecular ions from solution samples for a variety of spectroscopic experiments. ESI was used to produce free multiply-charged anions (MCAs) for photoelectron spectroscopy (PES) in the late 1990 s, allowing many interesting properties of this class of exotic species to be investigated. Free MCAs are characterized by strong intramolecular Coulomb repulsions, which create a repulsive Coulomb barrier (RCB) for electron emission. The RCB endows many fascinating properties to MCAs, giving rise to meta-stable anions with negative electron binding energies. Recent development in the PES of MCAs includes photoelectron imaging to examine the influence of the RCB on the electron emission dynamics, pump-probe experiments to examine electron tunneling through the RCB, and isomer-specific experiments by coupling PES with ion mobility for biological MCAs. The development of a cryogenically cooled Paul trap has led to much better resolved PE spectra for MCAs by creating vibrationally cold anions from the room temperature ESI source. Recent advances in coupling the cryogenic Paul trap with PE imaging have allowed high-resolution PE spectra to be obtained for singly charged anions produced by ESI. In particular, the observation of dipole-bound excited states has made it possible to conduct vibrational autodetachment spectroscopy and resonant PES, which yield much richer vibrational spectroscopic information for dipolar free radicals than traditional PES.

  3. The time-resolved photoelectron spectrum of toluene using a perturbation theory approach

    SciTech Connect

    Richings, Gareth W.; Worth, Graham A.

    2014-12-28

    A theoretical study of the intra-molecular vibrational-energy redistribution of toluene using time-resolved photo-electron spectra calculated using nuclear quantum dynamics and a simple, two-mode model is presented. Calculations have been carried out using the multi-configuration time-dependent Hartree method, using three levels of approximation for the calculation of the spectra. The first is a full quantum dynamics simulation with a discretisation of the continuum wavefunction of the ejected electron, whilst the second uses first-order perturbation theory to calculate the wavefunction of the ion. Both methods rely on the explicit inclusion of both the pump and probe laser pulses. The third method includes only the pump pulse and generates the photo-electron spectrum by projection of the pumped wavepacket onto the ion potential energy surface, followed by evaluation of the Fourier transform of the autocorrelation function of the subsequently propagated wavepacket. The calculations performed have been used to study the periodic population flow between the 6a and 10b16b modes in the S{sub 1} excited state, and compared to recent experimental data. We obtain results in excellent agreement with the experiment and note the efficiency of the perturbation method.

  4. Perspective: Electrospray photoelectron spectroscopy: From multiply-charged anions to ultracold anions

    SciTech Connect

    Wang, Lai-Sheng

    2015-07-28

    Electrospray ionization (ESI) has become an essential tool in chemical physics and physical chemistry for the production of novel molecular ions from solution samples for a variety of spectroscopic experiments. ESI was used to produce free multiply-charged anions (MCAs) for photoelectron spectroscopy (PES) in the late 1990 s, allowing many interesting properties of this class of exotic species to be investigated. Free MCAs are characterized by strong intramolecular Coulomb repulsions, which create a repulsive Coulomb barrier (RCB) for electron emission. The RCB endows many fascinating properties to MCAs, giving rise to meta-stable anions with negative electron binding energies. Recent development in the PES of MCAs includes photoelectron imaging to examine the influence of the RCB on the electron emission dynamics, pump-probe experiments to examine electron tunneling through the RCB, and isomer-specific experiments by coupling PES with ion mobility for biological MCAs. The development of a cryogenically cooled Paul trap has led to much better resolved PE spectra for MCAs by creating vibrationally cold anions from the room temperature ESI source. Recent advances in coupling the cryogenic Paul trap with PE imaging have allowed high-resolution PE spectra to be obtained for singly charged anions produced by ESI. In particular, the observation of dipole-bound excited states has made it possible to conduct vibrational autodetachment spectroscopy and resonant PES, which yield much richer vibrational spectroscopic information for dipolar free radicals than traditional PES.

  5. 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).

  6. Electronic structure transformation in small bare Au clusters as seen by x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Andersson, T.; Zhang, C.; Björneholm, O.; Mikkelä, M.-H.; Jänkälä, K.; Anin, D.; Urpelainen, S.; Huttula, M.; Tchaplyguine, M.

    2017-01-01

    Free bare gold clusters in the size range from few tens to few hundred atoms (≤1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped ‘on the fly’ by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters ( N ∼ 103) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N ∼ 102 and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis.

  7. Expansion dynamics of supercritical water probed by picosecond time-resolved photoelectron spectroscopy.

    PubMed

    Gladytz, Thomas; Abel, Bernd; Siefermann, Katrin R

    2015-02-21

    Vibrational excitation of liquid water with femtosecond laser pulses can create extreme states of water. Yet, the dynamics directly after initial sub-picosecond delocalization of molecular vibrations remain largely unclear. We study the ultrafast expansion dynamics of an accordingly prepared supercritical water phase with a picosecond time resolution. Our experimental setup combines vacuum-compatible liquid micro-jet technology and a table top High Harmonic light source driven by a femtosecond laser system. An ultrashort laser pulse centered at a wavelength of 2900 nm excites the OH-stretch vibration of water molecules in the liquid. The deposited energy corresponds to a supercritical phase with a temperature of about 1000 K and a pressure of more than 1 GPa. We use a time-delayed extreme ultraviolet pulse centered at 38.6 eV, and obtained via High Harmonic generation (HHG), to record valence band photoelectron spectra of the expanding water sample. The series of photoelectron spectra is analyzed with noise-corrected target transform fitting (cTTF), a specifically developed multivariate method. Together with a simple fluid dynamics simulation, the following picture emerges: when a supercritical phase of water expands into vacuum, temperature and density of the first few nanometers of the expanding phase drop below the critical values within a few picoseconds. This results in a supersaturated phase, in which condensation seeds form and grow from small clusters to large clusters on a 100 picosecond timescale.

  8. A Remedy for Network Operators against Increasing P2P Traffic: Enabling Packet Cache for P2P Applications

    NASA Astrophysics Data System (ADS)

    Nakao, Akihiro; Sasaki, Kengo; Yamamoto, Shu

    We observe that P2P traffic has peculiar characteristics as opposed to the other type of traffic such as web browsing and file transfer. Since they exploit swarm effect — a multitude of end points downloading the same content piece by piece nearly at the same time, thus, increasing the effectiveness of caching — the same pieces of data end up traversing the network over and over again within mostly a short time window. In the light of this observation, we propose a network layer packet-level caching for reducing the volume of emerging P2P traffic, transparently to the P2P applications — without affecting operations of the P2P applications at all — rather than banning it, restricting it, or modifying P2P systems themselves. Unlike the other caching techniques, we aim to provide as generic a caching mechanism as possible at network layer — without knowing much detail of P2P application protocols — to extend applicability to arbitrary P2P protocols. Our preliminary evaluation shows that our approach is expected to reduce a significant amount of P2P traffic transparently to P2P applications.

  9. Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions

    NASA Astrophysics Data System (ADS)

    Zubova, N. A.; Malyshev, A. V.; Tupitsyn, I. I.; Shabaev, V. M.; Kozhedub, Y. S.; Plunien, G.; Brandau, C.; Stöhlker, Th.

    2016-05-01

    Isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z =8 -92 . The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large-scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2 p3 /2-2 p1 /2 transition in B-like ions is significantly improved.

  10. Direct work function measurement by gas phase photoelectron spectroscopy and its application on PbS nanoparticles.

    PubMed

    Axnanda, Stephanus; Scheele, Marcus; Crumlin, Ethan; Mao, Baohua; Chang, Rui; Rani, Sana; Faiz, Mohamed; Wang, Suidong; Alivisatos, A Paul; Liu, Zhi

    2013-01-01

    Work function is a fundamental property of a material's surface. It is playing an ever more important role in engineering new energy materials and efficient energy devices, especially in the field of photovoltaic devices, catalysis, semiconductor heterojunctions, nanotechnology, and electrochemistry. Using ambient pressure X-ray photoelectron spectroscopy (APXPS), we have measured the binding energies of core level photoelectrons of Ar gas in the vicinity of several reference materials with known work functions (Au(111), Pt(111), graphite) and PbS nanoparticles. We demonstrate an unambiguously negative correlation between the work functions of reference samples and the binding energies of Ar 2p core level photoelectrons detected from the Ar gas near the sample surface region. Using this experimentally determined linear relationship between the surface work function and Ar gas core level photoelectron binding energy, we can measure the surface work function of different materials under different gas environments. To demonstrate the potential applications of this ambient pressure XPS technique in nanotechnology and solar energy research, we investigate the work functions of PbS nanoparticles with various capping ligands: methoxide, mercaptopropionic acid, and ethanedithiol. Significant Fermi level position changes are observed for PbS nanoparticles when the nanoparticle size and capping ligands are varied. The corresponding changes in the valence band maximum illustrate that an efficient quantum dot solar cell design has to take into account the electrochemical effect of the capping ligand as well.

  11. Increased photoelectron transmission in High-pressure photoelectron spectrometers using "swift acceleration"

    NASA Astrophysics Data System (ADS)

    Edwards, Mårten O. M.; Karlsson, Patrik G.; Eriksson, Susanna K.; Hahlin, Maria; Siegbahn, Hans; Rensmo, Håkan; Kahk, Juhan M.; Villar-Garcia, Ignacio J.; Payne, David J.; Åhlund, John

    2015-06-01

    A new operation mode of a HPXPS (high-pressure X-ray photoelectron spectroscopy) analyzer is evaluated on a HPXPS system fitted with an Al Kα X-ray source. A variety of metal foil samples (gold, silver and copper) were measured in different sample gas environments (N2 and H2O), and a front aperture diameter of 0.8 mm. The new design concept is based upon "swiftly" accelerating the photoelectrons to kinetic energies of several keV after they pass the analyzer front aperture. Compared to the standard mode, in which the front section between the two first apertures is field-free, this gives a wider angular collection and a lower tendency for electron losses in collisions with gas molecules within the analyzer. With the swift-acceleration mode we attain, depending on the experimental conditions, up to about 3 times higher peak intensities in vacuum and about 10 to 20 times higher peak intensities in the 6-9 mbar regime, depending on kinetic energy. These experimental findings agree well with simulated transmission functions for the analyzer. The new mode of operation enables faster data acquisition than the standard mode of operation, particularly valuable in a home laboratory environment. Further demonstrations of performance are highlighted by measurements of the valence band structure in dye-sensitized solar cell photoelectrodes under a 2 mbar H2O atmosphere, a molecularly modified surface of interest in photoelectrochemical devices.

  12. Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Liu, Yuzhu; Knopp, Gregor; Qin, Chaochao; Gerber, Thomas

    2015-01-01

    Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multi-photon ionization and two-color pump-probe ionization are obtained and analyzed. Photoelectron bands are assigned to the related states. The time evolution of the photoelectron signal by pump-probe ionization can be well described by a biexponential decay: two rapid relaxation pathways with time constants of ∼15 fs and 85 (±11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S2 state to the vibrationally hot S1 state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S1 state and the formation of α-carbene and β-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding.

  13. High-resolution photoelectron imaging of cold C{sub 60}{sup −} anions and accurate determination of the electron affinity of C{sub 60}

    SciTech Connect

    Huang, Dao-Ling; Dau, Phuong Diem; Liu, Hong-Tao; Wang, Lai-Sheng

    2014-06-14

    High-resolution photoelectron imaging and spectroscopy of cold C{sub 60}{sup −} anions are reported using a newly built photoelectron imaging apparatus coupled with an electrospray ionization source and a temperature-controlled cryogenic ion trap. Vibrationally resolved photoelectron spectra are obtained for the detachment transition from the ground state of C{sub 60}{sup −} to that of C{sub 60} at various detachment wavelengths from 354.84 nm to 461.35 nm. The electron affinity of C{sub 60} is accurately measured to be 2.6835 ± 0.0006 eV. Numerous unexpected vibrational excitations are observed in the photoelectron spectra due to the Jahn-Teller effect in C{sub 60}{sup −} and Hertzberg-Teller vibronic coupling in both C{sub 60}{sup −} and C{sub 60}. Both the relative intensities of vibrational peaks and their photoelectron angular distributions provide evidence for the vibronic couplings. The observed p-wave-like behavior in the angular distribution of the 0{sub 0}{sup 0} transition suggests that the electron is detached from an s-type orbital.

  14. Valence photoelectron spectroscopy of Gd silicides

    SciTech Connect

    Braicovich, L. ); Puppin, E.; Lindau, I. ); Iandelli, A.; Olcese, G.L.; Palenzona, A. )

    1990-02-15

    Gd{sub 3}Si{sub 5}, GdSi, and Gd{sub 5}Si{sub 3} were investigated with photoemission spectroscopy in the photon-energy range 40.8--149 eV by exploiting the energy dependence of the photoemission cross sections and the valence resonance at the crossing of the Gd 4{ital d}-4{ital f} threshold. The modification of the spectra versus photon energy, along with their stoichiometry dependence, show the relevance of covalent mixed Gd 5{ital d}--Si 3{ital sp} states in the formation of the chemical bond. In the region close to the Fermi level an increase of the {ital d} contribution is observed. These points are discussed in connection with the existing models of the silicide bond.

  15. Photoelectron imaging of cells: photoconductivity extends the range of applicability.

    PubMed Central

    Habliston, D L; Hedberg, K K; Birrell, G B; Rempfer, G F; Griffith, O H

    1995-01-01

    Photoelectron imaging is a sensitive surface technique in which photons are used to excite electron emission. This novel method has been applied successfully in studies of relatively flat cultured cells, viruses, and protein-DNA complexes. However, rounded-up cell types such as tumor cells frequently are more difficult to image. By comparing photoelectron images of uncoated and metal-coated MCF-7 human breast carcinoma cells, it is shown that the problem is specimen charging rather than a fundamental limitation of the electron imaging process. This is confirmed by emission current measurements on uncoated monolayers of MCF-7 carcinoma cells and flatter, normal Wi-38 fibroblasts. We report here that sample charging in photoelectron microscopy can be eliminated in most specimens by simultaneous use of two light sources--the standard UV excitation source (e.g., 254 nm) and a longer wavelength light source (e.g., 325 nm). The reduction in sample charging results largely from enhanced photoconduction in the bulk sample and greatly extends the range of cells that can be examined by photoelectron imaging. The contributions of photoconductivity, the electric field of the imaging system, and the short escape depths of the photoelectrons combine to make photoelectron imaging a uniquely sensitive technique for the study of biological surfaces. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 PMID:8534832

  16. Photoelectron diffraction k-space volumes of the c(2x2) Mn/Ni(100) structure

    SciTech Connect

    Banerjee, S.; Denlinger, J.; Chen, X.

    1997-04-01

    Traditionally, x-ray photoelectron diffraction (XPD) studies have either been done by scanning the diffraction angle for fixed kinetic energy (ADPD), or scanning the kinetic energy at fixed exit angle (EDPD). Both of these methods collect subsets of the full diffraction pattern, or volume, which is the intensity of photoemission as a function of momentum direction and magnitude. With the high density available at the Spectromicroscopy Facility (BL 7.0) {open_quotes}ultraESCA{close_quotes} station, the authors are able to completely characterize the photoelectron diffraction patterns of surface structures, up to several hundred electron volts kinetic energy. This large diffraction `volume` can then be analyzed in many ways. The k-space volume contains as a subset the energy dependent photoelectron diffraction spectra along all emission angles. It also contains individual, hemispherical, diffraction patterns at specific kinetic energies. Other `cuts` through the data set are also possible, revealing new ways of viewing photoelectron diffraction data, and potentially new information about the surface structure being studied. In this article the authors report a brief summary of a structural study being done on the c(2x2) Mn/Ni(100) surface alloy. This system is interesting for both structural and magnetic reasons. Magnetically, the Mn/Ni(100) surface alloy exhibits parallel coupling of the Mn and Ni moments, which is opposite to the reported coupling for the bulk, disordered, alloy. Structurally, the Mn atoms are believed to lie well above the surface plane.

  17. High-resolution photoelectron imaging spectroscopy of cryogenically cooled Fe4O- and Fe5O-

    NASA Astrophysics Data System (ADS)

    Weichman, Marissa L.; DeVine, Jessalyn A.; Neumark, Daniel M.

    2016-08-01

    We report high-resolution photodetachment spectra of the cryogenically cooled iron monoxide clusters Fe4O- and Fe5O- obtained with slow photoelectron velocity-map imaging (cryo-SEVI). Well-resolved vibrational progressions are observed in both sets of spectra, and transitions to low-lying excited states of both species are seen. In order to identify the structural isomers, electronic states, and vibrational modes that contribute to the cryo-SEVI spectra of these clusters, experimental results are compared with density functional theory calculations and Franck-Condon simulations. The main bands observed in the SEVI spectra are assigned to the 15A2←16B2 photodetachment transition of Fe4O- and the 17A'←18A″ photodetachment transition of Fe5O-. We report electron affinities of 1.6980(3) eV for Fe4O and 1.8616(3) eV for Fe5O, although there is some uncertainty as to whether the 15A2 state is the true ground state of Fe4O. The iron atoms have a distorted tetrahedral geometry in Fe4O0/- and a distorted trigonal-bipyramidal arrangement in Fe5O0/-. For both neutral and anionic species, the oxygen atom preferably binds in a μ2-oxo configuration along the cluster edge. This finding is in contrast to prior predictions that Fe5O0/- exhibits a μ3 face-bound structure.

  18. X-ray photoelectron spectroscopy and structural analysis of amorphous SiO{sub x}N{sub y} films deposited at low temperatures

    SciTech Connect

    Cova, P.; Poulin, S.; Masut, R.A.

    2005-11-01

    We establish, using a tetrahedral model, the bonding properties of amorphous silicon oxynitride (a-SiO{sub x}N{sub y}) films deposited at low temperatures (LTs) by electron-cyclotron resonance chemical-vapor deposition (ECRCVD) on several substrates and under various conditions of gas flows and total gas pressure in a dilute mixture of SiH{sub 4}+N{sub 2} in Ar. The atomic percentage of each tetrahedral unit incorporated in the film network is calculated from the deconvolution of the high-resolution x-ray photoelectron spectroscopy (XPS) spectra in the Si 2p{sub 3/2} region and corroborated by the results obtained from both survey scans and the high-resolution XPS spectra in the N 1s region. The Si{sub 3}N{sub 4} phase is the most important one and the only bonding unit which is incorporated in all our LT ECRCVD SiO{sub x}N{sub y} films. The incorporation of all the other component tetrahedrons depends strongly on growth conditions. The threshold values of the N/Si atomic ratio for which intrinsic defects, such as Si-Si bonds, are not incorporated in the network depend on the O/Si ratio incorporated in the films, mainly due to the competition between oxygen and nitrogen atoms in their reaction with silicon dangling bonds. The effect of the total gas pressure on the atomic percentages of the oxidation states present in the LT ECRCVD SiO{sub x}N{sub y} films is qualitatively similar to the effect of the ion bombarding energy or the plasma density. O-N bonds are present only in samples having high amount of oxygen and nitrogen in their networks. For these films, our results show unambiguously the presence of the N-Si{sub 2}O tetrahedron and suggest that N-Si{sub 3-{nu}}O{sub {nu}} tetrahedrons with {nu}{>=}2 are not incorporated in their networks. A correlation is observed between the N-Si{sub 2}O and the Si-O{sub 3}(ON) tetrahedrons whose component peak is localized at (104.0{+-}0.2) eV in the Si 2p{sub 3/2} region of the XPS data, which suggests that both bonding

  19. Photoelectron spectroscopy of s-triazine anion clusters: Polarization-induced electron binding in aza-aromatic molecule

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Hyun; Song, Jae Kyu; Park, Hyokeun; Lee, Sang Hak; Han, Sang Yun; Kim, Seong Keun

    2003-08-01

    Photoelectron spectroscopy was carried out for the mass-selected cluster anions of s-triazine molecule, Tzn- (n=1-6). The mass spectrum and vibrationally resolved photoelectron spectrum of Tz- showed that unlike pyridine and pyrazine, Tz binds an electron and thus becomes the first molecule in the azabenzene series with a positive electron affinity (0.03 eV). This indicates that the local charge polarization in the aromatic ring by the three nitrogen atoms is large enough to facilitate electron binding to a homologue of benzene. A Jahn-Teller distortion was proposed to explain the vibrational progressions of the photoelectron spectrum of Tz-. A series of Ar-solvated clusters of Tz-, Tz-ṡArm (m=1-7), have been also studied. Their photoelectron spectra showed a drop in the incremental electron binding energy when going from m=4 to 5, indicating the closure of a solvation shell with four Ar atoms. In the mass abundance spectrum of Tzn-, a distinctly high intensity for Tz2- indicated its exceptional stability, which was also manifested by the large increase by more than 0.5 eV in the vertical detachment energy of the photoelectron spectrum. Theoretical calculations were carried out to obtain optimized geometries of the neutral and anion of Tz and Tz2. We confirmed the Jahn-Teller distortion in Tz- and also addressed the role of hydrogen bonding in determining the geometries of Tz2-. A common feature for the two most stable forms of Tz2- with comparable energies was that they achieve their unique stability through equal sharing of the negative charge between their two molecular constituents. A new photoelectron band was found to emerge from Tzn- for n⩾2 by the 355 nm light, in addition to the photoelectron band at lower electron binding energy observed for n⩾1 at 532 nm. The relative intensity of this new band decreased as n increased, and its position was 1.6-1.8 eV above the first band. Photodetachment to an electronically excited state was suggested to give

  20. Observation of a Quasideuteron Component in the Reaction 12C(π+, 2p)

    NASA Astrophysics Data System (ADS)

    Altman, A.; Piasetzky, E.; Lichtenstadt, J.; Yavin, A. I.; Ashery, D.; Powers, R. J.; Bertl, W.; Felawka, L.; Walter, H. K.; Winter, R. G.; Pluym, J. V. D.

    1983-04-01

    The reaction 12C(π+, 2p) was studied at 165 and 245 MeV over a broad kinematic range by coincidence measurement of the outgoing protons. The p-p angular correlations and proton energy spectra allow an identification of the "quasideuteron" component of the reaction. The angular distribution of this component has a shape similar to that of the π+d-->pp reaction. It is found that one-step quasideuteron absorption accounts for at most 25% of the total absorption cross section.

  1. Investigation on the neutral and anionic BxAlyH2 (x + y = 7, 8, 9) clusters using density functional theory combined with photoelectron spectroscopy.

    PubMed

    Ding, Li-Ping; Shao, Peng; Lu, Cheng; Zhang, Fang-Hui; Ding, Lei; Yuan, Tao Li

    2016-08-17

    The structure and bonding nature of neutral and negatively charged BxAlyH2 (x + y = 7, 8, 9) clusters are investigated with the aid of previously published experimental photoelectron spectra combined with the present density functional theory calculations. The comparison between the experimental photoelectron spectra and theoretical simulated spectra helps to identify the ground state structures. The accuracy of the obtained ground state structures is further verified by calculating their adiabatic electron affinities and vertical detachment energies and comparing them against available experimental data. The results show that the structures of BxAlyH2 transform from three-dimensional to planar structures as the number of boron atoms increases. Moreover, boron atoms tend to bind together forming Bn units. The hydrogen atoms prefer to bind with boron atoms rather than aluminum atoms. The analyses of the molecular orbital on the ground state structures further support the abovementioned results.

  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. Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission

    SciTech Connect

    Sen, Ananya; Matthews, Edward M.; Dessent, Caroline E. H. E-mail: xuebin.wang@pnnl.gov; Hou, Gao-Lei; Wang, Xue-Bin E-mail: xuebin.wang@pnnl.gov

    2015-11-14

    We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine, and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ∼1.7 eV, values that are lower than the RCB of the uncomplexed PtCl{sub 6}{sup 2−} dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl{sub 6}{sup 2−} ⋅ thymine and PtCl{sub 6}{sup 2−} ⋅ adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes [A. Sen et al., J. Phys. Chem. B 119, 11626 (2015)]. The observation of delayed electron emission bands in the PtCl{sub 6}{sup 2−} ⋅ nucleobase spectra obtained in this work, as for the previously studied Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes, is attributed to one-photon excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a “dynamic tag” which has the propensity to emit electrons when the attached nucleobase decays over a time scale long enough to

  4. Photoelectron imaging spectroscopy of MoC{sup −} and NbN{sup −} diatomic anions: A comparative study

    SciTech Connect

    Liu, Qing-Yu; Li, Zi-Yu; He, Sheng-Gui E-mail: chenh@iccas.ac.cn; Hu, Lianrui; Chen, Hui E-mail: chenh@iccas.ac.cn; Ning, Chuan-Gang; Ma, Jia-Bi

    2015-04-28

    The isoeletronic diatomic MoC{sup −} and NbN{sup −} anions have been prepared by laser ablation and studied by photoelectron imaging spectroscopy combined with quantum chemistry calculations. The photoelectron spectra of NbN{sup −} can be very well assigned on the basis of literature reported optical spectroscopy of NbN. In contrast, the photoelectron spectra of MoC{sup −} are rather complex and the assignments suffered from the presence of many electronically hot bands and limited information from the reported optical spectroscopy of MoC. The electron affinities of NbN and MoC have been determined to be 1.450 ± 0.003 eV and 1.360  ±  0.003 eV, respectively. The good resolution of the imaging spectroscopy provided a chance to resolve the Ω splittings of the X{sup 3}Σ{sup −} (Ω = 0 and 1) state of MoC and the X{sup 4}Σ{sup −} (Ω = 1/2 and 3/2) state of MoC{sup −} for the first time. The spin-orbit splittings of the X{sup 2}Δ state of NbN{sup −} and the a{sup 2}Δ state of MoC{sup −} were also determined. The similarities and differences between the electronic structures of the NbN and MoC systems were discussed.

  5. Photoelectron imaging and spectroscopy of MI(2)(-) (M = Cs, Cu, Au): evolution from ionic to covalent bonding.

    PubMed

    Wang, Yi-Lei; Wang, Xue-Bin; Xing, Xiao-Peng; Wei, Fan; Li, Jun; Wang, Lai-Sheng

    2010-10-28

    We report a combined experimental and theoretical investigation of MI(2)(-) (M = Cs, Cu, Ag, Au) to explore the chemical bonding in the group IA and IB diiodide complexes. Both photoelectron imaging and low-temperature photoelectron spectroscopy are applied to MI(2)(-) (M = Cs, Cu, Au), yielding vibrationally resolved spectra for CuI(2)(-) and AuI(2)(-) and accurate electron affinities, 4.52 ± 0.02, 4.256 ± 0.010, and 4.226 ± 0.010 eV for CsI(2), CuI(2), and AuI(2), respectively. Spin-orbit coupling is found to be important in all the diiodide complexes and ab initio calculations including spin-orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses (charge population, bond order, and electron localization functions) have been carried out, revealing a gradual transition from the expected ionic behavior in CsI(2)(-) to relatively strong covalent bonding in AuI(2)(-). Both relativistic effects and electron correlation are shown to enhance the covalency in the gold diiodide complex.

  6. Communication: Observation of dipole-bound state and high-resolution photoelectron imaging of cold acetate anions

    SciTech Connect

    Huang, Dao-Ling; Zhu, Guo-Zhu; Wang, Lai-Sheng

    2015-03-07

    We report the observation of a dipole-bound state and a high-resolution photoelectron imaging study of cryogenically cooled acetate anions (CH{sub 3}COO{sup −}). Both high-resolution non-resonant and resonant photoelectron spectra via the dipole-bound state of CH{sub 3}COO{sup −} are obtained. The binding energy of the dipole-bound state relative to the detachment threshold is determined to be 53 ± 8 cm{sup −1}. The electron affinity of the CH{sub 3}COO neutral radical is measured accurately as 26 236 ± 8 cm{sup −1} (3.2528 ± 0.0010 eV) using high-resolution photoelectron imaging. This accurate electron affinity is validated by observation of autodetachment from two vibrational levels of the dipole-bound state of CH{sub 3}COO{sup −}. Excitation spectra to the dipole-bound states yield rotational profiles, allowing the rotational temperature of the trapped CH{sub 3}COO{sup −} anions to be evaluated.

  7. Trisomy 2p: Analysis of unusual phenotypic findings

    SciTech Connect

    Lurie, I.W.; Ilyina, H.G.; Gurevich, D.B.

    1995-01-16

    We present three probands with partial trisomies 2p21-23 due to ins(4;2)(q21;p21p23) pat, 2p23-pter due to t(2;4)(p23;q35)mat, and 2p21-pter due to t(2;11)(p21;q23.3)mat. More than 50 cases of partial trisomy 2p have been reviewed and some abnormalities, unusual for most other types of structural autosomal imbalance, have been found in patients with inherited forms of 2p trisomy and in their non-karyotyped sibs. Neural tube defects (anencephaly, occipital encephalocele, and spina bifida) were found in five probands and 4/6 affected non-karyotyped sibs. The only triplicated segment common to all was 2p24. Different forms of {open_quotes}broncho-pulmonary a/hypoplasia{close_quotes} (including two cases of lung agenesis) were described in four patients (overlapping triplicated segment was 2p21-p25). Three patients (with overlapping triplicated segment 2p23-p25) had diaphragmatic hernia. Abnormal rotation of the heart or L-transposition of large vessels (with or without visceral heterotaxia) was found in two infants (overlapping triplicated segment 2p23-p24). In two patients with common triplicated segment 2p22.3-p25, neuroblastoma has been described. The occurrence of all these defects may be explained either by the action of the same gene(s) mapped to 2p24 or by action of some independent factors located in different segments of the short arm. Although the latter hypothesis is much less probable, it can not be rejected at the present time. We propose the existence of a genetic system controlling surveillance of an abnormal embryo to explain the phenotypic differences between patients with the same imbalance within a family. In some {open_quotes}restrictive{close_quotes} combinations the abnormal embryos will die, although in {open_quotes}permissive{close_quotes} combinations they can survive. 47 refs., 2 figs., 3 tabs.

  8. Oxygen-induced changes in electron-energy-loss spectra for Al, Be and Ni. [Al; Be; Ni

    SciTech Connect

    Madden, H.H.; Landers, R.; Kleiman, G.G. , 13081-970 Campinas, Sao Paulo, Brasil); Zehner, D.M. )

    1999-09-01

    Electron-energy-loss spectroscopy (EELS) data are presented to illustrate line shape changes that occur as a result of oxygen interaction with metal surfaces. The metals were aluminum, beryllium and nickel. Core-level EELS data were taken for excitations from Al(2p), Be(1s), Ni(3p/3s) and O(1s) levels to the conduction band (CB) density of states (DOS) of the materials. The primary beam energies for the spectra were 300, 450, 300, and 1135 eV, respectively. The data are presented in both the (as measured) first-derivative and the integral forms. The integral spectra were corrected for coherent background losses and analyzed for CB DOS information. These spectra were found to be in qualitative agreement with published experimental and theoretical studies of these materials. One peak in the spectra for Al oxide is analyzed for its correlation with excitonic screening of the Al(2p) core hole. Similar evidence for exciton formation is found in the Ni(3p) spectra for Ni oxide. Data are also presented showing oxygen-induced changes in the lower-loss-energy EELS curves that, in the pure metal, are dominated by plasmon-loss and interband-transition signals. Single-scattering loss profiles in the integral form of the data were calculated using a procedure of Tougaard and Chorkendorff [S. Tougaard and I. Chorkendorff, Phys. Rev. B. [bold 35], 6570 (1987)]. For all three oxides these profiles are dominated by a feature with a loss energy of around 20[endash]25 eV. Although this feature has been ascribed by other researchers as due to bulk plasmon losses in the oxide, an alternative explanation is that the feature is simply due to O(2s)-to-CB-level excitations. An even stronger feature is found at 7 eV loss energy for Ni oxide. Speculation is given as to its source. The line shapes in both the core-level and noncore-level spectra can also be used simply as [open quotes]fingerprints[close quotes] of the surface chemistry of the materials. Our data were taken using commercially

  9. Network Awareness in P2P-TV Applications

    NASA Astrophysics Data System (ADS)

    Traverso, Stefano; Leonardi, Emilio; Mellia, Marco; Meo, Michela

    The increasing popularity of applications for video-streaming based on P2P paradigm (P2P-TV) is raising the interest of both broadcasters and network operators. The former see a promising technology to reduce the cost of streaming content over the Internet, while offering a world-wide service. The latter instead fear that the traffic offered by these applications can grow without control, affecting other services, and possibly causing network congestion and collapse. The “Network-Aware P2P-TV Application over Wise Networks” FP7 project aims at studying and developing a novel P2P-TV application offering the chance to broadcast high definition video to broadcasters and to carefully manage the traffic offered by peers to the network, therefore avoiding worries to Internet providers about network overload. In such context, we design a simulator to evaluate performance of different P2P-TV solutions, to compare them both considering end-users’ and network providers’ perspectives, such as quality of service perceived by subscribers and link utilization. In this paper, we provide some results that show how effective can be a network aware P2P-TV system.

  10. Improving P2P live-content delivery using SVC

    NASA Astrophysics Data System (ADS)

    Schierl, T.; Sánchez, Y.; Hellge, C.; Wiegand, T.

    2010-07-01

    P2P content delivery techniques for video transmission have become of high interest in the last years. With the involvement of client into the delivery process, P2P approaches can significantly reduce the load and cost on servers, especially for popular services. However, previous studies have already pointed out the unreliability of P2P-based live streaming approaches due to peer churn, where peers may ungracefully leave the P2P infrastructure, typically an overlay networks. Peers ungracefully leaving the system cause connection losses in the overlay, which require repair operations. During such repair operations, which typically take a few roundtrip times, no data is received from the lost connection. While taking low delay for fast-channel tune-in into account as a key feature for broadcast-like streaming applications, the P2P live streaming approach can only rely on a certain media pre-buffer during such repair operations. In this paper, multi-tree based Application Layer Multicast as a P2P overlay technique for live streaming is considered. The use of Flow Forwarding (FF), a.k.a. Retransmission, or Forward Error Correction (FEC) in combination with Scalable video Coding (SVC) for concealment during overlay repair operations is shown. Furthermore the benefits of using SVC over the use of AVC single layer transmission are presented.

  11. Ionospheric photoelectrons: Comparing Venus, Earth, Mars and Titan

    NASA Astrophysics Data System (ADS)

    Coates, A. J.; Tsang, S. M. E.; Wellbrock, A.; Frahm, R. A.; Winningham, J. D.; Barabash, S.; Lundin, R.; Young, D. T.; Crary, F. J.

    2011-08-01

    The sunlit portion of planetary ionospheres is sustained by photoionization. This was first confirmed using measurements and modelling at Earth, but recently the Mars Express, Venus Express and Cassini-Huygens missions have revealed the importance of this process at Mars, Venus and Titan, respectively. The primary neutral atmospheric constituents involved (O and CO 2 in the case of Venus and Mars, O and N 2 in the case of Earth and N 2 in the case of Titan) are ionized at each object by EUV solar photons. This process produces photoelectrons with particular spectral characteristics. The electron spectrometers on Venus Express and Mars Express (part of ASPERA-3 and 4, respectively) were designed with excellent energy resolution (Δ E/ E=8%) specifically in order to examine the photoelectron spectrum. In addition, the Cassini CAPS electron spectrometer at Saturn also has adequate resolution (Δ E/ E=16.7%) to study this population at Titan. At Earth, photoelectrons are well established by in situ measurements, and are even seen in the magnetosphere at up to 7 RE. At Mars, photoelectrons are seen in situ in the ionosphere, but also in the tail at distances out to the Mars Express apoapsis (˜3 RM). At both Venus and Titan, photoelectrons are seen in situ in the ionosphere and in the tail (at up to 1.45 RV and 6.8 RT, respectively). Here, we compare photoelectron measurements at Earth, Venus, Mars and Titan, and in particular show examples of their observation at remote locations from their production point in the dayside ionosphere. This process is found to be common between magnetized and unmagnetized objects. We discuss the role of photoelectrons as tracers of the magnetic connection to the dayside ionosphere, and their possible role in enhancing ion escape.

  12. Study of the C2H4/Si(100)-(2×1) Interface by Derivative Photoelectron Holography

    NASA Astrophysics Data System (ADS)

    Xu, S. H.; Wu, H. S.; Tong, S. Y.; Keeffe, M.; Lapeyre, G. J.; Rotenberg, E.

    The k derivative spectra (KDS) transform is used for construction of the three-dimensional atomic structure of the C2H4/Si(100)-(2×1) system from photoelectron diffraction data. The image function obtained by the KDS transform clearly observes the second-layer Si atoms and the C emitters apart from the first-layer Si atoms. The observations of the second-layer Si atoms and the C emitters make it easy to measure the C-C bond length correctly. Then a conclusive adsorption model — the di-σ model — for the C2H4/Si(100)-(2×1) system is established. In comparison with the KDS transform, the normal small-cone transform hardly measures the C-C bond length. The ability to observe more scatterers of a photoelectron emitter by the KDS transform expands the applicability of holographic imaging.

  13. The PtAl{sup −} and PtAl{sub 2}{sup −} anions: Theoretical and photoelectron spectroscopic characterization

    SciTech Connect

    Zhang, Xinxing; Ganteför, Gerd; Bowen, Kit H. E-mail: ana@chem.ucla.edu; Alexandrova, Anastassia N. E-mail: ana@chem.ucla.edu

    2014-04-28

    We report a joint photoelectron spectroscopic and theoretical study of the PtAl{sup −} and PtAl{sub 2}{sup −} anions. The ground state structures and electronic configurations of these species were identified to be C{sub ∞v}, {sup 1}Σ{sup +} for PtAl{sup −}, and C{sub 2v}, {sup 2}B{sub 1} for PtAl{sub 2}{sup −}. Structured anion photoelectron spectra of these clusters were recorded and interpreted using ab initio calculations. Good agreement between theory and experiment was found. All experimental features were successfully assigned to one-electron transitions from the ground state of the anions to the ground or excited states of the corresponding neutral species.

  14. Adiabatic electron affinity of pentacene and perfluoropentacene molecules studied by anion photoelectron spectroscopy: Molecular insights into electronic properties.

    PubMed

    Masubuchi, Tsugunosuke; Sugawara, Yoshito; Nakajima, Atsushi

    2016-12-28

    Pentacene (C22H14, PEN) and perfluoropentacene (C22F14, PFP) are considered promising building blocks of organic semiconductors. Using gas-phase anion photoelectron spectroscopy, the adiabatic electron affinity of PEN and PFP molecules is determined to be 1.43 ± 0.03 and 2.74 ± 0.03 eV, respectively, and the S0-T1 transition energies of PEN and PFP are evaluated to be 0.96 ± 0.06 and 0.72 ± 0.05 eV, respectively. Photoelectron spectra indicate that the vibronic coupling in PFP is stronger than that in PEN. Quantum chemistry calculations demonstrate that the strong vibronic coupling originates from significant structural displacement upon electron injection to PFP.

  15. Surface study of stainless steel electrode deposition from soil electrokinetic (EK) treatment using X-ray photoelectron spectroscopy (XPS)

    SciTech Connect

    Embong, Zaidi; Johar, Saffuwan; Tajudin, Saiful Azhar Ahmad; Sahdan, Mohd Zainizan

    2015-04-29

    Electrokinetic (EK) remediation relies upon application of a low-intensity direct current through the soil between stainless steel electrodes that are divided into a cathode array and an anode array. This mobilizes charged species, causing ions and water to move toward the electrodes. Metal ions and positively charged organic compounds move toward the cathode. Anions such as chloride, fluoride, nitrate, and negatively charged organic compounds move toward the anode. Here, this remediation techniques lead to a formation of a deposition at the both cathode and anode surface that mainly contributed byanion and cation from the remediated soil. In this research, Renggam-Jerangau soil species (HaplicAcrisol + RhodicFerralsol) with a surveymeter reading of 38.0 ± 3.9 μR/hr has been investigation in order to study the mobility of the anion and cation under the influence electric field. Prior to the EK treatment, the elemental composition of the soil and the stainless steel electrode are measured using XRF analyses. Next, the soil sample is remediated at a constant electric potential of 30 V within an hour of treatment period. A surface study for the deposition layer of the cathode and anode using X-ray Photoelectron spectroscopy (XPS) revealed that a narrow photoelectron signal from oxygen O 1s, carbon, C 1s silica, Si 2p, aluminium, Al 2p and chromium, Cr 2p exhibited on the electrode surface and indicate that a different in photoelectron intensity for each element on both electrode surface. In this paper, the mechanism of Si{sup 2+} and Al{sup 2+} cation mobility under the influence of voltage potential between the cathode and anode will be discussed in detail.

  16. Surface composition analysis of HF vapour cleaned silicon by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Ermolieff, A.; Martin, F.; Amouroux, A.; Marthon, S.; Westendorp, J. F. M.

    1991-06-01

    X-ray photoelectron spectroscopy (XPS) measurements on silicon surfaces treated by HF gaseous cleaning are described. Various cleaning recipes, which essentially differ by the amount of water present during the reaction were studied; the composition of the silicon surface was measured in terms of monolayer coverage of oxygen, fluorine and carbon. These gaseous cleaned surfaces are compared with those of commonly deglazed silicon samples by using an aqueous HF bath. The F(1s), O(1s), Si(2p), C(1s) photoelectron lines were monitored, and concentrations determined as usual by integration of the lines after removal of the non-linear backgroune. The F(1s), C(1s) and Si(2p) lines were decomposed into several components corresponding to different chemical bonds. The results show that the amount of fluorine is directly correlated with the amount of oxygen: the higher the oxygen level on the sample, the more important is the fluorine content till 0.7 ML, essentially in a O sbnd Si sbnd F bonding state. For more aggresive etching leaving less than one monolayer of oxygen, the Si sbnd F bond becomes predominant. The ratio of the SiF to OSiF concentrations is a significant signature of the deoxidation state of the surface. Hydrophobicity of the water appears in the range of 25% Si sbnd F bonds. With very aggresive etching processes, 67% Si sbnd F bonds and 33% O sbnd Si sbnd F bonds are reached and the total amount of fluoride drops below 0.3 ML. For comparison, only Si sbnd F bonds are observed after a wet etching in a dilute HF bath without a rinse with a much lower fluorine concentration. The balance between Si sbnd F and O sbnd Si sbnd F remains stable and seems to be representative of the surface states provided by the etching process.

  17. Managing Linguistic Data Summaries in Advanced P2P Applications

    NASA Astrophysics Data System (ADS)

    Hayek, Rabab; Raschia, Guillaume; Valduriez, Patrick; Mouaddib, Noureddine

    As the amount of stored data increases, data localization techniques become no longer sufficient in P2P systems. A practical approach is to rely on compact database summaries rather than raw database records, whose access is costly in large P2P systems. In this chapter, we describe a solution for managing linguistic data summaries in advanced P2P applications which are dealing with semantically rich data. The produced summaries are synthetic, multidimensional views over relational tables. The novelty of this proposal relies on the double summary exploitation in distributed P2P systems. First, as semantic indexes, they support locating relevant nodes based on their data descriptions. Second, due to their intelligibility, these summaries can be directly queried and thus approximately answer a query without the need for exploring original data. The proposed solution consists first in defining a summary model for hierarchical P2P systems. Second, appropriate algorithms for summary creation and maintenance are presented. A query processing mechanism, which relies on summary querying, is then proposed to demonstrate the benefits that might be obtained from summary exploitation.

  18. Determinants of Default in P2P Lending.

    PubMed

    Serrano-Cinca, Carlos; Gutiérrez-Nieto, Begoña; López-Palacios, Luz

    2015-01-01

    This paper studies P2P lending and the factors explaining loan default. This is an important issue because in P2P lending individual investors bear the credit risk, instead of financial institutions, which are experts in dealing with this risk. P2P lenders suffer a severe problem of information asymmetry, because they are at a disadvantage facing the borrower. For this reason, P2P lending sites provide potential lenders with information about borrowers and their loan purpose. They also assign a grade to each loan. The empirical study is based on loans' data collected from Lending Club (N = 24,449) from 2008 to 2014 that are first analyzed by using univariate means tests and survival analysis. Factors explaining default are loan purpose, annual income, current housing situation, credit history and indebtedness. Secondly, a logistic regression model is developed to predict defaults. The grade assigned by the P2P lending site is the most predictive factor of default, but the accuracy of the model is improved by adding other information, especially the borrower's debt level.

  19. Determinants of Default in P2P Lending

    PubMed Central

    2015-01-01

    This paper studies P2P lending and the factors explaining loan default. This is an important issue because in P2P lending individual investors bear the credit risk, instead of financial institutions, which are experts in dealing with this risk. P2P lenders suffer a severe problem of information asymmetry, because they are at a disadvantage facing the borrower. For this reason, P2P lending sites provide potential lenders with information about borrowers and their loan purpose. They also assign a grade to each loan. The empirical study is based on loans’ data collected from Lending Club (N = 24,449) from 2008 to 2014 that are first analyzed by using univariate means tests and survival analysis. Factors explaining default are loan purpose, annual income, current housing situation, credit history and indebtedness. Secondly, a logistic regression model is developed to predict defaults. The grade assigned by the P2P lending site is the most predictive factor of default, but the accuracy of the model is improved by adding other information, especially the borrower’s debt level. PMID:26425854

  20. Protecting Data Privacy in Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Jawad, Mohamed; Serrano-Alvarado, Patricia; Valduriez, Patrick

    P2P systems are increasingly used for efficient, scalable data sharing. Popular applications focus on massive file sharing. However, advanced applications such as online communities (e.g., medical or research communities) need to share private or sensitive data. Currently, in P2P systems, untrusted peers can easily violate data privacy by using data for malicious purposes (e.g., fraudulence, profiling). To prevent such behavior, the well accepted Hippocratic database principle states that data owners should specify the purpose for which their data will be collected. In this paper, we apply such principles as well as reputation techniques to support purpose and trust in structured P2P systems. Hippocratic databases enforce purpose-based privacy while reputation techniques guarantee trust. We propose a P2P data privacy model which combines the Hippocratic principles and the trust notions. We also present the algorithms of PriServ, a DHT-based P2P privacy service which supports this model and prevents data privacy violation. We show, in a performance evaluation, that PriServ introduces a small overhead.

  1. An efficient query mechanism base on P2P networks

    NASA Astrophysics Data System (ADS)

    Wang, Xiaohua; Mu, Aiqin; Zhao, Defang

    2013-07-01

    How to implement the efficient query is the key problem deployed on P2P networks. This paper analyses the shortage of several query algorithm, and presents a new algorithm DDI, which means distributed searching with double indices. It discusses the popularity of documents and the linking status of the networks, and calculates the availability of the nodes in whole network, determines the route of the query process. It compares the items of time using, the quantity of requests and update information by the emulate experiments. Along with the rapid development of computer network technology, peer-to-peer (referred to as P2P) network research has gradually become mature, and it is widely used in different fields, some large P2P computing project has entered the implementation stage. At present, many more popular software systems such as Gnutella, Freenet, Napster are deployed based on P2P technology. How to achieve effective information query has become one of the key problems of P2P research.

  2. Variable growth modes of CaF2 on Si(111) determined by x-ray photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Denlinger, J. D.; Rotenberg, Eli; Hessinger, Uwe; Leskovar, M.; Olmstead, Marjorie A.

    1993-04-01

    Chemical discrimination of bulk and interface Ca 2p x-ray photoelectron diffraction modulations is used to identify three growth regimes during the initial stages of CaF2 epitaxy on Si(111). Low flux, high temperature conditions produce island growth atop a nonwetting, chemically reacted Ca-F interface layer. Changing the growth kinetics by increasing the flux produces more laminar growth. Lowering the substrate temperature produces a more stoichiometric CaF2 interface layer that results in immediate wetting and laminar growth.

  3. Molecular orientation in thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on graphite studied by angle-resolved photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Hasegawa, Shinji; Tanaka, Shoji; Yamashita, Yoshiro; Inokuchi, Hiroo; Fujimoto, Hitoshi; Kamiya, Koji; Seki, Kazuhiko; Ueno, Nobuo

    1993-07-01

    Angle-resolved ultraviolet photoelectron spectra using synchrotron radiation were measured for oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) on a cleaved highly oriented pyrolytic graphite (HOPG) surface. The observed takeoff angle dependence of the photoelectron intensity was analyzed by using the independent-atomic-center approximation and modified neglect of diatomic overlap molecular-orbital calculations. The calculated results agree well with the experimental ones. From the comparison between these results, the molecules in the thin film are estimated to lie flat with the inclination angle β<=10° to the HOPG surface. This analysis method is useful as a first step to a quantitative analysis for angular distribution of photoelectrons from thin films of large and complex organic molecules.

  4. High Performance Rh2P Electrocatalyst for Efficient Water Splitting.

    PubMed

    Duan, Haohong; Li, Dongguo; Tang, Yan; He, Yang; Fang, Ji Shu; Wang, Rongyue; Lv, Haifeng; Lopes, Pietro P; Paulikas, Arvydas P; Li, Haoyi; Mao, Scott X; Wang, Chong-Min; Markovic, Nenad M; Li, Jun; Stamenkovic, Vojislav R; Li, Yadong

    2017-03-26

    Search for active, stable and cost-efficient electrocataltysts for hydrogen production via water splitting could make substantial impact to the energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high surface area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C exhibit remarkable performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) compared to Rh/C and Pt/C catalysts. The atomic structure of the Rh2P NCs was directly observed by annular dark-field scanning transmission electron microscopy (ADF-STEM), which revealed phosphorous-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorous plays crucial role in determining the robust catalyst properties.

  5. Fragrance material review on 2-(p-tolyloxy)ethyl acetate.

    PubMed

    McGinty, D; Letizia, C S; Api, A M

    2012-09-01

    A toxicologic and dermatologic review of 2-(p-tolyloxy)ethyl acetate when used as a fragrance ingredient is presented. 2-(p-tolyloxy)ethyl acetate is a member of the fragrance structural group aryl alkyl alcohol simple acid esters (AAASAE). The AAASAE fragrance ingredients are prepared by reacting an aryl alkyl alcohol with a simple carboxylic acid (a chain of 1-4 carbons) to generate formate, acetate, propionate, butyrate, isobutyrate and carbonate esters. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for 2-(p-tolyloxy)ethyl acetate were evaluated, then summarized, and includes physical properties data. A safety assessment of the entire AAASAE will be published simultaneously with this document. Please refer to Belsito et al. (2012) for an overall assessment of the safe use of this material and all AAASAE in fragrances.

  6. Market Design for a P2P Backup System

    NASA Astrophysics Data System (ADS)

    Seuken, Sven; Charles, Denis; Chickering, Max; Puri, Sidd

    Peer-to-peer (P2P) backup systems are an attractive alternative to server-based systems because the immense costs of large data centers can be saved by using idle resources on millions of private computers instead. This paper presents the design and theoretical analysis of a market for a P2P backup system. While our long-term goal is an open resource exchange market using real money, here we consider a system where monetary transfers are prohibited. A user who wants to backup his data must in return supply some of his resources (storage space, upload and download bandwidth) to the system.We propose a hybrid P2P architecture where all backup data is transferred directly between peers, but a dedicated server coordinates all operations and maintains meta-data. We achieve high reliability guarantees while keeping our data replication factor low by adopting sophisticated erasure coding technology (cf., [2]).

  7. Photoelectron angular distributions of ultrathin Ni/Cu(001) films

    SciTech Connect

    Mankey, G.J.; Subramanian, K.; Stockbauer, R.L.; Kurtz, R.L.

    1996-12-31

    The authors present measurements of the evolution with film thickness of the 3d electronic states at the Fermi energy of ultrathin Ni films. The morphology and thickness of the films is determined from x-ray photoelectron spectroscopy, x-ray photoelectron diffraction and x-ray magnetic linear dichroism using synchrotron radiation. Photoelectron angular distributions were measured using an ellipsoidal mirror analyzer. Even at submonolayer Ni coverages, the 3d electronic states exhibit bulk-like properties. This is attributed to the short screening length of electrons in metals, the localization of the 3d electrons, the similarity of the Ni and Cu ion cores, and finally the interaction with the underlying fcc periodic potential.

  8. Model insights into energetic photoelectrons measured at Mars by MAVEN

    NASA Astrophysics Data System (ADS)

    Sakai, Shotaro; Rahmati, Ali; Mitchell, David L.; Cravens, Thomas E.; Bougher, Stephen W.; Mazelle, Christian; Peterson, W. K.; Eparvier, Francis G.; Fontenla, Juan M.; Jakosky, Bruce M.

    2015-11-01

    Photoelectrons are important for heating, ionization, and airglow production in planetary atmospheres. Measured electron fluxes provide insight into the sources and sinks of energy in the Martian upper atmosphere. The Solar Wind Electron Analyzer instrument on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft measured photoelectrons including Auger electrons with 500 eV energies. A two-stream electron transport code was used to interpret the observations, including Auger electrons associated with K shell ionization of carbon, oxygen, and nitrogen. It explains the processes that control the photoelectron spectrum, such as the solar irradiance at different wavelengths, external electron fluxes from the Martian magnetosheath or tail, and the structure of the upper atmosphere (e.g., the thermal electron density). Our understanding of the complex processes related to the conversion of solar irradiances to thermal energy in the Martian ionosphere will be advanced by model comparisons with measurements of suprathermal electrons by MAVEN.

  9. Collision-induced dissociation reactions and pulsed field ionization photoelectron

    SciTech Connect

    Stimson, Stephanie

    1999-02-12

    This report summarized the four parts of the research study and describes the general conclusions. Individual chapters have been removed for separate processing. The chapter titles are: A study of the dissociation of CH3SH+ by collisional activation: Observation of non-statistical behavior; High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS+(X2π): An experimental and theoretical study; Rotationally resolved pulsed field ionization photoelectron bands of H2+2Σ+g, v+ = 0--18); and Rotationally resolved pulsed field ionization photoelectron bands of HD+2Σ+, v+ = 0--21).

  10. Conformation-Selective Resonant Photoelectron Spectroscopy via Dipole-Bound States of Cold Anions.

    PubMed

    Huang, Dao-Ling; Liu, Hong-Tao; Ning, Chuan-Gang; Wang, Lai-Sheng

    2015-06-18

    Molecular conformation is important in chemistry and biochemistry. Conformers connected by low energy barriers can only be observed at low temperatures and are difficult to be separated. Here we report a new method to obtain conformation-selective spectroscopic information about dipolar molecular radicals via dipole-bound excited states of the corresponding anions cooled in a cryogenic ion trap. We observed two conformers of cold 3-hydroxyphenoxide anions [m-HO(C6H4)O(-)] in high-resolution photoelectron spectroscopy and measured different electron affinities, 18,850(8) and 18,917(5) cm(-1), for the syn and anti 3-hydroxyphenoxy radicals, respectively. We also observed dipole-bound excited states for m-HO(C6H4)O(-) with different binding energies for the two conformers due to the different dipole moments of the corresponding 3-hydroxyphenoxy radicals. Excitations to selected vibrational levels of the dipole-bound states result in conformation-selective photoelectron spectra. This method should be applicable to conformation-selective spectroscopic studies of any anions with dipolar neutral cores.

  11. A combined photoelectron spectroscopy and ab initio study of the quasi-planar B24- cluster

    NASA Astrophysics Data System (ADS)

    Popov, Ivan A.; Piazza, Zachary A.; Li, Wei-Li; Wang, Lai-Sheng; Boldyrev, Alexander I.

    2013-10-01

    The structure and chemical bonding of the 24-atom boron cluster are investigated using photoelectron spectroscopy and ab initio calculations. The joint experimental and theoretical investigation shows that B24- possesses a quasi-planar structure containing fifteen outer and nine inner atoms with six of the inner atoms forming a filled pentagonal moiety. The central atom of the pentagonal moiety is puckered out of plane by 0.9 Å, reminiscent of the six-atom pentagonal caps of the well-known B12 icosahedral unit. The next closest isomer at the ROCCSD(T) level of theory has a tubular double-ring structure. Comparison of the simulated spectra with the experimental data shows that the global minimum quasi-planar B24- isomer is the major contributor to the observed photoelectron spectrum, while the tubular isomer has no contribution to the experiment. Chemical bonding analyses reveal that the periphery of the quasi-planar B24 constitutes 15 classical 2c-2e B-B σ-bonds, whereas delocalized σ- and π-bonds are found in the interior of the cluster with one unique 6c-2e π-bond responsible for bonding in the B-centered pentagon. The current work suggests that the 24-atom boron cluster continues to be quasi-2D, albeit the tendency to form filled pentagonal units, characteristic of 3D cage-like structures of bulk boron, is observed.

  12. Scanning photoelectron microscope for nanoscale three-dimensional spatial-resolved electron spectroscopy for chemical analysis

    NASA Astrophysics Data System (ADS)

    Horiba, K.; Nakamura, Y.; Nagamura, N.; Toyoda, S.; Kumigashira, H.; Oshima, M.; Amemiya, K.; Senba, Y.; Ohashi, H.

    2011-11-01

    In order to achieve nondestructive observation of the three-dimensional spatially resolved electronic structure of solids, we have developed a scanning photoelectron microscope system with the capability of depth profiling in electron spectroscopy for chemical analysis (ESCA). We call this system 3D nano-ESCA. For focusing the x-ray, a Fresnel zone plate with a diameter of 200 μm and an outermost zone width of 35 nm is used. In order to obtain the angular dependence of the photoelectron spectra for the depth-profile analysis without rotating the sample, we adopted a modified VG Scienta R3000 analyzer with an acceptance angle of 60° as a high-resolution angle-resolved electron spectrometer. The system has been installed at the University-of-Tokyo Materials Science Outstation beamline, BL07LSU, at SPring-8. From the results of the line-scan profiles of the poly-Si/high-k gate patterns, we achieved a total spatial resolution better than 70 nm. The capability of our system for pinpoint depth-profile analysis and high-resolution chemical state analysis is demonstrated.

  13. Threshold photoelectron study of naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene

    NASA Astrophysics Data System (ADS)

    Mayer, Paul M.; Blanchet, Valerie; Joblin, Christine

    2011-06-01

    Threshold photoelectron spectra (TPESs) were obtained for naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene using imaging photoelectron photoion coincidence spectroscopy, from threshold to a photon energy of ˜20 eV. Outer valence Green's function calculations at the OVGF/cc-pVTZ level of theory were used to assign molecular orbitals to the observed TPES features. There is generally good agreement between the predicted and observed bands. Threshold regions for each molecule exhibit vibrational structure which is readily assigned based on previous PES studies. While the measured adiabatic ionization energies (IEa) for naphthalene, anthracene, and pyrene are in good agreement with previous works, new values are reported for the two dihydro species (1,2-dihydronaphthalene, 8.010 ± 0.010 eV and 9,10-dihydroanthracene, 8.335 ± 0.010 eV). A comparison is also made with the G3//B3LYP composite method, which consistently overestimates the IE values by 0.06-0.09 eV. The double ionization energies for anthracene and pyrene have been measured to be 19.3 ± 0.2 and 19.8 ± 0.2 eV, respectively.

  14. 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.

  15. Ionization energies of aqueous nucleic acids: photoelectron spectroscopy of pyrimidine nucleosides and ab initio calculations.

    PubMed

    Slavícek, Petr; Winter, Bernd; Faubel, Manfred; Bradforth, Stephen E; Jungwirth, Pavel

    2009-05-13

    Vertical ionization energies of the nucleosides cytidine and deoxythymidine in water, the lowest ones amounting in both cases to 8.3 eV, are obtained from photoelectron spectroscopy measurements in aqueous microjets. Ab initio calculations employing a nonequilibrium polarizable continuum model quantitatively reproduce the experimental spectra and provide molecular interpretation of the individual peaks of the photoelectron spectrum, showing also that lowest ionization originates from the base. Comparison of calculated vertical ionization potentials of pyrimidine bases, nucleosides, and nucleotides in water and in the gas phase underlines the dramatic effect of bulk hydration on the electronic structure. In the gas phase, the presence of sugar and, in particular, of phosphate has a strong effect on the energetics of ionization of the base. Upon bulk hydration, the ionization potential of the base in contrast becomes rather insensitive to the presence of the sugar and phosphate, which indicates a remarkable screening ability of the aqueous solvent. Accurate aqueous-phase vertical ionization potentials provide a significant improvement to the corrected gas-phase values used in the literature and represent important information in assessing the threshold energies for photooxidation and oxidation free energies of solvent-exposed DNA components. Likewise, such energetic data should allow improved assessment of delocalization and charge-hopping mechanisms in DNA ionized by radiation.

  16. Scanning photoelectron microscope for nanoscale three-dimensional spatial-resolved electron spectroscopy for chemical analysis

    SciTech Connect

    Horiba, K.; Oshima, M.; Nakamura, Y.; Nagamura, N.; Toyoda, S.; Kumigashira, H.; Amemiya, K.; Senba, Y.; Ohashi, H.

    2011-11-15

    In order to achieve nondestructive observation of the three-dimensional spatially resolved electronic structure of solids, we have developed a scanning photoelectron microscope system with the capability of depth profiling in electron spectroscopy for chemical analysis (ESCA). We call this system 3D nano-ESCA. For focusing the x-ray, a Fresnel zone plate with a diameter of 200 {mu}m and an outermost zone width of 35 nm is used. In order to obtain the angular dependence of the photoelectron spectra for the depth-profile analysis without rotating the sample, we adopted a modified VG Scienta R3000 analyzer with an acceptance angle of 60 deg. as a high-resolution angle-resolved electron spectrometer. The system has been installed at the University-of-Tokyo Materials Science Outstation beamline, BL07LSU, at SPring-8. From the results of the line-scan profiles of the poly-Si/high-k gate patterns, we achieved a total spatial resolution better than 70 nm. The capability of our system for pinpoint depth-profile analysis and high-resolution chemical state analysis is demonstrated.

  17. Photodetachment spectroscopy and resonant photoelectron imaging of cryogenically-cooled deprotonated 2-hydroxypyrimidine anions

    NASA Astrophysics Data System (ADS)

    Huang, Dao-Ling; Zhu, Guo-Zhu; Liu, Yuan; Wang, Lai-Sheng

    2017-02-01

    We report a photodetachment and high-resolution photoelectron imaging study of cold deprotonated 2-hydroxypyrimidine anions, C4H3N2O-. Photodetachment spectroscopy reveals an excited dipole-bound state (DBS) of C4H3N2O- with a binding energy of 598 ± 5 cm-1 below the detachment threshold of 26,010 ± 5 cm-1. Twenty vibrational levels of the DBS are observed as resonances in the photodetachment spectrum, with three below the detachment threshold and seventeen above the threshold. By tuning the detachment laser to the above-threshold vibrational resonances, highly non-Franck-Condon photoelectron spectra are obtained. Nine fundamental vibrational frequencies are resolved, including six symmetry-forbidden modes. The 598 cm-1 binding energy for the DBS is quite high due to the large dipole moment of the C4H3N2O (>6 D). However, no evidence of a second DBS is observed below the detachment threshold.

  18. 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.

  19. X-ray photoelectron spectroscopy of graphitic carbon nanomaterials doped with heteroatoms.

    PubMed

    Susi, Toma; Pichler, Thomas; Ayala, Paola

    2015-01-01

    X-ray photoelectron spectroscopy (XPS) is one of the best tools for studying the chemical modification of surfaces, and in particular the distribution and bonding of heteroatom dopants in carbon nanomaterials such as graphene and carbon nanotubes. Although these materials have superb intrinsic properties, these often need to be modified in a controlled way for specific applications. Towards this aim, the most studied dopants are neighbors to carbon in the periodic table, nitrogen and boron, with phosphorus starting to emerge as an interesting new alternative. Hundreds of studies have used XPS for analyzing the concentration and bonding of dopants in various materials. Although the majority of works has concentrated on nitrogen, important work is still ongoing to identify its precise atomic bonding configurations. In general, care should be taken in the preparation of a suitable sample, consideration of the intrinsic photoemission response of the material in question, and the appropriate spectral analysis. If this is not the case, incorrect conclusions can easily be drawn, especially in the assignment of measured binding energies into specific atomic configurations. Starting from the characteristics of pristine materials, this review provides a practical guide for interpreting X-ray photoelectron spectra of doped graphitic carbon nanomaterials, and a reference for their binding energies that are vital for compositional analysis via XPS.

  20. Ionospheric photoelectrons: comparing Venus, Earth, Mars and Titan

    NASA Astrophysics Data System (ADS)

    Coates, Andrew; Tsang, Sharon; Wellbrock, Anne; Frahm, Rudy; Winningham, David; Barabash, Stas; Lundin, Rickard; Young, David; Crary, Frank

    2010-05-01

    The sunlit portion of planetary ionospheres is sustained by photoionization. This was first confirmed using measurements and modelling at Earth, but recently the Mars Express, Venus Express and Cassini-Huygens missions have revealed the importance of this process at Mars, Venus and Titan respectively. The primary neutral atmospheric constituents (CO2 in the case of Venus and Mars, and N2 in the case of Earth and Titan) are ionized at each object by EUV solar photons. This process produces photoelectrons with particular spectral characteristics. The electron spectrometers on Venus Express and Mars Express (part of ASPERA-3 and 4 respectively) were designed with excellent energy resolution (ΔE/E=8%) specifically in order to examine the photoelectron spectrum. In addition, the CAPS electron spectrometer at Saturn also has adequate resolution (ΔE/E=16.7%) to study this population at Titan. At Earth, photoelectrons are well established by in-situ measurements, and are even seen in the magnetosphere at up to 7 RE. At Mars, photoelectrons are seen in situ in the ionosphere but also in the tail at distances out to the Mars Express apoapsis (~3RM). At both Venus and Titan, photoelectrons are seen in situ in the ionosphere and in the tail (at up to 1.45 RV and 6.8 RT respectively). Here, we compare photoelectron measurements at Earth, Venus, Mars and Titan. We discuss their role as a tracer of the magnetic connection to the dayside ionosphere, and their possible role in enhancing ion escape.

  1. Faraday effect in Sn2P2S6 crystals.

    PubMed

    Krupych, Oleh; Adamenko, Dmytro; Mys, Oksana; Grabar, Aleksandr; Vlokh, Rostyslav

    2008-11-10

    We have revealed a large Faraday rotation in tin thiohypodiphosphate (Sn(2)P(2)S(6)) crystals, which makes this material promising for magneto-optics. The effective Faraday tensor component and the Verdet constant for the direction of the optic axis have been determined by measuring the pure Faraday rotation in Sn(2)P(2)S(6) crystals with both the single-ray and small-angular polarimetric methods at the normal conditions and a wavelength of 632.8 nm. The effective Verdet constant is found to be equal to 115 rad/T x m.

  2. Mini Magnetospheric Plasma Propulsion (M2P2)

    NASA Technical Reports Server (NTRS)

    Gallagher, Dennis; Winglee, Robert

    2000-01-01

    The M2P2 concept is based on the transfer of momentum from the solar wind to an artificial magnetic field structure like that naturally occurs at all magnetized planets in the Solar System, called the magnetosphere. The objectives of this program include the following: (1) Demonstrate artificial magnetospheric inflation through cold plasma filling in vacuum; (2) Demonstrate deflection of a surrogate solar wind by an artificial magnetosphere in the laboratory vacuum chamber; (3) Compare theoretical calculations for thrust forces with laboratory measurements; (4) Develop flight control algorithms for planning mission specific trajectories; and (5) Develop M2P2 system concept.

  3. The Social Impact of P2P Systems

    NASA Astrophysics Data System (ADS)

    Glorioso, Andrea; Pagallo, Ugo; Ruffo, Giancarlo

    The chapter deals with the social impact of P2P systems in light of a bidirectional connection by which technological developments influence, in a complex and often unpredictable way, the social environment whereas the dynamic evolution of the latter does affect technological progress. From this perspective, the aim is to deepen legal issues, sociological trends, economical aspects, and political dimensions of P2P technology, along with some of its next possible outputs, in order to assess one of the most compelling alternatives to the traditional frame of highly centralized human interaction.

  4. Autoionization study of the Argon 2p satellites excited near the argon 2s threshold

    SciTech Connect

    Wang, H.; Glans, P.; Hemmers, O.

    1997-04-01

    The dynamics of near-threshold photoionization is a complex phenomenon in which the many-electron character of the wavefunctions plays an important role. According to generalized time-independent resonant scattering theory, the transition matrix element from an initial state to a final state is the summation of the amplitudes of direct photoionization and an indirect term in which intermediate states are involved and the resonant behavior is embedded. Studies of the interference effects of intermediate states have been explored in the cases where the direct term is negligible. In the present work, electron time-of-flight spectra of the Ar 2p satellites were measured at two angles (magic and 0{degrees}) in the dipole plane with the exciting photon energy tuned in the vicinity of the Ar 2s threshold. For excitation far below or above the 2s threshold, the 2p satellites spectrum is dominated by 3p to np shakeup contributions upon the ionization of a 2p electron.

  5. Reactor Neutrino Spectra

    NASA Astrophysics Data System (ADS)

    Hayes, Anna C.; Vogel, Petr

    2016-10-01

    We present a review of the antineutrino spectra emitted from reactors. Knowledge of these spectra and their associated uncertainties is crucial for neutrino oscillation studies. The spectra used to date have been determined either by converting measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that make up the spectra, using modern databases as input. The uncertainties in the subdominant corrections to β-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.

  6. Probing deeper by hard x-ray photoelectron spectroscopy

    SciTech Connect

    Risterucci, P.; Renault, O. Martinez, E.; Delaye, V.; Detlefs, B.; Zegenhagen, J.; Gaumer, C.; Grenet, G.; Tougaard, S.

    2014-02-03

    We report an hard x-ray photoelectron spectroscopy method combining high excitation energy (15 keV) and improved modelling of the core-level energy loss features. It provides depth distribution of deeply buried layers with very high sensitivity. We show that a conventional approach relying on intensities of the core-level peaks is unreliable due to intense plasmon losses. We reliably determine the depth distribution of 1 ML La in a high-κ/metal gate stack capped with 50 nm a-Si. The method extends the sensitivity of photoelectron spectroscopy to depths beyond 50 nm.

  7. Background reduction using single-photoelectron counting for WIMP search

    NASA Astrophysics Data System (ADS)

    Ogawa, I.; Hazama, R.; Mukaida, K.; Kishimoto, K.; Kobayashi, T.; Tomii, S.; Sakai, H.; Katsuki, A.; Itamura, T.; Tanaka, Y.; Umehara, S.; Yoshida, S.; Matsuoka, K.; Kishimoto, T.

    2013-03-01

    We have developed a new background reduction method based on single photoelectron counting of scintillators for the WIMP search experiment. We introduced this method to our detector system ELEGANT VI, which has an active shield in all directions (4π) using a pulse height or, equivalently, the difference in the number of photoelectrons between two (left and right) photomultiplier tubes attached to CaF2 scintillators. The number distribution is uniquely described by a binomial function, via which we developed the unambiguous background subtraction method. This method reduces the backgrounds further compared to charge-sensitive ADC and offers improved sensitivity for the search for WIMPs.

  8. Methyliminopropadienone CH3-N═C═C═C═O: photoelectron spectrum and electronic structure.

    PubMed

    Chrostowska, Anna; Dargelos, Alain; Khayar, Saïd; Wentrup, Curt

    2012-09-20

    N-Methyliminopropadienone MeN═C═C═C═O 1a was generated by flash vacuum thermolysis of three 5-(aminomethylene)-1,3-dioxane-4,6-diones (Meldrum's acid derivatives). Online monitoring of the reactions permitted the recording of the UV-photoelectron spectra and the determination of the first two ionization energies of 1a as 9.0 and 12.4 eV. The first ionization energy (and the calculated highest occupied molecular orbital energy) of 1a are more comparable with those of N-methylketenimine than with ketene. In contrast, the calculated lowest unoccupied molecular orbital energy is significantly lower than those of both ketene and N-methylketenimine, thereby making iminopropadienones powerful electrophiles. Calculated charge densities indicate that electrophiles should attack at C3 or O and nucleophiles at C2 or C4 in broad agreement with experimental observations.

  9. Energy level alignment between C 60 and Al using ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Seo, J. H.; Kang, S. J.; Kim, C. Y.; Cho, S. W.; Yoo, K.-H.; Whang, C. N.

    2006-09-01

    The energy level alignment between C 60 and Al has been investigated by using ultraviolet photoelectron spectroscopy. To obtain the interfacial electronic structure between C 60 and Al, C 60 was deposited on a clean Al substrate in a stepwise manner. The valence-band spectra were measured immediately after each step of C 60 deposition without breaking the vacuum. The measured onset of the highest occupied molecular orbital energy level was located at 1.59 eV from the Fermi level of Al. The vacuum level was shifted 0.68 eV toward lower binding energy with additional C 60 layers. The observed vacuum level shift means that the interface dipole exists at the interface between C 60 and Al. The barrier height of electron injection from Al to C 60 is 0.11 eV, which is smaller value than that of hole injection.

  10. X-ray laser-induced photoelectron spectroscopy for single-state measurements

    NASA Astrophysics Data System (ADS)

    Nelson, A. J.; Dunn, J.; van Buuren, T.; Hunter, J.

    2004-12-01

    We demonstrate single-shot x-ray laser-induced time-of-flight photoelectron spectroscopy on metal and semiconductor surfaces with picosecond time resolution. Our compact multipulse terawatt tabletop x-ray laser source provides the necessary high photon flux (>1012/pulse), monochromaticity, picosecond pulse duration, and coherence for probing ultrafast changes in the chemical and electronic structure of these materials. Static valence band and shallow core-level photoemission spectra are presented for ambient temperature polycrystalline Cu foils and Ge(100). Surface contamination was removed by UV ozone cleaning prior to analysis. The ultrafast nature of this technique lends itself to true single-state measurements of shocked and heated materials.

  11. X-Ray Laser Induced Photoelectron Spectroscopy for Single-State Measurements

    SciTech Connect

    Nelson, A J; Dunn, J; van Buuren, T; Hunter, J

    2004-07-14

    We demonstrate single-shot x-ray laser induced time-of-flight photoelectron spectroscopy on metal and semiconductor surfaces with picosecond time resolution. The LLNL COMET compact tabletop x-ray laser source provides the necessary high photon flux (>10{sup 12}/pulse), monochromaticity, picosecond pulse duration, and coherence for probing ultrafast changes in the chemical and electronic structure of these materials. Static valence band and shallow core-level photoemission spectra are presented for ambient temperature polycrystalline Cu foils and Ge(100). Surface contamination was removed by UV ozone cleaning prior to analysis. The ultrafast nature of this technique lends itself to true single-state measurements of shocked and heated materials.

  12. Determination of band profiles in GaN films using hard X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Saito, Shinji; Yoshiki, Masahiko; Nunoue, Shinya; Sano, Nobuyuki

    2017-02-01

    We investigated band-profile control by introducing interlayers between a semiconductor and metal contact layers to improve the electrical properties of GaN-based semiconductor devices. We evaluated the electronic structure of the semiconductor surface and the metal/semiconductor interface by hard X-ray photoelectron spectroscopy. We also performed Monte Carlo simulations using the Boltzmann transport equation under the potential profile obtained using the Poisson equation. The band profile in the semiconductor substrate was then examined by comparing the energy spectra from the simulations with those from the experiments. We obtained good agreement between the two results. The present experimental and theoretical methods allow one to determine the band profile near the surface of a semiconductor as well as that in a metal interface. This approach may become a useful tool in the design and/or evaluation of processing conditions.

  13. An investigation into low-lying electronic states of HCS{sub 2} via threshold photoelectron imaging

    SciTech Connect

    Qin, Zhengbo; Cong, Ran; Liu, Zhiling; Xie, Hua; Tang, Zichao E-mail: fanhj@dicp.ac.cn; Fan, Hongjun E-mail: fanhj@dicp.ac.cn

    2014-06-07

    Low-energy photoelectron imaging spectra of HCS{sub 2}{sup −} are reported for the first time. Vibrationally resolved photodetachment transitions from the ground state of HCS{sub 2}{sup −} to the ground state and low-lying excited states of HCS{sub 2} are observed. Combined with the ab intio calculations and Franck-Condon simulations, well-resolved vibrational spectra demonstrate definitive evidence for the resolution of the ground-state and excited states of HCS{sub 2} radical in the gaseous phase. The ground state and two low-lying excited states of HCS{sub 2} radical are assigned as {sup 2}B{sub 2}, {sup 2}A{sub 2}, and {sup 2}A{sub 1} states, respectively. The adiabatic electron affinity is determined to be 2.910 ± 0.007 eV. And the term energies of the excited states, T{sub 0} = 0.451 ± 0.009 eV and 0.553 ± 0.009 eV, are directly measured from the experimental data, respectively. Angular filtering photoelectron spectra are carried out to assist in the spectral band assignment.

  14. Development of High-Energy-Resolution Display-Type Photoelectron Spectrometer in the Ultraviolet Photoelectron Spectroscopy Region

    NASA Astrophysics Data System (ADS)

    Nohno, Tomohito; Matsui, Fumihiko; Hamada, Yohji; Matsumoto, Hideaki; Takeda, Sakura; Hattori, Ken; Daimon, Hiroshi

    2003-07-01

    We have built a newly designed 2D-photoelectron spectroscopy (PES) analyzer for the measurement of wide-angle photoelectron angular distribution patterns in the ultraviolet photoelectron spectroscopy (UPS) region with no distortion. The spherical electric field inside the analyzer is achieved by the 158 tin obstacle rings placed on the inner surface of the machinable ceramic outer hemisphere. The inner surface of the outer hemisphere is covered with graphite powder to avoid charging. Hence, the ideal shape and the smooth change of the potential on the surface of the hemisphere could be realized. The energy resolution (Δ E/ EP) is estimated to be 0.43% (73 meV) at a kinetic energy of 16.85 eV and 0.16% at a kinetic energy of 300 eV.

  15. Measurement and analysis of P2P IPTV program resource.

    PubMed

    Wang, Wenxian; Chen, Xingshu; Wang, Haizhou; Zhang, Qi; Wang, Cheng

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program names, which obstructs searching and organizing programs. Thus, we focus on characteristic analysis of program resources, including the distributions of length of program names, the entropy of the character types, and hierarchy depth of programs. These analyses reveal the disorderly naming conventions of P2P IPTV programs. The analysis results can help to purify and extract useful information from chaotic names for better retrieval and accelerate automatic sorting of program and establishment of IPTV repository. In order to represent popularity of programs and to predict user behavior and popularity of hot programs over a period, we also put forward an analytical model of hot programs.

  16. Measurement and Analysis of P2P IPTV Program Resource

    PubMed Central

    Chen, Xingshu; Wang, Haizhou; Zhang, Qi

    2014-01-01

    With the rapid development of P2P technology, P2P IPTV applications have received more and more attention. And program resource distribution is very important to P2P IPTV applications. In order to collect IPTV program resources, a distributed multi-protocol crawler is proposed. And the crawler has collected more than 13 million pieces of information of IPTV programs from 2009 to 2012. In addition, the distribution of IPTV programs is independent and incompact, resulting in chaos of program names, which obstructs searching and organizing programs. Thus, we focus on characteristic analysis of program resources, including the distributions of length of program names, the entropy of the character types, and hierarchy depth of programs. These analyses reveal the disorderly naming conventions of P2P IPTV programs. The analysis results can help to purify and extract useful information from chaotic names for better retrieval and accelerate automatic sorting of program and establishment of IPTV repository. In order to represent popularity of programs and to predict user behavior and popularity of hot programs over a period, we also put forward an analytical model of hot programs. PMID:24772008

  17. Study of radicals, clusters and transition state species by anion photoelectron spectroscopy

    SciTech Connect

    Arnold, Don Wesley

    1994-08-01

    Free radicals, elemental and van der Waals clusters and transition state species for bimolecular chemical reactions are investigated using anion photoelectron spectroscopy. Several low-lying electronic states of ozone have been identified via photoelectron spectroscopy of O3-. A characterization of these states is important to models for atmospheric ozone reaction kinetics. The fluoroformyloxyl radical, FCO2, has been investigated, providing vibrational frequencies and energies for two electronic states. The technique has also been employed to make the first direct observation and characterization of the NNO2 molecule. Several electronic states are observed for this species which is believed to play a role as a reactive intermediate in the N + NO2 reaction. The experimental results for all three of these radicals are supplemented by ab initio investigations of their molecular properties. The clusters investigations include studies of elemental carbon clusters (C2- - C11-), and van der Waals clusters (X-(CO2)n, X = I, Br, Cl; n {le} 13 and I- (N2O)n=1--11). Primarily linear clusters are observed for the smaller carbon clusters, while the spectra of the larger clusters contain contribution from cyclic anion photodetachment. Very interesting ion-solvent interactions are observed in the X-(CO2)n clusters. The transition state regions for several bimolecular chemical reactions have also been investigated by photodetachment of a negative ion precursor possessing a geometry similar to that of the transition state species. These spectra show features which are assigned to motions of the unstable neutral complex existing between reactants and products.

  18. A Study of NbCr and NbCr^{-} by Anion Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Baudhuin, Melissa A.; Boopalachandran, Praveenkumar; Rajan, Srijay S.; Leopold, Doreen G.

    2013-06-01

    We report the 488 nm photoelectron spectrum of the NbCr^{-} anion. For the ^{2}Δ ground state of neutral NbCr, the short bond length (1.894 Å) and high bond energy (D_0 3.0263(6) eV) measured by R2PI spectroscopy indicate high order multiple bonding. We find that the NbCr^{-} anion has a ^{1}Σ^{+} ground state, in which the "extra" electron occupies the (4d)δ bonding orbital, giving a 1σ^{2}1π^{4}1δ^{4}2σ^{2} valence electron configuration and a formal bond order of 6. Low-lying excited states of NbCr (assigned as two ^{2}Σ^{+} states) and NbCr^{-} (^{3}Δ) are also observed. The spectra provide the electron affinity of NbCr, energies of the ^{2}Σ^{+} and the ^{3}Δ excited states, vibrational frequencies for the NbCr and NbCr^{-} ground states and for the ^{2}Σ^{+} excited states, and (from Franck-Condon analyses) differences among the bond lengths of the observed states. These results are compared with our previous data for the Group 5/6 congeners NbMo, VCr, and VMo, and with DFT predictions. We also report results for ongoing experiments on the flow tube reactions of the Group V metals Nb and Ta with butadiene, and the vibrationally-resolved photoelectron spectra of some of the organometallic reaction product anions. S. M. Sickafoose, J. D. Langenberg, and M. D. Morse, J. Phys. Chem. A. 104, 3521-3527 (2000).

  19. Anion photoelectron spectroscopy of deprotonated ortho-, meta-, and para-methylphenol.

    PubMed

    Nelson, Daniel J; Gichuhi, Wilson K; Miller, Elisa M; Lehman, Julia H; Lineberger, W Carl

    2017-02-21

    The anion photoelectron spectra of ortho-, meta-, and para-methylphenoxide, as well as methyl deprotonated meta-methylphenol, were measured. Using the Slow Electron Velocity Map Imaging technique, the Electron Affinities (EAs) of the o-, m-, and p-methylphenoxyl radicals were measured as follows: 2.1991±0.0014, 2.2177±0.0014, and 2.1199±0.0014 eV, respectively. The EA of m-methylenephenol was also obtained, 1.024±0.008 eV. In all four cases, the dominant vibrational progressions observed are due to several ring distortion vibrational normal modes that were activated upon photodetachment, leading to vibrational progressions spaced by ∼500 cm(-1). Using the methylphenol O-H bond dissociation energies reported by King et al. and revised by Karsili et al., a thermodynamic cycle was constructed and the acidities of the methylphenol isomers were determined as follows: ΔacidH298K(0)=348.39±0.25, 348.82±0.25, 350.08±0.25, and 349.60±0.25 kcal/mol for cis-ortho-, trans-ortho-, m-, and p-methylphenol, respectively. The excitation energies for the ground doublet state to the lowest excited doublet state electronic transition in o-, m-, and p-methylphenoxyl were also measured as follows: 1.029±0.009, 0.962±0.002, and 1.029±0.009 eV, respectively. In the photoelectron spectra of the neutral excited states, C-O stretching modes were excited in addition to ring distortion modes. Electron autodetachment was observed in the cases of both m- and p-methylphenoxide, with the para isomer showing a lower photon energy onset for this phenomenon.

  20. Anion photoelectron spectroscopy of deprotonated ortho-, meta-, and para-methylphenol

    NASA Astrophysics Data System (ADS)

    Nelson, Daniel J.; Gichuhi, Wilson K.; Miller, Elisa M.; Lehman, Julia H.; Lineberger, W. Carl

    2017-02-01

    The anion photoelectron spectra of ortho-, meta-, and para-methylphenoxide, as well as methyl deprotonated meta-methylphenol, were measured. Using the Slow Electron Velocity Map Imaging technique, the Electron Affinities (EAs) of the o-, m-, and p-methylphenoxyl radicals were measured as follows: 2.1991±0.0014, 2.2177±0.0014, and 2.1199±0.0014 eV, respectively. The EA of m-methylenephenol was also obtained, 1.024±0.008 eV. In all four cases, the dominant vibrational progressions observed are due to several ring distortion vibrational normal modes that were activated upon photodetachment, leading to vibrational progressions spaced by ˜500 cm-1. Using the methylphenol O-H bond dissociation energies reported by King et al. and revised by Karsili et al., a thermodynamic cycle was constructed and the acidities of the methylphenol isomers were determined as follows: Δa c i dH298K 0=348.39 ±0.25 , 348.82±0.25, 350.08±0.25, and 349.60±0.25 kcal/mol for cis-ortho-, trans-ortho-, m-, and p-methylphenol, respectively. The excitation energies for the ground doublet state to the lowest excited doublet state electronic transition in o-, m-, and p-methylphenoxyl were also measured as follows: 1.029±0.009, 0.962±0.002, and 1.029±0.009 eV, respectively. In the photoelectron spectra of the neutral excited states, C-O stretching modes were excited in addition to ring distortion modes. Electron autodetachment was observed in the cases of both m- and p-methylphenoxide, with the para isomer showing a lower photon energy onset for this phenomenon.

  1. 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.

  2. 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.

  3. Breit-Pauli energy levels belonging to 2p 4, 2s2p 5, 2p 6, 2p 33ℓ configurations and all E1 transitions among these levels in Mg V

    NASA Astrophysics Data System (ADS)

    Deb, N. C.; Hibbert, A.

    2007-07-01

    We present accurate oscillator strengths, line strengths and radiative rates for 1073 E1 transitions among the 86 levels belonging to 2s 22p 4, 2s2p 5, 2p 6, and 2s 22p 3( 4S o, 2D o, 2P o)3ℓ configurations in Mg V. We have used 1s and 2s Hartree-Fock orbitals, re-optimized 2p on 2p 3( 2D o)3s 3D o and optimized 3s,3p,3d orbitals on real states. Sixteen additional orbitals up to 8d are optimized either as a correction to n = 3 physical orbitals or as a correlation orbital. A very large set of configurations including up to three electron promotions are used to account for all important correlation effects. All of the main five terms in the Breit-Pauli operator (except the orbit-orbit interaction) are included in order to account for the relativistic effects. Small adjustments to the diagonal elements of the Hamiltonian matrix are made to bring the calculated energies within a few cm -1 of the corresponding NIST recommended data wherever available. The calculated oscillator strengths, line strengths, and radiative rates for almost all of the E1 transitions show excellent agreement with the corresponding MCDF results of Fischer. The recent results of Bhatia et al. are found to be consistently higher by 20-45%. The accuracy of the present calculation is considered to be better than the NIST accuracy ratings for various transitions.

  4. Effects of proton irradiation on single-stranded DNA studied by using X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, E.; Lee, Cheol Eui; Han, J. H.

    2016-08-01

    X-ray photoelectron spectroscopy (XPS) has been employed in order to study the effects of proton irradiation on herring sperm single-stranded DNA. Systematic changes of the chemical shifts in the C, N, O, and P XPS line components as functions of the irradiation dose were observed, indicative of the bonding configurations in the DNA system. While the C 1 s XPS lines showed weak blueshifts, the N 1 s, O 1 s, and P 2 p XPS lines showed blueshifts with a marked dependence on the irradiation dose in a prominent manner. Our results show that linear energy transfer by charged particles and photons may have distinct molecular-level effects as the C 1 s, N 1 s, O 1 s, and P 2 p XPS lines showed redshifts in our previous study of effects of the γ-ray irradiation on the same system.

  5. Surface characterization of immunosensor conjugated with gold nanoparticles based on cyclic voltammetry and X-ray photoelectron spectroscopy.

    PubMed

    Lai, Lee-Jene; Yang, Yaw-Wen; Lin, Yao-Kwang; Huang, Li-Ling; Hsieh, Yi-Heui

    2009-02-01

    This investigation describes the surface characterization of rabbit immunoglobulin G (IgG) conjugated with gold nanoparticles. Goat anti-rabbit immunoglobulin G tagged with 5nm gold nanoparticles was applied to detect the IgG. Then, the autocatalyzed deposition of Au(3+) onto the surface of anti-IgGAu increased the surface area per gold nanoparticle. The immobilization chemistries and the atomic concentrations of Au(4f), P(2p), S(2p), C(1s), N(1s) and O(1s) of the resulting antibody-modified Au electrodes were determined by X-ray photoelectron spectroscopy (XPS). The sulfur that is involved in the cysteamine binding and the enlargement of the gold nanoparticles are identified using cyclic voltammetry. The results reveal that the surface area per gold particle, following the autocatalyzed deposition Au(3+) on the surface of anti-IgGAu, was approximately seven times higher than that before deposition.

  6. Transitions of the type 2s-2p in fluorinelike and oxygenlike As, Se, Br, and Rb

    NASA Technical Reports Server (NTRS)

    Feldman, U.; Seely, J. F.; Behring, W. E.; Richardson, M. C.; Goldsmith, S.

    1985-01-01

    Transitions of the type 2s-2p in the F I and O I isoelectronic sequences of arsenic, selenium, bromine, and rubidium have been identified in spectra from laser-produced plasmas. Wavelengths in the range 50 to 90 A were measured to an accuracy of 0.01 A or better. The wavelengths of the magnetic-dipole transitions within the ground configurations are predicted.

  7. On some limitations on temporal resolution in imaging subpicosecond photoelectronics

    SciTech Connect

    Shchelev, M Ya; Andreev, S V; Degtyareva, V P; Kopaev, I A; Monastyrskiy, M A; Greenfield, D E

    2015-05-31

    Numerical modelling is used to analyse some effects restricting the enhancement of temporal resolution into the area better than 100 fs in streak image tubes and photoelectron guns. A particular attention is paid to broadening of an electron bunch as a result of Coulomb interaction. Possible ways to overcome the limitations under consideration are discussed. (extreme light fields and their applications)

  8. Investigation of the spectral sensitivity of photoelectronic instruments.

    NASA Astrophysics Data System (ADS)

    Georgieva, G. A.; Debur, V. G.; Rylov, V. S.

    A description of a device for investigating the spectral sensitivity or quantum yield of photoelectronic instruments (PEIs) and methods of measuring it are given. The results of using various PEIs as standard photodetectors and sources of spectral sensitivity measurement errors are examined. The device and methods have been being used successfully at the observatory since 1975.

  9. Angular distribution of photoelectrons from atomic oxygen, nitrogen, and carbon

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    The angular distribution of photoelectrons from atomic oxygen is investigated using Hartree-Fock (HF) wave functions. The correct formulation is used to compare HS and HF results. Agreement between these results is good and the HS calculations have been extended to atomic nitrogen and carbon as well.

  10. Multi-photon photoelectron spectromicroscopy of supported polystyrene spheres

    NASA Astrophysics Data System (ADS)

    Lilienkamp, Gerhard; Lindla, Florian; Senft, Christoph; Daum, Winfried

    2008-08-01

    Multi-photon photoemission excited by 100 fs, 400 nm laser pulses leads to an unexpected high contrast in photoelectron images of polystyrene spheres on a platinum substrate. The total, energy-integrated photoelectron yield shows clear signatures of two-photon photoemission from the substrate while photoemission from polystyrene is dominated by one-photon processes for low laser power and multi-photon processes for higher laser power. For excitation with UV light from a conventional Hg arc lamp, we observe a marked energy shift of the photoelectron spectrum of polystyrene with respect to that of the substrate. This shift is related to the different surface potentials of the conductive substrate and the dielectric spheres in the strong electric field of the objective lens of the microscope. Laser illumination causes photoconductivity in polystyrene by efficient two-photon excitation of long-lived states and induces a shifting of the surface potential of the polystyrene spheres. Pump-probe experiments support our conclusion that photoemission from polystyrene takes place from these long-lived intermediate states via a one-photon process for sufficiently low laser power. We suggest that photoelectron spectromicroscopy might be useful as a non-scanning method for fast height profiling of supported dielectric structures.

  11. [Study on pollution for the photoelectronic material InP].

    PubMed

    Xu, Jian-cheng; Ding, Xiao-ping; Chen, Ding-qin

    2002-08-01

    The mass spectrum analysis of crystal face (100) and (111) and the photoluminescence analysis of crystal face (100) in the photoelectronic material InP were given. The Hall coefficient, charge carrier concentration and Hall mobility were determined. Experimental results indicate that the pollution of silicon is predominant.

  12. Photoelectron and X-ray Absorption Spectroscopy Of Pu

    SciTech Connect

    Tobin, J; Chung, B; Schulze, R; Farr, J; Shuh, D

    2003-11-12

    We have performed Photoelectron Spectroscopy and X-Ray Absorption Spectroscopy upon highly radioactive samples of Plutonium at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as plans for future studies of actinide studies.

  13. Photoelectron spectroscopy in heavy fermions: Inconsistencies with the Kondo model

    SciTech Connect

    Arko, A.J.; Joyce, J.J.; Blyth, R.R.; Canfield, P.C.; Thompson, J.D.; Bartlett, R.J.; Fisk, Z.; Lawrence, J.; Tang, J.; Riseborough, P.

    1992-09-01

    We have investigated a number of Ce and Yb heavy fermion compounds via photoelectron spectroscopy and compared the results to the predictions of the Imurity Anderson Hamiltonian within the Gunnarson-Schonhammer approach. For the low T{sub K} materials investigated we find little or no correlation with T{sub K}, the only parameter that can be determined independent of photoemission.

  14. Application of maximum-entropy spectral estimation to deconvolution of XPS data. [X-ray Photoelectron Spectroscopy

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Klein, J. D.; Barton, J. J.; Grunthaner, F. J.

    1981-01-01

    A comparison is made between maximum-entropy spectral estimation and traditional methods of deconvolution used in electron spectroscopy. The maximum-entropy method is found to have higher resolution-enhancement capabilities and, if the broadening function is known, can be used with no adjustable parameters with a high degree of reliability. The method and its use in practice are briefly described, and a criterion is given for choosing the optimal order for the prediction filter based on the prediction-error power sequence. The method is demonstrated on a test case and applied to X-ray photoelectron spectra.

  15. Theory of probing attosecond electron wave packets via two-path interference of angle-resolved photoelectrons

    SciTech Connect

    Choi, N. N.; Jiang, T. F.; Morishita, T.; Lee, M.-H.; Lin, C. D.

    2010-07-15

    We study theoretically the electron wave packet generated by an attosecond pulse train (APT) which is probed with a time-delayed infrared (IR) laser pulse. The APT creates an excited state and a continuum electron wave packet. By ionizing the excited state with an IR, a delayed new continuum electron wave packet is created. The interference of the wave packets from the two paths, as reflected in angle-resolved photoelectron spectra, is analyzed analytically. Using the analytical expressions, we examine the possibility of retrieving information on the electron wave packet generated by the APT.

  16. Photoelectron spectroscopy of cluster anions of naphthalene and related aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Ando, Naoto; Mitsui, Masaaki; Nakajima, Atsushi

    2008-04-01

    The electronic structures and structural morphologies of naphthalene cluster anions, (naphthalene)n- (n=3-150), and its related aromatic cluster anions, (acenaphthene)n- (n=4-100) and (azulene)n- (n=1-100), are studied using anion photoelectron spectroscopy. For (naphthalene)n- clusters, two isomers coexist over a wide size range: isomers I and II-1 (28⩽n⩽60) or isomers I and II-2 (n⩾˜60). Their contributions to the photoelectron spectra can be separated using an anion beam hole-burning technique. In contrast, such an isomer coexistence is not observed for (acenaphthene)n- and (azulene)n- clusters, where isomer I is exclusively formed throughout the whole size range. The vertical detachment energies (VDEs) of isomer I (7⩽n⩽100) in all the anionic clusters depend linearly on n-1/3 and their size-dependent energetics are quite similar to one another. On the other hand, the VDEs of isomers II-1 and II-2 produced in (naphthalene)n- clusters with n ⩾˜30 remain constant at 0.84 and 0.99eV, respectively, 0.4-0.6eV lower than those of isomer I. Based upon the ion source condition dependence and the hole-burning photoelectron spectra experiments for each isomer, the energetics and characteristics of isomers I, II-1, and II-2 are discussed: isomer I is an internalized anion state accompanied by a large change in its cluster geometry after electron attachment, while isomers II-1 and II-2 are crystal-like states with little structural relaxation. The nonappearance of isomers II-1 and II-2 for (acenaphthene)n- and (azulene)n- and a comparison with other aromatic cluster anions indicate that a highly anisotropic and symmetric π-conjugated molecular framework, such as found in the linear oligoacenes, is an essential factor for the formation of the crystal-like ordered forms (isomers II-1 and II-2). On the other hand, lowering the molecular symmetry makes their production unfavorable.

  17. Chromosome 2 (2p16) abnormalities in Carney complex tumours

    PubMed Central

    Matyakhina, L; Pack, S; Kirschner, L; Pak, E; Mannan, P; Jaikumar, J; Taymans, S; Sandrini, F; Carney, J; Stratakis, C

    2003-01-01

    Carney complex (CNC) is an autosomal dominant multiple endocrine neoplasia and lentiginosis syndrome characterised by spotty skin pigmentation, cardiac, skin, and breast myxomas, and a variety of endocrine and other tumours. The disease is genetically heterogeneous; two loci have been mapped to chromosomes 17q22–24 (the CNC1 locus) and 2p16 (CNC2). Mutations in the PRKAR1A tumour suppressor gene were recently found in CNC1 mapping kindreds, while the CNC2 and perhaps other genes remain unidentified. Analysis of tumour chromosome rearrangements is a useful tool for uncovering genes with a role in tumorigenesis and/or tumour progression. CGH analysis showed a low level 2p amplification recurrently in four of eight CNC tumours; one tumour showed specific amplification of the 2p16-p23 region only. To define more precisely the 2p amplicon in these and other tumours, we completed the genomic mapping of the CNC2 region, and analysed 46 tumour samples from CNC patients with and without PRKAR1A mutations by fluorescence in situ hybridisation (FISH) using bacterial artificial chromosomes (BACs). Consistent cytogenetic changes of the region were detected in 40 (87%) of the samples analysed. Twenty-four samples (60%) showed amplification of the region represented as homogeneously stained regions (HSRs). The size of the amplicon varied from case to case, and frequently from cell to cell in the same tumour. Three tumours (8%) showed both amplification and deletion of the region in their cells. Thirteen tumours (32%) showed deletions only. These molecular cytogenetic changes included the region that is covered by BACs 400-P-14 and 514-O-11 and, in the genetic map, corresponds to an area flanked by polymorphic markers D2S2251 and D2S2292; other BACs on the centromeric and telomeric end of this region were included in varying degrees. We conclude that cytogenetic changes of the 2p16 chromosomal region that harbours the CNC2 locus are frequently observed in tumours from CNC

  18. Vibrational state-selective autodetachment photoelectron spectroscopy from dipole-bound states of cold 2-hydroxyphenoxide: o − HO(C{sub 6}H{sub 4})O{sup −}

    SciTech Connect

    Huang, Dao-Ling; Wang, Lai-Sheng; Liu, Hong-Tao; Ning, Chuan-Gang

    2015-03-28

    We report a photodetachment and high-resolution photoelectron imaging study of cold 2-hydroxyphenoxide anion, o − HO(C{sub 6}H{sub 4})O{sup −}, cooled in a cryogenic ion trap. Photodetachment spectroscopy revealed a dipole-bound state (DBS) of the anion, 25 ± 5 cm{sup −1}, below the detachment threshold of 18784 ± 5 cm{sup −1} (2.3289 ± 0.0006 eV ), i.e., the electron affinity of the 2-hydroxyphenoxy radical o − HO(C{sub 6}H{sub 4})O{sup ⋅}. Twenty-two vibrational levels of the DBS are observed as resonances in the photodetachment spectrum. By tuning the detachment laser to these DBS vibrational levels, we obtain 22 high-resolution resonant photoelectron spectra, which are highly non-Franck-Condon due to mode-selective autodetachment and the Δv = − 1 propensity rule. Numerous Franck-Condon inactive vibrational modes are observed in the resonant photoelectron spectra, significantly expanding the vibrational information that is available in traditional high-resolution photoelectron spectroscopy. A total of 15 fundamental vibrational frequencies are obtained for the o − HO(C{sub 6}H{sub 4})O{sup ⋅}  radical from both the photodetachment spectrum and the resonant photoelectron spectra, including six symmetry-forbidden out-of-plane modes as a result of resonant enhancement.

  19. Supporting seamless mobility for P2P live streaming.

    PubMed

    Kim, Eunsam; Kim, Sangjin; Lee, Choonhwa

    2014-01-01

    With advent of various mobile devices with powerful networking and computing capabilities, the users' demand to enjoy live video streaming services such as IPTV with mobile devices has been increasing rapidly. However, it is challenging to get over the degradation of service quality due to data loss caused by the handover. Although many handover schemes were proposed at protocol layers below the application layer, they inherently suffer from data loss while the network is being disconnected during the handover. We therefore propose an efficient application-layer handover scheme to support seamless mobility for P2P live streaming. By simulation experiments, we show that the P2P live streaming system with our proposed handover scheme can improve the playback continuity significantly compared to that without our scheme.

  20. Supporting Seamless Mobility for P2P Live Streaming

    PubMed Central

    Kim, Eunsam; Kim, Sangjin; Lee, Choonhwa

    2014-01-01

    With advent of various mobile devices with powerful networking and computing capabilities, the users' demand to enjoy live video streaming services such as IPTV with mobile devices has been increasing rapidly. However, it is challenging to get over the degradation of service quality due to data loss caused by the handover. Although many handover schemes were proposed at protocol layers below the application layer, they inherently suffer from data loss while the network is being disconnected during the handover. We therefore propose an efficient application-layer handover scheme to support seamless mobility for P2P live streaming. By simulation experiments, we show that the P2P live streaming system with our proposed handover scheme can improve the playback continuity significantly compared to that without our scheme. PMID:24977171

  1. K2P Potassium Channels, Mysterious and Paradoxically Exciting

    PubMed Central

    Goldstein, Steve A. N.

    2013-01-01

    New evidence reveals that the common electrolyte disorder hypokalemia can induce K2P1 channels that are normally selective for K+ to break the rules and conduct Na+. This defiant behavior leads to paradoxical depolarization of many cells in the heart, increasing the risk for lethal arrhythmia. The new research resolves a mystery uncovered 50 years ago and bestows an array of new riddles. Here, I discuss how K2P1 might achieve this alchemy—through stable residence of the K+ selectivity filter in a Na+-conductive state between its open and C-inactive configurations—and predict that other K+ channels and environmental stimuli will be discovered to produce the same excitatory misconduct. PMID:21868351

  2. Fine Structure of the Upsilon 2p States.

    NASA Astrophysics Data System (ADS)

    Lovelock, Dale Michael John

    1990-01-01

    The Columbia-Stony Brook (CUSB) collaboration has measured the photon spectrum resulting from the decays Upsilon (3S)togamma + hadrons using the CUSB-II BGO calorimeter. The spectrum contains the signal from the electromagnetic transitions Upsilon (3S)togammachi _{b,J=0,1,2} (2P). From this signal the masses of the chi_{b}(2P) states were determined to be 10268.0 +/- 0.8, 10255.4 +/- 0.8, and 10233.9 +/- 1.2 MeV for the J = 2, 1, and 0 states respectively. The ratio of the mass splittings, (M_{chi _{b2}} - M_{chi_{b1}} )/(M_{chi_{b1 }} - M_ {chi_{b0}}) imply that the long range confining piece of the inter-quark potential transforms as a Lorentz scalar.

  3. Aquatic Toxicity of Decontaminating Solutions DS-2/DS-2P

    DTIC Science & Technology

    1994-09-01

    Daphnia magna , fathead minnow, Photobacteriumphosphoreum, and earthworm, 14 SUBJECT TERMS 15, NUMBER OF PAGES Aquatic toxicology Ea.thworm 16 . Daphnia magna ...toxicity of the DS-2 and DS-2P mixtures on Daphnia magna , (water flea), Pimephales promelas (fathead minnow), Eisenia foetida (earthwonm) and...chloroform procedures 151 and proved to be within specifications. 2.1 Dapbnia Assays The Daphnia magna were obtained from Dr. Freida Taub [61 at the

  4. A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO-

    NASA Astrophysics Data System (ADS)

    Roy, Soumendra K.; Jian, Tian; Lopez, Gary V.; Li, Wei-Li; Su, Jing; Bross, David H.; Peterson, Kirk A.; Wang, Lai-Sheng; Li, Jun

    2016-02-01

    The observation of the gaseous UFO- anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO- is linear with an O-U-F structure and a 3H4 spectral term derived from a U 7sσ25fφ15fδ1 electron configuration, whereas the ground state of neutral UFO has a 4H7/2 spectral term with a U 7sσ15fφ15fδ1 electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.

  5. Identifying and Understanding Strong Vibronic Interaction Effects Observed in the Asymmetry of Chiral Molecule Photoelectron Angular Distributions.

    PubMed

    Garcia, Gustavo A; Dossmann, Héloïse; Nahon, Laurent; Daly, Steven; Powis, Ivan

    2017-03-03

    Electron-ion coincidence imaging is used to study chiral asymmetry in the angular distribution of electrons emitted from randomly-oriented enantiomers of two molecules, methyloxirane and trifluoromethyloxirane, upon ionization by circularly polarized VUV synchrotron radiation. Vibrationally-resolved photoelectron circular dichroism (PECD) measurements of the outermost orbital ionization reveal unanticipated large fluctuations in the magnitude of the forward-backward electron scattering asymmetry, including even a complete reversal of direction. Identification and assignment of the vibrational excitations is supported by Franck-Condon simulations of the photoelectron spectra. A previously proposed quasi-diatomic model for PECD is developed and extended to treat polyatomic systems. The parametric dependence of the electronic dipole matrix elements on nuclear geometry is evaluated in the adiabatic approximation. It provokes vibrational level dependent shifts in amplitude and phase, to which the chiral photoelectron angular distributions are especially sensitive. It is shown that single quantum excitation of those vibrational modes, which experience only a relatively small displacement of the ion equilibrium geometry along the normal coordinate and which are then only weakly excited in the Franck-Condon limit, can be accompanied by big shifts in scattering phase; hence the observed big fluctuations in PECD asymmetry for such modes.

  6. Load Balancing in Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Zhu, Yingwu

    In this chapter we start by addressing the importance and necessity of load balancing in structured P2P networks, due to three main reasons. First, structured P2P networks assume uniform peer capacities while peer capacities are heterogeneous in deployed P2P networks. Second, resorting to pseudo-uniformity of the hash function used to generate node IDs and data item keys leads to imbalanced overlay address space and item distribution. Lastly, placement of data items cannot be randomized in some applications (e.g., range searching). We then present an overview of load aggregation and dissemination techniques that are required by many load balancing algorithms. Two techniques are discussed including tree structure-based approach and gossip-based approach. They make different tradeoffs between estimate/aggregate accuracy and failure resilience. To address the issue of load imbalance, three main solutions are described: virtual server-based approach, power of two choices, and address-space and item balancing. While different in their designs, they all aim to improve balance on the address space and data item distribution. As a case study, the chapter discusses a virtual server-based load balancing algorithm that strives to ensure fair load distribution among nodes and minimize load balancing cost in bandwidth. Finally, the chapter concludes with future research and a summary.

  7. Uniform Sampling for Directed P2P Networks

    NASA Astrophysics Data System (ADS)

    Hall, Cyrus; Carzaniga, Antonio

    Selecting a random peer with uniform probability across a peer-to-peer (P2P) network is a fundamental function for unstructured search, data replication, and monitoring algorithms. Such uniform sampling is supported by several techniques. However, current techniques suffer from sample bias and limited applicability. In this paper, we present a sampling algorithm that achieves a desired uniformity while making essentially no assumptions about the underlying P2P network. This algorithm, called doubly stochastic converge (DSC), iteratively adjusts the probabilities of crossing each link in the network during a random walk, such that the resulting transition matrix is doubly stochastic. DSC is fully decentralized and is designed to work on both directed and undirected topologies, making it suitable for virtually any P2P network. Our simulations show that DSC converges quickly on a wide variety of topologies, and that the random walks needed for sampling are short for most topologies. In simulation studies with FreePastry, we show that DSC is resilient to high levels of churn, while incurring a minimal sample bias.

  8. Pure P2P mediation system: A mappings discovery approach

    NASA Astrophysics Data System (ADS)

    selma, El yahyaoui El idrissi; Zellou, Ahmed; Idri, Ali

    2015-02-01

    The information integration systems consist in offering a uniform interface to provide access to a set of autonomous and distributed information sources. The most important advantage of this system is that it allows users to specify what they want, rather than thinking about how to get the responses. The works realized in this area have particular leads to two major classes of integration systems: the mediation systems based on the paradigm mediator / adapter and peer to peer systems (P2P). The combination of both systems has led to a third type; is the mediation P2P systems. The P2P systems are large-scale systems, self-organized and distributed. They allow the resource management in a completely decentralized way. However, the integration of structured information sources, heterogeneous and distributed proves to be a complex problem. The objective of this work is to propose an approach to resolve conflicts and establish a mapping between the heterogeneous elements. This approach is based on clustering; the latter is to group similar Peers that share common information in the same subnet. Thus, to facilitate the heterogeneity, we introduced three additional layers of our hierarchy of peers: internal schema, external schema and Schema directory peer. We used linguistic techniques, and precisely the name correspondence technique, that is based on the similarity of names to propose a correspondence.

  9. An Overlapping Structured P2P for REIK Overlay Network

    NASA Astrophysics Data System (ADS)

    Liu, Wenjun; Song, Jingjing; Yu, Jiguo

    REIK is based on a ring which embedded an inverse Kautz digraph, to enable multi-path P2P routing. It has the constant degree and the logarithmic diameter DHT scheme with constant congestion and Byzantine fault tolerance. However, REIK did not consider the interconnection of many independent smaller networks. In this paper, we propose a new approach to build overlay network, OLS-REIK which is an overlapping structured P2P for REIK overlay network. It is a more flexible interconnecting different REIK network. Peers can belong to several rings, allowing this interconnection. By connecting smaller structured overlay networks in an unstructured way, it provides a cost effective alternative to hierarchical structured P2P systems requiring costly merging. Routing of lookup messages is performed as in REIK within one ring, but a peer belonging to several rings forwards the request to the different rings it belongs to. Furthermore a small number of across point is enough to ensure a high exhaustiveness level.

  10. DNA Compaction by Yeast Mitochondrial Protein ABF2p

    SciTech Connect

    Friddle, R W; Klare, J E; Noy, A; Corzett, M; Balhorn, R; Baskin, R J; Martin, S S; Baldwin, E P

    2003-05-09

    We used high resolution Atomic Force Microscopy (AFM) to image compaction of linear and circular DNA by the yeast mitochondrial protein ABF2p , which plays a major role in maintaining mitochondrial DNA. AFM images show that protein binding induces drastic bends in the DNA backbone for both linear and circular DNA. At high concentration of ABF2p DNA collapses into a tight globular structure. We quantified the compaction of linear DNA by measuring the end-to-end distance of the DNA molecule at increasing concentrations of ABF2p. We also derived a polymer statistical mechanics model that gives quantitative description of compaction observed in our experiments. This model shows that a number of sharp bends in the DNA backbone is often sufficient to cause DNA compaction. Comparison of our model with the experimental data showed excellent quantitative correlation and allowed us to determine binding characteristics for ABF2. Our studies indicate that ABF2 compacts DNA through a novel mechanism that involves bending of DNA backbone. We discuss the implications of such a mechanism for mitochondrial DNA maintenance.

  11. The mechano-gated K(2P) channel TREK-1.

    PubMed

    Dedman, Alexandra; Sharif-Naeini, Reza; Folgering, Joost H A; Duprat, Fabrice; Patel, Amanda; Honoré, Eric

    2009-03-01

    The versatility of neuronal electrical activity is largely conditioned by the expression of different structural and functional classes of K+ channels. More than 80 genes encoding the main K+ channel alpha subunits have been identified in the human genome. Alternative splicing, heteromultimeric assembly, post-translational modification and interaction with auxiliary regulatory subunits further increase the molecular and functional diversity of K+ channels. Mammalian two-pore domain K+ channels (K(2P)) make up one class of K+ channels along with the inward rectifiers and the voltage- and/or calcium-dependent K+ channels. Each K(2P) channel subunit is made up of four transmembrane segments and two pore-forming (P) domains, which are arranged in tandem and function as either homo- or heterodimeric channels. This novel structural arrangement is associated with unusual gating properties including "background" or "leak" K+ channel activity, in which the channels show constitutive activity at rest. In this review article, we will focus on the lipid-sensitive mechano-gated K(2P) channel TREK-1 and will emphasize on the polymodal function of this "unconventional" K+ channel.

  12. Crack spectra analysis

    SciTech Connect

    Tiernan, M.

    1980-09-01

    Crack spectra derived from velocity data have been shown to exhibit systematics which reflect microstructural and textural differences between samples (Warren and Tiernan, 1980). Further research into both properties and information content of crack spectra have yielded the following: Spectral features are reproducible even at low pressures; certain observed spectral features may correspond to non-in-situ crack populations created during sample retrieval; the functional form of a crack spectra may be diagnostic of the sample's grain texture; hysteresis is observed in crack spectra between up and down pressure runs - it may be due to friction between the faces of closed crack populations.

  13. Photographic spectra of fireballs

    NASA Astrophysics Data System (ADS)

    Borovička, J.

    2016-01-01

    Two methods of spectroscopy of meteors using image intensified video cameras and classical photographic film cameras are compared. Video cameras provide large number of low resolution spectra of meteors of normal brightness, which can be used for statistical studies. Large format film cameras have been used through the history and provide high resolution spectra, which can be used to derive temperature, density and absolute abundances of various elements in the radiating plasma. The sensitivity of films is, however, low and only spectra of bright meteors (fireballs) can be studied. Examples of photographic fireball spectra are provided.

  14. Radiative transitions involving the (2p2)(3 Pe) metastable autodetaching of H(-)

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.; Bhatia, A. K.; Temkin, A.

    1974-01-01

    The absorption coefficient for the free-bound transition H (ls) + e(-)+ h omega yields H(-)(2 sq p,(3)P(e)) is calculated (together with the differential emission rate for the inverse process) using ls - 2s - 2p close coupling continuum wave functions and a Hylleraas bound state wave function. A maximum in the absorption and emission spectra is found to occur at a photon wavelength of 1219.5 A, which is 2 A closer to the Lyman alpha line than predicted by the calculations of Drake, and is in closer agreement with the stellar absorption feature identified by Heap and Stecher. The free-bound absorption process appears to be a significant source of continuous ultraviolet opacity.

  15. Transitions of the type 2s-2p in highly ionized Cu, Zn, Ga, and Ge

    NASA Technical Reports Server (NTRS)

    Behring, W. E.; Cohen, L.; Seely, J. F.; Feldman, U.; Goldsmith, S.; Richardson, M.

    1985-01-01

    Transitions of the type 2s-2p in the F I, O I, N I, and C I isoelectronic sequences of copper, zinc, gallium, and germanium have been identified in the spectra from plasmas produced by the Omega laser system at the University of Rochester. The wavelengths are in the range 50 to 112 A and are measured using silicon and oxygen lines as wavelength standards for gallium and using several lines from the F I, O I, and Na I isoelectronic sequences as wavelength standards for copper, zinc, and germanium. The energy levels that are determined from the measured wavelengths are also presented. Based on these measurements, the wavelengths for a number of magnetic-dipole transitions within the ground configurations of the F I, O I, and N I isoelectronic sequences are predicted.

  16. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    National Institute of Standards and Technology Data Gateway

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  17. Oxidation and surface segregation of chromium in Fe-Cr alloys studied by Mössbauer and X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Idczak, R.; Idczak, K.; Konieczny, R.

    2014-09-01

    The room temperature 57Fe Mössbauer and XPS spectra were measured for polycrystalline iron-based Fe-Cr alloys. The spectra were collected using three techniques: the transmission Mössbauer spectroscopy (TMS), the conversion electron Mössbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The combination of these experimental techniques allows to determine changes in Cr concentration and the presence of oxygen in bulk, in the 300 nm pre-surface layer and on the surface of the studied alloys.

  18. On the photoelectron velocity-map imaging of lutetium monoxide anion LuO{sup −}

    SciTech Connect

    Liu, Zhiling; Xie, Hua; Qin, Zhengbo; Cong, Ran; Wu, Xia; Tang, Zichao Fan, Hongjun; Li, Quanjiang

    2014-01-21

    We report a combined photoelectron velocity-map imaging spectroscopy and density functional theory investigation on lutetium monoxide anion. Transition between the X {sup 1}Σ{sup +} anion electronic ground state and the neutral X {sup 2}Σ{sup +} electronic ground state is observed. Vibrationally resolved spectra were obtained at four different photon energies, providing a wealth of spectroscopic information for the electronic ground states of the anionic lutetium monoxide and corresponding neutral species. Franck-Condon simulations of the ground-state transition are performed to assign vibrational structure in the spectra and to assist in identifying the observed spectral bands. The electronic ground state of LuO{sup −} is found to have a vibrational frequency of 743 ± 10 cm{sup −1} and an equilibrium bond length of 1.841 Å. The electron affinity of LuO is measured to be 1.624 ± 0.002 eV. The fundamental frequency of ground-state LuO is estimated to be 839 ± 10 cm{sup −1}.

  19. On the photoelectron velocity-map imaging of lutetium monoxide anion LuO(-).

    PubMed

    Liu, Zhiling; Xie, Hua; Li, Quanjiang; Qin, Zhengbo; Cong, Ran; Wu, Xia; Tang, Zichao; Fan, Hongjun

    2014-01-21

    We report a combined photoelectron velocity-map imaging spectroscopy and density functional theory investigation on lutetium monoxide anion. Transition between the X (1)Σ(+) anion electronic ground state and the neutral X (2)Σ(+) electronic ground state is observed. Vibrationally resolved spectra were obtained at four different photon energies, providing a wealth of spectroscopic information for the electronic ground states of the anionic lutetium monoxide and corresponding neutral species. Franck-Condon simulations of the ground-state transition are performed to assign vibrational structure in the spectra and to assist in identifying the observed spectral bands. The electronic ground state of LuO(-) is found to have a vibrational frequency of 743 ± 10 cm(-1) and an equilibrium bond length of 1.841 Å. The electron affinity of LuO is measured to be 1.624 ± 0.002 eV. The fundamental frequency of ground-state LuO is estimated to be 839 ± 10 cm(-1).

  20. Vibronic structure of VO{sub 2} probed by slow photoelectron velocity-map imaging spectroscopy

    SciTech Connect

    Kim, Jongjin B.; Weichman, Marissa L.; Neumark, Daniel M.

    2014-01-21

    We report high-resolution anion photoelectron spectra of vanadium dioxide (VO{sub 2}{sup −}) obtained by slow electron velocity-map imaging of trapped and cryogenically cooled anions. Vibrationally resolved spectra are obtained for photodetachment to the first three neutral electronic states, giving an electron affinity of 1.8357(5) eV for the X-tilde{sup 2} A{sub 1} ground state and term energies of 0.1845(8) eV and 0.8130(5) eV for the A-tilde{sup 2}B{sub 1} and B-tilde{sup 2}A{sub 1} excited states, respectively. The vibrational fundamentals ν{sub 1} and ν{sub 2} are obtained for all three states. Experimental assignments are confirmed by energies from electronic structure calculations and Franck-Condon spectral simulations. These simulations support assigning the anion ground state as the X-tilde{sup 3}B{sub 1} state. With this assignment, photodetachment to the B-tilde{sup 2}A{sub 1} state involves a nominally forbidden two-electron transition, suggesting extensive configuration interaction in neutral VO{sub 2}.

  1. Difluorophosphoryl nitrene F2P(O)N: matrix isolation and unexpected rearrangement to F2PNO.

    PubMed

    Zeng, Xiaoqing; Beckers, Helmut; Willner, Helge; Neuhaus, Patrik; Grote, Dirk; Sander, Wolfram

    2009-12-14

    Triplet difluorophosphoryl nitrene F(2)P(O)N (X(3)A'') was generated on ArF excimer laser irradiation (lambda=193 nm) of F(2)P(O)N(3) in solid argon matrix at 16 K, and characterized by its matrix IR, UV/Vis, and EPR spectra, in combination with DFT and CBS-QB3 calculations. On visible light irradiation (lambda>420 nm) at 16 K F(2)P(O)N reacts with molecular nitrogen and some of the azide is regenerated. UV irradiation (lambda=255 nm) of F(2)P(O)N (X(3)A'') induced a Curtius-type rearrangement, but instead of a 1,3-fluorine shift, nitrogen migration to give F(2)PON is proposed to be the first step of the photoisomerization of F(2)P(O)N into F(2)PNO (difluoronitrosophosphine). Formation of novel F(2)PNO was confirmed with (15)N- and (18)O-enriched isotopomers by IR spectroscopy and DFT calculations. Theoretical calculations predict a rather long P-N bond of 1.922 A [B3LYP/6-311+G(3df)] and low bond-dissociation energy of 76.3 kJ mol(-1) (CBS-QB3) for F(2)PNO.

  2. O-2p holes in tetravalent oxides of Ce and Pr and the Fehrenbacher-Rice hybrid in PrBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Hu, Z.; Meier, R.; Schüßler-Langeheine, C.; Weschke, E.; Kaindl, G.; Felner, I.; Merz, M.; Nücker, N.; Schuppler, S.; Erb, A.

    1999-07-01

    We report on an x-ray absorption near-edge structure (XANES) study of O-2p holes induced by Ln-4f/O-2p covalence in LnO2 (Ln=Ce,Pr) and BaLnO3 (Ln=Ce,Pr,Tb). The pre-edge peak in the O-1s XANES spectra, associated with O-2p holes, shifts to lower energy from Ce to Pr, in agreement with theoretical expectation, and its intensity scales with the strength of the 4f/2p covalence. In Pr(IV) oxides, the pre-edge peak is at the energy of the ``Fehrenbacher-Rice'' state in PrBa2Cu3O7-δ , supporting the view that the suppression of superconductivity in PrBa2Cu3O7-δ is due to Pr-4f/O-2p hybridization.

  3. Effect of collisions on photoelectron sheath in a gas

    NASA Astrophysics Data System (ADS)

    Sodha, Mahendra Singh; Mishra, S. K.

    2016-02-01

    This paper presents a study of the effect of the collision of electrons with atoms/molecules on the structure of a photoelectron sheath. Considering the half Fermi-Dirac distribution of photo-emitted electrons, an expression for the electron density in the sheath has been derived in terms of the electric potential and the structure of the sheath has been investigated by incorporating Poisson's equation in the analysis. The method of successive approximations has been used to solve Poisson's equation with the solution for the electric potential in the case of vacuum, obtained earlier [Sodha and Mishra, Phys. Plasmas 21, 093704 (2014)], being used as the zeroth order solution for the present analysis. The inclusion of collisions influences the photoelectron sheath structure significantly; a reduction in the sheath width with increasing collisions is obtained.

  4. Theoretical scheme for simultaneously observing forward-backward photoelectron holography.

    PubMed

    Du, Hongchuan; Wu, Hongmei; Wang, Huiqiao; Yue, Shengjun; Hu, Bitao

    2016-02-15

    Photoelectron angular momentum distribution of He+ driven by a few-cycle laser is investigated numerically. We simultaneously observe two dominant interference patterns with one shot of lasers by solving the 3D time-dependent Schrodinger equation. Analysis of a semiclassical model identifies these two interference patterns as two types of photoelectron holography. The interference pattern with Pz0 is a type of forward rescattering holography, which comes from the interference between direct (reference) and rescattered (signal) forward electrons ionized in the same quarter-cycle. The interference pattern with Pz<0 is a type of backward rescattering holography, which comes from the interference between a direct electron ionized in the third quarter-cycle and rescattered backward electron ionized in the first quarter-cycle. Moreover, we propose a method to distinguish this backward rescattering holography and intracycle interference patterns of direct electrons.

  5. Laser-polarization-dependent photoelectron angular distributions from polar molecules.

    PubMed

    Zhu, Xiaosong; Zhang, Qingbin; Hong, Weiyi; Lu, Peixiang; Xu, Zhizhan

    2011-11-21

    Photoelectron angular distributions (PADs) of oriented polar molecules in response to different polarized lasers are systematically investigated. It is found that the PADs of polar CO molecules show three distinct styles excited by linearly, elliptically and circularly polarized lasers respectively. In the case of elliptical polarization, a deep suppression is observed along the major axis and the distribution concentrates approximately along the minor axis. Additionally, it is also found that the concentrated distributions rotate clockwise as the ellipticity increases. Our investigation presents a method to manipulate the motion and angular distribution of photoelectrons by varying the polarization of the exciting pulses, and also implies the possibility to control the processes in laser-molecule interactions in future work.

  6. Molecular photoelectron holography with circularly polarized laser pulses.

    PubMed

    Yang, Weifeng; Sheng, Zhihao; Feng, Xingpan; Wu, Miaoli; Chen, Zhangjin; Song, Xiaohong

    2014-02-10

    We investigate the photoelectron momentum distribution of molecular-ion H2+driven by ultrashort intense circularly polarized laser pulses. Both numerical solutions of the time-dependent Schrödinger equation (TDSE) and a quasiclassical model indicate that the photoelectron holography (PH) with circularly polarized pulses can occur in molecule. It is demonstrated that the interference between the direct electron wave and rescattered electron wave from one core to its neighboring core induces the PH. Moreover, the results of the TDSE predict that there is a tilt angle between the interference pattern of the PH and the direction perpendicular to the molecular axis. Furthermore, the tilt angle is sensitively dependent on the wavelength of the driven circularly polarized pulse, which is confirmed by the quasiclassical calculations. The PH induced by circularly polarized laser pulses provides a tool to resolve the electron dynamics and explore the spatial information of molecular structures.

  7. Operational Experience with the Nb/Pb SRF Photoelectron Gun

    SciTech Connect

    Kamps, T; Barday, R; Jankowiak, A; Knoblock, J; Kugeler, O; Matveenko, A N; Neumann, A; Quast, T; Rudolph, J; Schubert, S G; Volker, J; Kneisel, P; Nietubyc, R; Sekutowicz, J K; Smedley, J; Teichert, J; Volkov, V; Will, I

    2012-07-01

    SRF photoelectron guns offer the promise of high brightness, high average current beam production for the next generation of accelerator driven light sources such as free electron lasers, THz radiation sources or energy-recovery linac driven synchrotron radiation sources. In a first step a fully superconducting RF (SRF) photoelectron gun is under development by a collaboration between HZB, DESY, JLAB, BNL and NCBJ. The aim of the experiment is to understand and improve the performance of a Nb SRF gun cavity coated with a small metallic Pb cathode film on the cavity backplane. This paper describes the highlights from the commissioning and beam parameter measurements. The main focus is on lessons learned from operation of the SRF gun.

  8. Metal Doping Effect of the M-Co2P/Nitrogen-Doped Carbon Nanotubes (M = Fe, Ni, Cu) Hydrogen Evolution Hybrid Catalysts.

    PubMed

    Pan, Yuan; Liu, Yunqi; Lin, Yan; Liu, Chenguang

    2016-06-08

    The enhancement of catalytic performance of cobalt phosphide-based catalysts for the hydrogen evolution reaction (HER) is still challenging. In this work, the doping effect of some transition metal (M = Fe, Ni, Cu) on the electrocatalytic performance of the M-Co2P/NCNTs (NCNTs, nitrogen-doped carbon nanotubes) hybrid catalysts for the HER was studied systematically. The M-Co2P/NCNTs hybrid catalysts were synthesized via a simple in situ thermal decomposition process. A series of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometry, transmission electron microscopy, and N2 sorption were used to characterize the as-synthesized M-Co2P/NCNTs hybrid catalysts. Electrochemical measurements showed the catalytic performance according to the following order of Fe-Co2P/NCNTs > Ni-Co2P/NCNTs > Cu-Co2P/NCNTs, which can be ascribed to the difference of structure, morphology, and electronic property after doping. The doping of Fe atoms promote the growth of the [111] crystal plane, resulting in a large specific area and exposing more catalytic active sites. Meanwhile, the Fe(δ+) has the highest positive charge among all the M-Co2P/NCNTs hybrid catalysts after doping. All these changes can be used to contribute the highest electrocatalytic activity of the Fe-Co2P/NCNTs hybrid catalyst for HER. Furthermore, an optimal HER electrocatalytic activity was obtained by adjusting the doping ratio of Fe atoms. Our current research indicates that the doping of metal is also an important strategy to improve the electrocatalytic activity for the HER.

  9. Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

    NASA Astrophysics Data System (ADS)

    Van Duzor, Matthew; Mbaiwa, Foster; Wei, Jie; Singh, Tulsi; Mabbs, Richard; Sanov, Andrei; Cavanagh, Steven J.; Gibson, Stephen T.; Lewis, Brenton R.; Gascooke, Jason R.

    2010-11-01

    We present a comprehensive photoelectron imaging study of the O2(X Σg-3,v '=0-6)←O2-(X Π2g,v ″=0) and O2(aΔ1g,v '=0-4)←O2-(X Π2g,v ″=0) photodetachment bands at wavelengths between 900 and 455 nm, examining the effect of vibronic coupling on the photoelectron angular distribution (PAD). This work extends the v'=1-4 data for detachment into the ground electronic state, presented in a recent communication [R. Mabbs, F. Mbaiwa, J. Wei, M. Van Duzor, S. T. Gibson, S. J. Cavanagh, and B. R. Lewis, Phys. Rev. A 82, 011401-R (2010)]. Measured vibronic intensities are compared to Franck-Condon predictions and used as supporting evidence of vibronic coupling. The results are analyzed within the context of the one-electron, zero core contribution (ZCC) model [R. M. Stehman and S. B. Woo, Phys. Rev. A 23, 2866 (1981)]. For both bands, the photoelectron anisotropy parameter variation with electron kinetic energy, β(E ), displays the characteristics of photodetachment from a d-like orbital, consistent with the πg∗ 2p highest occupied molecular orbital of O2-. However, differences exist between the β(E ) trends for detachment into different vibrational levels of the X Σg-3 and a Δ1g electronic states of O2. The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O2: the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.

  10. Femtosecond time-resolved XUV + UV photoelectron imaging of pure helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Ziemkiewicz, Michael P.; Bacellar, Camila; Siefermann, Katrin R.; Leone, Stephen R.; Neumark, Daniel M.; Gessner, Oliver

    2014-11-01

    Liquid helium nanodroplets, consisting of on average 2 × 106 atoms, are examined using femtosecond time-resolved photoelectron imaging. The droplets are excited by an extreme ultraviolet light pulse centered at 23.7 eV photon energy, leading to states within a band that is associated with the 1s3p and 1s4p Rydberg levels of free helium atoms. The initially excited states and subsequent relaxation dynamics are probed by photoionizing transient species with a 3.2 eV pulse and using velocity map imaging to measure time-dependent photoelectron kinetic energy distributions. Significant differences are seen compared to previous studies with a lower energy (1.6 eV) probe pulse. Three distinct time-dependent signals are analyzed by global fitting. A broad intense signal, centered at an electron kinetic energy (eKE) of 2.3 eV, grows in faster than the experimental time resolution and decays in ˜100 fs. This feature is attributed to the initially excited droplet state. A second broad transient feature, with eKE ranging from 0.5 to 4 eV, appears at a rate similar to the decay of the initially excited state and is attributed to rapid atomic reconfiguration resulting in Franck-Condon overlap with a broader range of cation geometries, possibly involving formation of a Rydberg-excited (Hen)* core within the droplet. An additional relaxation pathway leads to another short-lived feature with vertical binding energies ≳2.4 eV, which is identified as a transient population within the lower-lying 1s2p Rydberg band. Ionization at 3.2 eV shows an enhanced contribution from electronically excited droplet states compared to ejected Rydberg atoms, which dominate at 1.6 eV. This is possibly the result of increased photoelectron generation from the bulk of the droplet by the more energetic probe photons.

  11. Experiments on the use of CCD's to detect photoelectron images

    NASA Technical Reports Server (NTRS)

    Choisser, J. P.

    1975-01-01

    Image tube design and processing requirements for building an ICCD are discussed. Work is under way at EVC for building an ICCD using the Fairchild CCD 201 (100 x 100) array, and progress will be reported. Demountable tests have been made, exposing parts of a CCD 201 to 15 kilovolt electrons over five radiation levels from approximately 10 to 1 million rads. Other tubes built by EVC over the last few years which successfully use semiconductors to detect photoelectrons will be described briefly.

  12. Photoelectron spectroscopic study of carbon aluminum hydride cluster anions

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxing; Wang, Haopeng; Ganteför, Gerd; Eichhorn, Bryan W.; Kiran, Boggavarapu; Bowen, Kit H.

    2016-10-01

    Numerous previously unknown carbon aluminum hydride cluster anions were generated in the gas phase, identified by time-of-flight mass spectrometry and characterized by anion photoelectron spectroscopy, revealing their electronic structure. Density functional theory calculations on the CAl5-9H- and CAl5-7H2- found that several of them possess unusually high carbon atom coordination numbers. These cluster compositions have potential as the basis for new energetic materials.

  13. Photoelectron escape fluxes over the equatorial and midlatitude regions

    NASA Technical Reports Server (NTRS)

    Narasingarao, B. C.; Singh, R. N.; Maier, E. J.

    1972-01-01

    Satellite measurements of photoelectron escape flux around noontime made by Explorer 31 in 600-800 km altitude range are reported for the equatorial and midlatitude regions. The pitch angle distributions and the spectral distributions are derived from the data. Analyzed data show that the flux for equatorial regions is lower by a factor 2 to 3 in comparison to that of midlatitude regions. Theoretical calculations are also made to compare with observed escape fluxes.

  14. Photoelectron spectroscopic study of carbon aluminum hydride cluster anions.

    PubMed

    Zhang, Xinxing; Wang, Haopeng; Ganteför, Gerd; Eichhorn, Bryan W; Kiran, Boggavarapu; Bowen, Kit H

    2016-10-21

    Numerous previously unknown carbon aluminum hydride cluster anions were generated in the gas phase, identified by time-of-flight mass spectrometry and characterized by anion photoelectron spectroscopy, revealing their electronic structure. Density functional theory calculations on the CAl5-9H(-) and CAl5-7H2(-) found that several of them possess unusually high carbon atom coordination numbers. These cluster compositions have potential as the basis for new energetic materials.

  15. Recent applications of hard x-ray photoelectron spectroscopy

    DOE PAGES

    Weiland, Conan; Rumaiz, Abdul K.; Pianetta, Piero; ...

    2016-05-05

    Recent applications of hard x-ray photoelectron spectroscopy (HAXPES) demonstrate its many capabilities in addition to several of its limitations. Examples are given, including measurement of buried interfaces and materials under in-situ or in-operando conditions, as well as measurements under x-ray standing-wave and resonant excitation. We also present physical considerations that differentiate HAXPES from photoemission measurements utilizing soft and ultraviolet x rays.

  16. Operation of a Langmuir Probe in a Photoelectron Plasma

    SciTech Connect

    Dove, Adrienne; Robertson, Scott; Horanyi, Mihaly; Poppe, Andrew; Wang Xu

    2011-11-29

    Dust transport on the lunar surface is likely facilitated by the variable electric fields that are generated by changing plasma conditions. We have developed an experimental apparatus to study lunar photoelectric phenomena and gain a better understanding of the conditions controlling dust transport. As an initial step, Langmuir probe measurements are used to characterize the photoelectron plasma produced above a Zr surface, and these techniques will be extended to CeO{sub 2} and lunar simulant surfaces.

  17. Secular variation of activity in comets 2P/Encke and 9P/Tempel 1

    NASA Technical Reports Server (NTRS)

    Haken, Michael; AHearn, Michael F.; Feldman, Paul D.; Budzien, Scott A.

    1995-01-01

    We compare production rates of H20 derived from International Ultraviolet Explorer (IUE) spectra from multiple apparitions of 2 comets, 2P/Encke and 9P/Tempel 1, whose orbits are in near-resonance with that of the Earth. Since model-induced errors are primarily a function of observing geometry, the close geometrical matches afforded by the resonance condition results in the cancellation of such errors when taking ratios of production rates. Giving careful attention to the variation of model parameters with solar activity, we find marginal evidence of change in 2P/Encke: a 1-sigma pre-perihelion decrease averaging 4%/revolution over 4 apparitions from 1980-1994, and a 1-sigma post-perihelion increase of 16%/revolution for 2 successive apparitions in 1984 and 1987. We find for 9P/Tempel 1, however, a 7-sigma decrease of 29%/revolution over 3 apparitions from 1983-1994, even after correcting for a tracking problem which made the fluxes systematically low. We speculate on a possible association of the character of long-term brightness variations with physical properties of the nucleus, and discuss implications for future research.

  18. Spitzer Observations of Comet 2P/Encke: Six Months Post-Perihelion

    NASA Astrophysics Data System (ADS)

    Kelley, M. S.; Woodward, C. E.; Gehrz, R. D.; Reach, W. T.

    2004-12-01

    Comet dust trails are the long lived, large particle remnants of cometary mass loss episodes. These particles (sizes of order 1 mm or larger) remain in an orbit similar to the parent comet unless they are perturbed by planetary interactions that do not affect the comet nucleus. The Jupiter-family comet 2P/Encke has a very stable orbit and this is reflected by its extensive dust trail as observed by IRAS [1]. We present Spitzer IRAC, MIPS, and IRS observations of comet 2P/Encke from June 2004, six months after perihelion. Images show a prominent dust jet and dust trail similar to the Reach et al. [2] July 1997 ISO observation (2 months post-perihelion) and more detailed than the Epifani et al. [3] October 1997 ISO observation (5 months post-perihelion). Spectra show no silicate feature, as expected for a comet which mostly releases large particles. We present model images of the dust distribution produced with our own dynamical model employing a Monte-Carlo technique. We use this model to discuss the size and ejection velocity of particles leaving the nucleus. References: [1] M. V. Sykes and R. G. Walker (1992), Icarus, 95, 180, 1992; [2] W. T. Reach et al. (2000), Icarus, 148, 80; [3] E. Epifani et al. (2001), Icarus, 149, 339.

  19. Identification of photoelectron energy peaks in Saturn's inner neutral torus

    NASA Astrophysics Data System (ADS)

    Schippers, P.; André, N.; Johnson, R. E.; Blanc, M.; Dandouras, I.; Coates, A. J.; Krimigis, S. M.; Young, D. T.

    2009-12-01

    We present observations from the Cassini Plasma Electron Spectrometer (CAPS/ELS) of characteristic peaks in the electron energy spectrum that are identified in the innermost regions of the Saturnian magnetosphere during low-latitude orbits of the Cassini spacecraft around Saturn. We show how a narrow electron energy peak at about 20 eV and a possible peak at about 42 eV can be extracted from the background in CAPS observations after the contamination from high-energy particles has been removed from the measurements. We estimate the density of the newly discovered electron population to be a small fraction (10%) of the electron density measured in the CAPS/ELS energy range, and a much smaller fraction (about 1%) of the total electron density measured by Radio and Plasma Wave Science since our measurements are affected by spacecraft negative potential. We suggest that this population corresponds to photoelectrons generated by the solar EUV photoionization of the extended cloud of neutral gas observed in these regions. We use pitch angle information to assess the near-equatorial source of these photoelectrons and a simple model of chemistry in order to further support our interpretation. Therefore, photoionization seems to be an additional process for plasma production in the innermost Saturnian magnetosphere. Finally, we mention that the comparison of the modeled and the observed photoelectron peak energies could be used to estimate the spacecraft potential in this region which is measured independently by the Langmuir Probe.

  20. Modeling, Theoretical and Observational Studies of the Lunar Photoelectron Sheath

    NASA Astrophysics Data System (ADS)

    Poppe, Andrew Reinhold

    2011-08-01

    The Moon, lacking an atmosphere and a global magnetic field, is directly exposed to both solar ultraviolet radiation and a variety of ambient plasmas. On the lunar dayside, a photoelectron sheath develops and the surface typically charges positively since the photoemission current is at least an order-of-magnitude greater than any ambient current. This sheath dominates the nearsurface plasma environment and controls the charging, levitation and transport of micron-sized dust grains. In this thesis, we first model the lunar near-surface plasma environment via a one-dimensional particle-in-cell code. The sheath potential, electric field and plasma densities are presented over a wide range of plasma parameters. Additionally, the charging and transport of micron- and submicron sized dust grains is modeled via a test-particle approach in an attempt to explain Apolloera observations of lunar dust dynamics. Secondly, we present a comparison of the particle-in-cell results with theoretical, kinetic derivations of the lunar photoelectron sheath. We extend previous theories to include the presence of a kappa-distribution for the solar wind electrons. Finally, we present a comparison of in-situ measurements of the lunar photoelectron sheet in the terrestrial plasma sheet by the Lunar Prospector Electron Reflectometer with particle-in-cell simulations to confirm the presence of non-monotonic sheath potentials above the Moon. Future work in all three sections, (simulation, theory and observation) is presented as a guide for continuing research.

  1. Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

    PubMed Central

    DeVine, Jessalyn A.; Levine, Daniel S.; Kim, Jongjin B.; Neumark, Daniel M.

    2016-01-01

    Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm−1 resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck–Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck–Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data. PMID:26792521

  2. Precision lifetime measurements of the 2p levels in lithium

    SciTech Connect

    Berry, H.G.; Kurtz, C.; Tanner, C.E.

    1995-08-01

    These measurements are motivated by the theoretical challenges posed by lithium. The three-electron lithium atom is one of the simplest atomic systems with which to test atomic structure calculations. Recently, there were several ab initio calculations of the lithium 2s-2p oscillator strengths, which agree to 0.15%. However, the theoretical results differ by 5 sigma from the precise fast-beam-laser lifetime measurement of Gaupp and Andra (Berlin). Hence the need for a new independent and precise measurement. Improvements were added to the fast beam laser techniques developed for cesium in order to measure the lithium 2p state lifetime. Although the technique is similar to that of cesium, the lithium atom presents a few new complications. Since the atom is lighter, it travels more quickly through the interaction and detection regions. Therefore, the 670 nm wavelength requires a dye laser to produce sufficient intensity to populate the excited state. Unfortunately, the intensity of the dye laser is inherently less stable than that of a diode laser. Another complication is that the ion-beam intensity is much more sensitive to fluctuations in the accelerating voltage. Two detectors were added: one to monitor the ion-beam intensity, and the other to monitor the laser power. With the information from the additional detectors, a new data analysis scheme was developed. Sufficient data were taken to evaluate the benefits of the new detectors. No additional work is planned at Argonne for this experiment.

  3. P2P Reputation Management Through Social Networking

    NASA Astrophysics Data System (ADS)

    Despotovic, Zoran

    Reputation systems offer a viable solution to the problem of risk reduction in online communities, in situation in which other mechanism such as litigation or security cannot help. Building on the assumption that its participating entities engage in repeated interactions, a reputation system can either signal what happened in the past or aggregate the past feedback in such a way as to influence the future actions of the concerned entity. In the former case, the concerned entity's behavior is seen as static, while the sent signal is expected to be indicative of the entity's future actions. In the latter case, behavior is dynamic in the sense that the entity can adjust it given the observed feedback, while the purpose of the reputation system is to induce adjustments according to the designer's needs. In this chapter, we discuss these two classes of solutions in detail. In particular, we investigate how they apply to P2P networks, what additional problems and difficulties the P2P environment introduces and what scalable solutions to these problems the current research offers.

  4. Principal spectra describing magnetooptic permittivity tensor in cubic crystals

    NASA Astrophysics Data System (ADS)

    Hamrlová, Jana; Legut, Dominik; Veis, Martin; Pištora, Jaromír; Hamrle, Jaroslav

    2016-12-01

    We provide unified phenomenological description of magnetooptic effects being linear and quadratic in magnetization. The description is based on few principal spectra, describing elements of permittivity tensor up to the second order in magnetization. Each permittivity tensor element for any magnetization direction and any sample surface orientation is simply determined by weighted summation of the principal spectra, where weights are given by crystallographic and magnetization orientations. The number of principal spectra depends on the symmetry of the crystal. In cubic crystals owning point symmetry we need only four principal spectra. Here, the principal spectra are expressed by ab initio calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard and soft x-ray energy range, i.e. at the 2p- and 3p-edges. We also express principal spectra analytically using modified Kubo formula.

  5. Electronic absorption spectra from first principles

    NASA Astrophysics Data System (ADS)

    Hazra, Anirban

    Methods for simulating electronic absorption spectra of molecules from first principles (i.e., without any experimental input, using quantum mechanics) are developed and compared. The electronic excitation and photoelectron spectra of ethylene are simulated, using the EOM-CCSD method for the electronic structure calculations. The different approaches for simulating spectra are broadly of two types---Frank-Condon (FC) approaches and vibronic coupling approaches. For treating the vibrational motion, the former use the Born-Oppenheimer or single surface approximation while the latter do not. Moreover, in our FC approaches the vibrational Hamiltonian is additively separable along normal mode coordinates, while in vibronic approaches a model Hamiltonian (obtained from ab initio electronic structure theory) provides an intricate coupling between both normal modes and electronic states. A method called vertical FC is proposed, where in accord with the short-time picture of molecular spectroscopy, the approximate excited-state potential energy surface that is used to calculate the electronic spectrum is taken to reproduce the ab initio potential at the ground-state equilibrium geometry. The potential energy surface along normal modes may be treated either in the harmonic approximation or using the full one-dimensional potential. Systems with highly anharmonic potential surfaces can be treated and expensive geometry optimizations are not required, unlike the traditional FC approach. The ultraviolet spectrum of ethylene between 6.2 and 8.7 eV is simulated using vertical FC. While FC approaches for simulation are computationally very efficient, they are not accurate when the underlying approximations are unreasonable. Then, vibronic coupling model Hamiltonians are necessary. Since these Hamiltonians have an analytic form, they are used to map the potential energy surfaces and understand their topology. Spectra are obtained by numerical diagonalization of the Hamiltonians. The

  6. Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Wells, J. R.; Nicovich, J. M.

    1997-01-01

    The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

  7. Electronic Structures of Uranium Compounds Studied by Soft X-ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Ōnuki, Yoshichika

    2016-06-01

    The electronic structures of uranium-based compounds have been studied by photoelectron spectroscopy with soft X-ray synchrotron radiation. Angle-resolved photoelectron spectroscopy with soft X-rays has made it possible to directly observe their bulk band structures and Fermi surfaces. It has been shown that the band structures and Fermi surfaces of itinerant compounds such as UB2, UN, and UFeGa5 are quantitatively described by a band-structure calculation treating all U 5f electrons as itinerant. Furthermore, the overall electronic structures of heavy-fermion compounds such as UPd2Al3, UNi2Al3, and URu2Si2 are also explained by a band-structure calculation, although some disagreements exist, which might originate from the electron correlation effect. This suggests that the itinerant description of U 5f states is an appropriate starting point for the description of their electronic structures. The situation is similar for ferromagnetic superconductors such as UGe2, URhGe, UCoGe, and UIr, although the complications from their low-symmetry crystal structures make it more difficult to describe their detailed electronic structures. The local electronic structures of the uranium site have been probed by core-level photoelectron spectroscopy with soft X-rays. The comparisons of core-level spectra of heavy-fermion compounds with typical itinerant and localized compounds suggest that the local electronic structures of most itinerant and heavy-fermion compounds are close to the U 5f3 configuration except for UPd2Al3 and UPt3. The core-level spectrum of UPd2Al3 has similarities to those of both itinerant and localized compounds, suggesting that it is located at the boundary between the itinerant and localized states. Moreover, the spectrum of UPt3 is very close to that of the localized compound UPd3, suggesting that it is nearly localized, although there are narrow quasi-particle bands in the vicinity of EF.

  8. Lily Pad Spectra

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The color image on the lower left from the panoramic camera on the Mars Exploration Rover Opportunity shows the 'Lily Pad' bounce-mark area at Meridiani Planum, Mars. This image was acquired on the 3rd sol, or martian day, of Opportunity's mission (Jan.26, 2004). The upper left image is a monochrome (single filter) image from the rover's panoramic camera, showing regions from which spectra were extracted from the 'Lily Pad' area. As noted by the line graph on the right, the green spectra is from the undisturbed surface and the red spectra is from the airbag bounce mark.

  9. Visible and Infrared Study of Comet 2P/Encke's Nucleus During Its 2013 Apparition

    NASA Astrophysics Data System (ADS)

    Fernandez, Yanga R.; Mueller, Beatrice E.; Samarasinha, Nalin H.; Woodney, Laura M.; Abell, Paul A.

    2014-11-01

    The 2013 apparition of comet 2P/Encke provided an opportunity to study the comet while it was relatively close to Earth (0.48 AU on October 17, the closest pass until 2030). We initiated a multiwavelength observing campaign for September and October with the goal of further characterizing the physical, thermal, and rotational properties of 2P's nucleus. Spectral observations were timed to coincide with an equator-on view of the nucleus, a rarely-seen vantage point compared to previous data (e.g. [1,2,3,4]). The spectra span both Wien-side thermal emission and reflected sunlight, covering 0.7 to 2.5 μm, and sample all of the nucleus's rotational longitudes. They were obtained using the SpeX instrument at the NASA Infrared Telescope Facility (IRTF). We will present results on thermal inertia and albedo from a preliminary analysis of these data. Visible observations over the past 13 years have shown that the rotation period of 2P's nucleus increases by ~4 minutes per orbit [5,6], and that the light curve has a two-humped shape but that the humps have quite different amplitudes (e.g. [7]). Thus the equator-on view gave us the chance to further investigate 2P's rotation state and shape. We used the CSUSB Murillo Family Observatory 0.5-meter telescope [8], the NOAO Kitt Peak 2.1-meter telescope, and the MORIS instrument at NASA/IRTF to obtain R-band, time-series photometry of the nucleus. We will present new, preliminary constraints on the secular changes in the nucleus's spin state and on the nucleus's shape based on these new data. We thank the allocation committees of the IRTF and NOAO telescopes for granting the time used for this project. References: [1] Y. R. Fernandez et al. 2000, Icarus 147, 145. [2] M. S. Kelley et al. 2006, ApJ 651, 1256. [3] Y. R. Fernandez et al. 2008, 40th Meeting of the DPS, #16.24. [4] P. Abell et al. 2009, 41st Meeting of the DPS, #20.02. [5] B. E. A. Mueller et al. 2008, 40th Meeting of the DPS, #16.25. [6] N. H. Samarasinha and B. E. A

  10. Structures and spectroscopic properties of sulfur-nitrogen-pnictogen chains: R2P-Ndbnd Sdbnd N-PR2 and R2P-Ndbnd Sdbnd N-AsR2

    NASA Astrophysics Data System (ADS)

    Bal, Kristof M.; Cautereels, Julie; Blockhuys, Frank

    2017-03-01

    The conformational and configurational preferences of Me2P-Ndbnd Sdbnd N-PMe2 (3) and Me2P-Ndbnd Sdbnd N-AsMe2 (4) have been identified using quantum chemical calculations at the DFT/B3LYP/6-311+G* level of theory. An approach in which energetic, structural (geometries and bond orders), electronic (analysis of the electron density) and spectroscopic properties are combined leads to the conclusion that these sulfur-nitrogen-pnictogen chains share many of the properties of their chalcogen-nitrogen analogues but that the through-space intramolecular interactions favouring the Z,Z configuration are even weaker than in these latter compounds. The results of this analysis also lead to an unambiguous assignment of the variable-temperature 31P and 15N NMR spectra of these compounds and their structures both in solution and in the solid state.

  11. Recent approaches for bridging the pressure gap in photoelectron microspectroscopy

    PubMed Central

    Kolmakov, Andrei; Gregoratti, Luca; Kiskinova, Maya; Günther, Sebastian

    2016-01-01

    Ambient-pressure photoelectron spectroscopy (APPES) and microscopy are at the frontier of modern chemical analysis at liquid-gas, solid-liquid and solid-gas interfaces, bridging science and engineering of functional materials. Complementing the current state-of-the art of the instruments, we survey in this short review several alternative APPES approaches, developed recently in the scanning photoelectron microscope (SPEM) at the Elettra laboratory. In particular, we report on experimental setups for dynamic near-ambient pressure environment, using pulsed-gas injection in the vicinity of samples or reaction cells with very small apertures, allowing for experiments without introducing additional differential pumping stages. The major part of the review is dedicated to the construction and performance of novel environmental cells using ultrathin electron-transparent but molecularly impermeable membranes to isolate the gas or liquid ambient from the electron detector operating in ultra-high vacuum (UHV). We demonstrate that two dimensional materials, such as graphene and derivatives, are mechanically robust to withstand atmospheric - UHV pressure differences and are sufficiently transparent for the photoelectrons emitted from samples immersed in the liquid or gaseous media. There are many unique opportunities for APPES using X-rays over a wide energy range. We show representative results that illustrate the potential of these ‘ambient-pressure’ approaches. Combined with the ca 100 nm lateral resolution of SPEM, they can overcome the pressure gap challenges and address the evolution of chemical composition and electronic structure at surface and interfaces under realistic operation conditions with unprecedented lateral and spectral resolution. PMID:28008215

  12. Time-resolved photoelectron spectroscopy using synchrotron radiation time structure.

    PubMed

    Bergeard, N; Silly, M G; Krizmancic, D; Chauvet, C; Guzzo, M; Ricaud, J P; Izquierdo, M; Stebel, L; Pittana, P; Sergo, R; Cautero, G; Dufour, G; Rochet, F; Sirotti, F

    2011-03-01

    Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with pump-probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera-based two-dimensional detection of electron energy analyzers has been replaced by a new delay-line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two-dimensional delay-line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump-probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station.

  13. Energetic Landscape of MDM2-p53 Interactions by Computational Mutagenesis of the MDM2-p53 Interaction.

    PubMed

    Thayer, Kelly M; Beyer, George A

    2016-01-01

    The ubiquitin ligase MDM2, a principle regulator of the tumor suppressor p53, plays an integral role in regulating cellular levels of p53 and thus a prominent role in current cancer research. Computational analysis used MUMBO to rotamerize the MDM2-p53 crystal structure 1YCR to obtain an exhaustive search of point mutations, resulting in the calculation of the ΔΔG comprehensive energy landscape for the p53-bound regulator. The results herein have revealed a set of residues R65-E69 on MDM2 proximal to the p53 hydrophobic binding pocket that exhibited an energetic profile deviating significantly from similar residues elsewhere in the protein. In light of the continued search for novel competitive inhibitors for MDM2, we discuss possible implications of our findings on the drug discovery field.

  14. A simple interpretation of the Fe2(-) photoelectron spectrum

    NASA Technical Reports Server (NTRS)

    Leopold, Doreen G.; Almlof, Jan; Lineberger, W. C.; Taylor, Peter R.

    1988-01-01

    A simple interpretation of the Fe2(-) photoelectron spectrum is proposed based on detachment of 4s(sigma)-asterisk(u) electrons from a (4s sigma/g/)2 (4s sigma-asterisk/u/) (3d) 13 anion. This interpretation implies a (4s sigma/g/)2 (4s sigma-asterisk/u/)1 (3d)13 ground state configuration for Fe2, rather than the (4s sigma/g/)2 (3d)14 configuration that has generally been assumed. The results of preliminary valence CI calculations provide strong support for the proposed Fe2 and Fe2(-) configurations.

  15. Correlations between heterocycle ring size and x-ray spectra

    NASA Astrophysics Data System (ADS)

    Doomes, E. E.; McCarley, R. L.; Poliakoff, E. D.

    2003-08-01

    X-ray absorption spectra are reported for two classes of ring systems, cyclic polymethylene sulfides and organochromium ring compounds with phosphorus-complexing bidentate ligands. For the cyclic polymethylene sulfides, spectra were acquired in the region of the sulfur K-edge. For the organochromium complexes, spectra were acquired at both the chromium K-edge and at the phosphorus K-edge. These systems allow one to interrogate how the spectra evolve as the bond angle about the absorbing atom is varied. Systematic trends are observed as a function of ring size/bond angle. For the cyclic sulfides, the peaks in the continuum above the sulfur K-edge shift to higher energy and broaden with increasing ring size. These continuum features are assigned to shape resonances. In the chromium K-edge measurements, changes in the P-Cr-C bond angle do not influence the spectra appreciably, indicating that the four carbonyl groups dominate the photoelectron scattering processes. However, the phosphorus K-edge spectra are sensitive to changes in the endocyclic Cr-P-C bond angle. The trends observed in the phosphorus K-edge region for the organometallic continuum features are consistent with those observed for the cyclic polymethylene sulfides.

  16. Photoelectron Imaging and Spectroscopy of MI2- (M = Cs, Cu, Au): Evolution from Ionic to Covalent Bonding

    SciTech Connect

    Wang, Yi-Lei; Wang, Xue B; Xing, Xiaopeng; Wei, Fan; Li, Jun; Wang, Lai S

    2010-10-28

    We report a combined experimental and theoretical investigation on MI2- (M = Cs, Cu, Ag, Au) to explore the chemical bonding in the group IA and IB di-iodide complexes. Both photoelectron imaging and low-temperature photoelectron spectroscopy are applied to MI2- (M = Cs, Cu, Au), yielding vibrationally resolved spectra for CuI2- and AuI2- and accurate electron affinities, 4.52 ± 0.02, 4.256 ± 0.010, and 4.226 ± 0.010 eV for CsI2, CuI2, and AuI2, respectively. Spin-orbit coupling is found to be important in all the di-iodide complexes and ab initio calculations including spin-orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses (charge population, bond order, and electron localization functions) have been carried out, revealing a gradual transition from the expected ionic behavior in CsI2- to strong covalent bonding in AuI2-. Both relativistic effects and electron correlation are shown to enhance the covalency in the gold di-iodide complex.

  17. Analysis of Band Offset in GaNAs/GaAs by X-Ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kitatani, Takeshi; Kondow, Masahiko; Kikawa, Takeshi; Yazawa, Yoshiaki; Okai, Makoto; Uomi, Kazuhisa

    1999-09-01

    We used X-ray photoelectron spectroscopy (XPS) to measure the energy discontinuity in the valence band (ΔEv) of Ga1-xNxAs/AlAs (x=0, 0.014, 0.034) and estimated ΔEv of GaNAs/GaAs by using the Al2p energy level as a reference. The change in ΔEv for GaNAs/GaAs with an increasing nitrogen content was -(0.019±0.053) eV/%N. This suggests that the valence-band edge (Ev) in GaNAs decreases in proportion to the nitrogen content. Based on the decrease in the bandgap energy of GaNAs, we found that the energy discontinuity in the conduction band (ΔEc) of GaNAs/GaAs is -(0.175±0.053) eV/%N. This large effect of bandgap bowing on the conduction band indicates that an ideal carrier confinement in the well can be obtained by using GaInNAs as an active layer in long-wavelength laser diodes.

  18. Migration of Dust Particles from Comet 2P Encke

    NASA Technical Reports Server (NTRS)

    Ipatov, S. I.

    2003-01-01

    We investigated the migration of dust particles under the gravitational influence of all planets (except for Pluto), radiation pressure, Poynting-Robertson drag and solar wind drag for Beta equal to 0.002, 0.004, 0.01, 0.05, 0.1, 0.2, and 0.4. For silicate particles such values of Beta correspond to diameters equal to about 200, 100, 40, 9, 4, 2, and 1 microns, respectively. We used the Bulirsh-Stoer method of integration, and the relative error per integration step was taken to be less than lo-'. Initial orbits of the particles were close to the orbit of Comet 2P Encke. We considered initial particles near perihelion (runs denoted as Delta tsub o, = 0), near aphelion (Delta tsub o, = 0.5), and also studied their initial positions when the comet moved for Pa/4 after perihelion passage (such runs are denoted as Delta tsub o, =i 0.25), where Pa is the period of the comet. Variations in time T when perihelion was passed was varied with a step 0.1 day for series 'S' and with a step 1 day for series 'L'. For each Beta we considered N = 101 particles for "S" runs and 150 particles for "L" runs.

  19. Multicast Services over Structured P2P Networks

    NASA Astrophysics Data System (ADS)

    Manzanares-Lopez, Pilar; Malgosa-Sanahuja, Josemaria; Muñoz-Gea, Juan Pedro; Sanchez-Aarnoutse, Juan Carlos

    IP multicast functionality was defined as an efficient method to transmit datagrams to a group of receivers. However, although a lot of research work has been done in this technology, IP multicast has not spread out over the Internet as much as expected, reducing its use for local environments (i.e., LANs). The peer-to-peer networks paradigm can be used to overcome the IP multicast limitations. In this new scenario (called Application Layer Multicast or ALM), the multicast functionality is changed from network to application layer. Although ALM solution can be classified into unstructured and structured solutions, the last ones are the best option to offer multicast services due to the effectiveness in the discovery nodes, their mathematical definition and the totally decentralized management. In this chapter we are going to offer a tutorial of the main structured ALM solutions, but introducing two novelties with respect to related surveys in the past: first, the systematic description of most representative structured ALM solution in OverSim (one of the most popular p2p simulation frameworks). Second, some simulation comparatives between flooding-based and tree-based structured ALM solution are also presented.

  20. New type of silicon photoelectronic negative resistance devices: PDUBAT

    NASA Astrophysics Data System (ADS)

    Sha, Yanan; Varadan, Vijay K.; Varadan, Vasundara V.; Li, Shuyong; Guo, Weilian; Zheng, Yunguang

    2001-08-01

    Photoelectronic DUal Base Transistor (PDUBAT) is a novel kind of photoelectronic negative resistance devices, which features 'N' type negative resistance and small negative resistance RN. PDUBAT consists of a vertical NPN bipolar transistor and a P type diffusion region with large area over a specific distance. The base and collector of the vertical NPN BJT with a large P diffusion region form a lateral PNP BJT. The emitter and collector of the vertical NPN BJT are connected to the ground and voltage supply respectively, while the P diffusion region is left floated to detect input light signal. When the device is exposed to light, a large number of electron-hole pairs are generated at the PN junction under the P diffusion region. The holes travel along the base of the lateral PNP BJT and become the driving current of the vertical NPN BJT. In experiments, we found that PDUBAT acts as a pulse oscillator without the load of inductors, whose frequency and magnitude are modulated by the intensity of incident light. The oscillating frequency increases while the magnitude decreases with the increasing of light intensity. The manufacturing process of PDUBAT is compatible with that of JBTs, so that it can be incorporated with the ICs.

  1. Graphene oxide windows for in situ environmental cell photoelectron spectroscopy.

    PubMed

    Kolmakov, Andrei; Dikin, Dmitriy A; Cote, Laura J; Huang, Jiaxing; Abyaneh, Majid Kazemian; Amati, Matteo; Gregoratti, Luca; Günther, Sebastian; Kiskinova, Maya

    2011-08-28

    The performance of new materials and devices often depends on processes taking place at the interface between an active solid element and the environment (such as air, water or other fluids). Understanding and controlling such interfacial processes require surface-specific spectroscopic information acquired under real-world operating conditions, which can be challenging because standard approaches such as X-ray photoelectron spectroscopy generally require high-vacuum conditions. The state-of-the-art approach to this problem relies on unique and expensive apparatus including electron analysers coupled with sophisticated differentially pumped lenses. Here, we develop a simple environmental cell with graphene oxide windows that are transparent to low-energy electrons (down to 400 eV), and demonstrate the feasibility of X-ray photoelectron spectroscopy measurements on model samples such as gold nanoparticles and aqueous salt solution placed on the back side of a window. These proof-of-principle results show the potential of using graphene oxide, graphene and other emerging ultrathin membrane windows for the fabrication of low-cost, single-use environmental cells compatible with commercial X-ray and Auger microprobes as well as scanning or transmission electron microscopes.

  2. Band alignment of InGaZnO4/Si interface by hard x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Kyeongmi; Nomura, Kenji; Yanagi, Hiroshi; Kamiya, Toshio; Ikenaga, Eiji; Sugiyama, Takeharu; Kobayashi, Keisuke; Hosono, Hideo

    2012-08-01

    Although amorphous InGaZnO4 has intensively been studied for a semiconductor channel material of thin-film transistors in next-generation flat-panel displays, its electronic structure parameters have not been reported. In this work, the electron affinities (χ) and the ionization potentials (Ip) of crystalline and amorphous InGaZnO4 (c-IGZO and a-IGZO) were measured using bulk-sensitive hard x-ray photoelectron spectroscopy. First, the χ and Ip values of c-IGZO and a-IGZO thin films were estimated by aligning the Zn 2p3/2 core level energies to a literature value for ZnO, which provided χ = 3.90 eV and Ip = 7.58 eV for c-IGZO and 4.31 eV and 7.41 eV for a-IGZO. It was also confirmed that the escape depth of the photoelectrons excited by the photon energy of 5950.2 eV is 3.3 nm for a-IGZO and large enough for directly measuring the interface electronic structure using a-IGZO/c-Si heterojunctions. It provided the valence band offset of ˜2.3 eV, which agrees well with the above data. The present results substantiate that the a-IGZO/c-Si interface follows well the Schottky-Mott rule.

  3. X-ray photoelectron spectroscopy study of irradiation-induced amorphizaton of Gd2Ti2O7

    NASA Astrophysics Data System (ADS)

    Chen, J.; Lian, J.; Wang, L. M.; Ewing, R. C.; Boatner, L. A.

    2001-09-01

    The radiation-induced evolution of the microstructure of Gd2Ti2O7, an important pyrochlore phase in radioactive waste disposal ceramics and a potential solid electrolyte and oxygen gas sensor, has been characterized using transmission electron microscopy and x-ray photoelectron spectroscopy. Following the irradiation of a Gd2Ti2O7 single crystal with 1.5 MeV Xe+ ions at a fluence of 1.7×1014Xe+/cm2, cross-sectional transmission electron microscopy revealed a 300-nm-thick amorphous layer at the specimen surface. X-ray photoelectron spectroscopy analysis of the Ti 2p and O 1s electron binding energy shifts of Gd2Ti2O7 before and after amorphization showed that the main results of ion-irradiation-induced disorder are a decrease in the coordination number of titanium and a transformation of the Gd-O bond. These features resemble those occurring in titanate glass formation, and they have implications for the chemical stability and electronic properties of pyrochlores subjected to displacive radiation damage.

  4. Electronic structure of Al- and Ga-doped ZnO films studied by hard X-ray photoelectron spectroscopy

    SciTech Connect

    Gabás, M.; Ramos Barrado, José R.; Torelli, P.; Barrett, N. T.

    2014-01-01

    Al- and Ga-doped sputtered ZnO films (AZO, GZO) are semiconducting and metallic, respectively, despite the same electronic valence structure of the dopants. Using hard X-ray photoelectron spectroscopy we observe that both dopants induce a band in the electronic structure near the Fermi level, accompanied by a narrowing of the Zn 3d/O 2p gap in the valence band and, in the case of GZO, a substantial shift in the Zn 3d. Ga occupies substitutional sites, whereas Al dopants are in both substitutional and interstitial sites. The latter could induce O and Zn defects, which act as acceptors explaining the semiconducting character of AZO and the lack of variation in the optical gap. By contrast, mainly substitutional doping is consistent with the metallic-like behavior of GZO.

  5. Characterization of SiC fibers by soft x-ray photoelectron and photoabsorption spectroscopies and scanning Auger microscopy

    SciTech Connect

    Ma, Qing; McDowell, M.W.; Rosenberg, R.A.

    1996-08-01

    Synchrotron radiation soft x-ray photoelectron and photoabsorption spectroscopy was used to characterize commercially obtained SiC fibers produced by CVD on a W core and followed by a C passivating layer. Depth profiling of the fiber through the C/SiC interface was done by making Si 2p and C 1s core level PES and PAS, as well as scanning Auger microscopy, measurements following Ar{sup +} sputtering. No significant changes in either photoemission or absorption or Auger line shapes were observed versus depth, indicating no significant interfacial reaction. The line shapes of the carbonaceous coatings are predominantely graphite-like and those of the CVD SiC coatings are microcrystalline, with disorder present to some extent in both cases.

  6. Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis

    PubMed Central

    Mant, Alexandra; Williams, Sarah E; O'Kelly, Ita

    2013-01-01

    Acid-sensitive, two-pore domain potassium channels, K2P3.1 and K2P9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K2P3.1 and K2P9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K2P3.1 and K2P9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K2P3.1 and K2P9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K2P3.1 and K2P9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K2P3.1 and K2P9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K2P3.1 and K2P9.1 trafficking can be further studied. PMID:23807092

  7. Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis.

    PubMed

    Mant, Alexandra; Williams, Sarah; O'Kelly, Ita

    2013-01-01

    Acid-sensitive, two-pore domain potassium channels, K(2P)3.1 and K(2P)9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K(2P)3.1 and K(2P)9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K(2P)3.1 and K(2P)9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K(2P)3.1 and K(2P)9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K(2P)3.1 and K(2P)9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K(2P)3.1 and K(2P)9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K(2P)3.1 and K(2P)9.1 trafficking can be further studied.

  8. The casein kinases Yck1p and Yck2p act in the secretory pathway, in part, by regulating the Rab exchange factor Sec2p

    PubMed Central

    Stalder, Danièle; Novick, Peter J.

    2016-01-01

    Sec2p is a guanine nucleotide exchange factor that activates Sec4p, the final Rab GTPase of the yeast secretory pathway. Sec2p is recruited to secretory vesicles by the upstream Rab Ypt32p acting in concert with phosphatidylinositol-4-phosphate (PI(4)P). Sec2p also binds to the Sec4p effector Sec15p, yet Ypt32p and Sec15p compete against each other for binding to Sec2p. We report here that the redundant casein kinases Yck1p and Yck2p phosphorylate sites within the Ypt32p/Sec15p binding region and in doing so promote binding to Sec15p and inhibit binding to Ypt32p. We show that Yck2p binds to the autoinhibitory domain of Sec2p, adjacent to the PI(4)P binding site, and that addition of PI(4)P inhibits Sec2p phosphorylation by Yck2p. Loss of Yck1p and Yck2p function leads to accumulation of an intracellular pool of the secreted glucanase Bgl2p, as well as to accumulation of Golgi-related structures in the cytoplasm. We propose that Sec2p is phosphorylated after it has been recruited to secretory vesicles and the level of PI(4)P has been reduced. This promotes Sec2p function by stimulating its interaction with Sec15p. Finally, Sec2p is dephosphorylated very late in the exocytic reaction to facilitate recycling. PMID:26700316

  9. Magnetic and hyperfine properties of Fe2P nanoparticles dispersed in a porous carbon matrix

    NASA Astrophysics Data System (ADS)

    Viali, G. L.; Gonçalves, G. R.; Passamani, E. C.; Freitas, J. C. C.; Schettino, M. A.; Takeuchi, A. Y.; Larica, C.

    2016-03-01

    Structural and magnetic properties of nanocomposite, consisting of Fe2P particles dispersed in a porous carbon matrix, have fully been investigated using X-ray diffraction, Mössbauer and ac and dc magnetization measurements. Besides production of the nanocomposite, using an activated carbon (prepared by chemical activation of a char with H3PO4), impregnation with a Fe3+ salt in aqueous medium and subsequent heat treatments under N2 flow, we found a formation of hexagonal Fe2-xP and orthorhombic FeP in a mass ratio of 4:1, respectively. Low temperature Mössbauer spectra revealed that a large fraction (ca. 28%) of the material is in the paramagnetic state, suggesting that part of the Fe2-xP phase appears in the form of very small particles. A metamagnetic phase transition was also observed for non-stoichiometric Fe2-xP nanoparticles. It is observed at about 150 K, well below the ordering temperature of the Fe2P phase (230 K), and is dependent on the dc-probe fields. Also, the Fe2-xP nanoparticles were found to have a hard-like magnetic character at low temperatures, with coercive field HC of 1.3 KOe. Considering these interesting magnetic and hyperfine properties and also the large specific surface area of the porous carbon matrix, which is not severely reduced after impregnation with the Fe-containing compounds, one may point to promising technological applications of the produced nanocomposite.

  10. The Ultraviolet Photoelectron Spectroscopy of Group IV 2-15 Atom Cluster Anions

    NASA Astrophysics Data System (ADS)

    Craycraft, Mary Jo.

    The ability to map valence electronic structure is the result of a recent advance in photoelectron spectroscopy; its union with cluster molecular beam technology. The task of interpreting the spectra is hampered by a serious lack of understanding of cluster electronic structure in general. Recently progress has been made in finding models for single s valence electron systems. Alkali and noble metal clusters can be treated as free electron systems and simple interatomic potentials can be used with rare gas clusters. Neither a smeared jellium background nor a simple interatomic potential is adequate to describe covalent bonding, however. The isoelectronic Group IV members have a valence configuration of ns^2 np^2. All readily form clusters, and the elements differ in both their atomic and bulk properties; thus the series provides an ideal system for studying electronic structure. The mass selected cluster ion beam is crossed with a beam (6.42 or 7.9eV) and the resulting photodetached electrons collected with the aid of judiciously arranged magnetic fields. The spectra are found to be unique for each size cluster. Some spectra show a significant gap between the two lowest binding energy features, indicating that the neutral cluster is a closed shell species. The clusters with such gaps are minima in a plot of EA as a function of cluster size. The UPS also vary with the cluster composition. Carbon is unique; an even -odd alternation in electron affinities switches from odd minima for clusters containing less than ten atoms to odd maxima for larger clusters. This corresponds with an alternation in singlet and triplet ground states and a switch from chain to ring structures previously predicted by theory (K. S. Pitzer, E. Clementi, J. Amer. Chem. Soc. 81 4477 (1958) and R. Hoffmann, Tetrahedron 22 521 (1965)). The spectra of the remaining group IV members are remarkably similar to each other for clusters of up to ten atoms, as is the trend in the electron affinities as

  11. Development of a miniature double-pass cylindrical mirror electron energy analyzer (DPCMA), and its application to Auger photoelectron coincidence spectroscopy (APECS)

    NASA Astrophysics Data System (ADS)

    Kobayashi, Eiichi; Seo, Junya; Nambu, Akira; Mase, Kazuhiko

    2007-09-01

    We have developed a miniature double-pass cylindrical mirror electron energy analyzer (DPCMA) with an outer diameter of 26 mm. The DPCMA consists of a shield for the electric field, inner and outer cylinders, two pinholes with a diameter of 2.0 mm, and an electron multiplier. By assembling the DPCMA in a coaxially symmetric mirror electron energy analyzer (ASMA) coaxially and confocally we developed an analyzer for Auger photoelectron coincidence spectroscopy (APECS). The performance was estimated by measuring the Si-LVV-Auger Si-1s-photoelectron coincidence spectra of clean Si(1 1 1). The electron-energy resolution of the DPCMA was estimated to be E/Δ E = 20. This value is better than that of the miniature single-pass CMA ( E/Δ E = 12) that was used in the previous APECS analyzer.

  12. Photoelectron spectroscopy and ab initio calculations of small Si{sub n}S{sub m}{sup −} (n = 1,2; m = 1–4) clusters

    SciTech Connect

    Xu, Xi-Ling; Deng, Xiao-Jiao; Xu, Hong-Guang; Zheng, Wei-Jun

    2014-09-28

    Binary cluster anions composed of silicon and sulfur elements, Si{sub n}S{sub m}{sup −} (n = 1,2; m = 1-4), were investigated by using photoelectron spectroscopy and ab initio calculations. The vertical detachment energies and the adiabatic detachment energies of these clusters were obtained from their photoelectron spectra. The electron affinity of SiS molecule is determined to be 0.477 ± 0.040 eV. The results show that the most stable structures of the anionic and neutral Si{sub n}S{sub m} (n = 1,2; m = 1-4) clusters prefer to adopt planar configurations except that the structures of Si{sub 2}S{sub 4}{sup −} and Si{sub 2}S{sub 2} are slightly bent.

  13. Spectra of Surface Waves

    DTIC Science & Technology

    1989-03-22

    with a wave follower during Marsen. J. Gophysical Res. 88, 9844-9849. 11. Hughes, B.A., 1978. The effects on internal waves on surface waves : 2...Spectra of Surface Waves K. Watson March 1989 JSR-88-130 Approved for public release; distribution unlimited. DTIC SELECTE JUN0 11989 0 JASONE The...Arlington, VA 22209 8503Z 11. TITLE (hlde Secvfty Cof.kaftn) SPECTRA OF SURFACE WAVES (U) 12. PERSONAL AUTHOfRS) K. Watson 13a. TYPE OF REPORT 13b. TIME

  14. A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO(-).

    PubMed

    Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun

    2016-02-28

    The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.

  15. Hydration of potassium iodide dimer studied by photoelectron spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Li, Ren-Zhong; Zeng, Zhen; Hou, Gao-Lei; Xu, Hong-Guang; Zhao, Xiang; Gao, Yi Qin; Zheng, Wei-Jun

    2016-11-01

    We measured the photoelectron spectra of (KI)2-(H2O)n (n = 0-3) and conducted ab initio calculations on (KI)2-(H2O)n anions and their corresponding neutrals up to n = 6. Two types of spectral features are observed in the experimental spectra of (KI)2-(H2O) and (KI)2-(H2O)2, indicating that two types of isomers coexist, in which the high EBE feature corresponds to the hydrated chain-like (KI)2- while the low EBE feature corresponds to the hydrated pyramidal (KI)2-. In (KI)2-(H2O)3, the (KI)2- unit prefers a pyramidal configuration, and one of the K-I distances is elongated significantly, thus a K atom is firstly separated out from the (KI)2- unit. As for the neutrals, the bare (KI)2 has a rhombus structure, and the structures of (KI)2(H2O)n are evolved from the rhombus (KI)2 unit by the addition of H2O. When the number of water molecules reaches 4, the K-I distances have significant increment and one of the I atoms prefers to leave the (KI)2 unit. The comparison of (KI)2(H2O)n and (NaI)2(H2O)n indicates that it is slightly more difficult to pry apart (KI)2 than (NaI)2 via hydration, which is in agreement with the lower solubility of KI compared to that of NaI.

  16. Low-lying electronic structure of EuH, EuOH, and EuO neutrals and anions determined by anion photoelectron spectroscopy and DFT calculations

    SciTech Connect

    Kafader, Jared O.; Ray, Manisha; Jarrold, Caroline Chick

    2015-07-21

    The anion photoelectron (PE) spectra of EuH{sup −} and the PE spectrum of overlapping EuOH{sup −} and EuO{sup −} anions are presented and analyzed with supporting results from density functional theory calculations on the various anions and neutrals. Results point to ionically bound, high-spin species. EuH and EuOH anions and neutrals exhibit analogous electronic structures: Transitions from {sup 8}Σ{sup −} anion ground states arising from the 4f{sup 7}σ{sub 6s}{sup 2} superconfiguration to the close-lying neutral {sup 9}Σ{sup −} and {sup 7}Σ{sup −} states arising from the 4f{sup 7}σ{sub 6s} superconfiguration are observed spaced by an energy interval similar to the free Eu{sup +} [4f{sup 7}6s] {sup 9}S - {sup 7}S splitting. The electron affinities (EAs) of EuH and EuOH are determined to be 0.771 ± 0.009 eV and 0.700 ± 0.011 eV, respectively. Analysis of spectroscopic features attributed to EuO{sup −} photodetachment is complicated by the likely presence of two energetically competitive electronic states of EuO{sup −} populating the ion beam. However, based on the calculated relative energies of the close-lying anion states arising from the 4f{sup 7}σ{sub 6s} and 4f{sup 6}σ{sub 6s}{sup 2} configurations and the relative energies of the one-electron accessible 4f{sup 7} and 4f{sup 6}σ{sub 6s} neutral states based on ligand-field theory [M. Dulick, E. Murad, and R. F. Barrow, J. Chem. Phys. 85, 385 (1986)], the remaining features are consistent with the 4f{sup 6}σ{sub 6s}{sup 2}  {sup 7}Σ{sup −} and 4f{sup 7}σ{sub 6s}{sup 7}Σ{sup −} anion states lying very close in energy (the former was calculated to be 0.15 eV lower in energy than the latter), though the true anion ground state and neutral EA could not be established unambiguously. Calculations on the various EuO anion and neutral states suggest 4f-orbital overlap with 2p orbitals in species with 4f{sup 6} occupancy.

  17. Ultraviolet photoelectron spectroscopy study of the thermochromic phase transition in urethane-substituted polydiacetylenes.

    PubMed

    Wang, Xiaoyu; Whitten, James E; Sandman, Daniel J

    2007-05-14

    Threshold solid-state ionization energies determined from ultraviolet photoelectron spectra are reported for the thermochromic polydiacetylenes (PDAs) from the bis-ethyl- and bis-n-propyl urethanes of 5,7-dodecadiyn-1,12-diol (ETCD and PUDO, respectively) and the nonthermochromic 1,6-bis-p-toluenesulfonate of 2,4-hexadiyne-1,6-diol (PTS) at temperatures above and below the thermochromic phase transition. PDA-PTS has an ionization energy of 5.66 eV which does not change significantly as the temperature is raised above 140 degrees C. At 25 degrees C, PDA-ETCD and PDA-PUDO have threshold ionization energies of 5.65 and 5.51 eV, respectively. The ionization energies of these PDAs increase by approximately 0.34 eV as temperature is raised above 140 degrees C and returns to the lower values as temperature is reduced to 25 degrees C. The magnitude of the increase in ionization energy on heating to temperatures above the thermochromic transition is very close to the shift in energy of the electronic spectrum over the same temperature range. These observations suggest that the structural changes that take place in the course of the thermochromic transition are primarily associated with the valence band and are consistent with partial relief of mechanical strains.

  18. Photoelectron angular distributions of H ionization in low energy regime: Comparison between different potentials

    NASA Astrophysics Data System (ADS)

    Song, Shu-Na; Liang, Hao; Peng, Liang-You; Jiang, Hong-Bing

    2016-09-01

    We theoretically investigate the low energy part of the photoelectron spectra in the tunneling ionization regime by numerically solving the time-dependent Schrdinger equation for different atomic potentials at various wavelengths. We find that the shift of the first above-threshold ionization (ATI) peak is closely related to the interferences between electron wave packets, which are controlled by the laser field and largely independent of the potential. By gradually changing the short-range potential to the long-range Coulomb potential, we show that the long-range potential’s effect is mainly to focus the electrons along the laser’s polarization and to generate the spider structure by enhancing the rescattering process with the parent ion. In addition, we find that the intermediate transitions and the Rydberg states have important influences on the number and the shape of the lobes near the threshold. Project supported by the National Natural Science Foundation of China (Grant Nos. 11322437 and 11574010) and the National Basic Research Program of China (Grant No. 2013CB922402).

  19. Characterization of oxidized platinum surfaces by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Peuckert, M.; Bonzel, H. P.

    1984-09-01

    Various adlayers were grown on the (111) surface of a platinum crystal by four different oxidizing treatments. The resulting surface phases were characterized by X-ray photoelectron spectroscopy. According to the Pt 4f and O 1s XPS spectra, treatment in 0.1 MPa O 2 at 900 K yielded about two monolayers of PtO 2; anodic polarization in 0.5M H 2SO 4 acid electrolyte at 3 V versus standard hydrogen electrode gave a thick (> 5 nm) layer of Pt(OH) 4, while by polarization in 1M NaOH base electrolyte at 3 V versus Ag/AgCl reference electrode a thick film of an oxyhydroxide (approximately PtO(OH) 2) was formed. Etching in boiling conc. HNO 3 led to a thin layer of about 1 nm of a hydrated oxide, PtO 2 · xH 2O. Identification of the different surface phases was supported by comparative experiments with bulk PtO 2. The thermal stability of all compounds was investigated by heating the samples in ultrahigh vacuum. They all decomposed at about 400 K. Initially, not a pure metal phase was formed, but a mixed phase containing Pt metal and oxide, which was stable over a wide temperature range. No oxygen could be detected on the surface at 1070 K by XPS or Auger spectroscopy.

  20. 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.

  1. Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun

    2016-07-01

    We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen‑ (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen‑ clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen‑/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters.

  2. Slow Photoelectron Spectroscopy and State-Selected Unimolecular Decomposition of Ionized DNA Bases Analogues

    NASA Astrophysics Data System (ADS)

    Mahjoub, Ahmed; Hochlaf, Majdi; Poisson, Lionel; Garcia, Gustavo A.; Nahon, Laurent

    2013-06-01

    We studied the single-photon ionization of gas-phase 2-Piperidone (DNA basis analogue) and of its dimer using vacuum-ultraviolet (VUV) synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer The slow photoelectron spectrum (SPES) of the monomer is dominated by the vibrational transitions to the ground state. These spectra are assigned with the help of theoretical calculations dealing with the equilibrium geometries, electronic-state patterns and evolutions, harmonic and anharmonic wavenumbers. After its formation, dimer is subject of intramolecular isomerization, H transfer and then unimolecular fragmentation processes. The near threshold photofragmentation pattern of the cationic 2-Piperidone cation and its dimer has been recorded. The experimental method yields the fragment intensity as a function of the internal energy deposited into the parent cation. In parallel, ab initio studies on ionic and neutral fragmentation products have been performed with the aim of determining the isomers of the ionic products observed experimentally as well as of their neutral counterparts. L. Nahon, N. De Oliveria,J. F. Gil,B. Pilette,O. Marcouillé, B. La garde and F. Polack Journal of Synchrotron Radiation {19}(4), 508-520; 2012

  3. Photoelectron Spectroscopy and Electronic Structure of Heavy GroupIV-VI Diatomics

    SciTech Connect

    Wang, L.-S.; Niu, B.; Lee, Yuan T.; Shirley, D.A.; Balasubramanian, K.

    1989-09-01

    Vibrationally-resolved HeI (584{angstrom}) photoelectron spectra of the heavy group IV-VI diatomics SnSe, SnTe, PbSe, and PbTe were obtained with a new high temperature molecular beam source. Ionization potentials and spectroscopic constants are reported for all the ionic states observed. Relativistic complete active space MCSCF followed by multireference singles + doubles relativistic CI calculations which included up to 200,000 configurations were made on both the neutral diatomics and their positive ions. Ionization potentials and spectroscopic constants were calculated and were in good agreement with the experimentally-measured values. Relativistic CI potential energy curves were calculated for all the neutral ground states and the ionic states involved. Relativistic effects were shown to play an important role in these heavy diatomics. The {sup 2}{Sigma}{sub 1/2}{sup +} and {sup 2}{Pi}{sub 1/2} states for all four molecular ions showed avoided curve crossings, which resulted in pronounced shoulders in the {Omega} = 1/2 potential energy curves of PbTe{sup +}. Experimentally, autoionization transitions were also observed for the PbTe{sup +} spectrum. The importance of the relativistic effect and chemical bonding in the heavy diatomics are discussed.

  4. Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations

    PubMed Central

    Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun

    2016-01-01

    We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters. PMID:27439955

  5. Chemistry of carbon polymer composite electrode - An X-ray photoelectron spectroscopy study

    NASA Astrophysics Data System (ADS)

    Andersen, Shuang Ma; Dhiman, Rajnish; Skou, Eivind

    2015-01-01

    Surface chemistry of the electrodes in a proton exchange membrane fuel cell is of great importance for the cell performance. Many groups have reported that electrode preparation condition has a direct influence on the resulting electrode properties. In this work, the oxidation state of electrode components and the composites (catalyst ionomer mixtures) in various electrode structures were systematically studied with X-ray photoelectron spectroscopy (XPS). Based on the spectra, when catalyst is physically mixed with Nafion ionomer, the resulting electrode surface chemistry is a combination of the two components. When the electrode is prepared with a lamination procedure, the ratio between fluorocarbon and graphitic carbon is decreased. Moreover, ether type oxide content is decreased although carbon oxide is slightly increased. This indicates structure change of the catalyst layer due to an interaction between the ionomer and the catalyst and possible polymer structural change during electrode fabrication. The surface of micro porous layer was found to be much more influenced by the lamination, especially when it is in contact with catalysts in the interphase. Higher amount of platinum oxide was observed in the electrode structures (catalyst ionomer mixture) compared to the catalyst powder. This also indicates a certain interaction between the functional groups in the polymer and platinum surface.

  6. Adsorption of 2-propanol on ice probed by ambient pressure X-ray photoelectron spectroscopy

    DOE PAGES

    Newberg, John T.; Bluhm, Hendrik

    2015-08-18

    The interaction of 2-propanol with ice was examined via ambient pressure X-ray photoelectron spectroscopy (APXPS), a surface sensitive technique that probes the adsorbed 2-propanol directly with submonolayer resolution. Isothermal uptake experiments were performed on vapor deposited ice at 227 K in the presence of the equilibrium water vapor pressure of 0.05 Torr and 2-propanol partial pressures ranging from 5 × 10-5 to 2 × 10-3 Torr. The C 1s APXPS spectra of adsorbed 2-propanol showed two characteristic peaks associated with the COH alcohol group and CMe methyl groups in a 1 : 2 ratio, respectively. Coverage increased with 2-propanol partialmore » pressure and followed first order Langmuir kinetics with a Langmuir constant of K = 6.3 × 103 Torr-1. The 1 : 2 ratio of COH : CMe remained constant with increasing coverage, indicating there is no chemical reaction upon adsorption. The observed Langmuir kinetics using APXPS is consistent with previous observations of other small chain alcohols via indirect adsorption methods using, e.g., Knudsen cell and coated wall flow tube reactors.« less

  7. Adsorption of 2-propanol on ice probed by ambient pressure X-ray photoelectron spectroscopy

    SciTech Connect

    Newberg, John T.; Bluhm, Hendrik

    2015-08-18

    The interaction of 2-propanol with ice was examined via ambient pressure X-ray photoelectron spectroscopy (APXPS), a surface sensitive technique that probes the adsorbed 2-propanol directly with submonolayer resolution. Isothermal uptake experiments were performed on vapor deposited ice at 227 K in the presence of the equilibrium water vapor pressure of 0.05 Torr and 2-propanol partial pressures ranging from 5 × 10-5 to 2 × 10-3 Torr. The C 1s APXPS spectra of adsorbed 2-propanol showed two characteristic peaks associated with the COH alcohol group and CMe methyl groups in a 1 : 2 ratio, respectively. Coverage increased with 2-propanol partial pressure and followed first order Langmuir kinetics with a Langmuir constant of K = 6.3 × 103 Torr-1. The 1 : 2 ratio of COH : CMe remained constant with increasing coverage, indicating there is no chemical reaction upon adsorption. The observed Langmuir kinetics using APXPS is consistent with previous observations of other small chain alcohols via indirect adsorption methods using, e.g., Knudsen cell and coated wall flow tube reactors.

  8. Negative ion photoelectron spectroscopy of the copper-aspartic acid anion and its hydrated complexes

    NASA Astrophysics Data System (ADS)

    Li, Xiang; Wang, Haopeng; Bowen, Kit H.; Martínez, Ana; Salpin, Jean-Yves; Schermann, Jean-Pierre

    2010-08-01

    Negative ions of copper-aspartic acid Cu(Asp)- and its hydrated complexes have been produced in the gas phase and studied by anion photoelectron spectroscopy. The vertical detachment energies (VDE) of Cu(Asp)- and Cu(Asp)-(H2O)1,2 were determined to be 1.6, 1.95, and 2.20 eV, respectively. The spectral profiles of Cu(Asp)-(H2O)1 and Cu(Asp)-(H2O)2 closely resembled that of Cu(Asp)-, indicating that hydration had not changed the structure of Cu(Asp)- significantly. The successive shifts to higher electron binding energies by the spectra of the hydrated species provided measures of their stepwise solvation energies. Density functional calculations were performed on anionic Cu(Asp)- and on its corresponding neutral. The agreement between the calculated and measured VDE values implied that the structure of the Cu(Asp)- complex originated with a zwitterionic form of aspartic acid in which a copper atom had inserted into the N-H bond.

  9. Note: Alignment/focus dependent core-line sensitivity for quantitative chemical analysis in hard x-ray photoelectron spectroscopy using a hemispherical electron analyzer

    SciTech Connect

    Weiland, Conan; Browning, Raymond; Karlin, Barry A.; Fischer, Daniel A.; Woicik, Joseph C.

    2013-03-15

    X-ray photoelectron spectroscopy is an established technique for quantitative chemical analysis requiring accurate peak intensity analysis. We present evidence of focus/alignment dependence of relative peak intensities for peaks over a broad kinetic energy range with a hemispherical electron analyzer operated in a position imaging mode. A decrease of over 50% in the Ag 2p{sub 3/2} to Ag 3d ratio is observed in a Ag specimen. No focus/alignment dependence is observed when using an angular imaging mode, necessitating the use of angular mode for quantitative chemical analysis.

  10. Photoelectron decay kinetics of cubic silver chloride microcrystal film adsorbing plentiful dye excited by laser

    NASA Astrophysics Data System (ADS)

    Zhang, Rongxiang; Zhang, Jixian; Lai, Weidong; Hu, Yanxia; Dai, Xiuhong; Han, Li; Li, Xiaowei

    2007-12-01

    There will be large numbers of carriers coming into being in the interior of silver chloride microcrystals when illumination acts on it. Microwave absorption and dielectric spectrum detection technology with high temporal resolution (1ns) can detect instantaneous decay process of photoelectrons. In this work, the photoelectron decay action of spectral sensitized silver chloride emulsion is measured by microwave absorption and dielectric spectrum detection technology. By analyzing the measured results, it is found that when plentiful dye adsorb on silver chloride microcrystals film, the photoelectron decay of silver chloride emulsion becomes faster than that of pure emulsion. However it is not that the more the dye is adsorbed, the faster the photoelectron decay will be. When the adsorbed dye reaches a certain level, the photoelectron decay becomes slower than the fastest instance. Combining with photoelectron decay kinetics theory it is found that the above results are induced by two kinds of effect from dye adsorption.

  11. Comment on 'Origin of light-induced states in intense laser fields and their observability in photoelectron spectra'

    SciTech Connect

    Stroe, Marius; Boca, Malina

    2005-01-01

    We report discrepancies between the results presented in Fig. 1 of a recent paper of Yasuike and Someda [Phys. Rev. A 66, 053410 (2002)] and our independent calculation. At the frequency {omega}=0.55 a.u., we find that the state of the one-dimensional modified Poeschl-Teller potential, described by the authors as light induced and originating from a shadow of the field-free ground state, is in fact physical for {alpha}{sub 0}<10 a.u. and its origin is the zero-energy antibound state of the bare potential. For {omega}=0.45 a.u., we also find differences in one of the presented quasienergy trajectories in the low {alpha}{sub 0} region ({alpha}{sub 0}<0.4 a.u.), but we confirm the starting point at E=-0.5 a.u. for both quasienergies, as found by Yasuike and Someda.

  12. Quantum spectra and dynamics

    NASA Astrophysics Data System (ADS)

    Arce, Julio Cesar

    This work focuses on time-dependent quantum theory and methods for the study of the spectra and dynamics of atomic and molecular systems. Specifically, we have addressed the following two problems: (1) Development of a time-dependent spectral method for the construction of spectra of simple quantum systems. This includes the calculation of eigenenergies, the construction of bound and continuum eigenfunctions, and the calculation of photo cross-sections. Computational applications include the quadrupole photoabsorption spectra and dissociation cross-sections of molecular hydrogen from various vibrational states in its ground electronic potential-energy curve. This method is seen to provide an advantageous alternative, both from the computational and conceptual point of view, to existing standard methods. (2) Explicit time-dependent formulation of photoabsorption processes -- Analytical solutions of the time-dependent Schrodinger equation are constructed and employed for the calculation of probability densities, momentum distributions, fluxes, transition rates, expectation values and correlation functions. These quantities are seen to establish the link between the dynamics and the calculated, or measured, spectra and cross-sections, and to clarify the dynamical nature of the excitation, transition and ejection processes. Numerical calculations on atomic and molecular hydrogen corroborate and complement the previous results, allowing the identification of different regimes during the photoabsorption process.

  13. Quantum Spectra and Dynamics

    NASA Astrophysics Data System (ADS)

    Arce, Julio Cesar

    1992-01-01

    This work focuses on time-dependent quantum theory and methods for the study of the spectra and dynamics of atomic and molecular systems. Specifically, we have addressed the following two problems: (i) Development of a time-dependent spectral method for the construction of spectra of simple quantum systems--This includes the calculation of eigenenergies, the construction of bound and continuum eigenfunctions, and the calculation of photo cross-sections. Computational applications include the quadrupole photoabsorption spectra and dissociation cross-sections of molecular hydrogen from various vibrational states in its ground electronic potential -energy curve. This method is seen to provide an advantageous alternative, both from the computational and conceptual point of view, to existing standard methods. (ii) Explicit time-dependent formulation of photoabsorption processes --Analytical solutions of the time-dependent Schrodinger equation are constructed and employed for the calculation of probability densities, momentum distributions, fluxes, transition rates, expectation values and correlation functions. These quantities are seen to establish the link between the dynamics and the calculated, or measured, spectra and cross-sections, and to clarify the dynamical nature of the excitation, transition and ejection processes. Numerical calculations on atomic and molecular hydrogen corroborate and complement the previous results, allowing the identification of different regimes during the photoabsorption process.

  14. Atomic Spectra Database (ASD)

    National Institute of Standards and Technology Data Gateway

    SRD 78 NIST Atomic Spectra Database (ASD) (Web, free access)   This database provides access and search capability for NIST critically evaluated data on atomic energy levels, wavelengths, and transition probabilities that are reasonably up-to-date. The NIST Atomic Spectroscopy Data Center has carried out these critical compilations.

  15. A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

    SciTech Connect

    Arrell, C. A. Ojeda, J.; Mourik, F. van; Chergui, M.; Sabbar, M.; Gallmann, L.; Keller, U.; Okell, W. A.; Witting, T.; Siegel, T.; Diveki, Z.; Hutchinson, S.; Tisch, J. W.G.; Marangos, J. P.; Chapman, R. T.; Cacho, C.; Rodrigues, N.; Turcu, I. C.E.; Springate, E.

    2014-10-01

    We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10⁻¹ mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

  16. Photoelectron angular distributions as a probe of anisotropic electron-ion interactions

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Expressions are given for atomic photoelectron angular distributions in LS coupling in which the role of anisotropic final state electron-ion interactions emerges explicitly. Calculations of photoelectron angular distributions for atomic sulfur are presented in which these anisotropic interactions produce pronounced deviations from the predictions of the Cooper-Zare model. Such effects are expected to be a general feature of photoelectron angular distributions for most open shell atoms.

  17. Photoelectron angular distributions as a probe of anisotropic electron-ion interactions

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Expressions are given for atomic photoelectron angular distributions in LS coupling in which the role of anisotropic final state electron-ion interactions emerges explicitly. Calculations of photoelectron angular distributions for atomic sulfur are presented in which these anisotropic interactions produce clear deviations from the predictions of the Cooper-Zare model. Such effects are expected to be a general feature of photoelectron angular distributions for most open-shell atoms.

  18. Pump-probe photoelectron spectroscopy by a high-power 90 nm vacuum-ultraviolet laser

    NASA Astrophysics Data System (ADS)

    Sato, Motoki; Suzuki, Yoshi-ichi; Suzuki, Toshinori; Adachi, Shunsuke

    2016-02-01

    We present pump-probe photoelectron spectroscopy of Kr and NO using a high-power vacuum-ultraviolet (VUV) laser at a wavelength of 90 nm. Clear quantum beats are observed in the photoelectron angular distributions as well as in the photoelectron yields, resulting from the coherent excitation of two Kr Rydberg states by the VUV pump. The entire Franck-Condon envelope of the NO A(2Σ+) excited state is also successfully captured by the VUV probe.

  19. Visible and infrared study of comet 2P/Encke's nucleus during its 2013 apparition

    NASA Astrophysics Data System (ADS)

    Fernandez, Y.; Mueller, B.; Samarasinha, N.; Woodney, L.; Abell, P.

    2014-07-01

    The 2013 apparition of comet 2P/Encke provided an opportunity to study the comet while it was relatively close to the Earth. The comet passed 0.48 au from the Earth on October 17, the closest such passage since 2003 and until 2030. We initiated a visible and infrared observational campaign for the apparition with the goal of further characterizing the physical, thermal, and rotational properties of the P/Encke nucleus. While thermal-emission data on the nucleus have been obtained in the past (e.g. [1--4]), observations in 2013 timed to coincide with an equator-on view afforded us the chance to have a rarely-seen vantage point of the nucleus. Low-resolution spectra over wavelengths from 0.7 to 2.5 μ m were obtained over four nights (UT Sept. 26, 28, 30, Oct. 1) that span all of the nucleus rotational longitudes. The spectra were acquired at the NASA Infrared Telescope Facility (IRTF) using its SpeX instrument, and they sample reflected sunlight at the short wavelengths and Wien-side thermal emission at the long wavelengths. We will present results on thermal inertia and albedo from a preliminary analysis of these data. We have shown through observations over the past 13 years that the rotation period of P/Encke's nucleus changes by about 4 minutes per orbit [5,6]. Furthermore, the typical lightcurve has the normal two-humped shape but with humps that have vastly different amplitudes (e.g., [7]). Thus, the equator-on view gave us the chance to further investigate P/Encke's rotation state and shape. We obtained visible-wavelength photometry of the nucleus in the R band at NASA/IRTF with the MORIS instrument on the aforementioned dates, at the NOAO Kitt Peak 2.1-meter telescope over UT Sept. 11, 12, 13, and 14, and at the CSUSB Murrillo Family Observatory 0.5-meter telescope over several dates in Sept. and Oct. [8]. The MORIS data in particular gave us the rotational context and absolute flux calibration for the spectra. We will present new, preliminary constraints on

  20. Inverse photoelectron spectrometer with magnetically focused electron gun

    NASA Technical Reports Server (NTRS)

    Krainsky, Isay L.

    1991-01-01

    An inverse photoelectron spectrometer is described which is based on the design of a magnetically focused low energy electron gun. The magnetic lens extends its field over a relatively large segment of the electron trajectory, which could provide a better focusing effect on a high-current-density low-velocity electron beam, providing the magnetic field in the vicinity of the target is reduced sufficiently to preserve the collinearity of the beam. In order to prove the concept, ray tracing is conducted using the Herrmannsfeldt program for solving electron trajectories in electrostatic and magnetostatic focusing systems. The program allows the calculation of the angles of the electron trajectories with the z axis, at the target location. The results of the ray-tracing procedure conducted for this gun are discussed. Some of the advantages of the magnetic focusing are also discussed.