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Sample records for 1s photoelectron spectra

  1. C1s and O1s photoelectron satellite spectra of CO with symmetry-dependent vibrational excitations

    NASA Astrophysics Data System (ADS)

    Ehara, M.; Kuramoto, K.; Nakatsuji, H.; Hoshino, M.; Tanaka, T.; Kitajima, M.; Tanaka, H.; De Fanis, A.; Tamenori, Y.; Ueda, K.

    2006-09-01

    The photoelectron shake-up satellite spectra that accompany the C1s and O1s main lines of carbon monoxide have been studied by a combination of high-resolution x-ray photoelectron spectroscopy and accurate ab initio calculations. The symmetry-adapted cluster-expansion configuration-interaction general-R method satisfactorily reproduces the satellite spectra over a wide energy region, and the quantitative assignments are proposed for the 16 and 12 satellite bands for C1s and O1s spectra, respectively. Satellite peaks above the π-1π * transitions are mainly assigned to the Rydberg excitations accompanying the inner-shell ionization. Many shake-up states, which interact strongly with three-electron processes such as π-2π*2 and n-2π*2, are calculated in the low-energy region, while the continuous Rydberg excitations are obtained with small intensities in the higher-energy region. The vibrational structures of low-lying shake-up states have been examined for both C1s and O1s ionizations. The vibrational structures appear in the low-lying C1s satellite states, and the symmetry-dependent angular distributions for the satellite emission have enabled the Σ and Π symmetries to be resolved. On the other hand, the potential curves of the low-lying O1s shake-up states are predicted to be weakly bound or repulsive.

  2. 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.

  3. 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)

  4. 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)

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Simulation of XPS C1s spectra of organic monolayers by quantum chemical methods.

    PubMed

    Giesbers, Marcel; Marcelis, Antonius T M; Zuilhof, Han

    2013-04-16

    Several simple methods are presented and evaluated to simulate the X-ray photoelectron spectra (XPS) of organic monolayers and polymeric layers by density functional theory (DFT) and second-order Møller-Plesset theory (MP2) in combination with a series of basis sets. The simulated carbon (C1s) XPS spectra as obtained via B3LYP/6-311G(d,p) or M11/6-311G(d,p) calculations are in good agreement (average mean error <0.3 eV) with the experimental spectra, and good estimates of C1s spectra can be obtained via E(C1s)(exp) = 0.9698EC1s(theory) + 20.34 (in eV) (B3LYP/6-311G(d,p)). As a result, the simulated C1s XPS spectra can elucidate the binding energies of the different carbon species within an organic layer and, in this way, greatly aid the assignment of complicated C1s XPS spectra. The paper gives a wide range of examples, including haloalkanes, esters, (thio-)ethers, leaving groups, clickable functionalities, and bioactive moieties.

  15. 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).

  16. 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.

  17. 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.

  18. X-ray photoelectron spectra of iron-sulphur proteins.

    PubMed Central

    Andrews, P T; Johnson, C E; Wallbank, B; Cammack, R; Hall, D O; Rao, K K

    1975-01-01

    The X-ray photoelectron spectra of the 2p, 3s and 3p levels of iron in oxidized Clostridium pasteurianum ferredoxin indicate that the eight iron atoms in the molecule are indistinguishable. Their magnetic state is indicated both by core polarization splitting of the 3s electrons, and by "shake-up' satellites on the 2p lines. Similar satellites are observed in the 2p lines of reduced Chromatium high-potential iron-sulphur proteins and oxidized spinach ferredoxin, indicating that there too the iron atoms are magnetic. The low observed magnetic susceptibility of these proteins is therefore due to spin-coupling between the iron atoms in the active centre. PMID:1180907

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

    SciTech Connect

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

    2014-01-28

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

  20. First experimental photoelectron spectra of superhalogens and their theoretical interpretations

    SciTech Connect

    Wang, X.; Ding, C.; Wang, L. |; Boldyrev, A.I.; Simons, J.

    1999-03-01

    Photoelectron spectra of the MX{sub 2}{sup {minus}} (M=Li, Na; X=Cl, Br, I) superhalogen anions have been obtained for the first time. The first vertical detachment energies (VDEs) were measured to be 5.92{plus_minus}0.04 (LiCl{sub 2}{sup {minus}}), 5.86{plus_minus}0.06 (NaCl{sub 2}{sup {minus}}), 5.42{plus_minus}0.03 (LiBr{sub 2}{sup {minus}}), 5.36{plus_minus}0.06 (NaBr{sub 2}{sup {minus}}), 4.88{plus_minus}0.03 (LiI{sub 2}{sup {minus}}), and 4.84{plus_minus}0.06 eV (NaI{sub 2}{sup {minus}}), which are all well above the 3.61 eV electron detachment energy of Cl{sup {minus}}, the highest among atomic anions. Experimental photoelectron spectra have been assigned on the basis of {ital ab initio} outer valence Green function (OVGF) calculations. The corresponding theoretical first VDEs were found to be 5.90 (LiCl{sub 2}{sup {minus}}), 5.81 (NaCl{sub 2}{sup {minus}}), 5.48 (LiBr{sub 2}{sup {minus}}), 5.43 (NaBr{sub 2}{sup {minus}}), 4.57 (LiI{sub 2}{sup {minus}}), and 4.50 eV (NaI{sub 2}{sup {minus}}), in excellent agreement with the experimental values. Photodetachment from the top four valence molecular orbitals (2{sigma}{sub g}{sup 2}2{sigma}{sub u}{sup 2}1{pi}{sub u}{sup 4}1{pi}{sub g}{sup 4}) of MX{sub 2}{sup {minus}} was observed. Analysis of the polestrength showed that all electron detachment channels in this study can be described as primarily one-electron processes. {copyright} {ital 1999 American Institute of Physics.}

  1. Theoretical Studies of Time-Resolved Photoelectron Spectra of IBr^-

    NASA Astrophysics Data System (ADS)

    Horvath, Samantha; McCoy, Anne B.; Pitzer, Russell M.

    2009-06-01

    In the present study, we examine the time-resolved photoelectron spectra of IBr^-. In the photodetachment studies performed by Sanov and co-workers and Lineberger and co-workers, the anionic species, prepared in its electronic ground state (^2Σ_{1/2}^+), is excited to either its \\Atilde' (^2Π_{3/2}) or \\Btilde (^2Σ_{1/2}^+) excited state, before electron photodetachment and dissociation on the \\Ctilde (^1Π_1) or higher-lying excited states of the neutral species, respectively. In this work, we use the electronic structure program Columbus to calculate the six lowest electronic states of IBr^- and the ten lowest Σ states of IBr at the MR-SO-CISD/aug-cc-pVDZ level of theory/basis, using relativistic core potentials for I and Br. Experimentally determined electronic states of IBr are also used. Vibrational eigenstates for these electronic states are calculated in a discrete variable representation, and propagation of the thermally populated \\Xtilde-state vibrational wave functions on either the \\Atilde' or \\Btilde electronic states of the anion is performed using a Lanczos scheme. We then take time-dependent overlaps between these propagated states and the vibrational eigenstates of the neutral surface. Results for IBr^- show good agreement with the experimental time-resolved spectra. Extensions to IBr^-(CO_2)_n (n < 2) will also be discussed. R. Mabbs, K. Pichugin, and A. Sanov, J. Chem. Phys., 2005 122, 174305 Leonid Sheps, Elisa M. Miller, and W. C. Lineberger (private communication) E. Wrede, S. Laubach, S. Schulenburg, A. Brown, E. R. Wouters, A. J. Orr-Ewing, and M. N. R. Ashfold, J. Chem. Phys., 2001, 114(6), 2629. D. T. Colbert and W. H. Miller, J. Chem. Phys., 1992, 96(3), 1982

  2. 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.

  3. Calculation of photoelectron spectra: A mean-field-based scheme

    NASA Astrophysics Data System (ADS)

    Dinh, P. M.; Romaniello, P.; Reinhard, P.-G.; Suraud, E.

    2013-03-01

    In a previous work, Pohl [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.84.5090 84, 5090 (2000)] have proposed a simple scheme for the evaluation of photoelectron spectra of clusters subject to a laser field by collecting one-particle wave functions at a given measuring point close to absorbing boundaries. The scheme gives reliable results for low and moderate laser fields, but it shows failures for strong laser fields. The formulation relies on the assumption of free-electron propagation close to the boundaries. The laser field, however, can still be active when the first bunches of outgoing electrons reach the measuring point, and therefore the free-particle scenario may not hold anymore in case of high laser intensities. In this paper, hence, we generalize the method by using a model of “free” particles in the presence of an electromagnetic dipole field. Numerical tests show that this generalized scheme reduces to that of Pohl for low and moderate laser intensities, whereas it considerably improves the results of the latter for high intensities, thus extending the applicability of the method.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

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

    SciTech Connect

    Gerchikov, L.; Sheinerman, S.

    2011-08-15

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

  12. Vibrationally Resolved Photoelectron Spectra of Si(3)- and Si(4)-

    DTIC Science & Technology

    1990-08-01

    3- and Si4- by T. N. Kitsopoulos, C. J. Chick, A. Weaver, and D. M. Neumark Submitted to the Journal of Chemical Physics : ’ " ., AUG 1 , ’J Ř...Diay ISAGE COUNT Interim Technical lpRIOM Jan 90 Y. July 90 190-7-31 15 1S. S..JPPLEMENTARY NOTATION Prepared for publication in the Journal of Chemical Physics 17

  13. XPS spectra of uranyl minerals and synthetic uranyl compounds. II: The O 1s spectrum

    NASA Astrophysics Data System (ADS)

    Schindler, M.; Hawthorne, F. C.; Freund, M. S.; Burns, P. C.

    2009-05-01

    The O 1s spectrum is examined for 19 uranyl minerals of different composition and structure. Spectra from single crystals were measured with a Kratos Axis Ultra X-ray Photoelectron Spectrometer with a magnetic-confinement charge-compensation system. Well-resolved spectra with distinct maxima, shoulders and inflections points, in combination with reported and measured binding energies for specific O 2- species and structural data of the uranyl minerals are used to resolve the fine structure of the O 1s envelope. The resolution of the O 1s spectra includes, for the first time, different O 2- bands, which are assigned to O atoms linking uranyl with uranyl polyhedra ( Usbnd Osbnd U) and O atoms of uranyl groups ( Odbnd Udbnd O). The resolved bands in the O 1s spectrum occur at distinct ranges in binding energy: bands for ( Usbnd Osbnd U) occur at 529.6-530.4 eV, bands for ( Odbnd Udbnd O) occur at 530.6-531.4 eV, bands for O 2- in the equatorial plane of the uranyl polyhedra linking uranyl polyhedra with ( TO n) groups ( T = Si, S, C, P, Se) ( Tsbnd O) occur at 530.9-532.2 eV; bands for (OH) groups in the equatorial plane of the uranyl polyhedra ( OH) occur at 532.0-532.5 eV, bands of (H 2O) groups in the interstitial complex of the uranyl minerals ( H2O interst) occur at 533.0-533.8 eV and bands of physisorbed (H 2O) groups on the surface of uranyl minerals ( H2O adsorb) occur at 534.8-535.2 eV. Treatment of uranyl minerals with acidic solutions results in a decrease in Usbnd Osbnd U and an increase in OH. Differences in the ratio of OH : Odbnd Udbnd O between the surface and bulk structure is larger for uranyl minerals with a high number of Usbnd Osbnd U and Tsbnd O species in the bulk structure which is explained by protonation of underbonded Usbnd O, Usbnd Osbnd U and Tsbnd O terminations on the surface. The difference in the ratio of H2O interst : Odbnd Udbnd O between the bulk and surface structures is larger for uranyl minerals with higher percentages of H2O

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    SciTech Connect

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

    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.

  17. 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.

  18. 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.

  19. Calculations of photoelectron momentum distributions and energy spectra at strong-field multiphoton ionization of sodium

    NASA Astrophysics Data System (ADS)

    Bunjac, Andrej; Popović, Duška B.; Simonović, Nenad S.

    2017-08-01

    Multiphoton ionization of sodium by a femtosecond laser pulse of 760 nm wavelength and different peak intensities is studied by inspecting the photoelectron angular and momentum distributions and the energy spectra. For this purpose a single-electron model of the atom interacting with the electromagnetic field is used, and the distributions are determined by calculating the evolution of the electron wave function. Beside the most prominent distribution maxima related to the four-photon ionization, the five-photon (above-threshold) ionization peaks are observed. Substructures in the main (nonresonant) maximum in the photoelectron spectra at the four-photon ionization are related to the resonantly enhanced multiphoton ionization via intermediate 4 s, 4 f, 5 p, 5 f and 6 p states.

  20. 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.

  1. 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.

  2. 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.

  3. A study of the photoelectron spectra of α-tetrahydrofurfuryl alcohol over the outer valence energy region (9-25 eV)

    NASA Astrophysics Data System (ADS)

    Dampc, Marcin; Mielewska, Brygida; Siggel-King, Michele R. F.; King, George C.; Zubek, Mariusz

    2017-07-01

    Photoelectron spectra of α-tetrahydrofurfuryl alcohol (THFA) molecules, the threshold spectrum and spectra for constant photoelectron energies, have been measured over the photon energy range 9-25 eV. Analysis of the photoelectron spectra has allowed overlapping photoionization bands to be separated, tentatively assigned and their vertical photoionization energies to be determined. These energies are compared with existing theoretical calculations. The photoelectron spectra indicate the predominance of one conformer in the population of gas-phase THFA.

  4. 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.

  5. Insight on hole-hole interaction and magnetic order from dichroic auger-photoelectron coincidence spectra.

    PubMed

    Cini, M; Perfetto, E; Gotter, R; Offi, F; Ruocco, A; Stefani, G

    2011-11-18

    The absence of sharp structures in the Auger line shapes of partially filled bands has severely limited the use of electron spectroscopy in magnetic crystals and other correlated materials. By a novel interplay of experimental and theoretical techniques we achieve a combined understanding of the photoelectron, Auger, and Auger-photoelectron coincidence spectra (APECS) of the antiferromagnetic CoO. A recently discovered dichroic effect in angle resolved (DEAR) APECS reveals a complex pattern in the Auger line shape, which is here explained in detail, labeling the final states by their total spin. Since the dichroic effect exists in the antiferromagnetic state but vanishes at the Néel temperature, the DEAR-APECS technique detects the phase transition from its local effects, thus providing a unique tool to observe and understand magnetic correlations where the usual methods are not applicable.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  7. Laser-induced electron diffraction: inversion of photo-electron spectra for molecular orbital imaging

    NASA Astrophysics Data System (ADS)

    Puthumpally-Joseph, R.; Viau-Trudel, J.; Peters, M.; Nguyen-Dang, T. T.; Atabek, O.; Charron, E.

    2017-08-01

    In this paper, we discuss the possibility of imaging molecular orbitals from photoelectron spectra obtained via Laser Induced Electron Diffraction (LIED) in linear molecules. This is an extension of our work published recently in Physical Review A \\textbf{94}, 023421 (2016) to the case of the HOMO-1 orbital of the carbon dioxide molecule. We show that such an imaging technique has the potential to image molecular orbitals at different internuclear distances in a sub-femtosecond time scale and with a resolution of a fraction of an Angstr\\"om.

  8. sp2/sp3 hybridization ratio in amorphous carbon from C 1s core-level shifts: X-ray photoelectron spectroscopy and first-principles calculation

    NASA Astrophysics Data System (ADS)

    Haerle, Rainer; Riedo, Elisa; Pasquarello, Alfredo; Baldereschi, Alfonso

    2002-01-01

    Using a combined experimental and theoretical approach, we address C 1s core-level shifts in amorphous carbon. Experimental results are obtained by x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) on thin-film samples of different atomic density, obtained by a pulsed-laser deposition growth process. The XPS spectra are deconvoluted into two contributions, which are attributed to sp2- and sp3-hybridized atoms, respectively, separated by 0.9 eV, independent of atomic density. The sp3 hybridization content extracted from XPS is consistent with the atomic density derived from the plasmon energy in the EELS spectrum. In our theoretical study, we generate several periodic model structures of amorphous carbon of different densities applying two schemes of increasing accuracy in sequence. We first use a molecular-dynamics approach, based on an environmental-dependent tight-binding Hamiltonian to quench the systems from the liquid phase. The final model structures are then obtained by further atomic relaxation using a first-principles pseudopotential plane-wave approach within density-functional theory. Within the latter framework, we also calculate carbon 1s core-level shifts for our disordered model structures. We find that the shifts associated to threefold- and fourfold- coordinated carbon atoms give rise to two distinct peaks separated by about 1.0 eV, independent of density, in close agreement with experimental observations. This provides strong support for decomposing the XPS spectra into two peaks resulting from sp2- and sp3-hybridized atoms. Core-hole relaxations effects account for about 30% of the calculated shifts.

  9. A poly-epoxy surface explored by Hartree-Fock ΔSCF simulations of C1s XPS spectra

    NASA Astrophysics Data System (ADS)

    Gavrielides, A.; Duguet, T.; Esvan, J.; Lacaze-Dufaure, C.; Bagus, P. S.

    2016-08-01

    Whereas poly-epoxy polymers represent a class of materials with a wide range of applications, the structural disorder makes them difficult to model. In the present work, we use good experimental model samples in the sense that they are pure, fully polymerized, flat and smooth, defect-free, and suitable for ultrahigh vacuum x-ray photoelectron spectroscopy, XPS, experiments. In parallel, we perform Hartree-Fock, HF, calculations of the binding energies, BEs, of the C1s electrons in a model molecule composed of the two constituents of the poly-epoxy sample. These C1s BEs were determined using the HF ΔSCF method, which is known to yield accurate values, especially for the shifts of the BEs, ΔBEs. We demonstrate the benefits of combining rigorous theory with careful XPS measurements in order to obtain correct assignments of the C1s XPS spectra of the polymer sample. Both the relative binding energies—by the ΔSCF method—and relative intensities—in the sudden approximation, SA, are calculated. It results in an excellent match with the experimental spectra. We are able to identify 9 different chemical environments under the C1s peak, where an exclusively experimental work would have found only 3 contributions. In addition, we observe that some contributions are localized at discrete binding energies, whereas others allow a much wider range because of the variation of their second neighbor bound polarization. Therefore, HF-ΔSCF simulations significantly increase the spectral resolution of XPS and thus offer a new avenue for the exploration of the surface of polymers.

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

    PubMed

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

    2010-05-07

    We present an approach for the simulation of time resolved photoelectron spectra based on the combination of the ab initio nonadiabatic molecular dynamics "on the fly" with the Stieltjes imaging method utilizing discrete neutral states above the ionization limit for the approximate description of the ionization continuum. Our approach has been implemented in the framework of the time-dependent density functional theory and has been applied to interrogate the ultrafast internal conversion between the S(2) and S(1) states in pyrazine. The simulations reveal that, parallel to the S(2)-->S(1) internal conversion, a change in the dominant ionization process (S(2)-->D(1) versus S(1)-->D(0)) occurs on the time scale of 20 fs such that no significant change in the photoelectron kinetic energy distribution is observed. The presented results are in full agreement with the experimental results presented in the accompanying paper [Suzuki et al., J. Chem. Phys. 132, 174302 (2010)] and provide an insight into the interplay between the nonradiative relaxation and the photoionization process in pyrazine as reflected in the time resolved photoelectron spectrum. Our approach represents a general tool for the investigation of ultrafast photoionization processes in complex systems and thus can be used to investigate the ultrafast femtochemistry of complex molecular systems including all degrees of freedom.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Interpretation of the photoelectron spectra of FeS(2)(-) by a multiconfiguration computational approach.

    PubMed

    Clima, Sergiu; Hendrickx, Marc F A

    2007-11-01

    The ground states of FeS(2) and FeS(2)(-), and several low-lying excited electronic states of FeS(2) that are responsible for the FeS(2)(-) photoelectron spectrum, are calculated. At the B3LYP level an open, quasi-linear [SFeS](-) conformation is found as the most stable structure, which is confirmed at the ab initio CASPT2 computational level. Both the neutral and the anionic unsaturated complexes possess high-spin electronic ground states. For the first time a complete assignment of the photoelectron spectrum of FeS(2)(-) is proposed. The lowest energy band in this spectrum is ascribed to an electron detachment from the two highest-lying 3dpi antibonding orbitals (with respect to the iron-sulfur bonding) of iron. The next-lowest experimental band corresponds to an electron removal from nonbonding, nearly pure sulfur orbitals. The two highest bands in the spectra are assigned as electron detachments from pi and sigma bonding mainly sulfur orbitals.

  17. [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.

  18. 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)].

  19. Ultraviolet photoelectron spectra of C 76 and K xC 76

    NASA Astrophysics Data System (ADS)

    Hino, Shojun; Matsumoto, K.; Hasegawa, Shinji; Inokuchi, Hiroo; Morikawa, Takashi; Takahashi, Takashi; Seki, Kazuhiko; Kikuchi, Koichi; Suzuki, Shinzo; Ikemoto, Isao; Achiba, Yohji

    1992-09-01

    Ultraviolet photoelectron spectra of C 76, one of the fullerene family of compounds, have been measured with a synchroton radiation light source. The photoemission spectral onset is 1.3 eV below the Fermi level, which is equal to that of C 84 but is about 0.5 eV smaller than that of C 60 or C 70. The relative intensity of the photoemission spectral features is independent of the incident photon energy change. Photoemission spectral changes for C 76 during potassium dosing are also measured. A new band becomes distinct between the Fermi level and the HOMO band, when the potassium content ( x in K xC 76) is equal to or greater than 1.1. The spectral onset moves toward the Fermi level with increasing potassium dosage, approaching it but never crossing it. This indicates that potassium-dosed C 76 could be a narrow gap semiconductor.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Photoelectron Imaging Spectra of O2(-)·VOC and O4(-)·VOC Complexes.

    PubMed

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

    2016-10-13

    The anion photoelectron imaging spectra of O2(-)·VOC and O4(-)·VOC (VOC = hexane, isoprene, benzene, and benzene-d6) complexes measured using 3.49 eV photon energy, along with the results of ab initio and density functional theory results are reported and analyzed. Photodetachment of these anionic complexes accesses neutrals that model collision complexes, offering a probe of the effects of symmetry-breaking collision events on the electronic structure of normally transparent neutral molecules. The energies of O2(-)·VOC spectral features compared to the bare O2(-) indicate that photodetachment of the anion accesses a modestly repulsive region of the O2-VOC potential energy surface, with subtle VOC dependence on the relative energies of the O2 (X (3)Σg(-))·VOC ground state and O2 (a (1)Δg)·VOC excited state. In contrast, a significantly higher intensity of the transition to the O2 (a (1)Δg)·VOC excited state relative to the O2 (X (3)Σg(-))·VOC ground state is observed for VOC = benzene, with a less pronounced effect observed for VOC = isoprene. Similar spectral effects are observed in the O4(-)·benzene and O4(-)·isoprene PE spectra. Several explanations are considered, with involvement of a temporary anion state emerging as the most plausible.

  5. 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].

  6. 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.

  7. 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…

  8. 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…

  9. 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.

  10. Vibrational branching ratios in the photoelectron spectra of N2 and CO: interference and diffraction effects.

    PubMed

    Plésiat, Etienne; Decleva, Piero; Martín, Fernando

    2012-08-21

    We present a detailed account of existing theoretical methods specially designed to provide vibrationally resolved photoionization cross sections of simple molecules within the Born-Oppenheimer approximation, with emphasis on newly developed methods based on density functional theory. The performance of these methods is shown for the case of N(2) and CO photoionization. Particular attention is paid to the region of high photon energies, where the electron wavelength is comparable to the bond length and, therefore, two-center interferences and diffraction are expected to occur. As shown in a recent work [Canton et al., Proc. Natl. Acad. Sci. U. S. A., 2011, 108, 7302-7306], the main experimental difficulty, which is to extract the relatively small diffraction features from the rapidly decreasing cross section, can be easily overcome by determining ratios of vibrationally resolved photoelectron spectra and existing theoretical calculations. From these ratios, one can thus get direct information about the molecular geometry. In this work, results obtained in a wide range of photon energies and for many different molecular orbitals of N(2) and CO are discussed and compared with the available experimental measurements. From this comparison, limitations and further possible improvements of the existing theoretical methods are discussed. The new results presented in the manuscript confirm that the conclusions reported in the above reference are of general validity.

  11. 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.

  12. 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.

  13. 4d{sup -1} photoelectron spectra and subsequent N{sub 4,5}OO Auger electron spectra of atomic Sb

    SciTech Connect

    Patanen, M.; Heinaesmaeki, S.; Urpelainen, S.; Aksela, S.; Aksela, H.

    2010-05-15

    4d{sup -1} photoelectron and subsequent N{sub 4,5}OO Auger electron spectra of Sb have been measured using synchrotron radiation. Features created by an open shell electronic structure of atomic Sb in the spectra have been interpreted using multiconfigurational Dirac-Fock calculations. The results are compared with the molecular Sb{sub 4} and the comparison shows that the relaxation pathways of the hole states in atomic and molecular Sb are very different, so that different groups of states are populated in the corresponding Auger spectra.

  14. 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.

  15. Matrix effects in the C 1s photoabsorption spectra of condensed naphthalene

    NASA Astrophysics Data System (ADS)

    Schmidt, Norman; Wenzel, Jan; Dreuw, Andreas; Fink, Rainer H.; Hieringer, Wolfgang

    2016-12-01

    High-resolution C 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of naphthalene are investigated. By comparing the spectral signatures of condensed naphthalene molecules with those of naphthalene in the gas phase, we are able to unambiguously identify spectral features which are affected by the intermolecular interactions in the condensed phase. With the help of calculations using time-dependent density-functional theory and the second-order algebraic-diagrammatic construction scheme for the polarization propagator, resonances in the relevant energy range can be assigned to valence and Rydberg-like excitations. Thus, we obtain a more detailed identification of NEXAFS resonances beyond the present literature.

  16. 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.

  17. The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

    SciTech Connect

    Vall-llosera, G.; Gao, B.; Kivimaeki, A.; Coreno, M.; Alvarez Ruiz, J.; Simone, M. de; Aagren, H.; Rachlew, E.

    2008-01-28

    Near edge x-ray absorption fine structure spectra have been measured and interpreted by means of density functional theory for five different azabenzenes (pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine) in the gas phase. The experimental and theoretical spectra at the N 1s and C 1s edges show a strong resonance assigned to the transition of the 1s electron in the respective N or C atoms to the lowest unoccupied molecular orbital with {pi}* symmetry. As opposed to the N 1s edge, at the C 1s edge this resonance is split due to the different environments of the core hole atom in the molecule. The shift in atomic core-level energy due to a specific chemical environment is explained with the higher electronegativity of the N atom compared to the C atom. The remaining resonances below the ionization potential (IP) are associated to {sigma} or {pi} orbitals with mixed valence/Rydberg character. Upon N addition, a reduction of intensity is observed in the Rydberg region at both edges as compared to the intensity in the continuum. Above the IP one or more resonances are seen and ascribed here to transitions to {sigma}* orbitals. Calculating the experimental and theoretical {delta}{sub {pi}} term values at both edges, we observe that they are almost the same within {+-}1 eV as expected for isoelectronic bonded pairs. The term values of the {pi}* and {sigma}* resonances are discussed in terms of the total Z number of the atoms participating in the bond.

  18. 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.

  19. Measurement of magnetic field aligned potential differences using high resolution conjugate photoelectron energy spectra

    NASA Technical Reports Server (NTRS)

    Peterson, W. K.; Doering, J. P.; Potemra, T. A.; Bostrom, C. O.; Brace, L. H.; Heelis, R. A.; Hanson, W. B.

    1977-01-01

    Simultaneous high-resolution observations of a distinctive feature in the energy spectrum of conjugate photoelectrons and spacecraft potential relative to the local ionosphere have allowed the net potential difference between magnetic conjugate points at latitudes below the region of low-energy (i.e., lower than 100 eV) auroral electron precipitation to be determined. Measurements made at 300 km from Atmosphere Explorer C show that there is normally no net potential difference between hemispheres in this region, which extended up to invariant latitudes as high as 74 deg. Two types of apparently related anomalous behavior were infrequently observed at high latitudes. During these periods the incident flux of conjugate photoelectrons was either decelerated by about 3 eV or was not detected.

  20. 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.

  1. 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.

  2. 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.

  3. Theoretical Analysis of Photoelectron Spectra of Pure and Mixed Metal Clusters: Disentangling Size, Structure, and Composition Effects

    DOE PAGES

    Acioli, Paulo H.; Jellinek, Julius

    2017-07-14

    A theoretical/computational description and analysis of the spectra of electron binding energies of Al12-, Al13- and Al12Ni- clusters, which differ in size and/or composition by a single atom yet possess strikingly different measured photoelectron spectra, is presented. It is shown that the measured spectra can not only be reproduced computationally with quantitative fidelity – this is achieved through a combination of state-of-the-art density functional theory with a highly accurate scheme for conversion of the Kohn-Sham eigenenergies into electron binding energies – but also explained in terms of the effects of size, structure/symmetry and composition. Furthermore, a new methodology is developedmore » and applied that provides for disentanglement and differential assignment of the separate roles played by size, structure/symmetry and composition in defining the observed differences in the measured spectra. The methodology is general and applicable to any finite system, homogeneous or heterogeneous. Finally, we project that in combination with advances in synthesis techniques this methodology will become an indispensable computation-based aid in the design of controlled synthesis protocols for manufacture of nanosystems and nanodevices with precisely desired electronic and other characteristics.« less

  4. 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

  5. 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.

  6. Valence photoelectron spectra of alkali bromides calculated within the propagator theory.

    PubMed

    Karpenko, Alexander; Iablonskyi, Denys; Aksela, Helena

    2013-04-28

    The valence ionization spectra covering the binding energy range 0-45 eV of alkali bromide XBr (X = Li, Na, K, Rb) vapors are studied within the framework of the propagator theory. Relativistic Algebraic Diagrammatic Construction calculations have been carried out in order to investigate photoionization processes and to describe molecular electronic structure. Theoretical results are compared with available experimental data.

  7. 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.

  8. Induced-field enhancement of band-structure effects in photoelectron spectra from Al surfaces by ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Ríos Rubiano, C. A.; Della Picca, R.; Mitnik, D. M.; Silkin, V. M.; Gravielle, M. S.

    2017-03-01

    The electron emission produced by the grazing incidence of ultrashort laser pulses on two faces of aluminum, Al(100) and Al(111), is investigated using the band-structure-based-Volkov (BSB-V) approximation. The present version of the BSB-V approach includes not only a realistic description of the surface interaction, accounting for band-structure effects, but also effects due to the induced potential that originates from the collective response of valence electrons to the external electromagnetic field. For both crystallographic orientations we found that the induced potential contributes to the emergence of band-structure signatures in the near-threshold region of photoelectron spectra. This result opens a window to scrutinize band-structure effects in metal surfaces via ultrashort-laser interactions.

  9. 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

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

    PubMed

    Taucher, Thomas C; Hehn, Iris; Hofmann, Oliver T; Zharnikov, Michael; Zojer, Egbert

    2016-02-18

    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.

  11. 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.

  12. 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

  13. 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.

  14. Determination of the absolute carrier-envelope phase by angle-resolved photoelectron spectra of Ar by intense circularly polarized few-cycle pulses

    NASA Astrophysics Data System (ADS)

    Fukahori, Shinichi; Ando, Toshiaki; Miura, Shun; Kanya, Reika; Yamanouchi, Kaoru; Rathje, Tim; Paulus, Gerhard G.

    2017-05-01

    The angle-resolved photoelectron spectra of Ar are recorded using intense circularly polarized near-infrared few-cycle laser pulses, and the effect of the depletion of Ar atoms by the ionization and the effect of the Coulombic potential are examined by the classical trajectory Monte Carlo simulations. On the basis of the comparison between the experimental and theoretical photoelectron spectra, a procedure for estimating the absolute carrier-envelope phase (CEP) of the few-cycle laser pulses interacting with atoms and molecules is proposed. It is confirmed that the absolute CEP can securely be estimated without any numerical calculations once the angular distribution of the yield of photoelectrons having the kinetic energy larger than 30 eV is measured with the peak laser intensity in the range between 1 ×1014 and 5 ×1014W /c m2 .

  15. Theoretical studies of photoelectron spectra of SO42-(H2O)n clusters and the extrapolation to bulk solution

    NASA Astrophysics Data System (ADS)

    Zhan, Chang-Guo; Zheng, Fang; Dixon, David A.

    2003-07-01

    Photoelectron spectra of hydrated doubly charged anion clusters, SO42-(H2O)n, have been studied by performing first-principles electronic structure calculations on SO42-(H2O)n (n=3-6, 12, and 13). The calculated adiabatic electron ionization energies are in good agreement with available experimental data. A detailed analysis of the calculated results suggests that for n⩾12 the observed threshold ionization energy of the low binding energy band in the recently reported photoelectron spectra of SO42-(H2O)n is associated with the electron ionization from the solute, SO42-, whereas the observed threshold ionization energy of the high binding energy band is associated with the electron ionization from the water molecules in the first solvation shell of SO42-. For n⩽6, both threshold ionization energies of the low and high binding energy bands are all associated with the electron ionizations from the solute. This shows that the bulk solution value (n→∞) extrapolated from those threshold ionization energies of the high binding energy band of the clusters should refer to the first ionization energy of the water molecules in the first solvation shell of SO42- in aqueous solution and, therefore, should be significantly smaller than the measured threshold ionization energy of liquid water. This differs from the recent result that the value of 10.05 eV extrapolated from the threshold ionization energies of the high binding energy band based on a simple 1/Rc model was nearly identical to the measured threshold ionization energy (10.06 eV) of liquid water. To address this difference, we have used a new approach for the extrapolation of solvated ion cluster data to bulk solution. We show that the new extrapolation approach consistently produces extrapolated bulk solution results in significantly better agreement with those observed directly in bulk solution for the first ionization energies of the ions in SO42-(H2O)n, Br-(H2O)n, and I-(H2O)n. The same extrapolation

  16. Theoretical studies on the photoelectron and absorption spectra of MnO4(-) and TcO4(-).

    PubMed

    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-EOM-CCSD(T) result in the literature. Combining our CCSD(T) and CR-EOM-CCSD(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 RAS-PT2 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.

  17. 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.

  18. Liquid-Jet X-ray Photoelectron Spectra of TiO(2) Nanoparticles in an Aqueous Electrolyte Solution.

    PubMed

    Makowski, Michael J; Galhenage, Randima P; Langford, Joel; Hemminger, John C

    2016-05-05

    Titania has attracted significant interest due to its broad catalytic applications, many of which involve titania nanoparticles in contact with aqueous electrolyte solutions. Understanding the titania nanoparticle/electrolyte interface is critical for the rational development of such systems. Here, we have employed liquid-jet ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to investigate the solid/electrolyte interface of 20 nm diameter TiO2 nanoparticles in 0.1 M aqueous nitric acid solution. The Ti 2p line shape and absolute binding energy reflect a fully oxidized stoichiometric titania lattice. Further, by increasing the X-ray excitation energy, the difference in O 1s binding energies between that of liquid water (O 1sliq) and the titania lattice (O 1slat) oxygen was measured as a function of probe depth into the particles. The titania lattice, O 1slat, binding energy decreases by 250 meV when probing from the particle surface into the bulk. This is interpreted as downward band bending at the interface.

  19. 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

  20. 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

  1. 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.

  2. Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra

    SciTech Connect

    Bravaya, Ksenia B.; Kostko, Oleg; Dolgikh, Stanislav; Landau, Arie; Ahmed, Musahid; Krylov, Anna I.

    2010-08-02

    We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed using equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the {omega}B97X-D functional. The ionization-induced geometry changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series G > C > A > T, the respective relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 eV for A,T,C and G, respectively) agree well with the onsets of the photoionization efficiency (PIE) curves (8.20 {+-} 0.05, 8.95 {+-} 0.05, 8.60 {+-} 0.05 and 7.75 {+-} 0.05 eV). Vibrational progressions for the S{sub 0}-D{sub 0} vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Monitoring non-adiabatic dynamics in CS2 with time- and energy-resolved photoelectron spectra of wavepackets

    NASA Astrophysics Data System (ADS)

    Wang, Kwanghsi; McKoy, Vincent; Hockett, Paul; Stolow, Albert; Schuurman, Michael S.

    2017-09-01

    We report results from a novel fully ab initio method for simulating the time-resolved photoelectron angular distributions around conical intersections in CS2. The technique employs wavepacket densities obtained with the multiple spawning method in conjunction with geometry- and energy-dependent photoionization matrix elements. The robust agreement of the calculated molecular-frame photoelectron angular distributions with measured values for CS2 demonstrates that this approach can successfully illuminate, and disentangle, the underlying coupled nuclear and electronic dynamics around conical intersections in polyatomic molecules.

  9. 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.

  10. 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].

  11. 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.

  12. 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.

  13. Derivation of Hamaker Dispersion Energy of Amorphous Carbon Surfaces in Contact with Liquids Using Photoelectron Energy-Loss Spectra

    NASA Astrophysics Data System (ADS)

    Godet, Christian; David, Denis

    2017-08-01

    Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ɛ (q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged <ɛ (q, ω) > q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) < Im[-1/ɛ (q, ω)] > q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A 132 (L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A 132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H 0 CVL = (H 0 CVC H 0 LVL )1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for A CVL, A CLC and A CLV values as a function of A CVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, {γ}_{CV}^d , and a guess value of the cutoff distance H 0 CVC of the solid. [Figure not available: see fulltext.

  14. Theoretical simulations of structure and X-ray photoelectron spectra of glycine and diglycine adsorbed on Cu(110).

    PubMed

    Carravetta, Vincenzo; Monti, Susanna; Li, Cui; Ågren, Hans

    2013-08-13

    The study of adsorption of glycine and glycylglycine (or diglycine) on a copper surface is an important step for the comprehension of mechanisms that determine the stability of biological functionalizers on metal substrates. These two molecules can be considered as prototypes and essential models to investigate, theoretically and experimentally, the adaptability of flexible short peptide chains to a definite interface. In this work, we have improved and updated earlier molecular dynamics simulations by including reactivity of the various species and the comparison of ab initio calculated C, N, and O core photoelectron chemical shifts with the ones found in previous studies. New diglycine-copper bonding is predicted, and the results of the chemical shift analysis are, in all cases, fully compatible with structural information obtained through experimental measurements. Moreover, we have found that the process of proton transfer, which is fundamental in the dynamics of amino acids and peptides, occurs mainly by intermolecular interaction between the first and second layer of the adsorbate.

  15. Rotationally resolved S1<-- S0 electronic spectra of fluorene, carbazole, and dibenzofuran: evidence for Herzberg-Teller coupling with the S2 state.

    PubMed

    Yi, John T; Alvarez-Valtierra, Leonardo; Pratt, David W

    2006-06-28

    Rotationally resolved fluorescence excitation spectra of the S1 <-- S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1 <-- S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.

  16. 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.

  17. Metal-ion Complexation Effects in C 1s-NEXAFS Spectra of Carboxylic Acids—Evidence by Quantum Chemical Calculations

    SciTech Connect

    Armbruster, M.; Schimmelpfennig, B; Plaschke, M; Rothe, J; Denecke, M; Klenze, R

    2009-01-01

    Previous systematic C 1s-NEXAFS studies carried out for humic acid (HA) loaded with polyvalent metal cations (Mn+) reveal spectral features which were postulated to result from metal ion complexation: a strong decrease of the C 1s (COO-) ? p*Cdouble bond; length as m-dashO transition intensity and the appearance of a new absorption feature at slightly lower energy adjacent to the carboxyl resonance. Although spectroscopic results for the Mn+-PAA (polyacrylic acid) system (selected as model for structurally ill-defined HA) reveal the same spectral features, evidence by an independent approach for interpretation of these features is desirable. It is well established that quantum chemical calculations are capable of reproducing transition features in C 1s core excitation spectra of small organic molecules, e.g., acetate, which is chosen here as a fragment containing the complexing group to model the macromolecular HA and PAA systems. In this study, the RI-ADC(2) approach, as implemented in the TURBOMOLE program package, is applied to calculate vertical core excitation spectra of various metal acetates and the acetate anion. An energy shift (?f) between the C 1s (COO-) ? p*Cdouble bond; length as m-dashO transition of the acetate anion and various metal cation acetates is established. Calculated shifts are very similar to the experimentally observed values for the energy difference between the C 1s (COO-) ? p*Cdouble bond; length as m-dashO peak and the absorption feature appearing after metal ion complexation in Mn+-PAA/PAA. According to our computations, structural changes of the acetate complexes (e.g., the O-CeO bond angle) compared to the free acetate anion are predominantly responsible for the spectral changes observed upon metal ion complexation.

  18. From photoelectron detachment spectra of BrHBr-, BrDBr- and IHI-, IDI- to vibrational bonding of BrMuBr and IMuI

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Photoelectron detachment XLX-(0000) + hν → XLX(vib) + e- + KER (X = Br or I, L = H or D) at sufficiently low temperatures photoionizes linear dihalogen anions XLX- in the vibrational ground state (v1v2lv3 = 0000) 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-(0000) 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 EXLX,vib of states XLX(vib) which are centered at linear transition state. The corresponding vibrational quantum numbers may be labeled vib = (v1v2lv3) = (000v3). Accordingly, the related most prominent peaks in the pds are labeled v3. We construct a model PES which mimics the "true" PES in the domain of transition state such that it supports vibrational states with energies EXLX,pds,000v3 close to the peaks of the pds labeled v3 = 0, 2, and 4. Subsequently, the same model PES is also used to calculate approximate values of the energies EXMuX,0000 of the isotopomers XMuX(0000). For the heavy isotopomers XHX and XDX, it turns out that all energies EXLX,000v3 are above the threshold for dissociation, which means that all heavy XLX(000v3) with wavefunctions centered at the transition state are unstable resonances with finite lifetimes. Turning the table, bound states of the heavy XLX are van der Waals (vdW) bonded. In contrast, the energies EXMuX,0000 of the light isotopomers XMuX(0000) are below the threshold for dissociation, with wavefunctions centered at the transition state. This

  19. 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}

  20. Revisiting Vibrational Circular Dichroism Spectra of (S)-(+)-Carvone and (1S,2R,5S)-(+)-Menthol Using SimIR/VCD Method.

    PubMed

    Shen, Jian; Li, Yi; Vaz, Roy; Izumi, Hiroshi

    2012-08-14

    The VCD spectra of (S)-(+)-carvone and (1S,2R,5S)-(+)-menthol are recalculated using the DFT method with extended conformation and configuration spaces. The calculated individual and averaged spectra are compared against observed ones using the previously reported similarity index, SV. It is found that the SV population forms approximately two normal distributions, depending on whether a spectrum matches the observed one or not. This statistical character can be used to estimate the error in absolute configuration (AC) assessments. To avoid erroneous AC assignments and incomplete conformation searching, it is advisible to employ a minimum |SV| of 0.2 and maximize it using conformation averaging. It is demonstrated that this approach is suitable and robust for flexible chiral molecules.

  1. Theoretical studies on the electronic structures and photoelectron spectra of tri-rhenium oxide clusters: Re3On- and Re3On (n = 1-6)

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  2. Theoretical characterization of four distinct isomer types in hydrated-electron clusters, and proposed assignments for photoelectron spectra of water cluster anions.

    PubMed

    Jacobson, Leif D; Herbert, John M

    2011-12-14

    Water cluster anions, (H(2)O)(N)(-), are examined using mixed quantum/classical molecular dynamics based on a one-electron pseudopotential model that incorporates many-body polarization and predicts vertical electron detachment energies (VDEs) with an accuracy of ~0.1 eV. By varying the initial conditions under which the clusters are formed, we are able to identify four distinct isomer types that exhibit different size-dependent VDEs. On the basis of a strong correlation between the electron's radius of gyration and its optical absorption maximum, and extrapolating to the bulk limit (N → ∞), our analysis supports the assignment of the "isomer Ib" data series, observed in photoelectron spectra of very cold clusters, as arising from cavity-bound (H(2)O)(N)(-) cluster isomers. The "isomer I" data reported in warmer experiments are assigned to surface-bound isomers in smaller clusters, transitioning to partially embedded isomers in larger clusters. The partially embedded isomers are characterized by a partially formed solvent cavity at the cluster surface, and they are spectroscopically quite similar to internalized cavity isomers. These assignments are consistent with various experimental data, and our theoretical characterization of these isomers sheds new light on a long-standing assignment problem. © 2011 American Chemical Society

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    PubMed

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

    2013-05-15

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaW2O9(-) cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the W3O9(+) cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Rotationally resolved vibrational spectra of AsH3 (+)X̃(2)A2 (″): Tunneling splittings studied by zero-kinetic-energy photoelectron spectroscopy.

    PubMed

    Sun, Wei; Dai, Zuyang; Wang, Jia; Mo, Yuxiang

    2016-06-21

    The rotationally resolved vibrational spectra of AsH3 (+)X̃(2)A2 (″) have been measured for the first time with vibrational energies up to 6000 cm(-1) above the ground state using the zero-kinetic-energy photoelectron method. The symmetric inversion vibrational energy levels (v2 (+)) and the corresponding rotational constants for v2 (+)=0-15 have been determined. The tunneling splittings of the inversion vibration energy levels have been observed and are 0.8 and 37.7 (±0.5) cm(-1) for the ground and the first excited vibrational states, respectively. The first adiabatic ionization energy for AsH3 was determined as 79 243.3 ± 1 cm(-1). The geometric parameters of AsH3 (+)X̃(2)A2 (″) as a function of inversion vibrational numbers have been determined, indicating that the geometric structure of the cation changes from near-planar to pyramidal with increasing inversion vibrational excitation. In addition to the experimental measurements, a two-dimensional theoretical calculation considering the two symmetric vibrational modes was performed to determine the energy levels of the symmetric inversion, which are in good agreement with the experimental results. The inversion vibrational energy levels of SbH3 (+)X̃(2)A2 (″) have also been calculated and are found to have much smaller energy splittings than those of AsH3 (+)X̃(2)A2 (″).

  6. 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.

  7. 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

  8. Numerical Method for Inverting 1s2p Resonant Inelastic X-ray Scattering Spectra: Interpretation of Hidden Electronic Excitations in CuO

    SciTech Connect

    Dräger, G.; Machek, P

    2009-01-01

    Direct inversion of resonant inelastic x-ray scattering spectra (RIXSS) has been carried out using a numerical method for solving first-kind Fredholm integral equations. Hereby, the oscillator strength distribution (OSD), which is proportional to the empty density of states at the absorption edge, has been obtained from the experimental Cu 1s2p RIXSS of CuO. In particular, the inversion of RIXSS measured at incident energies below the K level threshold provides OSD having a better resolution than it can be achieved with one of the customary x-ray absorption near-edge structure spectroscopies. This can be explained by the virtual character of the intermediate states at low energy excitation. By means of the presented method a so-called 'hidden electronic excitation' of CuO has been identified as a very weak core excitation. Furthermore, numerical interpretation of polarized spectra has revealed the py-like character of the excited states in a suitable local reference frame. The obtained results are promising for further applications of the method, preferred in the field of strongly correlated materials.

  9. Photoelectron Spectroscopy of Doped Helium Nanodroplets

    SciTech Connect

    Loginov, Evgeniy; Rossi, Dominic; Drabbels, Marcel

    2005-10-14

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

  10. Ultrafast Dynamics in Postcollision Interaction after Multiple Auger Decays in Argon 1s Photoionization

    NASA Astrophysics Data System (ADS)

    Guillemin, R.; Sheinerman, S.; Bomme, C.; Journel, L.; Marin, T.; Marchenko, T.; Kushawaha, R. K.; Trcera, N.; Piancastelli, M. N.; Simon, M.

    2012-07-01

    Argon 1s photoionization followed by multiple Auger decays is investigated both experimentally, by means of photoelectron-ion coincidences, and theoretically. A strong influence of the different Auger decays on the photoelectron spectra is observed through postcollision interaction which shifts the maximum of the energy distribution and distorts the spectral shape. A good agreement between the calculated and measured spectra for selected Arn+ ions (n=1-5) allows one to estimate the widths (lifetimes) of the intermediate states for each specific decay pathway.

  11. Site-specific fragmentation caused by core-level photoionization in F(3)SiCH(2)CH(2)Si(CH(3))(3) vapor: comparison between Si:1s and 2p photoionizations by means of photoelectron-photoion-photoion triple-coincidence spectroscopy.

    PubMed

    Nagaoka, Shin-ichi; Takemoto, Mai; Prümper, Georg; Fukuzawa, Hironobu; Tamenori, Yusuke; Suzuki, Isao H; Ueda, Kiyoshi

    2008-11-28

    Site-specific fragmentation caused by Si:1s and 2p core-level photoionizations in F(3)SiCH(2)CH(2)Si(CH(3))(3) vapor was studied by energy-selected-photoelectron photoion-photoion triple-coincidence spectroscopy. The difference between the chemical shifts of the two Si sites is larger for the 1s ionization than for the 2p (2s) ionization. The fragmentation caused by the Si:1s ionization is more violent than that caused by the Si:2p ionization. The ions and ion pairs showing high site specificity for the Si:1s ionization belong to small fragments compared to those in the Si:2p ionization. Criteria for high site-specificity in fragmentation are discussed in conjunction with the present results.

  12. 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.

  13. A General Approach for Calculating Strongly Anharmonic Vibronic Spectra with a High Density of States: The X2B1 <- X1A1 Photoelectron Spectrum of Difluoromethane.

    PubMed

    Petrenko, Taras; Rauhut, Guntram

    2017-09-22

    Due to a low lying fragmentation channel the X2B1 <- X1A1 photoelectron spectrum of difluoromethane is dominated by strong anharmonicity effects. We have used a time-independent eigenstate-free Raman wave function approach (RWF) to calculate the entire spectrum. Vibronic transitions with the most significant Franck-Condon factors were determined by employing our recently developed residual-based algorithm for the calculation of eigenpairs (RACE). An analysis of the factors controlling the accuracy of the predicted bandshape is provided. The calculated spectrum is in very close agreement with experimental results.

  14. 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

  15. 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.

  16. Accurate Retrieval of Structural Information from Laser-Induced Photoelectron and High-Order Harmonic Spectra by Few-Cycle Laser Pulses

    NASA Astrophysics Data System (ADS)

    Morishita, Toru; Le, Anh-Thu; Chen, Zhangjin; Lin, C. D.

    2008-01-01

    By analyzing accurate theoretical results from solving the time-dependent Schrödinger equation of atoms in few-cycle laser pulses, we established the general conclusion that laser-generated high-energy electron momentum spectra and high-order harmonic spectra can be used to extract accurate differential elastic scattering and photo-recombination cross sections of the target ion with free electrons, respectively. Since both electron scattering and photoionization (the inverse of photo-recombination) are the conventional means for interrogating the structure of atoms and molecules, this result implies that existing few-cycle infrared lasers can be implemented for ultrafast imaging of transient molecules with temporal resolution of a few femtoseconds.

  17. 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.

  18. Rotationally resolved S1<--S0 electronic spectra of fluorene, carbazole, and dibenzofuran: Evidence for Herzberg-Teller coupling with the S2 state

    NASA Astrophysics Data System (ADS)

    Yi, John T.; Alvarez-Valtierra, Leonardo; Pratt, David W.

    2006-06-01

    Rotationally resolved fluorescence excitation spectra of the S1←S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1←S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.

  19. 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.

  20. 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.

  1. Experimental and ab-initio calculated vcd spectra of the first OH-stretching overtone of (1R)-(-) and (1S)-(+)-endo-BORNEOL.

    PubMed

    Gangemi, Fabrizio; Gangemi, Roberto; Longhi, Giovanna; Abbate, Sergio

    2009-04-21

    The near infrared (NIR) absorption and NIR-vibrational circular dichroism (NIR-VCD) spectra of dilute solutions of the two enantiomers of endo-borneol have been measured in the first OH-stretching overtone region (1600-1300 nm). By density functional theory (DFT) we calculate mechanical parameters, i.e. the harmonic mechanical frequency and the anharmonicity constant for the OH stretching, and anharmonic electrical parameters; i.e. the dependence on OH-bond length of atomic polar tensors and atomic axial tensors. We evaluate transition integrals for the calculations of rotational and dipole strengths by Morse anharmonic wavefunctions depending on mechanical harmonic frequencies and mechanical anharmonicity parameters that are calculated ab initio. Experimental and calculated spectra compare quite well and this fact allows us to associate differently signed NIR-VCD features with different conformational states of the OH-bond. Absorption features for the fundamental and for the second overtone of the OH stretching are also compared with experiment.

  2. 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.

  3. 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.

  4. 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).

  5. 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

  6. 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

  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. 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.

  9. 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. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. 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.

  11. X-ray induced damage in DNA monitored by X-ray photoelectron spectroscopy.

    PubMed

    Ptasińska, Sylwia; Stypczyńska, Agnieszka; Nixon, Tony; Mason, Nigel J; Klyachko, Dimitri V; Sanche, Léon

    2008-08-14

    In this work, the chemical changes in calf thymus DNA samples were analyzed by X-ray photoelectron spectroscopy (XPS). The DNA samples were irradiated for over 5 h and spectra were taken repeatedly every 30 min. In this approach the X-ray beam both damages and probes the samples. In most cases, XPS spectra have complex shapes due to contributions of C, N, and O atoms bonded at several different sites. We show that from a comparative analysis of the modification in XPS line shapes of the C 1s, O 1s, N 1s, and P 2p peaks, one can gain insight into a number of reaction pathways leading to radiation damage to DNA.

  12. 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.

  13. 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.

  14. High-Resolution Photoelectron and Photoionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Merkt, F.

    2012-06-01

    Since its development in the late 1950s and early 1960s, photoelectron spectroscopy has established itself as an important method to study the electronic structure of molecules, their photoionization dynamics, and the structure and dynamics of molecular cations. In recent years, and particularly since the development of pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy, considerable progress has been made in the resolution that can be achieved by photoelectron spectroscopy. This progress relies on the systematic exploitation of the unusual physical properties of high Rydberg states and enables one today to resolve the rotational structure in the photoelectron spectra of even large molecules and the hyperfine structure in the photoelectron spectra of small molecules. This talk will begin with a brief historical review of photoelectron spectroscopy. Then, the relationship between photoelectron spectroscopy, photoionization spectroscopy and the spectroscopy of high Rydberg states will be discussed. It will be explained how this relationship is currently exploited to improve the resolution achievable by PFI-ZEKE photoelectron spectroscopy. Then, the physical principles that are at the heart of the latest methods related to high-resolution photoelectron spectroscopy will be described together with their fundamental limitations. Depending on the resolution and the spectral range needed to address a specific scientific problem, a choice can be made between several different methods with spectral resolutions ranging from 30 GHz to better than 1 MHz. The talk will summarize the current state of the art in gas-phase photoelectron spectroscopy and be illustrated by several examples, primarily taken from the research in my group, in which photoelectron spectroscopy has contributed to answer questions concerning the structure and dynamics of small-sized molecular cations. F. I. Vilesov, B. C. Kurbatov, and N. Terrenin, Soviet Phys. (Doklady) 6

  15. 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.

  16. X-ray Photoelectron Spectroscopy on Superconducting Tl2CaBa2Cu2O8 Thin Film

    NASA Astrophysics Data System (ADS)

    Zeng, Wensheng; Qiu, Ping; Yan, Shaolin; Li, Zengfa; Zhang, Guangyin

    1991-06-01

    We have prepared single-phase superconducting Tl2CaBa2Cu2O8 thin film by dc magnetron sputtering process and measured x-ray photoelectron spectra of the film at room and liquid nitrogen temperatures. From the relative intensities of the Ba3d, Tl4f. O1s and Cu2p spectra taken at different take-off angles, we have concluded that there is an adventitious contamination (nonsuperconducting phase) surface layer. After excluding contributions from these spurious phases, we have tentatively assigned which core-level shifts should be caused by the superconducting phase transition.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Photoelectron spectroscopy of boron aluminum hydride cluster anions

    SciTech Connect

    Wang, Haopeng; Zhang, Xinxing; Ko, Yeon Jae; Gantefoer, Gerd; Bowen, Kit H. E-mail: kiran@mcneese.edu; Li, Xiang; Kiran, Boggavarapu E-mail: kiran@mcneese.edu; Kandalam, Anil K.

    2014-04-28

    Boron aluminum hydride clusters are studied through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations. Boron aluminum hydride cluster anions, B{sub x}Al{sub y}H{sub z}{sup −}, were generated in a pulsed arc cluster ionization source and identified by time-of-flight mass spectrometry. After mass selection, their photoelectron spectra were measured by a magnetic bottle-type electron energy analyzer. The resultant photoelectron spectra as well as calculations on a selected series of stoichiometries reveal significant geometrical changes upon substitution of aluminum atoms by boron atoms.

  2. X-ray photoelectron spectroscopy under real ambient pressure conditions

    NASA Astrophysics Data System (ADS)

    Takagi, Yasumasa; Nakamura, Takahiro; Yu, Liwei; Chaveanghong, Suwilai; Sekizawa, Oki; Sakata, Tomohiro; Uruga, Tomoya; Tada, Mizuki; Iwasawa, Yasuhiro; Yokoyama, Toshihiko

    2017-07-01

    We have developed an ambient pressure hard-X-ray photoelectron spectroscopic system equipped with a differential pumping system at BL36XU of SPring-8. Photoelectron spectra from a Au(111) surface were recorded using excitation light of 8 keV focused to 20 × 20 µm2 and adopting an aperture diameter of 30 µm at the entrance of the electron lens and a working distance of 60 µm. The Au 4f and 3d5/2 spectra were measured by increasing the ambient pressure from 1 Pa to atmospheric pressure and demonstrated that the instrument is capable of measuring the photoelectron spectrum under atmospheric pressure.

  3. The C1s core line in irradiated graphite

    SciTech Connect

    Speranza, Giorgio; Minati, Luca; Anderle, Mariano

    2007-08-15

    Recently, plasma deposited amorphous carbon films have been the subject of extensive experimental and theoretical investigations aimed at correlating their electronic, structural, and mechanical properties to growth parameters. To investigate these properties, different spectral parameters reflecting the electronic structure of carbon-based materials are proposed in literature. The effects of various electronic configurations on the carbon photoelectron spectra are analyzed here with particular attention to C1s core line with the aim to better interpret its structure. The latter is commonly fitted under the assumption that it can be described by using just two spectral components related to sp{sup 2} and sp{sup 3} hybrids. Their relative intensities are then used to estimate the sp{sup 2} and sp{sup 3} phases. We show that, in the presence of an amorphous network, the C1s line shape is the result of a more complex mixture of electronic states. Ar{sup +} irradiated graphite and successive oxidation was used to identify spectral features to better describe the C1s line shape.

  4. Photoelectron Spectroscopy of Substituted Phenylnitrenes

    NASA Astrophysics Data System (ADS)

    Wijeratne, Neloni R.; Fonte, Maria Da; Wenthold, Paul G.

    2009-06-01

    Nitrenes are unusual molecular structures with unfilled electronic valences that are isoelectronic with carbenes. Although, both can be generated by either thermal or photochemical decomposition of appropriate precursors they usually exhibit different reactivities. In this work, we carry out spectroscopic studies of substituted phenylnitrene to determine how the introduction of substituents will affect the reactivity and its thermochemical properties. All studies were carried out by using the newly constructed time-of-flight negative ion photoelectron spectrometer (NIPES) at Purdue University. The 355 nm photoelectron spectra of the o-, m-, and p-chlorophenyl nitrene anions are fairly similar to that measured for phenylnitrene anion. All spectra show low energy triplet state and a high energy singlet state. The singlet state for the meta isomer is well-resolved, with a well defined origin and observable vibrational structure. Whereas the singlet states for the ortho and para isomers have lower energy onsets and no resolved structure. The isomeric dependence suggests that the geometry differences result from the resonance interaction between the nitrogen and the substituent. Quinoidal resonance structures are possible for the open-shell singlet states of the o- and p-chlorinated phenyl nitrenes. The advantages of this type of electronic structures for the open-shell singlet states is that the unpaired electrons can be more localized on separate atoms in the molecules, minimizing the repulsion between. Because the meta position is not in resonance with the nitrenes, substitution at that position should not affect the structure of the open-shell singlet state. The measured electron affinities (EA) of the triplet phenylnitrenes are in excellent agreement with the values predicted by electronic structure calculations. The largest EA, 1.82 eV is found for the meta isomer, with para being the smallest, 1.70 eV.

  5. Photoelectron spectroscopy of supersonic molecular beams

    SciTech Connect

    Pollard, J.E.

    1982-05-01

    A new technique for performing high resolution molecular photoelectron spectroscopy is described, beginning with its conceptual development, through the construction of a prototypal apparatus, to the initial applications on a particularly favorable molecular system. The distinguishing features of this technique are: (1) the introduction of the sample in the form of a collimated supersonic molecular beam; and (2) the use of an electrostatic deflection energy analyzer which is carefully optimized in terms of sensitivity and resolution. This combination makes it possible to obtain photoelectron spectra at a new level of detail for many small molecules. Three experiments are described which rely on the capability to perform rotationally-resolved photoelectron spectroscopy on the hydrogen molecule and its isotopes. The first is a measurement of the ionic vibrational and rotational spectroscopic constants and the vibrationally-selected photoionization cross sections. The second is a determination of the photoelectron asymmetry parameter, ..beta.., for selected rotational transitions. The third is an investigation of the rotational relaxation in a free jet expansion, using photoelectron spectroscopy as a probe of the rotational state population distributions. In the closing chapter an assessment is made of the successes and limitations of the technique, and an indication is given of areas for further improvement in future spectrometers.

  6. 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.

  7. 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)

  8. Photoelectrons observed in the polar wind

    NASA Astrophysics Data System (ADS)

    Kitamura, N.; Seki, K.; Nishimura, T.; Terada, N.; Ono, T.; Hori, T.; Strangeway, R. J.; McFadden, J. P.; Carlson, C. W.

    2011-12-01

    We have statistically examined photoelectron spectra in the polar cap obtained by the electron spectrometer aboard the Fast Auroral SnapshoT (FAST) satellite at about 3800 km altitude during geomagnetically quiet periods at solar maximum. The geomagnetically quiet periods is defined as the times when the Kp index is less than or equal to 2+ for the preceding 3 hours and when the SYM-H index ranges from -10 to 40 nT. The polar cap is defined by the lack of energetic ions [Andersson et al., 2004]. The data obtained during geomagnetically quiet periods in July 2002 are used for the statistical study. In this period, the apogee of the FAST satellite was located at high latitudes in the Northern (summer) Hemisphere. We found counter-streaming photoelectrons of up to more than 10 eV, indicating existence of a potential drop above the satellite altitude. Such distributions were frequently (more than 80% in occurrence frequency) observed in the polar cap. The estimated typical potential drop above the satellite is about 20 V, which is about a half of that predicted by photoelectron-driven polar wind models with a potential drop at high altitudes (about 7 RE) [Wilson et al., 1997; Su et al., 1998]. The net number flux of escaping photoelectrons negatively correlates with the magnitude of the potential drop. On the other hand, the net escape flux also negatively correlates with the number flux of upgoing photoelectrons. Since the flux of the escaping photoelectrons should be equal to the flux of the polar wind ions under the condition of the zero field-aligned current, this negative correlation indicates that the larger number flux of upgoing photoelectrons correspond to weaker polar wind. This fact seems to disagree with the idea that photoelectrons drive the polar wind, which was suggested by the modeling studies [e.g., Tam et al., 1998]. These results imply that relation between photoelectrons and the polar wind is not as simple as that predicted by modeling studies.

  9. 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.

  10. Photoelectronic Radiology Department

    NASA Astrophysics Data System (ADS)

    Capp, M. P.; Nudelman, Sol; Fisher, Donald; Ovitt, Theron W.; Pond, Gerald D.; Frost, Meryl M.; Roehrig, Hans; Seeger, Joachim; Oimette, Donald

    1981-11-01

    The University of Arizona Department of Radiology first considered establishing a photoelectronic radiology department in 1973. It seemed clear that the technology had progressed far enough for us to investigate the possibility of total film replacement.' Data from the space program in particular indicated at that time that sophisticated television images over 1000 x 1000 lines were approaching the detail seen on the traditional x-ray film. This technology has been known over many years of research and development as "photoelectronic imaging devices (PEID) ."14 However, at that time film replacement was out of the question. What was not out of the question was the consideration of using a subtraction technique, "digital video subtraction angiography." To this end, we, and independently the University of Wisconsin,314 proceeded to develop this technology.5'6 Our intravenous video subtraction images in patients started in our research laboratory in 1977 and in March of 1980 we opened a biplane special procedures room dedicated only to photoelectronic imaging (no film).7'8 Digital video subtraction angiography has been successful and is described in much greater detail in these Proceedings by other authors. Current efforts are under way toward total replacement of film. This is an immense problem, one that will require a much greater sophistication of computers, storage devices, system analysis, and cooperation from both the radiologist and the clinician.9'10 In a theoretical study we converted our 65,000 procedures-per-year department to complete photoelectronic imaging (no film) and estimated that we would save approximately five million dollars over ten years.15 Extrapolating this to the entire United States would result in a conservative estimate of saving one billion dollars per year. Not included in these mathematics are cost-effective savings of the physicians' time and effort.

  11. 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.

  12. 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.

  13. Bimolecular reaction dynamics from photoelectron spectroscopy of negative ions

    SciTech Connect

    Bradforth, Stephen Edmund

    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-, NCO- and NCS-. Transition state photoelectron spectra are presented for the following systems Br + HI, Cl + HI, F + HI, F + CH30H,F + C2H5OH,F + OH and F + H2. A time dependent framework for the simulation and interpretation of the bound → free transition state photoelectron spectra is subsequently developed and applied to the hydrogen transfer reactions Br + HI, F + OH → O(3P, 1D) + HF and F + H2. 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 + H2 system, comparisons with three-dimensional quantum calculations are made.

  14. 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}.

  15. High-kinetic-energy photoemission spectroscopy of Ni at 1s : 6-eV satellite at 4 eV

    NASA Astrophysics Data System (ADS)

    Karis, O.; Svensson, S.; Rusz, J.; Oppeneer, P. M.; Gorgoi, M.; Schäfers, F.; Braun, W.; Eberhardt, W.; Mårtensson, N.

    2008-12-01

    Electron correlations are responsible for many profound phenomena in solid-state physics. A classical example is the 6-eV satellite in the photoelectron spectrum of Ni. Until now the satellite structure has only been investigated at the L shell and more shallow levels. Here we report a high-kinetic-energy photoemission spectroscopy (HIKE) investigation of Ni metal. We present 1s and 2p photoelectron spectra, obtained using excitation energies up to 12.6 keV. Our investigation demonstrates that the energy position of the satellite relative to the main line is different for the 1s and the 2p levels. In combination with electronic structure calculations, we show that this energy shift is attributed to unique differences in the core-valence coupling for the K and L2,3 shells in 3d transition metals, resulting in different screening of the core holes.

  16. 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.

  17. 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

  18. Characteristic differences in the X-ray photoelectron spectrum between B-DNA and M-DNA monolayers on gold.

    PubMed

    Dinsmore, Michael J; Lee, Jeremy S

    2008-08-01

    Duplex DNA monolayers were self-assembled on gold through a disulfide linkage and both B- and M-DNA conformations were studied using X-ray photoelectron spectroscopy (XPS). The film thickness, density, elemental composition and ratios for samples were analyzed and compared. The DNA surface coverage, calculated from both XPS and electrochemical measurements, was approximately 1.2 x 10(13)molecules/cm(2) for B-DNA. All samples showed distinct peaks for C 1s, O 1s, N 1s, P 2p and S 2p as expected for a thiol-linked DNA. On addition of Zn(2+) to form M-DNA the C 1s, P 2p and S 2p showed only small changes while both the N 1s and O 1s spectra changed considerably. This result is consistent with Zn(2+) interacting with oxygen on the phosphate backbone as well as replacing the imino protons of thymine (T) and guanine (G) in M-DNA. Analysis of the Zn 2p spectra also demonstrated that the concentration of Zn(2+) present under M-DNA conditions is consistent with Zn(2+) binding to both the phosphate backbone as well as replacing the imino protons of T or G in each base pair. After the M-DNA monolayer is washed with a buffer containing only Na(+) the Zn(2+) bound to the phosphate backbone is removed while the Zn(2+) bound internally still remains.

  19. 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.

  20. 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.

  1. Angle-resolved X-ray photoelectron spectroscopy of the surface of imidazolium ionic liquids.

    PubMed

    Lockett, Vera; Sedev, Rossen; Bassell, Chris; Ralston, John

    2008-03-07

    The surfaces of three imidazolium based ionic liquids with a common anion were studied with angle-resolved X-ray photoelectron spectroscopy (XPS). The room temperature ionic liquids (RTILs): 1-butyl-3-methylimidazolium (bmim), 1-hexyl-3-methylimidazolium (hmim), and 1-octyl-3-methylimidazolium (omim) tetrafluoroborates, were meticulously purified and dried under vacuum. Survey and high-resolution spectra were obtained at different take-off angles (0-84 degrees ), thus increasing the surface sensitivity of the measurement. No impurities were detected and the survey spectra at normal emission (0 degrees ) confirmed the stoichiometric composition of the liquids. However, the spectra at take-off angles of 60, 70, 80 and 84 degrees indicated a higher amount of carbon. High resolution spectra of C1s, at these angles, showed an increased amount of aliphatic carbon when compared to the spectra at normal emission. The longer the side chain (R) of the imidazolium cation (Rmim), the larger was the amount of aliphatic carbon detected. Previous studies with other surface sensitive techniques have yielded contradictory conclusions about the surface orientation of the Rmim. We conclude unequivocally that the alkyl chain of the imidazolium ring of the investigated RTILs is oriented away from the liquid. Our study demonstrates the ability of XPS to probe the structure, along with the composition, of the free liquid surface by comparing signals from different penetration depths.

  2. 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.

  3. Photoelectron pumped phosphors

    NASA Astrophysics Data System (ADS)

    1989-07-01

    The investigation of cathodophosphors was undertaken in connection with the development of optical devices for the detection of long wavelength photons in which the initial photon-to-electron detection is performed by an optical diode. Then the photoelectrons being accelerated by the electric field penetrate into a phosphor screen and the screen produces multiple photons which are detected by a (close coupled) photomultiplier. The results are presented of a comprehensive analysis and systematization of the data relevant to the fast and very fast commercially available phosphors and developmental works on improved materials and processes in the field of phosphors, especially cathodophosphors. The investigation included analysis of II-VI phosphors, alkaline-earth chalcogenides, silicates, garnets, halides, and some ternary compounds with diamond-like crystal structure. The investigation included, also, analysis of data regarding the activators and coactivators as well as mixtures of phosphors with optically transparent conductive powders for the low energy electron cathodoluminescence.

  4. 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.

  5. 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.

  6. A versatile photoelectron spectrometer for pressures up to 30 mbar

    SciTech Connect

    Eriksson, Susanna K.; Edström, Kristina; Hagfeldt, Anders; Hahlin, Maria; Rensmo, Håkan; Siegbahn, Hans; Kahk, Juhan Matthias; Villar-Garcia, Ignacio J.; Payne, David J.; Webb, Matthew J.; Grennberg, Helena; Yakimova, Rositza; Edwards, Mårten O. M.; Karlsson, Patrik G.; Backlund, Klas; Åhlund, John

    2014-07-15

    High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Kα X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.

  7. Laser Photoelectron Spectroscopy of Organometallic Anions.

    NASA Astrophysics Data System (ADS)

    Cheng, Chun-Lin

    This thesis presents the first gas phase spectroscopic study of the FeC, FeC_2, FeC _2H, and FeC_2H _2 molecules and the corresponding anions. This series of molecules, as well as the related species CoC, were studied by negative ion laser photoelectron spectroscopy at an instrumental resolution of 4 meV. The apparatus employed in these studies is described, and its intracavity argon ion laser system is discussed in detail. The negative ion photoelectron spectra of FeC and CoC yield ground state vibrational frequencies of 860 and 930 cm^{-1} for the neutral molecules, respectively, and 860 and 890 cm ^{-1} for the corresponding anions. These high vibrational frequencies indicate that the metal d orbitals are strongly involved in the bonding. Both photoelectron spectra show that the neutral molecule ground states are formed by detachment of an electron from a fairly nonbonding orbital. It is suggested that this orbital is primarily a metal 4s orbital which is polarized away from the carbon center. Molecular orbital diagrams for FeC and CoC are proposed, and their ground states are assigned as ^3Delta and ^3Sigma states, respectively. The electron affinities of FeC (1.381 +/- 0.008 eV) and CoC (1.498 +/- 0.007 eV) are also measured. In addition, more accurate values for the fine structure splittings in the atomic Fe^- and Co ^- anions are reported. The negative ion photoelectron spectra of FeC _2, FeC_2H and FeC_2H_2 yield electron affinities of 1.977, 1.456 and 1.342 ( +/-0.007) eV, respectively. Neutral molecule vibrational frequencies of 550, 460 and 480 cm ^{-1} are observed for the three systems, respectively, and assigned to the Fe-C stretching modes. Based upon these and other considerations, it is suggested that the three species observed here have a linear FeCC, a linear FeCCH and a C_{rm 2v} Fe(HCCH) structure. Molecular orbital diagrams and ground state assignments are proposed for the neutral molecules and the corresponding anions. Finally, the iterative

  8. Non-adiabatic effects in photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Schuurman, Michael; Yarkony, David

    2007-03-01

    Recent developments in the construction of approximately diabatic second-order Hamiltonians in the vicinity of conical intersections have been employed to study photoelectron spectra of molecules in which nonadiabatic effects are preeminent. Our current approach explicitly includes all non-adiabatic coupling terms through second order, while requiring ab initio data at only (N[int] + 3) or (N[int] + 15) points for two and three-state intersections, respectively, where N[int] is the number of internal coordinates. This scaling allows very accurate wave functions to be used. Since the Hamiltonian is determined at a point of conical intersection, the method is ``self-policing'' in that the ability of the resultant surfaces to reproduce the vicinity of seams of intersection, as well as energy minima and the Franck-Condon region, is easily verified. We will report photoelectron spectra determined from these diabatic representations employing a harmonic oscillator basis and a Lanczos solver algorithm to diagonalize the resultant vibronic Hamiltonian matrices. The results of some initial applications will be discussed, with emphasis on the previously studied five membered heterogeneous ring systems, pyrazolyl (C3H3N2) and pyrrolyl (C4H4N) doublet radicals. These systems are of particular interest since they display low-lying conical intersections adjacent to both the neutral ground state geometries and the Franck-Condon region.

  9. 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.

  10. Intensity oscillations in the carbon 1s ionization cross sections of 2-butyne

    SciTech Connect

    Carroll, Thomas X.; Zahl, Maria G.; Borve, Knut J.; Saethre, Leif J.; Decleva, Piero; Ponzi, Aurora; Kas, Joshua J.; Vila, Fernando D.; Rehr, John J.; Thomas, T. Darrah

    2013-06-21

    Carbon 1s photoelectron spectra for 2-butyne (CH{sub 3}C{identical_to}CCH{sub 3}) measured in the photon energy range from threshold to 150 eV above threshold show oscillations in the intensity ratio C2,3/C1,4. Similar oscillations have been seen in chloroethanes, where the effect has been attributed to EXAFS-type scattering from the substituent chlorine atoms. In 2-butyne, however, there is no high-Z atom to provide a scattering center and, hence, oscillations of the magnitude observed are surprising. The results have been analyzed in terms of two different theoretical models: a density-functional model with B-spline atom-centered functions to represent the continuum electrons and a multiple-scattering model using muffin-tin potentials to represent the scattering centers. Both methods give a reasonable description of the energy dependence of the intensity ratios.

  11. 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.

  12. {{\\rm{H}}}_{2}\\,X{}^{1}{{\\rm{\\Sigma }}}_{g}^{+}-c{}^{3}{{\\rm{\\Pi }}}_{u} Excitation by Electron Impact: Energies, Spectra, Emission Yields, Cross-sections, and H(1s) Kinetic Energy Distributions

    NASA Astrophysics Data System (ADS)

    Liu, Xianming; Shemansky, Donald E.; Yoshii, Jean; Liu, Melinda J.; Johnson, Paul V.; Malone, Charles P.; Khakoo, Murtadha A.

    2017-10-01

    The c{}3{{{\\Pi }}}u state of the hydrogen molecule has the second largest triplet-state excitation cross-section, and plays an important role in the heating of the upper thermospheres of outer planets by electron excitation. Precise energies of the H2, D2, and HD c{}3{{{\\Pi }}}u-(v,N) levels are calculated from highly accurate ab initio potential energy curves that include relativistic, radiative, and empirical non-adiabatic corrections. The emission yields are determined from predissociation rates and refined radiative transition probabilities. The excitation function and excitation cross-section of the c{}3{{{\\Pi }}}u state are extracted from previous theoretical calculations and experimental measurements. The emission cross-section is determined from the calculated emission yield and the extracted excitation cross-section. The kinetic energy (E k ) distributions of H atoms produced via the predissociation of the c{}3{{{\\Pi }}}u state, the c{}3{{{\\Pi }}}u- – b{}3{{{Σ }}}u+ dissociative emission by the magnetic dipole and electric quadrupole, and the c{}3{{{\\Pi }}}u – a{}3{{{Σ }}}g+ – b{}3{{{Σ }}}u+ cascade dissociative emission by the electric dipole are obtained. The predissociation of the c{}3{{{\\Pi }}}u+ and c{}3{{{\\Pi }}}u- states both produce H(1s) atoms with an average E k of ∼4.1 eV/atom, while the c{}3{{{\\Pi }}}u- – b{}3{{{Σ }}}u+ dissociative emissions by the magnetic dipole and electric quadrupole give an average E k of ∼1.0 and ∼0.8 eV/atom, respectively. The c{}3{{{\\Pi }}}u – a{}3{{{Σ }}}g+ – b{}3{{{Σ }}}u+ cascade and dissociative emission gives an average E k of ∼1.3 eV/atom. On average, each H2 excited to the c{}3{{{\\Pi }}}u state in an H2-dominated atmosphere deposits ∼7.1 eV into the atmosphere while each H2 directly excited to the a{}3{{{Σ }}}g+ and d{}3{{{\\Pi }}}u states contribute ∼2.3 and ∼3.3 eV, respectively, to the atmosphere. The spectral distribution of the calculated continuum emission

  13. 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.

  14. Extended x-ray absorption fine structure in photoelectron emission

    SciTech Connect

    Rothberg, G.M.; Choudhary, K.M.; denBoer, M.L.; Williams, G.P.; Hecht, M.H.; Lindau, I.

    1984-09-17

    We report the first definitive measurements of extended x-ray absorption fine structure (EXAFS) made by monitoring the direct photoelectron emission as a function of photon energy. We have measured EXAFS associated with the Mn 3p and F 2s core levels in evaporated films of MnF/sub 2/ and found good agreement with bulk transmission EXAFS associated with the Mn 1s level. Photoelectron EXAFS makes possible surface-sensitive structural determinations using vacuum uv radiation on a virtually unlimited range of systems.

  15. 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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  18. 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.

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

    PubMed

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

    2016-05-27

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

  20. Versatile cluster based photoelectron spectrometer

    SciTech Connect

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

    2006-12-15

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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. X-ray Photoelectron Spectroscopy of High-κ Dielectrics

    NASA Astrophysics Data System (ADS)

    Mathew, A.; Demirkan, K.; Wang, C.-G.; Wilk, G. D.; Watson, D. G.; Opila, R. L.

    2005-09-01

    Photoelectron spectroscopy is a powerful technique for the analysis of gate dielectrics because it can determine the elemental composition, the chemical states, and the compositional depth profiles non-destructively. The sampling depth, determined by the escape depth of the photoelectrons, is comparable to the thickness of current gate oxides. A maximum entropy algorithm was used to convert photoelectron collection angle dependence of the spectra to compositional depth profiles. A nitrided hafnium silicate film is used to demonstrate the utility of the technique. The algorithm balances deviations from a simple assumed depth profile against a calculated depth profile that best fits the angular dependence of the photoelectron spectra. A flow chart of the program is included in this paper. The development of the profile is also shown as the program is iterated. Limitations of the technique include the electron escape depths and elemental sensitivity factors used to calculate the profile. The technique is also limited to profiles that extend to the depth of approximately twice the escape depth. These limitations restrict conclusions to comparison among a family of similar samples. Absolute conclusions about depths and concentrations must be used cautiously. Current work to improve the algorithm is also described.

  6. 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.

  7. 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.

  8. A spin- and angle-resolving photoelectron spectrometer

    SciTech Connect

    Berntsen, M. H.; Tjernberg, O.; Palmgren, P.; Leandersson, M.; Hahlin, A.; Aahlund, J.; Wannberg, B.; Maansson, M.

    2010-03-15

    A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

  9. 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.

  10. 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.

  11. Determination of the radiation resistance order of high explosives by the two dimensional correlation X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Sui, Heliang; Hao, Xiaofei; Luo, Yiwei; Xu, Jinjiang; Zhong, Fachun; Xu, Ruijuan

    2017-09-01

    Two-dimensional X-ray photoelectron spectroscopy (2DXPS) was employed to obtain the radiation resistance order of high explosives. Mixed hexanitrohexaazaisowurtzitane (CL-20) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were irradiated by X-ray radiation. The time-dependent N1s XPS spectra were collected. 2DXPS was used to analyze the variation of the binding energy peaks. The main degradation time of TATB was longer than that of CL-20. CL-20 changes occurred prior to that of TATB during radiation. These changes suggest that TATB exhibited higher radiation resistance property than CL-20. 2DXPS is a very useful method to distinguish the radiation resistance orders of materials.

  12. Optical and x-ray photoelectron spectroscopy studies of α-Al{sub 2}O{sub 3}

    SciTech Connect

    Prakash, Ram E-mail: ramprakash@smvdu.ac.in; Kumar, Sandeep; Kumar, Vinay; Choudhary, R. J.; Phase, D. M.

    2016-05-23

    α-Al{sub 2}O{sub 3} powder sample was synthesized at 550 °C via solution combustion synthesis (SCS) method using urea as an organic fuel. The sample was characterized by X-ray diffraction (XRD), Optical spectroscopy and X-ray photoelectron spectroscopy (XPS) without any further thermal treatment. XRD study reveals that the powder crystallized directly in the hexagons α-Al{sub 2}O{sub 3} phase. A band gap of 5.7 eV was estimated using diffuse reflectance spectra. For surface investigation X-ray photo electron spectroscopy (XPS) was carried out. The XPS survey scan study of α-Al{sub 2}O{sub 3} powder reveals that the sample is free from impurity. The core levels of Al-2s and O-1s are also reported.

  13. Photoelectron spectroscopy study of the electronic structures at CoPc/Bi(111) interface

    NASA Astrophysics Data System (ADS)

    Sun, Haoliang; Liang, Zhaofeng; Shen, Kongchao; Hu, Jinbang; Ji, Gengwu; Li, Zheshen; Li, Haiyang; Zhu, Zhiyuan; Li, Jiong; Gao, Xingyu; Han, Huang; Jiang, Zheng; Song, Fei

    2017-07-01

    Self-assembly of functional molecules on solid substrate has been recognized as an appealing approach for the fabrication of diverse nanostructures for nanoelectronics. Herein, we investigate the growth of cobalt phthalocyanine (CoPc) on a Bi(111) surface with focus on the interface electronic structures utilizing photoelectron spectroscopy. While charge transfer from bismuth substrate to the molecule results in the emergence of an interface component in the Co 3p core level at lower binding energy, core-levels associated to the molecular ligand (C 1s and N 1s) are less influenced by the adsorption. In addition, density functional theory (DFT) calculations also support the empirical inference that the molecule-substrate interaction mainly involves the out-of-plane empty Co 3d orbital and bismuth states. Finally, valence band spectra demonstrate the molecule-substrate interaction is induced by interface charge transfer, agreeing well with core level measurements. Charge transfer is shown to be mainly from the underlying bismuth substrate to the empty states located at the central Co atom in the CoPc molecules. This report may provide a fundamental basis to the on-surface engineering of interfaces for molecular devices and spintronics.

  14. Reactivity of the nitro-group of a π-conjugated polymer upon the interface formation with chromium: a photoelectron spectroscopy investigation

    NASA Astrophysics Data System (ADS)

    Iucci, G.; Polzonetti, G.; Altamura, P.; Paolucci, G.; Goldoni, A.; D'Amato, R.; Russo, M. V.

    1999-12-01

    X-ray photoelectron spectroscopy was used in order to investigate the interface formation between chromium and thin films of a newly synthesised π-conjugated polymer P(PA- pNO 2PA); the investigated material is a block copolymer consisting of phenylacetylene (PA) and para-nitro phenylacetylene ( pNO 2PA) units {[-(CHC-R) n-(CHC-R') m-] N; RC 6H 5, R'C 6H 4NO 2}. Chromium was evaporated stepwise in situ onto the polymer surface and the XPS spectra of the substrate polymer and of the metal overlayer were studied as a function of increasing chromium thickness. In the early stages of the interface formation, chromium was found to interact mainly with the nitrogen atoms of the -NO 2 groups, that are reduced to nitride-like species; the N-O bond is broken, as evidenced by the modifications occurring in the N1s and O1s spectra. The changes in the C1s spectra upon increasing metal deposition suggest the formation of a chromium-arene π-complex at low chromium coverage and of carbide-like species at higher chromium thickness.

  15. Photoelectron diffraction and holography: Present status and future prospects

    SciTech Connect

    Fadley, C.S. |; Thevuthasan, S.; Kaduwela, A.P.

    1993-07-01

    Photoelectron diffraction and photoelectron holography, a newly developed variant of it, can provide a rich range of information concerning surface structure. These methods are sensitive to atomic type, chemical state, and spin state. The theoretical prediction of diffraction patterns is also well developed at both the single scattering and multiple scattering levels, and quantitative fits of experiment to theory can lead to structures with accuracies in the {plus_minus}0.03 {Angstrom} range. Direct structural information can also be derived from forward scattering in scanned-angle measurements at higher energies, path length differences contained in scanned-energy data at lower energies, and holographic inversions of data sets spanning some region in angle and energy space. Diffraction can also affect average photoelectron emission depths. Circular dichroism in core-level emission can be fruitfully interpreted in terms of photoelectron diffraction theory, as can measurements with spin-resolved core-spectra, and studies of surface magnetic structures and phase transitions should be possible with these methods. Synchrotron radiation is a key element of fully utilizing these techniques.

  16. 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.

  17. 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.

  18. 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

  19. 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. Copyright © 2014 Elsevier B.V. All rights reserved.

  20. Note: Energy calibration of a femtosecond photoelectron imaging detector with correction for the ponderomotive shift of atomic ionization energies

    NASA Astrophysics Data System (ADS)

    Hüter, O.; Temps, F.

    2017-04-01

    Femtosecond photoelectron imaging spectroscopy is a powerful technique for following state-resolved molecular transformations in complex coupled potential energy landscapes. To avoid unwanted nonlinear side-effects, the employed laser pulse energies are usually reduced to minimal values. However, the energy calibration of the photoelectron imaging detector is ideally performed using multi-photon above-threshold ionization of suitable atomic species, for which rather high laser intensities are required. In this work, we show that the calibration spectra of xenon obtained with high laser pulse energies cannot be directly used for the evaluation of molecular photoelectron spectra recorded using low-energy laser pulses. The reason is the intensity-dependent AC Stark shift of the atomic ionization energies to larger values, which in turn leads to a corresponding decrease of the photoelectron kinetic energies. We present a simple procedure to quantify this so-called ponderomotive shift and calculate the theoretically expected un-shifted photoelectron energies.

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

    SciTech Connect

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

    2016-04-15

    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-L{sub 23} 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. X-ray Photoelectron Spectroscopy of Pyridinium-Based Ionic Liquids: Comparison to Imidazolium- and Pyrrolidinium-Based Analogues.

    PubMed

    Men, Shuang; Mitchell, Daniel S; Lovelock, Kevin R J; Licence, Peter

    2015-07-20

    We investigate eight 1-alkylpyridinium-based ionic liquids of the form [Cn Py][A] by using X-ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake-up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic-liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C8 Py][A] and analogues including 1-octyl-1-methylpyrrolidinium- ([C8 C1 Pyrr][A]), and 1-octyl-3-methylimidazolium- ([C8 C1 Im][A]) based samples, where X is common to all ionic liquids.

  7. X‐ray Photoelectron Spectroscopy of Pyridinium‐Based Ionic Liquids: Comparison to Imidazolium‐ and Pyrrolidinium‐Based Analogues

    PubMed Central

    Mitchell, Daniel S.; Lovelock, Kevin R. J.

    2015-01-01

    Abstract We investigate eight 1‐alkylpyridinium‐based ionic liquids of the form [CnPy][A] by using X‐ray photoelectron spectroscopy (XPS). The electronic environment of each element of the ionic liquids is analyzed. In particular, a reliable fitting model is developed for the C 1s region that applies to each of the ionic liquids. This model allows the accurate charge correction of binding energies and the determination of reliable and reproducible binding energies for each ionic liquid. Shake‐up/off phenomena are determinedfor both C 1s and N 1s spectra. The electronic interaction between cations and anions is investigated for both simple ionic liquids and an example of an ionic‐liquid mixture; the effect of the anion on the electronic environment of the cation is also explored. Throughout the study, a detailed comparison is made between [C8Py][A] and analogues including 1‐octyl‐1‐methylpyrrolidinium‐ ([C8C1Pyrr][A]), and 1‐octyl‐3‐methylimidazolium‐ ([C8C1Im][A]) based samples, where X is common to all ionic liquids. PMID:25952131

  8. QED effects in 1s and 2s single and double ionization potentials of the noble gases

    NASA Astrophysics Data System (ADS)

    Niskanen, J.; Jänkälä, K.; Huttula, M.; Föhlisch, A.

    2017-04-01

    We present calculations on the quantum electrodynamics (QED) effects in 1s and 2s single and double ionization potentials of noble gases from Ne to Rn as perturbations on relativistic four-component Dirac-Fock wavefunctions. The most dominant effect originates from the self-energy of the core-electron that yields corrections of similar order as the transverse interaction. For 1s ionization potentials, a match within few eV against the known experimental values is obtained, and our work reveals considerable QED effects in the photoelectron binding energies across the periodic table—most strikingly even for Ne. We perform power-law fits for the corrections as a function of Z and interpolate the QED correction of ˜-0.55 eV for S1s. Due to this, the K-edge electron spectra of the third row and below need QED for a match in the absolute energy when using state-of-the-art instrumentation.

  9. QED effects in 1s and 2s single and double ionization potentials of the noble gases.

    PubMed

    Niskanen, J; Jänkälä, K; Huttula, M; Föhlisch, A

    2017-04-14

    We present calculations on the quantum electrodynamics (QED) effects in 1s and 2s single and double ionization potentials of noble gases from Ne to Rn as perturbations on relativistic four-component Dirac-Fock wavefunctions. The most dominant effect originates from the self-energy of the core-electron that yields corrections of similar order as the transverse interaction. For 1s ionization potentials, a match within few eV against the known experimental values is obtained, and our work reveals considerable QED effects in the photoelectron binding energies across the periodic table-most strikingly even for Ne. We perform power-law fits for the corrections as a function of Z and interpolate the QED correction of ∼-0.55 eV for S1s. Due to this, the K-edge electron spectra of the third row and below need QED for a match in the absolute energy when using state-of-the-art instrumentation.

  10. 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.

  11. 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.

  12. 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.

  13. Photoelectron holography of platinum (111)

    SciTech Connect

    Petersen, B.L.; Terminello, L.J.; Barton, J.J.; Shirley, D.A.

    1993-04-01

    Platinum atoms near a (111) single-crystal face have been imaged using photoelectron holography. Electron angular intensity patterns were collected at equally spaced wavenumbers from 6 to 12{Angstrom}{sup {minus}1}. Images of atoms near expected atomic positions are obtained from single-wavenumber analyses over the range of the data set. Positions are detected further from the emitter than we have seen previously, and symmetry assumptions are not required. We have also adopted a three dimensional means of representing the data in order to help understand the results. Twin image suppression and artifact reduction in the holographically reconstructed data are set are obtained when images at different wavenumbers are correctly phase-summed. We are assessing the capability of the technique for rendering true three-dimensional structural information for unknown systems.

  14. 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.

  15. Vibrationally Resolved B 1s Photoionization Cross Section of BF3.

    PubMed

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

    2015-06-11

    Photoelectron diffraction is a well-established technique for structural characterization of solids, based on the interference of the native photoelectron wave with those scattered from the neighboring atoms. For isolated systems in the gas phase similar studies suffer from orders of magnitude lower signals due to the very small sample density. Here we present a detailed study of the vibrationally resolved B 1s photoionization cross section of BF3 molecule. A combination of high-resolution photoelectron spectroscopy measurements and of state-of-the-art static-exchange and time-dependent DFT calculations shows the evolution of the photon energy dependence of the cross section from a complete trapping of the photoelectron wave (low energies) to oscillations due to photoelectron diffraction phenomena. The diffraction pattern allows one to access structural information both for the ground neutral state of the molecule and for the core-ionized cation. Due to a significant change in geometry between the ground and the B 1s(-1) core-ionized state in the BF3 molecule, several vibrational final states of the cation are populated, allowing investigation of eight different relative vibrationally resolved photoionization cross sections. Effects due to recoil induced by the photoelectron emission are also discussed.

  16. Photoelectron emission properties of hydrogen terminated intrinsic diamond

    NASA Astrophysics Data System (ADS)

    Takeuchi, D.; Nebel, C. E.; Yamasaki, S.

    2006-04-01

    Hydrogen terminated intrinsic diamond is characterized using photoelectron emission spectroscopy. Samples have been annealed at temperatures Ta from 200 to 1000 °C. The electron emission characteristics can be divided into three regimes: (I) (Ta<300 °C) is governed by surface band bending which allows only excitons to reach the surface with subsequent dissociation. (II) (300 °C<=Ta<=650 °C) shows increased electron emission and the surface band bending has been removed. Here, excitons and electrons contribute. (III) (Ta>650 °C) additional rise of emission is detected. The spectra are dominated by photon-phonon interactions which are discussed in detail.

  17. Photoelectron angular distributions from liquid water: effects of electron scattering.

    PubMed

    Thürmer, Stephan; Seidel, Robert; Faubel, Manfred; Eberhardt, Wolfgang; Hemminger, John C; Bradforth, Stephen E; Winter, Bernd

    2013-10-25

    Photoelectron angular distributions (PADs) from the liquid-water surface and from bulk liquid water are reported for water oxygen-1s ionization. Although less so than for the gas phase, the measured PADs from the liquid are remarkably anisotropic, even at electron kinetic energies lower than 100 eV, when elastic scattering cross sections for the outgoing electrons with other water molecules are large. The PADs reveal that theoretical estimates of the inelastic mean free path are likely too long at low kinetic energies, and hence the electron probing depth in water, near threshold ionization, appears to be considerably smaller than so far assumed.

  18. Photoelectron spectroscopy and density functional theory study of ConO- (n = 1-3)

    NASA Astrophysics Data System (ADS)

    Li, Ren-Zhong; Liang, Jun; Xu, Xi-Ling; Xu, Hong-Guang; Zheng, Wei-Jun

    2013-06-01

    ConO- (n = 1-3) clusters were investigated with photoelectron spectroscopy and density functional calculations. The vertical detachment energies (VDEs) of ConO- (n = 1-3) were measured to be 1.54 ± 0.04, 1.43 ± 0.08, and 1.42 ± 0.08 eV respectively from their photoelectron spectra. The electron affinity and term energy of CoO were determined to be 1.54 ± 0.04 eV and 0.31 ± 0.04 eV respectively based on the vibrationally resolved photoelectron spectrum of CoO- and theoretical calculations. The structures of ConO- (n = 1-3) were determined by comparison of photoelectron experiments and calculations. The analysis of molecular orbitals shows that the HOMOs of ConO- (n = 1-3) cluster anions are mainly localized on the Co atoms.

  19. 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.

  20. 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.

  1. 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.

  2. Surface characterization of ginger powder examined by X-ray photoelectron spectroscopy and scanning electron microscopy.

    PubMed

    Zhao, Xiaoyan; Ao, Qiang; Du, Fangling; Zhu, Junqing; Liu, Jie

    2010-09-01

    The surface composition of five types of ginger powders with the particle sizes of 300, 149, 74, 37 and 8.34 microm was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical-chemical characteristics regarding material particle size distributions, discoloration and chemical composition. The results show that the color differences are greater for superfine ground ginger than for conventional comminuted ones; the values of crude fibre, neutral detergent fiber (NDF) and acid detergent fiber (ADF) decrease with decreasing ginger particle size. However, no relationship with the surface fat, crude protein, ash and total solids exists. With superfine grinding the XPS O/C ratios of the five ginger powders were similar since the surfaces were not oxidized. Correlations were observed between the XPS N/C ratios and the high resolution XPS N 1s spectra. SEM observations revealed that the surface of ginger powder with a particle size of 300 microm is rougher, while superfine ground powders with particle sizes of 149, 74, 37 and 8.34 microm are similar to each other. This roughness difference between these surfaces correlates with the differences in their O/C ratios and the surface morphology of five ginger powders. Copyright 2010 Elsevier B.V. All rights reserved.

  3. X-Ray Photoelectron Spectroscopy Investigation of the Nitrogen Species in Photoactive Perfluorophenylazide-Modified Surfaces

    PubMed Central

    Zorn, Gilad; Liu, Li-Hong; Árnadóttir, Líney; Wang, Hui; Gamble, Lara J.; Castner, David G.; Yan, Mingdi

    2014-01-01

    X-ray Photoelectron Spectroscopy (XPS) was used to characterize the nitrogen species in perfluorophenylazide (PFPA) self-assembled monolayers. PFPA chemistry is a novel immobilization method for tailoring the surface properties of materials. It is a simple route for the efficient immobilization of graphene, proteins, carbohydrates and synthetic polymers onto a variety of surfaces. Upon light irradiation, the azido group in PFPA is converted to a highly reactive singlet nitrene species that readily undergoes CH insertion and C=C addition reactions. Here, the challenge of characterizing the PFPA modified surfaces was addressed by detailed XPS experimental analyses. The three nitrogen peaks detected in the XPS N1s spectra were assigned to amine/amide (400.5 eV) and azide (402.1 and 405.6 eV) species. The observed 2:1 ratio of the areas from the 402.1 eV to 405.6 eV peaks suggests the assignment of the peak at 402.1 eV to the two outer nitrogen atoms in the azido group and assignment of the peak at 405.6 eV to the central nitrogen atom in the azido group. The azide decomposition as the function of x-ray exposure was also determined. Finally, XPS analyses were conducted on patterned graphene to investigate the covalent bond formation between the PFPA and graphene. This study provides strong evidence for the formation of covalent bonds during the PFPA photocoupling process. PMID:24535931

  4. 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.

  5. X-ray photoelectron spectroscopy characterization of high dose carbon-implanted steel and titanium alloys

    NASA Astrophysics Data System (ADS)

    Viviente, J. L.; García, A.; Alonso, F.; Braceras, I.; Oñate, J. I.

    1999-04-01

    A study has been made of the depth dependence of the atomic fraction and chemical bonding states of AISI 440C martensitic stainless steel and Ti-6Al-4V alloy implanted with 75 keV C + at very high doses (above 10 18 ions cm -2), by means of X-ray photoelectron spectroscopy combined with an Ar + sputtering. A Gaussian-like carbon distribution was observed on both materials at the lowest implanted dose. More trapezoidal carbon depth-profiles were found with increasing implanted doses, and a pure carbon layer was observed only on the titanium alloy implanted at the highest dose. The implanted carbon was combined with both base metal and carbon itself to form metallic carbides and graphitic carbon. Furthermore, carbon-enriched carbides were also found by curve fitting the C 1s spectra. The titanium alloy showed a higher carbidic contribution than the steel implanted at the same C + doses. A critical carbon concentrations of about 33 at.% and 23 at.% were measured for the formation of C-C bonds in Ti-6Al-4V and steel samples, respectively. The carbon atoms were bound with metal to form carbidic compounds until these critical concentrations were reached; when this C concentration was exceeded the proportion of C-C bonds increased and resulted in the growth of carbonaceous layers.

  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. Effects of nitrogen substitution in amorphous carbon films on electronic structure and surface reactivity studied with x-ray and ultra-violet photoelectron spectroscopies

    NASA Astrophysics Data System (ADS)

    Murata, Yuma; Nakayama, Rempei; Ichihara, Fumihiko; Ono, Hiroshi; Choo, Cheow-Keong; Tanaka, Katsumi

    2017-03-01

    We investigated the effects of incorporating a low percentage of nitrogen on the local and the electronic structures of amorphous carbon (a-C) using X-ray photoelectron spectroscopy and ultra-violet photoelectron spectroscopy (UPS). Nitrogen-doped amorphous carbon films (a-CNx) with varying nitrogen contents were prepared by a thermal decomposition method using a mixture of CH4 + NH3 under atmosphere. A slight shift of the C 1s core-level spectrum toward the higher binding energy side was detected in a-CNx as a function of nitrogen content, whereas a shift of the Fermi level (EF) cannot be confirmed from the UPS results. This was interpreted as a chemical shift between carbon and nitrogen atoms rather than as a shift of the EF. The C 1s peak shifts can be explained by the presence of two kinds of C-N local structures and the charge transferred bulk C-C components by nitrogen atoms. The two kinds of deconvoluted C 1s components could be well correlated with the two N 1s components. Two localized states were detected below the EF in UPS spectra of a-CNx, which could be assigned to defect bands. These defects played a significant role in the surface reactivity, and were stabilized in a-CNx. The adsorption and reaction of NO were carried out on a-CNx as well as a-C films. It was found that both defect sites and O2- species were responsible on a-C, while O2- species were selectively active for NO adsorption on a-CNx. We concluded that nitrogen doping reduces defect density to stabilize the surface of a-C, while at the same time inducing the selective adsorption capability of NO.

  8. Photoelectron and photodissociation studies of free atoms and molecules, using synchrotron radiation

    SciTech Connect

    Medhurst, L.J.

    1991-11-01

    High resolution synchrotron radiation and Zero-Kinetic-Energy Photoelectron spectroscopy were used to study two-electron transitions in atomic systems at their ionization thresholds. Using this same technique the core-ionized mainline and satellite states of N{sub 2} and CO were studied with vibrational resolution. Vibrationally resolved synchrotron radiation was used to study the dissociation of N{sub 2}, C{sub 2}H{sub 4}, and CH{sub 3}Cl near the N 1s and C 1s thresholds. The photoelectron satellites of the argon 3s, krypton 4s and xenon 4d subshells were studied with zero kinetic energy photoelectron spectroscopy at their ionization thresholds. In all of these cases, satellites with lower binding energies are enhanced at their thresholds while those closer to the double ionization threshold are suppressed relative to their intensities at high incident light energies.

  9. Photoelectron and photodissociation studies of free atoms and molecules, using synchrotron radiation

    SciTech Connect

    Medhurst, Laura Jane

    1991-11-01

    High resolution synchrotron radiation and Zero-Kinetic-Energy Photoelectron spectroscopy were used to study two-electron transitions in atomic systems at their ionization thresholds. Using this same technique the core-ionized mainline and satellite states of N2 and CO were studied with vibrational resolution. Vibrationally resolved synchrotron radiation was used to study the dissociation of N2, C2H4, and CH3Cl near the N 1s and C 1s thresholds. The photoelectron satellites of the argon 3s, krypton 4s and xenon 4d subshells were studied with zero kinetic energy photoelectron spectroscopy at their ionization thresholds. In all of these cases, satellites with lower binding energies are enhanced at their thresholds while those closer to the double ionization threshold are suppressed relative to their intensities at high incident light energies.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Photoelectron angular distributions from two-photon ionizations of atoms

    NASA Astrophysics Data System (ADS)

    Haber, Louis Hamilton

    Photoelectron angular distributions provide detailed information about interferences between different quantum pathways of photoionization. Measurements of photoelectron energies and angular distributions from two-color two-photon ionizations of atoms using ultrashort pulses of extreme ultraviolet and optical light are performed using a novel, homebuilt experimental instrument. The setup is composed of an amplified femtosecond laser system, a high-order harmonic generation source, and an interaction region with photoelectron velocity map imaging The experimental temporal resolution is determined to be approximately 100 fs. Two different types of two-photon ionizations are investigated. Photoelectron angular distributions from resonant two-photon ionizations of helium are measured using the 15th high-order harmonic to excite from the ground state to either the 1s3p 1P1 state at 23.1 eV or to the 1s4p 1 P1 state at 23.7 eV and either 800, 400, or 267 nm to ionize. The anisotropy parameters allow for the determination of the energy-dependent ratios of radial dipole matrix elements and the phase shift differences between the S and D partial waves. Using available total cross section measurements, the absolute partial cross sections of the 1s3p1P 1 state are obtained, providing the complete information on photoionization. The experimental results are in excellent agreement with theoretical predictions using the one-electron model. Additional experiments are aimed at studying atomic free-free transitions. Two-color two-photon above threshold ionizations of helium and argon are investigated using selected high-order harmonics and perturbative infrared dressing fields. The measured anisotropy parameters and cross section ratios of the positive and negative above threshold ionization sidebands are compared to theoretical predictions using second-order perturbation theory and the soft-photon approximation. In general, deviations between the experimental results and the

  16. Photoelectron angular distribution from free SiO2 nanoparticles as a probe of elastic electron scattering.

    PubMed

    Antonsson, E; Langer, B; Halfpap, I; Gottwald, J; Rühl, E

    2017-06-28

    In order to gain quantitative information on the surface composition of nanoparticles from X-ray photoelectron spectroscopy, a detailed understanding of photoelectron transport phenomena in these samples is needed. Theoretical results on the elastic and inelastic scattering have been reported, but a rigorous experimental verification is lacking. We report in this work on the photoelectron angular distribution from free SiO2 nanoparticles (d = 122 ± 9 nm) after ionization by soft X-rays above the Si 2p and O 1s absorption edges, which gives insight into the relative importance of elastic and inelastic scattering channels in the sample particles. The photoelectron angular anisotropy is found to be lower for photoemission from SiO2 nanoparticles than that expected from the theoretical values for the isolated Si and O atoms in the photoelectron kinetic energy range 20-380 eV. The reduced angular anisotropy is explained by elastic scattering of the outgoing photoelectrons from neighboring atoms, smearing out the atomic distribution. Photoelectron angular distributions yield detailed information on photoelectron elastic scattering processes allowing for a quantification of the number of elastic scattering events the photoelectrons have undergone prior to leaving the sample. The interpretation of the experimental photoelectron angular distributions is complemented by Monte Carlo simulations, which take inelastic and elastic photoelectron scattering into account using theoretical values for the scattering cross sections. The results of the simulations reproduce the experimental photoelectron angular distributions and provide further support for the assignment that elastic and inelastic electron scattering processes need to be considered.

  17. Photoelectron angular distribution from free SiO2 nanoparticles as a probe of elastic electron scattering

    NASA Astrophysics Data System (ADS)

    Antonsson, E.; Langer, B.; Halfpap, I.; Gottwald, J.; Rühl, E.

    2017-06-01

    In order to gain quantitative information on the surface composition of nanoparticles from X-ray photoelectron spectroscopy, a detailed understanding of photoelectron transport phenomena in these samples is needed. Theoretical results on the elastic and inelastic scattering have been reported, but a rigorous experimental verification is lacking. We report in this work on the photoelectron angular distribution from free SiO2 nanoparticles (d = 122 ± 9 nm) after ionization by soft X-rays above the Si 2p and O 1s absorption edges, which gives insight into the relative importance of elastic and inelastic scattering channels in the sample particles. The photoelectron angular anisotropy is found to be lower for photoemission from SiO2 nanoparticles than that expected from the theoretical values for the isolated Si and O atoms in the photoelectron kinetic energy range 20-380 eV. The reduced angular anisotropy is explained by elastic scattering of the outgoing photoelectrons from neighboring atoms, smearing out the atomic distribution. Photoelectron angular distributions yield detailed information on photoelectron elastic scattering processes allowing for a quantification of the number of elastic scattering events the photoelectrons have undergone prior to leaving the sample. The interpretation of the experimental photoelectron angular distributions is complemented by Monte Carlo simulations, which take inelastic and elastic photoelectron scattering into account using theoretical values for the scattering cross sections. The results of the simulations reproduce the experimental photoelectron angular distributions and provide further support for the assignment that elastic and inelastic electron scattering processes need to be considered.

  18. 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.

  19. 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.

  20. X-ray photoelectron spectroscopy characterization of a nonsuperconducting Y-Ba-Cu-O superconductor-normal-metal-superconductor barrier material

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Hunt, B. D.; Foote, M. C.; Bajuk, L. J.

    1992-01-01

    A film of a novel nonsuperconducting Y-Ba-Cu-O (YBCO) barrier material was grown using conditions similar to those reported by Agostinelli et al. (1991) for forming a cubic semiconducting (c-YBCO) phase, and the material was characterized using X-ray photoelectron spectroscopy (XPS). A comparison of the XPS spectra of this material to those obtained from the orthorhombic and tetragonal phases of YBCO (o-YBCO and t-YBCO, respectively) showed that the barrier material had spectral characteristics different from those of o-YBCO and t-YBCO, particularly in the O 1s region. Features associated with the Cu-O chain and surface-reconstructed Cu-O planes were absent, consistent with expectations for the simple perovskite crystal structure of c-YBCO proposed by Agostinelli et al.

  1. X-ray photoelectron spectroscopy characterization of a nonsuperconducting Y-Ba-Cu-O superconductor-normal-metal-superconductor barrier material

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Hunt, B. D.; Foote, M. C.; Bajuk, L. J.

    1992-01-01

    A film of a novel nonsuperconducting Y-Ba-Cu-O (YBCO) barrier material was grown using conditions similar to those reported by Agostinelli et al. (1991) for forming a cubic semiconducting (c-YBCO) phase, and the material was characterized using X-ray photoelectron spectroscopy (XPS). A comparison of the XPS spectra of this material to those obtained from the orthorhombic and tetragonal phases of YBCO (o-YBCO and t-YBCO, respectively) showed that the barrier material had spectral characteristics different from those of o-YBCO and t-YBCO, particularly in the O 1s region. Features associated with the Cu-O chain and surface-reconstructed Cu-O planes were absent, consistent with expectations for the simple perovskite crystal structure of c-YBCO proposed by Agostinelli et al.

  2. 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.

  3. Emitter-site-selective photoelectron circular dichroism of trifluoromethyloxirane

    NASA Astrophysics Data System (ADS)

    Ilchen, M.; Hartmann, G.; Rupprecht, P.; Artemyev, A. N.; Coffee, R. N.; Li, Z.; Ohldag, H.; Ogasawara, H.; Osipov, T.; Ray, D.; Schmidt, Ph.; Wolf, T. J. A.; Ehresmann, A.; Moeller, S.; Knie, A.; Demekhin, Ph. V.

    2017-05-01

    The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane, C3H3F3O , is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly symmetric O 1 s and F 1 s electronic orbitals, which are localized on different molecular sites. The respective dichroic β1 and angular distribution β2 parameters are measured at the photoelectron kinetic energies from 1 to 16 eV by using variably polarized synchrotron radiation and velocity map imaging spectroscopy. The present experimental results are in good agreement with the outcome of ab initio electronic structure calculations. We report a sizable chiral asymmetry β1 of up to about 9% for the K -shell photoionization of oxygen atom. For the individual fluorine atoms, the present calculations predict asymmetries of similar size. However, being averaged over all fluorine atoms, it drops down to about 2%, as also observed in the present experiment. Our study demonstrates a strong emitter and site sensitivity of PECD in the one-photon inner-shell ionization of this chiral molecule.

  4. Emitter-site-selective photoelectron circular dichroism of trifluoromethyloxirane

    DOE PAGES

    Ilchen, M.; Hartmann, G.; Rupprecht, P.; ...

    2017-05-30

    The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane, C3H3F3O, is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly symmetric O 1s and F 1s electronic orbitals, which are localized on different molecular sites. The respective dichroic β1 and angular distribution β2 parameters are measured at the photoelectron kinetic energies from 1 to 16 eV by using variably polarized synchrotron radiation and velocity map imaging spectroscopy. The present experimental results are in good agreement with the outcome of ab initio electronic structure calculations. We report a sizable chiral asymmetry β1 of up to about 9% for themore » K -shell photoionization of oxygen atom. For the individual fluorine atoms, the present calculations predict asymmetries of similar size. However, being averaged over all fluorine atoms, it drops down to about 2%, as also observed in the present experiment. Our study demonstrates a strong emitter and site sensitivity of PECD in the one-photon inner-shell ionization of this chiral molecule.« less

  5. Experimental Investigations of the Lunar Photoelectron Sheath

    NASA Astrophysics Data System (ADS)

    Dove, A.; Sternovsky, Z.; Wang, X.; Robertson, S. H.; Lapanse, C.; Horanyi, M.; Collette, A.

    2010-12-01

    Solar ultraviolet radiation incident upon the dayside lunar surface produces a photoelectron gas that dominates the near-surface plasma environment, with a typical density of 60 cm-3 and a characteristic scale-length of ~1 m. It has traditionally been difficult to produce a photoelectron gas with sufficient density in a laboratory settings to study its properties. In our initial experiments, the characterization of the photoelectron density above a Zr surface (work function W=4.4 eV) illuminated by Xe excimer lamps (peak emission at a wavelength of 172 nm) indicated that a sheath with a Debye length on the order of 10 cm formed. We characterize the photoelectron population above the surface by utilizing an emissive probe to map the electric potential distribution above the surface, and a Langmuir probe to determine the number density and temperature of the photoelectrons. A grid is placed 7.5 cm above the Zr surface to repel photoelectrons emitted from the chamber walls. Emissive probe measurements show a potential dip of about 2 V extending ~1 cm above the zirconium surface. The size of this potential well is dependent on the number of lamps illuminating the surface, as the density of photoelectrons above the surface increases with greater illumination. The electrons in the sheath have a Maxwellian distribution with an electron temperature around 1 eV (maximum energies are expected to be approximately 2.8 eV). We will use this experimental apparatus to characterize the photoelectron sheath above other surfaces; powders, such as CeO2 have similar work functions, but different photoelectric yields. Lunar soil simulants are expected to have approximately an order of magnitude smaller yield than metallic surfaces, which will act to increase the characteristic length of the photoelectron sheath above the surface. The experiments and accompanying computer simulations are used to guide the development of new instrument concepts for future in situ plasma measurements on

  6. X-ray photoelectron spectroscopy analysis of boron defects in silicon crystal: A first-principles study

    NASA Astrophysics Data System (ADS)

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2016-05-01

    We carried out a comprehensive study on the B 1s core-level X-ray photoelectron spectroscopy (XPS) binding energies and formation energies for boron defects in crystalline silicon by first-principles calculation with careful evaluation of the local potential boundary condition for the model system using the supercell corresponding to 1000 Si atoms. It is reconfirmed that the cubo-octahedral B12 cluster in silicon crystal is unstable and exists at the saddle point decaying to the icosahedral and S4 B12 clusters. The electrically active clusters without any postannealing of ion-implanted Si are identified as icosahedral B12 clusters. The experimentally proposed threefold coordinated B is also identified as a ⟨ 001 ⟩ B - Si defect. For an as-doped sample prepared by plasma doping, the calculated XPS spectra for complexes consisting of vacancies and substitutional B atoms are consistent with the experimental spectra. It is proposed that, assuming that the XPS peak at 187.1 eV is due to substitutional B (Bs), the experimental XPS peaks at 187.9 and 186.7 eV correspond to interstitial B at the H-site and ⟨ 001 ⟩ B - Si defects, respectively. In the annealed samples, the complex of Bs and interstitial Si near the T-site is proposed as a candidate for the experimental XPS peak at 188.3 eV.

  7. Measuring the pK/pI of biomolecules using X-ray photoelectron spectroscopy.

    PubMed

    Fears, Kenan P

    2014-09-02

    Dissociation constants of GG-X-GG and X5 peptides (X = G, D, H, or K), and bovine albumin (BSA) and fibronectin (FN) were measured by X-ray photoelectron spectroscopy (XPS) in ultrahigh vacuum at room temperature. The biomolecules were deposited on Au substrates by drying 2.0 μL drops of 1.0 μg μL(-1) stock solutions in 100 mM sodium phosphate buffers (pH 1-12) at room temperature. Because of the ∼+1.3 eV shift in binding energy (BE) of protonated amines, pK values of basic amino acids were calculated by plotting the fraction of protonated amines as a function of solution pH. Similarly, the BE of carboxyl groups shifted ∼-1.3 eV upon deprotonation. While C 1s spectra were convoluted by the multiple chemical states of carbon present in the samples, the ratio of the C 1s components centered at BE = 289.0 ± 0.4 and BE = 287.9 ± 0.3 proved to reliably assess deprotonation of carboxyl groups. The pK values for the Asp (3.1 and 2.4), His (6.7), and Lys (11.3 and 10.6) peptides, and the pI of BSA (4.8) and FN (5.7), were consistent with published values; thus, these methods could potentially be used to determine the dissociation constants of surface-bound biomolecules.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Photoelectronic Sensor with Gold Nanoparticle Plasmon Antenna

    DTIC Science & Technology

    2016-07-20

    AFRL-AFOSR-JP-TR-2016-0081 Photoelectronic Sensor with Gold Nanoparticle Plasmon Antenna Yukiharu Uraoka NARA INSTITUTE OF SCIENCE AND TECHNOLOGY...REPORT TYPE Final 3. DATES COVERED (From - To) 17 Jul 2014 to 16 Jan 2016 4. TITLE AND SUBTITLE Photoelectronic Sensor with Gold Nanoparticle Plasmon...utilizing gold nanoparticles (GNPs), which are supposed to function not only as the Plasmon antenna but also as the sensing part. The photocurrent in the

  15. Multiphoton Ionization Mass and Photoelectron Spectroscopy.

    DTIC Science & Technology

    1984-07-01

    narro , band. tunable. frequency doubled dye laser Their relative importance depend% on the sample being studied ha- led to an cnormou, improcment in...block number) Mult iphoton Ionization Photoelectron Spectroscopy Laser Induced Ionization Ultraviolet Laser Radiation ft ArITAcr (camthIe i rvee ehl N...molecular ions generated by laser ionization have been monitored. Using a time of flight photoelectron spectrometer, the kinetic energy distribution of the

  16. 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.

  17. 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.

  18. Photoelectrons and solar ionizing radiation at Mars: Predictions versus MAVEN observations

    NASA Astrophysics Data System (ADS)

    Peterson, W. K.; Thiemann, E. M. B.; Eparvier, Francis G.; Andersson, Laila; Fowler, C. M.; Larson, Davin; Mitchell, Dave; Mazelle, Christian; Fontenla, Juan; Evans, J. Scott; Xu, Shaosui; Liemohn, Mike; Bougher, Stephen; Sakai, Shotaro; Cravens, T. E.; Elrod, M. K.; Benna, M.; Mahaffy, P.; Jakosky, Bruce

    2016-09-01

    Understanding the evolution of the Martian atmosphere requires knowledge of processes transforming solar irradiance into thermal energy well enough to model them accurately. Here we compare Martian photoelectron energy spectra measured at periapsis by Mars Atmosphere and Volatile Evolution MissioN (MAVEN) with calculations made using three photoelectron production codes and three solar irradiance models as well as modeled and measured CO2 densities. We restricted our comparisons to regions where the contribution from solar wind electrons and ions were negligible. The two intervals examined on 19 October 2014 have different observed incident solar irradiance spectra. In spite of the differences in photoionization cross sections and irradiance spectra used, we find the agreement between models to be within the combined uncertainties associated with the observations from the MAVEN neutral density, electron flux, and solar irradiance instruments.

  19. Slow photoelectron velocity-map imaging of cold tert-butyl peroxide

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

    Photoelectron spectra of cryogenically cooled X˜ 1A ' tert-butyl peroxide anions are obtained using slow electron velocity-map imaging. The spectra show highly structured bands corresponding to detachment to the X˜ 2A ″ and A˜ 2A' electronic states of the neutral radical and represent a notable improvement in resolution over previous photoelectron spectra. We report an electron affinity of 1.1962(20) eV and a term energy T0(A˜ 2A' ) of 0.9602(24) eV for the tert-butyl peroxy radical. New vibrational structure is resolved, providing several frequencies for both neutral states. Additionally, the threshold behavior of the photodetachment cross section is investigated within the context of Dyson orbital calculations.

  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. 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.

  2. 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.

  3. 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.

  4. 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.

  5. High-energy non-Franck-Condon vibrational excitation of CH4 by intramolecular photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Plésiat, E.; Kukk, E.; Ueda, K.; Decleva, P.; Martín, F.

    2012-11-01

    Distinct oscillations in vibrationally resolved cross section ratios for the photoionization of CH4 from the C 1s orbital at photon energies as high as 1keV are predicted. The oscillations are attributed to the different relative vibrational excitation due to the scattering of the photoelectron by the peripheral hydrogen atoms. The latter effect is also responsible for the well known EXAFS oscillations in the integrated photoelectron spectrum. The calculations are performed with an ab-initio DFT method [1], as well as with a single-particle semi-analytical model, which incorporate both the effect of the nuclear recoil and of the Coulomb corrections.

  6. 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.

  7. Exploring ultrafast dynamics of pyrazine by time-resolved photoelectron imaging.

    PubMed

    Tomasello, Gaia; Humeniuk, Alexander; Mitrić, Roland

    2014-09-18

    We present the simulation of time-resolved photoelectron imaging spectra of pyrazine in the gas phase. The approach we have adopted is based on the combination of the ab initio nonadiabatic molecular dynamics "on the fly" with an approximate treatment of the photoionization process using Dyson orbitals and Coulomb functions to describe the bound and ionized states of the photoelectron. The method has been implemented (Humeniuk, A.; et al. J. Chem. Phys 2013, 139, 134104) in the framework of the time-dependent density functional theory and has been applied here to interrogate the ultrafast internal conversion between the S2 and S1 states in pyrazine. Conventional time-resolved photoelectron spectra without angular resolution fail to locate the S2 → S1 internal conversion, because the ionization potentials relevant for the photoionization channels S2 → D1 (π(-1)) and S1 → D0 (n(-1)) are almost identical. Introducing the angular resolution in the photoelectron spectra reveals evidence of such ultrafast internal conversion and provides a more detailed picture of the overall dynamics. The simulated time- and energy-dependent anisotropy map obtained within the Dyson/time-dependent density functional theory approach is in good agreement with its experimental counterpart provided by Horio et al. (Horio, T.; et al. J. Am. Chem. Soc. 2009, 131, 10932). Our theoretical approach represents a general tool for mapping the time- and angle-resolved photoelectron spectra in complex systems and thus can be used to investigate the ultrafast relaxation processes occurring in isolated molecules.

  8. N1s and O1s double ionization of the NO and N{sub 2}O molecules

    SciTech Connect

    Hedin, L.; Zhaunerchyk, V.; Karlsson, L.; Pernestål, K.; Feifel, R.; Tashiro, M.; Ehara, M.; Linusson, P.; Eland, J. H. D.; Ueda, K.

    2014-01-28

    Single-site N1s and O1s double core ionisation of the NO and N{sub 2}O molecules has been studied using a magnetic bottle many-electron coincidence time-of-flight spectrometer at photon energies of 1100 eV and 1300 eV. The double core hole energies obtained for NO are 904.8 eV (N1s{sup −2}) and 1179.4 eV (O1s{sup −2}). The corresponding energies obtained for N{sub 2}O are 896.9 eV (terminal N1s{sup −2}), 906.5 eV (central N1s{sup −2}), and 1174.1 eV (O1s{sup −2}). The ratio between the double and single ionisation energies are in all cases close or equal to 2.20. Large chemical shifts are observed in some cases which suggest that reorganisation of the electrons upon the double ionization is significant. Δ-self-consistent field and complete active space self-consistent field (CASSCF) calculations were performed for both molecules and they are in good agreement with these results. Auger spectra of N{sub 2}O, associated with the decay of the terminal and central N1s{sup −2} as well as with the O1s{sup −2} dicationic states, were extracted showing the two electrons emitted as a result of filling the double core holes. The spectra, which are interpreted using CASSCF and complete active space configuration interaction calculations, show atomic-like character. The cross section ratio between double and single core hole creation was estimated as 1.6 × 10{sup −3} for nitrogen at 1100 eV and as 1.3 × 10{sup −3} for oxygen at 1300 eV.

  9. 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.

  10. 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.

  11. 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.

  12. Surface characterization of 7S and 11S globulin powders from soy protein examined by X-ray photoelectron spectroscopy and scanning electron microscopy.

    PubMed

    Zhao, Xiaoyan; Chen, Jun; Zhu, Qingjun; Du, Fangling; Ao, Qiang; Liu, Jie

    2011-09-01

    In this study the surface composition of 7S and 11S globulin powders from soybean proteins by aqueous buffer and reverse micelle extractions had been examined using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Analysis by XPS revealed that the O and N atomic percentage of 7S and 11S globulin surfaces from bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelle was higher than from aqueous buffer, but the C atomic percentage was lower. The O/C ratio of the 7S globulin powder from aqueous buffer and reverse micelle was similar while significant differences were obtained in the O/C ratio of the 11S globulin powder, N/C atom ratios of the 7S and 11S globulin powders and high-resolution XPS C 1s, N 1s, O 1s spectra. Powder microstructure after reverse micelle treatment showed the presence of small pores, indicating the effect of reverse micelle on the 7S and 11S globulin structure. The obtained results indicated that the reverse micelle could affect the C, O and N components on the surface of soybean proteins. Copyright © 2011 Elsevier B.V. All rights reserved.

  13. Understanding the Oxygen Evolution Reaction Mechanism on CoOx using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

    DOE PAGES

    Favaro, Marco; Yang, Jinhui; Nappini, Silvia; ...

    2017-06-09

    Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water-splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active Co3O4/Co(OH)2 biphasic electrocatalyst on Si by means of operando ambient-pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that the catalyst undergoes chemical-structuralmore » transformations as a function of the applied anodic potential, with complete conversion of the Co(OH)2 and partial conversion of the spinel Co3O4 phases to CoO(OH) under precatalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core-level regions to emerge under oxygen evolution reaction conditions on CoO(OH). The operando photoelectron spectra support assignment of these newly observed features to highly active Co4+ centers under catalytic conditions. Comparison of these results to those from a pure phase spinel Co3O4 catalyst supports this interpretation and reveals that the presence of Co(OH)2 enhances catalytic activity by promoting transformations to CoO(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.« less

  14. Reliability of Density Functional and Perturbation Theories for Calculating Core-Ionization Spectra of Free Radicals.

    PubMed

    Ljubić, Ivan

    2014-06-10

    The C 1s, N 1s, and O 1s ionization energies were calculated for the three stable nitroxide free radicals, viz., tempo and its two analogues, and compared to their most recent high-resolution core photoelectron spectra. We compare the performance of unrestricted and restricted open shell based ΔHF, ΔMP2, and ΔB3LYP methods. A mixed basis set is employed in all cases, which consists of the core-valence correlation-consistent triple-ζ basis set (cc-pCVTZ or cc-pwCVTZ) on the atom whose core-electron binding energy is calculated, model core potentials on the remaining first row atoms, and the cc-pVDZ basis set on the hydrogen atoms. The best overall performance for the three free radicals is offered by the restricted open shell based ΔB3LYP method. Surprisingly, both the restricted open and unrestricted second-order perturbation theories perform relatively poorly and typically do not warrant additional computational effort over the reference ΔHF methods. This is particularly true of the ΔZAPT method, which exhibits a number of grave failures that render it unsuitable for calculating the core-ionization spectra.

  15. 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.

  16. 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.

  17. Graphene defect formation by extreme ultraviolet generated photoelectrons

    SciTech Connect

    Gao, A. Lee, C. J.; Bijkerk, F.

    2014-08-07

    We have studied the effect of photoelectrons on defect formation in graphene during extreme ultraviolet (EUV) irradiation. Assuming the major role of these low energy electrons, we have mimicked the process by using low energy primary electrons. Graphene is irradiated by an electron beam with energy lower than 80 eV. After e-beam irradiation, it is found that the D peak, I(D), appears in the Raman spectrum, indicating defect formation in graphene. The evolution of I(D)/I(G) follows the amorphization trajectory with increasing irradiation dose, indicating that graphene goes through a transformation from microcrystalline to nanocrystalline and then further to amorphous carbon. Further, irradiation of graphene with increased water partial pressure does not significantly change the Raman spectra, which suggests that, in the extremely low energy range, e-beam induced chemical reactions between residual water and graphene are not the dominant mechanism driving defect formation in graphene. Single layer graphene, partially suspended over holes was irradiated with EUV radiation. By comparing with the Raman results from e-beam irradiation, it is concluded that the photoelectrons, especially those from the valence band, contribute to defect formation in graphene during irradiation.

  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. High resolution photoelectron spectroscopy and femtosecond intramolecular dynamics of H2CCO + and D2CCO +

    NASA Astrophysics Data System (ADS)

    Niu, Baohua; Bai, Ying; Shirley, David A.

    1993-08-01

    High resolution helium Iα (584 Å) photoelectron spectra of H2CCO and D2CCO are reported. The present spectra of the ground states of ketene cations show more vibrational fine structure than previously reported. The adiabatic ionization energies (AIEs) of the cations' first, second, and fifth excited states are determined unambiguously. The doubletlike fine structures present in the first excited states of ketene cations imply the excitation of a ``soft'' mode that was not observed before. It was assigned to the ν5 mode, which is characterized by the CH2 (CD2) group out-of-plane wagging motion. The complexity of the photoelectron spectra obtained for the ionic first excited states is attributed to the possible dissociation and predissociation of this state. Strong isotope effects are observed in the vibronic (vibrational) couplings in most of the ionic states. Vibrational autocorrelation functions are calculated from the high-resolution photoelectron spectra for four of the six ionic states observed. The dynamics of the ground states of the cations are characterized by a wave packet oscillating with small amplitude around the minimum of the upper potential energy surfaces (PES). The decay dynamics of the ionic first and fifth excited states of ketene are characterized by ultrafast intramolecular processes such as dissociation and predissociation.

  20. 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.

  1. 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.

  2. Ultraviolet photoelectron spectroscopy of Pd-Si glasses

    NASA Astrophysics Data System (ADS)

    Waclawski, B. J.; Boudreaux, D. S.

    1980-02-01

    In order to determine systematic changes in the density of states with alloy composition, photoelectron spectra at hv=21.2 eV were measured for several amorphous alloys based on the well-known Pd-Si glass system. Three binary alloys with 15, 20, and 25 at. % Si, two ternaries, Pd 80 Si 17 Cu 3 and Pd 80 Si 14 Cu 6, and polycrystalline Pd were analyzed. Compared to Pd, both the density of states at the Fermi energy and the d-band width are reduced in the glasses. The d-bands display an overall shift of 0.4 eV over the range of alloy compositions studied. Partial agreement with recent density of states calculations was obtained.

  3. X-Ray Photoelectron Spectroscopic Characterization of Iron Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Radu, T.; Iacovita, C.; Benea, D.; Turcu, R.

    2017-05-01

    We report X-ray photoelectron spectroscopy (XPS) results on iron oxide magnetic nanoparticle (Fe3O4) synthesized using solvothermal reduction in the presence of polyethylene glycol. The magnetite obtained was employed as precursor for the synthesis of γ-Fe2O3 (by oxygen dissociation) which in turn was transformed into α-Fe2O3. We confirmed the magnetite, maghemite and hematite structure by Fourier Transformed Spectroscopy (FTIR) and X-ray diffraction (XRD). The analysis of the XPS core level and valence band (VB) photoemission spectra for all investigated samples is discussed in terms of the degree of iron oxidation. This is of fundamental importance to better understand the electronic structure of the obtained iron oxide nanoparticles in order to control and improve their quality for specific biomedical applications. Moreover, theoretical band structure calculations are performed for magnetite and the separate contributions of Fe in tetragonal and octahedral environment are shown.

  4. Slow photoelectron imaging spectroscopy of CCO- and CCS-.

    PubMed

    Garand, Etienne; Yacovitch, Tara I; Neumark, Daniel M

    2008-08-21

    High-resolution photodetachment spectra of CCO(-) and CCS(-) using slow photoelectron velocity-map imaging spectroscopy are reported. Well-resolved transitions to the neutral X (3)Sigma(-), a (1)Delta, b (1)Sigma(+), and A (3)Pi states are seen for both species. The electron affinities of CCO and CCS are determined to be 2.3107+/-0.0006 and 2.7475+/-0.0006 eV, respectively, and precise term energies for the a (1)Delta, b (1)Sigma(+), and A (3)Pi excited states are also determined. The two low-lying singlet states of CCS are observed for the first time, as are several vibronic transitions within the four bands. Analysis of hot bands finds the spin-orbit orbit splitting in the X (2)Pi ground state of CCO(-) and CCS(-) to be 61 and 195 cm(-1), respectively.

  5. Core level photoelectron spectroscopy probed heterogeneous xenon/neon clusters

    NASA Astrophysics Data System (ADS)

    Pokapanich, Wandared; Björneholm, Olle; Öhrwall, Gunnar; Tchaplyguine, Maxim

    2017-06-01

    Binary rare gas clusters; xenon and neon which have a significant contrariety between sizes, produced by a co-expansion set up and have been studied using synchrotron radiation based x-ray photoelectron spectroscopy. Concentration ratios of the heterogeneous clusters; 1%, 3%, 5% and 10% were controlled. The core level spectra were used to determine structure of the mixed cluster and analyzed by considering screening mechanisms. Furthermore, electron binding energy shift calculations demonstrated cluster aggregation models which may occur in such process. The results showed that in the case of low mixing ratios of 3% and 5% of xenon in neon, the geometric structures exhibit xenon in the center and xenon/neon interfaced in the outer shells. However, neon cluster vanished when the concentration of xenon was increased to 10%.

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

    PubMed

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

    2014-06-06

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

  7. 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.

  8. 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

  9. Spin polarization of photoelectrons from topological insulators.

    PubMed

    Park, Cheol-Hwan; Louie, Steven G

    2012-08-31

    We show that the degree of spin polarization of photoelectrons from the surface states of topological insulators is 100% if fully polarized light is used as in typical photoemission measurements, and, hence, can be significantly higher than that of the initial state. Further, the spin orientation of these photoelectrons in general can also be very different from that of the initial surface state and is controlled by the photon polarization. A rich set of predicted phenomena have recently been confirmed by spin- and angle-resolved photoemission experiments.

  10. 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.

  11. 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.

  12. 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.

  13. Near-threshold photoelectron angular distributions from two-photon resonant photoionization of He

    NASA Astrophysics Data System (ADS)

    O'Keeffe, P.; Mihelič, A.; Bolognesi, P.; Žitnik, M.; Moise, A.; Richter, R.; Avaldi, L.

    2013-01-01

    Two-photon resonant photoionization of helium is investigated both experimentally and theoretically. Ground state helium atoms are excited to the 1s4p, 1s5p and 1s6p 1P states by synchrotron radiation and ionized by a synchronized infrared pulsed picosecond laser. The photoelectron angular distributions of the emitted electrons are measured using a velocity map imaging (VMI) spectrometer. The measured asymmetry parameters of the angular distribution allow the phase differences and the ratios of the dipole matrix elements of the 1sɛs and 1sɛd channels to be determined. The experimental results agree with the calculated values obtained in a configuration-interaction calculation with a Coulomb-Sturmian basis set. The effects of the radiative decay of the intermediate state and the static electric field of the VMI spectrometer on the measurements are discussed.

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

    SciTech Connect

    Zhou, Xin

    1998-11-30

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

  16. X-ray Photoelectron Spectroscopy Study of Argon-Plasma-Treated Fluoropolymers

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Lopata, Eugene S.; Finney, Lorie S.

    1994-01-01

    Films of poly(tetrafluoroethylene) (PTFE) and of a tetrafluoroethylene-perfluoroalkyl vinyl ether (approximately 49:1) copolymer (PFA) were exposed to a radio-frequency argon plasma and then examined by X-ray photoelectron spectroscopy (XPS). The use of fluoropolymer films nearly free of surface hydrocarbon contamination as well as the use of a monochromatized X-ray source for XPS removed two factors contributing to conflicting reports on the effect of exposure time on the fluorine-to-carbon (F/C) and oxygen-to-carbon (O/C) ratios for several Ar-plasma-treated fluoropolymers. Contrary to literature indications, a common pattern was found for PTFE and PFA: a moderate decrease in F/C ratio (from 1.99 to 1.40, and from 1.97 to 1.57, respectively), together with a moderate increase in O/C ratio (from negligible to about 0.10, and from 0.012 to about O.10, respectively) at very short exposures, after which the F/C ratios remained essentially constant on prolonged exposures, while the O/C ratios for PTFE and PFA leveled off at 0.11 and 0.15, respectively. The XPS C(sub 1s), spectra for these polymers exposed to the Ar plasma for 20 min were similar and presented, besides a prominent peak at 292.0 eV (CF2,) and a minor peak at 294.0 or 294.1 eV (CF3), a composite band of four curve-resolved peaks (approximately 285-290 eV) representing various CH, CC, CO, CN, and CF functionalities.

  17. 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.

  18. 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…

  19. 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.

  20. 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…

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  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. Photoelectron spectroscopy study of AlN films grown on n-type 6H-SiC by MOCVD

    NASA Astrophysics Data System (ADS)

    Liang, F.; Chen, P.; Zhao, D. G.; Jiang, D. S.; Zhao, Z. J.; Liu, Z. S.; Zhu, J. J.; Yang, J.; Liu, W.; He, X. G.; Li, X. J.; Li, X.; Liu, S. T.; Yang, H.; Liu, J. P.; Zhang, L. Q.; Zhang, Y. T.; Du, G. T.

    2016-09-01

    Photoelectron spectroscopy has been employed to analyze the content and chemical states of the elements on the surface of AlN films with different thickness, which are synthesized by metalorganic chemical vapor deposition on the n-type SiC substrates under low pressure. It is found that, besides the carbon and gallium on the AlN surface, the atom percentage of surface oxygen increases from 4.9 to 8.4, and the electron affinity also increases from 0.36 to 0.97 eV, when the thickness of AlN films increase from 50 to 400 nm. Furthermore, accompanying with the high-resolution XPS spectra of the O 1s, it is speculated that surface oxygen may be the major influence on the electron affinity, where the surface oxygen changes the surface chemical states through replacing N to form Al-O bond and Ga-O bond, although there are also a few of Ga and C contaminations in the chemical sate of Ga-O and C-C, respectively.

  8. 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

  9. 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.

  10. Toward a comprehensive understanding of solid-state core-level XPS linewidths: Experimental and theoretical studies on the Si2p and O1s linewidths in silicates

    NASA Astrophysics Data System (ADS)

    Bancroft, G. M.; Nesbitt, H. W.; Ho, R.; Shaw, D. M.; Tse, J. S.; Biesinger, M. C.

    2009-08-01

    High resolution X-ray Photoelectron Spectroscopy (XPS) core-level Si2p and O1s spectra of the nonconductors α-SiO2 (quartz) at 120 and 300 K and vitreous SiO2 at 300 K were obtained with a Kratos Axis Ultra XPS instrument (instrumental resolution of <0.4eV ) which incorporates a unique charge compensation system that minimizes differential charge broadening on nonconductors. The Si2p and O1s linewidths at 300 K ( ˜1.1 and ˜1.2eV , respectively) are similar for all silicates (and similar to previous thin film SiO2 spectra obtained previously), showing that differential charging does not contribute significantly to our spectra. At 120 K, there is a small decrease (0.04 eV) in the Si2p linewidth of α-SiO2 , but no measurable decrease in O1s linewidth. The O1s lines are generally and distinctly asymmetric. We consider all possible sources of line broadening and show that final state vibrational broadening (FSVB) and phonon broadening are the major causes of the broad and asymmetric lines. Previous high resolution gas phase XPS studies have identified large FSVB contributions to the Si2p spectra of SiCl4 , SiF4 , and Si(OCH3)4 molecules, and this vibrational structure leads total Si2p3/2 linewidths of up to ˜0.5eV , even with individual peak linewidths of <0.1eV . The Si atom of Si(OCH3)4 is an excellent analog for Si in crystalline SiO2 because the Si-O bond lengths and symmetric stretch frequencies are similar in both compounds. Similar vibrational contributions to the Si2p and O1s spectra of solid silicates are anticipated if the Si2p and O1s core-hole states produce similar changes to the Si-O bond length in both phases. To investigate the possibility, Car-Parrinello molecular dynamics calculations were performed and show that changes to Si-O bond lengths between ion and ground states (Δr) for both Si2p and O1s hole states are similar for both crystalline SiO2 and gaseous Si(OCH3)4 . Δr are -0.04Å for Si2p and ˜+0.05Å for O1s in both compounds. Indeed, the

  11. 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.

  12. A theoretical study of the XP and NEXAFS spectra of alanine: gas phase molecule, crystal, and adsorbate at the ZnO(10 ̅10) surface.

    PubMed

    Gao, You Kun; Traeger, Franziska; Kotsis, Konstantinos; Staemmler, Volker

    2011-06-14

    The adsorption of alanine on the mixed-terminated ZnO(10 ̅10) surface is studied by means of quantum-chemical ab initio calculations. Using a finite cluster model and the adsorption geometry as obtained both by periodic CPMD and embedded cluster calculations, the C1s, N1s and O1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra are calculated for single alanine molecules on ZnO(10 ̅10). These spectra are compared with the spectra calculated for alanine in the gas phase and in its crystalline form and with experimental XPS and NEXAFS data for the isolated alanine molecule and for alanine adsorbed on ZnO(10 ̅10) at multilayer and monolayer coverage. The excellent agreement between the experimental and calculated XP and NEXAFS spectra confirms the calculated adsorption geometry: A single alanine molecule is bound to ZnO(10 ̅10) in a dissociated bidentate form with the two O atoms of the acid group bound to two Zn atoms of the surface and the proton transferred to one O atom of the surface. Other possible structures, such as adsorption of alanine in one of its neutral or zwitterionic forms in which the proton of the -COOH group remains at this group or is transferred to the amino group, can be excluded since they would give rise to quite different XP spectra. In the multilayer coverage regime, on the other hand, alanine is in its crystalline form as is also shown by the analysis of the XP spectra.

  13. 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.

  14. 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. Beaulieu 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 (Beaulieu 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.

  15. Theory of photoelectron production, transport and energy loss

    NASA Technical Reports Server (NTRS)

    Nagy, A. F.

    1974-01-01

    Current understanding of the theory of ionospheric photoelectron production, transport and energy loss is summarized. The various approaches used in the theoretical calculations of photoelectron fluxes appear to be self consistent and sound; improved values for a number of input parameters are needed now in order to achieve significant improvements and more confidence in the results. The major remaining problem in the present day theory of photoelectron transport and energy loss is centered around the calculations of photoelectron transit through the protonosphere.

  16. 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.

  17. 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.

  18. Screening-Constant-by-Unit-Nuclear-Charge method investigations of high lying ({sup 1}D{sub 2},{sup 1}S{sub 0}) ns, nd Rydberg series in the photoionization spectra of the halogen-like ion Kr{sup +}

    SciTech Connect

    Sakho, I.

    2014-01-15

    Energy positions and quantum defects of the 4s{sup 2}4p{sup 4} ({sup 1}D{sub 2},{sup 1}S{sub 0}) ns, nd Rydberg series originating from the 4s{sup 2}4p{sup 52}P{sub 3/2}{sup ∘} ground state and from the 4s{sup 2}4p{sup 52}P{sub 1/2}{sup ∘} metastable state of Kr{sup +} are reported. Calculations are performed using the Screening Constant by Unit Nuclear Charge (SCUNC) method. The results obtained are in suitable agreement with recent experimental data from the combined ASTRID merged-beam set up and Fourier Transform Ion Cyclotron Resonance device (Bizau et al., 2011), ALS measurements (Hinojosa et al., 2012), and multi-channel R-matrix eigenphase derivative calculations (McLaughlin and Balance, 2012). In addition, analysis of the 4s{sup 2}4p{sup 4}({sup 1}D{sub 2})nd and the 4s{sup 2}4p{sup 4}({sup 1}S{sub 0})nd resonances is given via the SCUNC procedure. The excellent results obtained from our work point out that the SCUNC formalism may be used to confirm the results of the analysis from the standard quantum-defect expansion formulas. Eventual errors occurring in the analysis can then be automatically detected and corrected via the SCUNC procedure.

  19. 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.

  20. Rotationally Resolved Photoelectron Spectroscopy of {ArXe} and {KrXe}

    NASA Astrophysics Data System (ADS)

    Piticco, Lorena; Schäfer, Martin; Merkt, Frederic

    2012-06-01

    The high resolution spectroscopic information available on the low-lying electronic states of ArXe^+ and KrXe^+ is limited to vibrationally resolved emission spectra of the C_2 1/2 → (X 1/2, A_2 1/2), B 1/2 → (X 1/2, A_2 1/2) and C_1 3/2 → A_1 3/2 band systems and to vibrationally resolved threshold photoelectron spectra of ArXe and KrXe. Recently ab initio potential functions for these states have been reported. Rotationally resolved photoelectron spectra of the lowest three electronic states of ArXe^+ and KrXe^+ have been recorded by PFI-ZEKE photoelectron spectroscopy following 1{VUV}+1' resonant two-photon excitation from the X 0^+ ground state of ArXe and KrXe via selected rotational levels of the C 1 and D 0^+ excited states (C 0^+ and D 1 in the case of KrXe). The bandwidth of the vacuum-ultraviolet radiation used to access the intermediate states was narrow enough to enable the selection of individual isotopomers. Photoelectron spectra recorded from several rovibrational levels of the intermediate states provided access to the X 1/2 (v^+ = 0-15), A_1 3/2 (v^+ = 0-3) and A_2 1/2 (v^+ = 0-8) levels of ArXe^+ and the X 1/2 (v^+ = 5,22,28) and A_1 3/2 (v^+ = 3-5) levels of KrXe^+. The analysis of the rovibrational structure of the photoelectron spectra led to improved spectroscopic parameters for these states and to a better description of the low-lying electronic states of ArXe^+ and KrXe^+. K. P. Huber and R. H. Lipson, J. Mol. Spectrosc. 119, 433 (1986). M. Tsuji, M. Tanaka and Y. Nishimura, Chem. Phys. Lett. 262, 349 (1996). H. Yoshii, T. Hayaishi, T. Onuma, T. Aoto, Y. Morioka and K. Ito, J. Chem. Phys. 116, 7468 (2002). O. Zehnder and F. Merkt, J. Chem. Phys. 128, 014306 (2008). H. Yoshii, T. Tanaka, Y. Morioka, T. Hayaishi and K. Ito, J. Chem. Phys. 111, 10595 (1999). O. Zehnder and F. Merkt, Mol. Phys. 106, 1215 (2008). L. A. Viehland, B. R. Gray and T. G. Wright, Mol. Phys. 108, 547 (2010). L. Piticco, F. Merkt, A. A. Cholewinski, F. R. W. Mc

  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. C 1s and N 1s core excitation of aniline: Experiment by electron impact and ab initio calculations

    SciTech Connect

    Duflot, D.; Flament, J.-P.; Giuliani, A.; Heinesch, J.; Grogna, M.; Hubin-Franskin, M.-J.

    2007-05-15

    Core shell excitation spectra of aniline at the carbon and nitrogen 1s edges have been obtained by inner-shell electron energy-loss spectroscopy recorded under scattering conditions where electric dipolar conditions dominate, with higher resolution than in the previous studies. They are interpreted with the aid of ab initio configuration interaction calculations. The spectrum at the C 1s edge is dominated by an intense {pi}{sup *} band. The calculated chemical shift due to the different chemical environment at the carbon 1s edge calculated is in agreement with the experimental observations within a few tenths of an eV. The transition energies of the most intense bands in the C 1s excitation spectrum are discussed at different levels of calculations. In the nitrogen 1s excitation spectrum the most intense bands are due to Rydberg-valence transitions involving the {sigma}{sup *}-type molecular orbitals, in agreement with the experiment. This assignment is different from that of extended Hueckel molecular orbital calculations. The geometries of the core excited states have been calculated and compared to their equivalent core molecules and benzene.

  3. Imaging photoelectron circular dichroism of chiral molecules by femtosecond multiphoton coincidence detection.

    PubMed

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

    2013-12-21

    Here, we provide a detailed account of novel experiments employing electron-ion coincidence imaging to discriminate chiral molecules. The full three-dimensional angular scattering distribution of electrons is measured after photoexcitation with either left or right circular polarized light. The experiment is performed using a simplified photoelectron-photoion coincidence imaging setup employing only a single particle imaging detector. Results are reported applying this technique to enantiomers of the chiral molecule camphor after three-photon ionization by circularly polarized femtosecond laser pulses at 400 nm and 380 nm. The electron-ion coincidence imaging provides the photoelectron spectrum of mass-selected ions that are observed in the time-of-flight mass spectra. The coincident photoelectron spectra of the parent camphor ion and the various fragment ions are the same, so it can be concluded that fragmentation of camphor happens after ionization. We discuss the forward-backward asymmetry in the photoelectron angular distribution which is expressed in Legendre polynomials with moments up to order six. Furthermore, we present a method, similar to one-photon electron circular dichroism, to quantify the strength of the chiral electron asymmetry in a single parameter. The circular dichroism in the photoelectron angular distribution of camphor is measured to be 8% at 400 nm. The electron circular dichroism using femtosecond multiphoton excitation is of opposite sign and about 60% larger than the electron dichroism observed before in near-threshold one-photon ionization with synchrotron excitation. We interpret our multiphoton ionization as being resonant at the two-photon level with the 3s and 3p Rydberg states of camphor. Theoretical calculations are presented that model the photoelectron angular distribution from a prealigned camphor molecule using density functional theory and continuum multiple scattering X alpha photoelectron scattering calculations

  4. 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. © 2011 American Institute of Physics

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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 [C3H3({tilde X}{}^2B_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 C3H3. 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 {tilde X}^ + {- tilde X} 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(C3H3) value obtained based on the VUV-VMI-TPE measurement is consistent with the value determined by the VUV laser PIE spectrum of supersonically cooled C3H3({tilde X}{}^2B_1) radicals, which is also reported in this article.

  6. Angular distributions of molecular Auger electrons: The case of C 1s Auger emission in CO

    SciTech Connect

    Semenov, S. K.; Kuznetsov, V. V.; Cherepkov, N. A.; Bolognesi, P.; Feyer, V.; Lahmam-Bennani, A.; Casagrande, M. E. Staicu; Avaldi, L.

    2007-03-15

    The results of a study of the Auger-electron-photoelectron angular correlations in the case of the C 1s ionization of the CO molecule are presented and compared with theoretical calculations in the Hartree-Fock approximation based on the two-step model. The measurements have been performed at two photon energies, 305 and 318 eV, respectively, and at three angles of photoelectron emission relative to the light polarization vector: namely, 0 degree sign , 30 degree sign , and 60 degree sign . A general agreement is found between theory and experiment for the coincidence angular distributions and the relative magnitudes of the Auger-electron-photoelectron angular correlations. However, both experiment and theory show that the Auger-electron-photoelectron angular correlations are not sufficiently sensitive to the details of the Auger-electron wave function to allow a 'complete' Auger experiment in molecules. On the other hand, our calculations demonstrate that the Auger-electron angular distribution measured in the molecular frame is very sensitive to the individual contributions of different partial waves of the Auger electron. Therefore we conclude that the complete experiment for the Auger decay in molecules can be realized only measuring the Auger-electron angular distributions in the molecular frame.

  7. Photoelectron spectroscopic and computational studies of the Pt@Pb101- and Pt@Pb121-/2- anions

    PubMed Central

    Grubisic, Andrej; Wang, Haopeng; Li, Xiang; Ko, Yeon-Jae; Kocak, F. Sanem; Pederson, Mark R.; Bowen, Kit H.; Eichhorn, Bryan W.

    2011-01-01

    A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, and were prepared from “preassembled” clusters generated from crystalline samples of [K(2,2,2-crypt)]2[Pt @ Pb12] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)]2[Pt @ Pb12] also provided access to K[Pt @ Pbn]- anions in the gas phase (i.e., the K+ salts of the anions). Anion photoelectron spectra of , , and K[Pt @ Pb12]1- are presented. Extensive density functional theory calculations on and provided candidate structures and anion photoelectron spectra for and . Together, the calculated and measured photoelectron spectra show that and endohedral complexes maintain their respective D4d and slightly distorted Ih symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase. PMID:21876183

  8. 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-}].

  9. 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.

  10. 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.

  11. 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.

  12. Surface structure of lithiated graphite by X-ray photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Lee, Choong Man; Yang, S.-H.; Mun, B.-J.; Ross, Philip N.

    2001-04-01

    The surface composition and structure of a stage-one lithium intercalation compound (Li-GIC) was studied by X-ray photoelectron diffraction (XPD) from Li 1s and C 1s core levels. The Li-GIC was prepared in situ by vapor phase intercalation of lithium into highly oriented pyrolitic graphite (HOPG) in an ultra-high vacuum system. Stage-one Li-GIC, LiC 6, having a characteristic golden color, was obtained using Li evaporation onto a HOPG substrate at 400 K, while a metallic lithium overlayer was observed at depositions below room temperature. XPD patterns of Li 1s and C 1s intensities as a function of the polar emission angle were obtained at a fixed photon energy of 1253.6 eV. The experimental XPD patterns on the HOPG and the stage-one Li-GIC were both in quite good agreement with calculated XPD patterns based on Rehr-Albers separable representation for scattering of the emitted photoelectrons. The structural model for the surface of the Li-GIC producing the best fit to the experimental data has the bulk LiC 6 lattice with surface termination in the graphene plane.

  13. 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.

  14. Photoelectron imaging using an ellipsoidal display analyzer

    NASA Astrophysics Data System (ADS)

    Dütemeyer, T.; Quitmann, C.; Kitz, M.; Dörnemann, K.; Johansson, L. S. O.; Reihl, B.

    2001-06-01

    We have built an ellipsoidal display analyzer (EDA) for angle-resolved photoelectron spectroscopy and related techniques. The instrument is an improved version of a design by Eastman et al. [Nucl. Instrum. Methods 172, 327 (1980)] and measures the angle-resolved intensity distribution of photoelectrons at fixed energy I(θ,φ)|E=const.. Such two-dimensional cuts through the Brillouin zone are recorded using a position-sensitive detector. The large acceptance angle (Δθ=43° in the polar direction and Δφ=360° in the azimuthal direction) leads to a collection efficiency which exceeds that of conventional hemispherical analyzers by a factor of about 3000. Using ray-tracing calculations we analyze the electron optical properties of the various analyzer components and optimize their arrangement. This minimizes distortions and aberrations in the recorded images and greatly improves the performance compared to previous realizations of this analyzer. We present examples demonstrating the performance of the analyzer and its versatility. Using a commercial He-discharge lamp we are able to measure complete angular distribution patterns in less than 5 s. The energy and angular resolution are ΔEEDA=85 meV and Δθ=1.2°, respectively. Complete stacks of such cuts through the Brillouin zone at different kinetic energies E can be acquired automatically using custom software. The raw data are processed leading to a three-dimensional set (I(EB,k∥) of photoelectron intensity versus binding energy E and wave vector k∥. From this all relevant information, like the dispersion relations EB(k∥) along arbitrary directions of the Brillouin zone or Fermi-surface maps, can then be computed. An additional electron gun enables low-energy electron diffraction, Auger electron spectroscopy, and electron energy-loss spectroscopy. Switching between electrons and photons as the excitation source is possible without any movement of the sample or analyzer. Because of the high acquisition

  15. 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

  16. Vibrations of acrylonitrile in N 1s excited states

    NASA Astrophysics Data System (ADS)

    Ilakovac, V.; Carniato, S.; Gallet, J.-J.; Kukk, E.; Horvatić, D.; Ilakovac, A.

    2008-01-01

    The N 1s near edge x-ray absorption fine structure spectra of acrylonitrile gas are accurately reproduced by a complete ab initio multidimensional vibrational analysis. The role of π∗ -orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the π⊥∗(C=C-C≡N) delocalized orbital excites mostly stretching vibrations of the whole spinal column of the molecule. Promoting a core electron to the localized π∥∗(C≡N) produces C≡N stretching vibration combined with two strong bending modes of the C-C≡N end of the molecule, related to the change of carbon hybridization.

  17. 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.

  18. 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.

  19. Vanadium-doped small silicon clusters: Photoelectron spectroscopy and density-functional calculations

    NASA Astrophysics Data System (ADS)

    Xu, Hong-Guang; Zhang, Zeng-Guang; Feng, Yuan; Yuan, Jinyun; Zhao, Yuchao; Zheng, Weijun

    2010-03-01

    Vanadium-doped small silicon clusters, VSin- and VSin- ( n = 3-6), have been studied by anion photoelectron spectroscopy. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these clusters were obtained from their photoelectron spectra. We have also conducted density-functional calculations of VSin- and VSin- clusters and determined their structures by comparison of theoretical calculations with experimental results. Our results show that two V atoms in VSin- clusters tend to form a strong V-V bond. VSi6- has D3d symmetry with the six Si atoms forming a chair like six-membered ring similar to the ring in cyclohexane and the two vanadium atoms are joined with a δ bond.

  20. Photoelectron spectroscopy of quinoline derivatives. Correlation of experimental ionization potentials with calculated molecular energies

    NASA Astrophysics Data System (ADS)

    Ahmed, A. A.; Julliard, M.; Chanon, F.; Chanon, M.; Gracian, F.; Pfister-Guillouzo, G.

    1997-03-01

    Experimental ionization potentials of quinoline 1 and substituted quinolines: 6-methylquinoline 2, 2,6-dimethylquinoline 3, 6-methoxyquinoline 4, 3-bromoquinoline 5, 2-chloro-4-methylquinoline 6, 4-hydroxyquinoline 7, 4-hydroxy-2-methylquinoline 8, 2-hydroxy-4-methylquinoline 9, 4-methoxyquinoline 10, 4- methoxy-2-methylquinoline 11, 2-methoxy-4-methylquinoline 12, were measured by photoelectron spectroscopy. Molecular orbital energies of the same derivatives were calculated by the Austin Method 1. The assignments of the bands of the photoelectron spectra were done with the aid of the theoretical calculations and on the basis of the substituent effects. For quinolines 1-6 a good agreement was found between the experimental ionization potentials and the calculated orbital energies.

  1. 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.

  2. Electron Localization in Dissociating H2+ by Retroaction of a Photoelectron onto Its Source

    DOE PAGES

    Waitz, M.; Asliturk, D.; Wechselberger, N.; ...

    2016-01-26

    We investigate the dissociation of H2+ into a proton and a H0 after single ionization with photons of an energy close to the threshold. We find that the p+ and the H0 do not emerge symmetrically in the case of the H2+ dissociating along the 1sσg ground state. Instead, a preference for the ejection of the p+ in the direction of the escaping photoelectron can be observed. This symmetry breaking is strongest for very small electron energies. Our experiment is consistent with a recent prediction by Serov and Kheifets. In their model, which treats the photoelectron classically, the symmetry breakingmore » is induced by the retroaction of the long-range Coulomb potential onto the dissociating H2+.« less

  3. 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.

  4. 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.

  5. Photoelectron spectroscopy of supersonic molecular beams

    NASA Astrophysics Data System (ADS)

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

    1981-12-01

    A high-resolution photoelectron spectrometer which uses molecular beam sampling is described. Photons from a rare-gas resonance lamp or UV laser are crossed with the beam from a differentially pumped supersonic nozzle source. The resulting photoelectrons are collected by an electrostatic analyzer of a unique design consisting of a 90° spherical sector preanalyzer, a system of lenses, and a 180° hemispherical deflector. A multichannel detection system based on dual microchannel plates with a resistive anode position encoder provides an increase in counting efficiency by a factor of 12 over the equivalent single channel detector. The apparatus has demonstrated an instrumental resolution of better than 10 meV FWHM, limited largely by the photon source linewidth. A quadrupole mass spectrometer is used to characterize the composition of the molecular beam. Extensive differential pumping is provided to protect the critical surfaces of the analyzer and mass spectrometer from contamination. Because of the near elimination of Doppler and rotational broadenings, the practical resolution is the highest yet obtained in molecular PES.

  6. Quabantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

    PubMed Central

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

    2016-01-01

    Over the past decade, energy-dependent ambient pressure X-ray photoelectron spectroscopy (AP-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 at 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. PMID:27389231

  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. Gas phase anion photoelectron spectroscopy and theoretical investigation of gold acetylide species

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Zhang, Wenjing; Xu, Xi-Ling; Yuan, Jinyun; Xu, Hong-Guang; Zheng, Weijun

    2017-05-01

    We conducted gas phase anion photoelectron spectroscopy and density functional theory studies on a number of gold acetylide species, such as AuC2H, AuC2Au, and Au2C2H. Based on the photoelectron spectra, the electron affinities of AuC2H, AuC2Au, and Au2C2H are measured to be 1.54(±0.04), 1.60(±0.08), and 4.23(±0.08) eV, respectively. The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of AuC2H and AuC2Au are measured to be about 2.62 and 2.48 eV, respectively. It is interesting that photoelectron spectra of AuC2H- and AuC2Au- display similar spectral features. The comparison of experimental and theoretical results confirms that the ground-state structures of AuC2H-, AuC2Au-, and their neutrals are all linear with Au—C≡C—H and Au—C≡C—Au configurations. The similar geometric structures, spectral features, HOMO-LUMO gaps, and chemical bonding between AuC2H-/0 and AuC2Au-/0 demonstrate that Au atom behaves like H atom in these species. The photoelectron spectrum of Au2C2H- shows that Au2C2H has a high electron affinity of 4.23(±0.08) eV, indicating Au2C2H is a superhalogen. Further, we found an unusual similarity between the terminal Au atom of Au2C2H- and the iodine atom of IAuC2H-.

  9. 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.

  10. Satellite spectra of heliumlike nickel

    SciTech Connect

    Hsuan, H.; Bitter, M.; Hill, K.W.; von Goeler, S. Grek, B.; Johnson, D.; Johnson, L.C.; Sesnic, S.; Bhalla, C.P.; Karim, K.R.

    1987-02-01

    Spectra of heliumlike nickel, NiXXVII, have been observed from Tokamak Fusion Test Reactor (TFTR) plasmas with a high resolution crystal spectrometer. The experimental arrangement permits simultaneous observation of the heliumlike resonance line, the intercombination and forbidden lines, and all the associated satellites due to transitions 1s/sup 2/nl - 1s2l'nl'' with N greater than or equal to 2. Relative wavelengths and line intensities can thus be determined very accurately. The observed spectral data are in good agreement with results from the present Hartree-Fock-Slater atomic model calculations and predictions from the Z-expansion method.

  11. High-resolution photoelectron spectroscopy and calculations of the highest bound levels of {{\\rm{D}}}_{2}^{+} below the first dissociation threshold

    NASA Astrophysics Data System (ADS)

    Beyer, Maximilian; Merkt, Frédéric

    2017-08-01

    Pulsed-field ionization zero-kinetic-energy photoelectron spectra of D2 have been recorded from the intermediate \\bar{{{H}}}{}1{{{Σ }}}g+ state to determine the positions of bound rovibronic levels of {{{D}}}2+ located within 1400 cm-1 of the D+ + D(1s) dissociation threshold. The ion-pair character of the \\bar{{{H}}} intermediate state resulted in large changes {{Δ }}N={N}+-N of the rotational quantum number upon photoionization, which enabled the observation of levels of {{{D}}}2+ with rotational quantum number {N}+ as high as 10. The experimental data cover a range of levels within which the usual hierarchy of timescales of the electronic, vibrational and rotational motions is inverted. The term values of these levels with respect to the X {}1{{{Σ }}}g+(v=0,N=0) rovibronic ground state of D2 and the energy intervals of the ionic states, measured with an accuracy of typically 0.11 cm-1 and 0.02 cm-1, respectively, are compared with positions calculated ab initio at various degrees of approximation, starting from the Born-Oppenheimer approximation and successively including adiabatic, nonadiabatic, relativistic and radiative corrections. The comparison shows that the accuracy of the photoelectron-spectroscopic measurement is sufficient to reveal the effects of the adiabatic, nonadiabatic, relativistic and radiative corrections on the absolute term values. Comparing our calculations, which rely on an approximate evaluation of the nonadiabatic corrections based on effective R-dependent reduced masses, with the theoretical results for {N}+≤slant 5 by Moss (1993 J. Chem. Soc. Faraday Trans. 89 3851) and for {N}+≤slant 8 by Wolniewicz and Orlikowski (1991 Mol. Phys. 74 103) enables the quantification of the errors introduced by our approximative treatment of the nonadiabatic corrections. Improved rotational term values of the \\bar{{{H}}}(v=12) level were also derived.

  12. Spin-polarized photoelectron diffraction of nanoscale manganese structures

    NASA Astrophysics Data System (ADS)

    Keen, A. M.; Baker, S. H.; Binns, C.; Mozley, S. N.; Norris, C.; Derbyshire, H. S.

    1998-07-01

    Magnetic ordering in bulk Mn and nanoscale Mn islands deposited on highly oriented pyrolytic graphite has been investigated with spin-polarised photoelectron diffraction (SPPED). Results for the bulk film show the expected step in the ratio of intensities of the Mn 3 s core level 5S and 7S multiplets. This occurs at a temperature of 505 ± 20 K or 5.3 times TN, the bulk Néel temperature and compares well with similar data from Mn compounds. In contrast the equivalent step observed with mesoscopic Mn islands of mean size 6 nm is found to occur at 85 ± 15 K, that is, at about TN. The high proportion of surface atoms (˜25%) in the nanoscale system produced an enhanced photoemission signal from the surface allowing a deconvolution of surface and interior contributions to the 3 s spectra. We thus show that the step in the ratio of multiplet intensities arises entirely from the surface component of the 3 s spectrum. This supports a recent interpretation that the step is due to a surface specific transition in longrange magnetic order that can be well above TN,bulk for antiferromagnets and TC,bulk for ferromagnets.

  13. Retrieving plasmonic near-field information: A quantum-mechanical model for streaking photoelectron spectroscopy of gold nanospheres

    NASA Astrophysics Data System (ADS)

    Li, Jianxiong; Saydanzad, Erfan; Thumm, Uwe

    2016-11-01

    Streaked photoemission from nanostructures is characterized by size- and material-dependent nanometer-scale variations of the induced nanoplasmonic response to the electronic field of the streaking pulse and thus holds promise of allowing photoelectron imaging with both subfemtosecond temporal and nanometer spatial resolution. In order to scrutinize the driven collective electronic dynamics in 10-200-nm-diameter gold nanospheres, we calculated the plasmonic field induced by streaking pulses in the infrared and visible spectral range and developed a quantum-mechanical model for streaked photoemission by extreme ultraviolet pulses. Our simulated photoelectron spectra reveal a significant amplitude enhancement and phase shift of the photoelectron streaking trace relative to calculations that exclude the induced plasmonic field. Both are most pronounced for streaking pulses tuned to the plasmon frequency and retrace the plasmonic electromagnetic field enhancement and phase shift near the nanosphere surface.

  14. 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.

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

    PubMed

    Sen, Ananya; Matthews, Edward M; Hou, Gao-Lei; Wang, Xue-Bin; Dessent, Caroline E H

    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 [A. 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 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 allow autodetachment.

  16. High temperature photoelectron emission and surface photovoltage in semiconducting diamond

    NASA Astrophysics Data System (ADS)

    Williams, G. T.; Cooil, S. P.; Roberts, O. R.; Evans, S.; Langstaff, D. P.; Evans, D. A.

    2014-08-01

    A non-equilibrium photovoltage is generated in semiconducting diamond at above-ambient temperatures during x-ray and UV illumination that is sensitive to surface conductivity. The H-termination of a moderately doped p-type diamond (111) surface sustains a surface photovoltage up to 700 K, while the clean (2 × 1) reconstructed surface is not as severely affected. The flat-band C 1s binding energy is determined from 300 K measurement to be 283.87 eV. The true value for the H-terminated surface, determined from high temperature measurement, is (285.2 ± 0.1) eV, corresponding to a valence band maximum lying 1.6 eV below the Fermi level. This is similar to that of the reconstructed (2 × 1) surface, although this surface shows a wider spread of binding energy between 285.2 and 285.4 eV. Photovoltage quantification and correction are enabled by real-time photoelectron spectroscopy applied during annealing cycles between 300 K and 1200 K. A model is presented that accounts for the measured surface photovoltage in terms of a temperature-dependent resistance. A large, high-temperature photovoltage that is sensitive to surface conductivity and photon flux suggests a new way to use moderately B-doped diamond in voltage-based sensing devices.

  17. 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).

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. An imaging photoelectron-photoion coincidence investigation of homochiral 2R,3R-butanediol clusters

    NASA Astrophysics Data System (ADS)

    Daly, Steven; Powis, Ivan; Garcia, Gustavo A.; Tia, Maurice; Nahon, Laurent

    2017-07-01

    We report an experimental investigation of homochiral cluster formation in seeded molecular beam expansions of (2R,3R)-butanediol. Synchrotron radiation vacuum ultraviolet photoionization measurements have been performed using a double imaging electron-ion spectrometer in various configurations and modes of operation. These include measurements of the cluster ion mass spectra, wavelength scanned ion yields, and threshold electron spectra. Protonated cluster ions ranging up to n = 7 have been observed and size-selected photoelectron spectra and photoelectron circular dichroism (PECD) have been recorded by velocity map imaging, recorded in coincidence with ions, at a number of fixed photon energies. Translation temperatures of the cluster ions have been further examined by ion imaging measurements. As well as the sequence of protonated clusters with integral numbers of butanediol monomer units, a second series with half-integral monomer masses is observed and deduced to result from a facile cleavage of a butanediol monomer moiety within the nascent cluster. This second sequence of half-integral masses displays quite distinct behaviours. PECD measurements are used to show that the half-integral mass cluster ions do not share a common parentage with whole integer masses. Using an analogy developed with simple theoretical calculations of butanediol dimer structures, it is inferred that the dissociative branching into integral and half-integral ion mass sequences is controlled by the presence of different butanediol monomer conformations within the hydrogen bonded clusters.

  4. Rotationally resolved photoelectron spectroscopic study of the Jahn-Teller effect in allene

    NASA Astrophysics Data System (ADS)

    Schulenburg, A. M.; Merkt, F.

    2009-01-01

    The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of allene (C3H4) and perdeuterated allene have been recorded from the first adiabatic ionization energy up to 2200 cm-1 of internal energy in the cations at a resolution sufficient to observe the full rotational structure. The intensity distributions in the spectra are dominated by vibrational progressions in the torsional mode, which were analyzed in the realm of a two-dimensional model of the E ⊗(b1⊕b2) Jahn-Teller effect in the allene cation [C. Woywod and W. Domcke, Chem. Phys. 162, 349 (1992)]. Whereas the rotational structure of the transitions to the lowest torsional levels (00 and 41) are regular and can be qualitatively analyzed in terms of a simple orbital ionization model, the rotational structure of the spectra of the 42 and 43 levels are strongly perturbed. The photoelectron spectrum of C3H4 also reveals several weak vibrational bands in the immediate vicinity of these levels that are indicative of (ro)vibronic perturbations. A slight broadening of the transitions to the 41 levels compared to that of the vibronic ground state and the increase of the number of sharp features in the rotational structure of the spectrum of the 42 level point at the importance of large-amplitude motions not considered in previous treatments of the Jahn-Teller effect in the allene cation.

  5. 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.

  6. 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

  7. 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.

  8. Photoelectron wave function in photoionization: Plane wave or Coulomb wave? [Does photoionization of neutral targets produce Coulomb or plane waves?

    DOE PAGES

    Gozem, Samer; Gunina, Anastasia O.; Ichino, Takatoshi; ...

    2015-10-28

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

  9. X-ray photoelectron spectroscopy analysis of organic materials irradiated with gas cluster ion beam

    SciTech Connect

    Nakagiri, Motohiro; Toyoda, Noriaki; Yamada, Isao

    2011-01-07

    Irradiation effect of gas cluster ion beams (GCIB) on organic materials were studied with X-ray photoelectron spectroscopy by comparison to that with Ar-monomer ions. In the case of polyimide, the intensity of both N-C = O and -C-O- bond decreased with 500 eV Ar monomer ion irradiation. On the other hand, there was no significant change in the XPS spectra after Ar-GCIB irradiation. From the size-selected GCIB irradiation study, the damages in polyimide decreased with increasing the cluster size owing to the reduction of energy per atoms.

  10. 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.

  11. Investigation of low-Z Coster-Kronig transitions by means of Auger and photoelectron spectroscopy

    NASA Technical Reports Server (NTRS)

    Yin, L. I.; Tsang, T.; Adler, I.

    1972-01-01

    Experimental intensity ratios of Auger transitions for Co, Ni, Cu, and Zn as well as the relative L sub 2 and L sub 3 level widths of Cu and Zn, derived from their photoelectron spectra, are presented. Evidence is presented that a great deal of vacancy reorganization took place following photoionization and prior to Auger emission. These reorganizations are assumed to be due to Coster-Kronig transitions f sub 23. These results are compared with theoretical calculations and agree with predicted discontinuity at Z = 30 where f sub 23 transitions become energetically impossible.

  12. 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}.

  13. 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.

  14. Development of a single-shot CCD-based data acquisition system for time-resolved X-ray photoelectron spectroscopy at an X-ray free-electron laser facility

    PubMed Central

    Oura, Masaki; Wagai, Tatsuya; Chainani, Ashish; Miyawaki, Jun; Sato, Hiromi; Matsunami, Masaharu; Eguchi, Ritsuko; Kiss, Takayuki; Yamaguchi, Takashi; Nakatani, Yasuhiro; Togashi, Tadashi; Katayama, Tetsuo; Ogawa, Kanade; Yabashi, Makina; Tanaka, Yoshihito; Kohmura, Yoshiki; Tamasaku, Kenji; Shin, Shik; Ishikawa, Tetsuya

    2014-01-01

    In order to utilize high-brilliance photon sources, such as X-ray free-electron lasers (XFELs), for advanced time-resolved photoelectron spectroscopy (TR-PES), a single-shot CCD-based data acquisition system combined with a high-resolution hemispherical electron energy analyzer has been developed. The system’s design enables it to be controlled by an external trigger signal for single-shot pump–probe-type TR-PES. The basic performance of the system is demonstrated with an offline test, followed by online core-level photoelectron and Auger electron spectroscopy in ‘single-shot image’, ‘shot-to-shot image (image-to-image storage or block storage)’ and ‘shot-to-shot sweep’ modes at soft X-ray undulator beamline BL17SU of SPring-8. In the offline test the typical repetition rate for image-to-image storage mode has been confirmed to be about 15 Hz using a conventional pulse-generator. The function for correcting the shot-to-shot intensity fluctuations of the exciting photon beam, an important requirement for the TR-PES experiments at FEL sources, has been successfully tested at BL17SU by measuring Au 4f photoelectrons with intentionally controlled photon flux. The system has also been applied to hard X-ray PES (HAXPES) in ‘ordinary sweep’ mode as well as shot-to-shot image mode at the 27 m-long undulator beamline BL19LXU of SPring-8 and also at the SACLA XFEL facility. The XFEL-induced Ti 1s core-level spectrum of La-doped SrTiO3 is reported as a function of incident power density. The Ti 1s core-level spectrum obtained at low power density is consistent with the spectrum obtained using the synchrotron source. At high power densities the Ti 1s core-level spectra show space-charge effects which are analysed using a known mean-field model for ultrafast electron packet propagation. The results successfully confirm the capability of the present data acquisition system for carrying out the core-level HAXPES studies of condensed matter induced by the

  15. Development of a single-shot CCD-based data acquisition system for time-resolved X-ray photoelectron spectroscopy at an X-ray free-electron laser facility.

    PubMed

    Oura, Masaki; Wagai, Tatsuya; Chainani, Ashish; Miyawaki, Jun; Sato, Hiromi; Matsunami, Masaharu; Eguchi, Ritsuko; Kiss, Takayuki; Yamaguchi, Takashi; Nakatani, Yasuhiro; Togashi, Tadashi; Katayama, Tetsuo; Ogawa, Kanade; Yabashi, Makina; Tanaka, Yoshihito; Kohmura, Yoshiki; Tamasaku, Kenji; Shin, Shik; Ishikawa, Tetsuya

    2014-01-01

    In order to utilize high-brilliance photon sources, such as X-ray free-electron lasers (XFELs), for advanced time-resolved photoelectron spectroscopy (TR-PES), a single-shot CCD-based data acquisition system combined with a high-resolution hemispherical electron energy analyzer has been developed. The system's design enables it to be controlled by an external trigger signal for single-shot pump-probe-type TR-PES. The basic performance of the system is demonstrated with an offline test, followed by online core-level photoelectron and Auger electron spectroscopy in 'single-shot image', 'shot-to-shot image (image-to-image storage or block storage)' and `shot-to-shot sweep' modes at soft X-ray undulator beamline BL17SU of SPring-8. In the offline test the typical repetition rate for image-to-image storage mode has been confirmed to be about 15 Hz using a conventional pulse-generator. The function for correcting the shot-to-shot intensity fluctuations of the exciting photon beam, an important requirement for the TR-PES experiments at FEL sources, has been successfully tested at BL17SU by measuring Au 4f photoelectrons with intentionally controlled photon flux. The system has also been applied to hard X-ray PES (HAXPES) in `ordinary sweep' mode as well as shot-to-shot image mode at the 27 m-long undulator beamline BL19LXU of SPring-8 and also at the SACLA XFEL facility. The XFEL-induced Ti 1s core-level spectrum of La-doped SrTiO3 is reported as a function of incident power density. The Ti 1s core-level spectrum obtained at low power density is consistent with the spectrum obtained using the synchrotron source. At high power densities the Ti 1s core-level spectra show space-charge effects which are analysed using a known mean-field model for ultrafast electron packet propagation. The results successfully confirm the capability of the present data acquisition system for carrying out the core-level HAXPES studies of condensed matter induced by the XFEL.

  16. 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.

  17. 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.

  18. Valence double ionization electron spectra of CH3F, CH3Cl and CH3I

    NASA Astrophysics Data System (ADS)

    Hult Roos, A.; Eland, J. H. D.; Koulentianos, D.; Squibb, R. J.; Karlsson, L.; Feifel, R.

    2017-07-01

    Valence double ionization electron spectra of the methyl fluoride, methyl chloride, and methyl iodide molecules have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra are interpreted by comparison with existing ionization data, Auger spectra, and theoretical calculations. The lowest double ionization energies have been found to be around 35.0 eV, 30.6 eV, and 26.67 eV for CH3F, CH3Cl and CH3I, respectively. These energies are also compared with the predictions and implications of an empirical rule for the lowest double ionization energy in molecules.

  19. High-Resolution Photoelectron Spectroscopic Study of Cyclopropene (c-C_3H_4)

    NASA Astrophysics Data System (ADS)

    Vasilatou, Konstantina; Michaud, Julie M.; Grassi, Guido; Baykusheva, Denitsa; Merkt, Frederic

    2012-06-01

    The spectroscopic information available on the cyclopropene radical cation is limited to that contained in low-resolution He I photoelectron spectra. To better characterize the structure of this cation, we have recently measured high-resolution PFI-ZEKE photoelectron spectra of c-C_3H_4 and several of its deuterated isotopomers in the vicinity of the adiabatic ionization threshold. Our new data include fully rotationally resolved spectra of the origin band of the widetilde{X}^+←widetilde{X} transition of c-C_3H_4 and spectra of the low-vibrational levels of c-C_3H_4 and the deuterated isotopomers recorded at lower resolution. Because our efforts at synthesizing 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, the analysis of the isotopic shifts turned out to be challenging. Combining the information contained in the rotational structure of the origin band of c-C_3H_4 with the ionization energies of the isotopomers measured by photoionization mass spectrometry and the vibrational structure observed in the PFI-ZEKE spectra of the mixtures of deuterated isotopomers, we were able to draw conclusions on the structure of the cyclopropene radical cation based solely on experimental data. The adiabatic ionization energy of c-C_3H_4 was determined to be 77931.8(5) {cm}-1. M. B. Robin, C. R. Brundle, N. A. Kuebler, G. B. Ellison and K. B. Wiberg, J. Chem. Phys. 57, 1758 (1972). P. Bischof and E. Heilbronner, Helv. Chim. Acta 53, 1677 (1970).

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    SciTech Connect

    Weaver, Alexandra

    1991-12-01

    Negative ion photoelectron spectroscopy has been used to study two types of transient neutral species: bound free radicals (NO2 and NO3) and unstable neutral species ([IHI] and [FH2]). The negative ion time-of-flight photoelectron spectrometer used for these experiments is described in detail.

  6. 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…

  7. 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…

  8. 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.

  9. Conformation-selective resonant photoelectron imaging from dipole-bound states of cold 3-hydroxyphenoxide

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

    We report a photoelectron imaging and photodetachment study of cryogenically cooled 3-hydroxyphenoxide (3HOP) anions, m-HO(C6H4)O-. In a previous preliminary study, two conformations of the cold 3HOP anions with different dipole bound states were observed [D. L. Huang et al., J. Phys. Chem. Lett. 6, 2153 (2015)]. Five near-threshold vibrational resonances were revealed in the photodetachment spectrum from the dipole-bound excited states of the two conformations. Here, we report a more extensive investigation of the two conformers with observation of thirty above-threshold vibrational resonances in a wide spectral range between 18 850 and 19 920 cm-1 (˜1000 cm-1 above the detachment thresholds). By tuning the detachment laser to the vibrational resonances in the photodetachment spectrum, high-resolution conformation-selective resonant photoelectron images are obtained. Using information of the autodetachment channels and theoretical vibrational frequencies, we are able to assign the resonant peaks in the photodetachment spectrum: seventeen are assigned to vibrational levels of anti-3HOP, eight to syn-3HOP, and five to overlapping vibrational levels of both conformers. From the photodetachment spectrum and the conformation-selective resonant photoelectron spectra, we have obtained fourteen fundamental vibrational frequencies for the neutral syn- and anti-m-HO(C6H4)Oṡ radicals. The possibility to produce conformation-selected neutral beams using resonant photodetachment via dipole-bound excited states of anions is discussed.

  10. Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol, and hydroquinone

    NASA Astrophysics Data System (ADS)

    Livingstone, Ruth A.; Thompson, James O. F.; Iljina, Marija; Donaldson, Ross J.; Sussman, Benjamin J.; Paterson, Martin J.; Townsend, Dave

    2012-11-01

    Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S1 (ππ*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S1 potential surface. In catechol, the overall S1 state lifetime was observed to be 12.1 ps, which is 1-2 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S1 state and the close lying S2 (πσ*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S1/S2 interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.

  11. Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol, and hydroquinone.

    PubMed

    Livingstone, Ruth A; Thompson, James O F; Iljina, Marija; Donaldson, Ross J; Sussman, Benjamin J; Paterson, Martin J; Townsend, Dave

    2012-11-14

    Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S(1) (ππ*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S(1) potential surface. In catechol, the overall S(1) state lifetime was observed to be 12.1 ps, which is 1-2 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S(1) state and the close lying S(2) (πσ*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S(1)/S(2) interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.

  12. Photoelectron Spectroscopy of Energetic Materials and Catalytic Clusters with a 26.5 eV Tabletop Laser

    DTIC Science & Technology

    2015-04-03

    Photoelectron Spectroscopy of Energetic Materials and Catalytic Clusters with a 26.5 eV Tabletop Laser This DURIP grant was for the design and...catalytic clusters . The apparatus is now finished and presently acquiring data on representative sample in both areas.We present data for FeO2 as an...initial first experiment for mass spectra and PES of a known sample. The clusters are generated by laser ablation and the electrons are collected

  13. Auger and X-ray PhotoelectronSpectroscopy Study of the Density ofOxygen States in Bismuth, Aluminum, Silicon, and Uranium Oxides

    SciTech Connect

    Teterin, Yu A.; Ivanov, K.E.; Teterin, A. Yu; Lebedev, A.M.; Utkin, I.O.; Vukchevich, L.

    1998-08-03

    The correlation of relative partial electron density at the oxygen ions with the intensity of Auger O KLL lines in Bi2O3, Al2O3, SiO2 and UO2 has been determined by Auger and X-ray photoelectron spectroscopic methods. The dependence of the relative intensities of Auger O KL2-3L2-3 and O KL1L2-3-lines was characterized from the binding energy of O 1s electrons. The electron density of the outer valence levels of oxygen increases as the relative intensities of Anger OKL2-3L2-3 and O KL1L2-3-lines increase. The fine structure observed in the O KL1L2-3 Auger and the O 2s XPS spectra has been explained by the formation of inner valence molecular orbitals (IVMO) from the interaction of electrons of the O 2s and filled metal ns shells.

  14. 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.

  15. Plasmon-mediated Photoelectron Emission from Single, Supported Metal Nanoparticles

    NASA Astrophysics Data System (ADS)

    Grubisic, Andrej; Nesbitt, David

    2014-03-01

    Coherent multiphoton photoelectron emission (MPPE) from supported metal nanoparticles/structures has been studied at a single-particle level via scanning photoemission imaging microscopy (SPIM). Resonant excitation of localized surface plasmons (LSPs) with ultrafast laser pulses is shown to greatly amplify the photoelectron emission rate from metallic nanoparticles. In the limit of a large number of plasmon excitations, the n-photon photoelectron current scales rapidly with the electromagnetic near-field enhancement factor (|E|/|E0|)2n, indicating coherent MPPE as an extremely sensitive probe of the particle near-field. Additionally, our velocity map imaging (VMI) measurements of angle- and energy- resolved photoelectron distributions emitted from single plasmonic nanoparticles will be highlighted, with results shedding light into the complex dynamics of plasmon-induced photoelectron emission. We gratefully acknowledge Air Force Office of Scientific Research, National Science Foundation, and the National Institute of Standards and Technology for support of this work.

  16. 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

  17. Vibrationally resolved high-resolution NEXAFS and XPS spectra of phenanthrene and coronene

    SciTech Connect

    Fronzoni, Giovanna; Baseggio, Oscar; Stener, Mauro; Hua, Weijie; Tian, Guangjun; Luo, Yi; Apicella, Barbara; Alfé, Michela; Simone, Monica de; Kivimäki, Antti; Coreno, Marcello

    2014-07-28

    We performed a combined experimental and theoretical study of the C1s Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy and X-ray Photoelectron Spectroscopy in the gas phase of two polycyclic aromatic hydrocarbons (phenanthrene and coronene), typically formed in combustion reactions. In the NEXAFS of both molecules, a double-peak structure appears in the C1s → LUMO region, which differ by less than 1 eV in transition energies. The vibronic coupling is found to play an important role in such systems. It leads to weakening of the lower-energy peak and strengthening of the higher-energy one because the 0 − n (n > 0) vibrational progressions of the lower-energy peak appear in nearly the same region of the higher-energy peak. Vibrationally resolved theoretical spectra computed within the Frank-Condon (FC) approximation and linear coupling model agree well with the high-resolution experimental results. We find that FC-active normal modes all correspond to in-plane vibrations.

  18. Photoelectron energy spectra of opaque photocathodes in the extreme and far ultraviolet

    NASA Technical Reports Server (NTRS)

    Siegmund, Oswald H. W.; Gaines, Geoffrey A.

    1990-01-01

    Measurements of the EUV quantum detection efficiency (QDE) of opaque RbBr, CsBr, and KBr photocathodes are described and investigations of their photoemission characteristics over the 44-1560 A wavelength range are reported. The results show that high QDEs can be obtained in the EUV. Narrow QDE peaks at soft X-ray wavelengths occur at slightly different wavelengths for each of the materials studied. The long-wavelength thresholds vary according to the material band gap. Data on the photoemission from the photocathode layer on the microchannel plate interchannel web area are used to determine the number and energy distribution of the emitted photoelelectrons as a function of wavelength.

  19. 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.

  20. Photoelectron spectroscopy of the aluminum hydride anions: AlH2-, AlH3-, Al2H6-, Al3H9-, and Al4H12-

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxing; Wang, Haopeng; Collins, Evan; Lim, Alane; Ganteför, Gerd; Kiran, Boggavarapu; Schnöckel, Hansgeorg; Eichhorn, Bryan; Bowen, Kit

    2013-03-01

    We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2-, AlH3-, Al2H6-, Al3H9-, and Al4H12-. From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2-, AlH3-, and Al2H6- were also compared with previous predictions by theory.

  1. Photoelectron spectroscopy of the aluminum hydride anions: AlH2(-), AlH3(-), Al2H6(-), Al3H9(-), and Al4H12(-).

    PubMed

    Zhang, Xinxing; Wang, Haopeng; Collins, Evan; Lim, Alane; Ganteför, Gerd; Kiran, Boggavarapu; Schnöckel, Hansgeorg; Eichhorn, Bryan; Bowen, Kit

    2013-03-28

    We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2(-), AlH3(-), Al2H6(-), Al3H9(-), and Al4H12(-). From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2(-), AlH3(-), and Al2H6(-) were also compared with previous predictions by theory.

  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. Attosecond time-resolved streaked photoelectron spectroscopy of transition-metal nanospheres

    NASA Astrophysics Data System (ADS)

    Li, Jianxiong; Saydanzad, Erfan; Thumm, Uwe

    2017-04-01

    Streaked photoemission from nanostructured surfaces and nanoparticles by attosecond extreme ultraviolet pulses into an infrared (IR) or visible streaking pulse allows for sub-fs-resolution of the plasmonically enhanced streaking-pulse electric field. It thus holds promise for the time-resolved imaging of the dielectric response in and plasmonic fields near nanostructures. After calculating the plasmonic field induced by IR and visible streaking pulses in 10- to 200-nm diameter Au, Ag, and Cu nanospheres, we numerically simulated streaked photoelectron spectra within a quantum-mechanical model. Our spectra show significant oscillation-amplitude enhancements and phase shifts relative to calculations that neglect the induced plasmonic field. We trace these observable effects to the distinct dielectric properties of the three investigated metals, demonstrating the applicability of streaking spectroscopy to the element-specific investigation of induced time-dependent electric fields near nanoparticle surfaces.

  6. 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.

  7. 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.

  8. Effect of X-ray flux on polytetrafluoroethylene in X-ray photoelectron spectroscopy

    NASA Technical Reports Server (NTRS)

    Wheeler, D. R.; Pepper, S. V.

    1982-01-01

    The effect of the X-ray flux in X-ray photoelectron spectroscopy (STAT) on the constitution of the polytetrafluoroethylene (PTFE) surface has been examined. The radiation dose rate for our specimen was about 10 to the 7th rad/s. The structure, magnitude and binding energy of the C(1s) and F(1s) features of the XPS spectrum and the mass spectrum of gaseous species evolved during irradiation are observed. The strong time dependence of these signals over a period of several hours indicated that the surface constitution of PTFE is greatly affected by this level of radiation dose. The results are consistent with the development of a heavily cross-linked or branched structure in the PTFE surface region and the evolution of short chain fragments into the gas phase.

  9. AgO investigated by photoelectron spectroscopy: Evidence for mixed valence

    NASA Astrophysics Data System (ADS)

    Bielmann, M.; Schwaller, P.; Ruffieux, P.; Gröning, O.; Schlapbach, L.; Gröning, P.

    2002-06-01

    We present photoelectron spectroscopy investigations of in-situ prepared AgO. The sample was prepared by room temperature oxidation of Ag in an electron cyclotron resonance O2 plasma. In contrast to other measurements based on ex situ prepared AgO powder samples, our investigations show a distinct double peak structure of the O 1s signal with a remarkable chemical shift of 2.9 eV between the two O 1s components. These two components can not be motivated from a crystallographic point of view as the oxygen sites are all equivalent in the unit cell. We interpret this double peak structure as a characteristic feature of AgO and discuss it in terms of mixed valences.

  10. Effect of X-ray flux on polytetrafluoroethylene in X-ray photoelectron spectroscopy

    NASA Technical Reports Server (NTRS)

    Wheeler, D. R.; Pepper, S. V.

    1982-01-01

    The effect of the X-ray flux in X-ray photoelectron spectroscopy (STAT) on the constitution of the polytetrafluoroethylene (PTFE) surface has been examined. The radiation dose rate for our specimen was about 10 to the 7th rad/s. The structure, magnitude and binding energy of the C(1s) and F(1s) features of the XPS spectrum and the mass spectrum of gaseous species evolved during irradiation are observed. The strong time dependence of these signals over a period of several hours indicated that the surface constitution of PTFE is greatly affected by this level of radiation dose. The results are consistent with the development of a heavily cross-linked or branched structure in the PTFE surface region and the evolution of short chain fragments into the gas phase.

  11. 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).

  12. 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.

  13. 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.

  14. Photoelectron imaging of tetrahydrofuran cluster anions (THF)n- (1<=n<=100)

    NASA Astrophysics Data System (ADS)

    Young, Ryan M.; Yandell, Margaret A.; Niemeyer, Markus; Neumark, Daniel M.

    2010-10-01

    Anionic tetrahydrofuran clusters (THF)n- (1≤n≤100) are studied with photoelectron imaging as gas-phase precursors for electrons solvated in THF. Photoelectron spectra of clusters up to n =5 show two peaks, one of which is attributed to a solvated open chain radical anion and the other to the closed THF ring. At n =6, the spectra change shape abruptly, which become more characteristic of (THF)n- clusters containing solvated electrons. From n =6-100, the vertical detachment energies (VDEs) of these solvated electron clusters increase from 1.96 to 2.71 eV, scaling linearly with n-1/3. For fully deuterated (THF-d8)n- clusters, the apparent transition to a solvated electron cluster is delayed to n =11. Extrapolation of the VDEs to infinite cluster size yields a value of 3.10 eV for the bulk photoelectric threshold. The relatively large VDEs at onset and small stabilization with increasing cluster size compared to other solvated electron clusters may reflect the tendency of the bulk solvent to form preexisting voids that can readily solvate a free electron.

  15. Photoelectron imaging of tetrahydrofuran cluster anions (THF)(n) (-) (1≤n≤100).

    PubMed

    Young, Ryan M; Yandell, Margaret A; Niemeyer, Markus; Neumark, Daniel M

    2010-10-21

    Anionic tetrahydrofuran clusters (THF)(n) (-) (1≤n≤100) are studied with photoelectron imaging as gas-phase precursors for electrons solvated in THF. Photoelectron spectra of clusters up to n=5 show two peaks, one of which is attributed to a solvated open chain radical anion and the other to the closed THF ring. At n=6, the spectra change shape abruptly, which become more characteristic of (THF)(n) (-) clusters containing solvated electrons. From n=6-100, the vertical detachment energies (VDEs) of these solvated electron clusters increase from 1.96 to 2.71 eV, scaling linearly with n(-1/3). For fully deuterated (THF-d8)(n) (-) clusters, the apparent transition to a solvated electron cluster is delayed to n=11. Extrapolation of the VDEs to infinite cluster size yields a value of 3.10 eV for the bulk photoelectric threshold. The relatively large VDEs at onset and small stabilization with increasing cluster size compared to other solvated electron clusters may reflect the tendency of the bulk solvent to form preexisting voids that can readily solvate a free electron.

  16. Photoelectron-photoion coincidence spectroscopy for multiplexed detection of intermediate species in a flame.

    PubMed

    Krüger, Julia; Garcia, Gustavo A; Felsmann, Daniel; Moshammer, Kai; Lackner, Alexander; Brockhinke, Andreas; Nahon, Laurent; Kohse-Höinghaus, Katharina

    2014-11-07

    Complex reactive processes in the gas phase often proceed via numerous reaction steps and intermediate species that must be identified and quantified to develop an understanding of the reaction pathways and establish suitable reaction mechanisms. Here, photoelectron-photoion coincidence (PEPICO) spectroscopy has been applied to analyse combustion intermediates present in a premixed fuel-rich (ϕ = 1.7) ethene-oxygen flame diluted with 25% argon, burning at a reduced pressure of 40 mbar. For the first time, multiplexing fixed-photon-energy PEPICO measurements were demonstrated in a chemically complex reactive system such as a flame in comparison with the scanning "threshold" TPEPICO approach used in recent pioneering combustion investigations. The technique presented here is capable of detecting and identifying multiple species by their cations' vibronic fingerprints, including radicals and pairs or triplets of isomers, from a single time-efficient measurement at a selected fixed photon energy. Vibrational structures for these species have been obtained in very good agreement with scanning-mode threshold photoelectron spectra taken under the same conditions. From such spectra, the temperature in the ionisation volume was determined. Exemplary analysis of species profiles and mole fraction ratios for isomers shows favourable agreement with results obtained by more common electron ionisation and photoionisation mass spectrometry experiments. It is expected that the multiplexing fixed-photon-energy PEPICO technique can contribute effectively to the analysis of chemical reactivity and kinetics in and beyond combustion.

  17. 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.

  18. 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.

  19. The LVV Auger line shape of sulfur on copper studied by Auger photoelectron coincidence spectroscopy.

    PubMed

    Di Filippo, G; Trioni, M I; Fratesi, G; Schumann, F O; Wei, Z; Li, C H; Behnke, L; Patil, S; Kirschner, J; Stefani, G

    2015-03-04

    We have studied the line shapes of Cu(0 0 1)-p (2 × 2)S L2VV and L3VV Auger decay by means of Auger photoelectron coincidence spectroscopy. Measuring the LVV Auger spectrum in coincidence with S 2p1/2 and 2p3/2 photoelectrons respectively, we have been able to separate the two overlapping Auger spectra and determine their intrinsic line shapes. The two Auger transitions, though shifted in energy, display an identical line shape whose main features can be qualitatively understood considering a single particle approximation but are better described within a Cini-Sawatzky (CS) approach. Comparison between the experimental and the CS calculated spectra confirms that a substantial part of the Auger lines (∼20%) can be ascribed to decay events accompanied by the excitation of one additional electron-hole pair in the valence band. For the first time, the locality of the Auger process combined with the surface sensitivity of the APECS technique and its ability to separate overlapping structures are used to study Auger transitions taking place at the the surface states of a S/noble-metal interface.

  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. 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.

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

    PubMed

    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 S1 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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).

  7. 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.

  8. 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)

  9. pH-induced protonation of lysine in aqueous solution causes chemical shifts in X-ray photoelectron spectroscopy.

    PubMed

    Nolting, Dirk; Aziz, Emad F; Ottosson, Niklas; Faubel, Manfred; Hertel, Ingolf V; Winter, Bernd

    2007-11-14

    We demonstrate the applicability of X-ray photoelectron spectroscopy to obtain charge- and site-specific electronic structural information of biomolecules in aqueous solution. Changing the pH of an aqueous solution of lysine from basic to acidic results in nitrogen 1s and carbon 1s chemical shifts to higher binding energies. These shifts are associated with the sequential protonation of the two amino groups, which affects both charge state and hydrogen bonding to the surrounding water molecules. The N1s chemical shift is 2.2 eV, and for carbon atoms directly neighboring a nitrogen the shift for C1s is approximately 0.4 eV. The experimental binding energies agree reasonably with our calculated energies of lysine(aq) for different pH values.

  10. 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

  11. Surface state photoelectrons in topological insulators: Green's function approach.

    PubMed

    Schmeltzer, D; Saxena, A

    2015-12-09

    We compute the photoemission intensity and polarization for the surface states in topological insulators. Due to the chirality and linear energy dispersion the effective electron-photon coupling is normalized by the tunneling amplitude (τ) into the vacuum. We investigate a chiral Dirac Hamiltonian for different cases: helical, Zeeman and warping, allowing us to study spin textures. Using the Green's function formalism we obtain exact results for the emitted photoelectrons to second order in the laser field. The number of emitted photoelectrons is sensitive to the laser coherent state intensity whereas the photoelectron polarization is sensitive to the surface topology of electronic states and incoming photon polarization.

  12. 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.

  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. 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.

  15. Study of the oxidation of W(110) by full-solid-angle photoelectron diffraction with chemical state and time resolution

    SciTech Connect

    Ynzunza, R. X.; Palomares, F. J.; Tober, E. D.; Wang, Z.; Morais, J.; Denecke, R.; Daimon, H.; Chen, Y.; Hussain, Z; Liesengang, J.; Van Hove, M. A.; Fadley, C. S.

    1997-04-01

    The brightness of third-generation synchrotron radiation from beamline 9.3.2 at the Advanced Light Source has been combined with the high-intensities and energy resolutions possible with its advanced photoelectron spectrometer/diffractometer experimental station in order to study the time dependence of the oxidation of the W(110) surface. This has been done via chemical-state-resolved core-level photoelectron spectroscopy and diffraction. This system has been studied previously by other methods such as LEED and STM, but several questions remain as to the basic kinetics of oxidation and the precise adsorption structures involved. By studying the decay and growth with time of various peaks in the W 4f{sub 7/2} photoelectron spectra, it should be possible to draw quantitative conclusions concerning the reaction kinetics involved. The authors have also measured full-solid-angle photoelectron diffraction patterns for the two oxygen-induced W states, and these should permit fully defining the different structures involved in this oxidation process.

  16. Evaluation of Two Methods for Determining Shell Thicknesses of Core-Shell Nanoparticles by X-ray Photoelectron Spectroscopy.

    PubMed

    Powell, C J; Werner, W S M; Shard, A G; Castner, D G

    2016-10-06

    We evaluated two methods for determining shell thicknesses of core-shell nanoparticles (NPs) by X-ray photoelectron spectroscopy (XPS). One of these methods had been developed for determining thicknesses of films on a planar substrate while the other was developed specifically for NPs. Our evaluations were based on simulated Cu 2p3/2 spectra from Cu-core/Cu-shell NPs with a wide range of core diameters and shell thicknesses. Copper was chosen for our tests because elastic-scattering effects for Cu 2p3/2 photoelectrons excited by Al Kα X-rays are known to be strong. Elastic scattering could also be switched off in our simulations so that the two methods could be evaluated in the limit of no elastic scattering. We found that the first method, based on both core and shell photoelectron intensities, was unsatisfactory for all conditions. The second method, based on an empirical equation for NPs developed by Shard, also utilized both core and shell photoelectron intensities and was found to be satisfactory for all conditions. The average deviation between shell thicknesses derived from the Shard equation and the true values was -4.1 % when elastic scattering was switched on and -2.2 % when elastic scattering was switched off. If elastic scattering was switched on, the effective attenuation length for a Cu film on a planar substrate was the appropriate length parameter while the inelastic mean free path was the appropriate parameter when elastic scattering was switched off.

  17. 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.

  18. Conjugate photoelectron excitation of O I 4368 airglow emission.

    NASA Technical Reports Server (NTRS)

    Christensen, A. B.; Teixeira, N. R.; Angreji, P. D.

    1973-01-01

    Conjugate photoelectron fluxes are shown to be mainly responsible for the excitation of O I 4368 radiation observed with a grille spectrometer located at Langmuir Laboratory, New Mexico (L equals 1.7). On the basis of observations of O I 7774 and 4368 tropical emissions at Agulhas, Negras, Brazil (L equals 1.1), the contribution of radiative recombination to the New Mexico intensity is shown to be small. Conjugate photoelectron excitation at the Brazilian site has not been observed.

  19. 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.

  20. 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

  1. Full k-space visualization of photoelectron diffraction

    SciTech Connect

    Denlinger, J. D.; Rotenberg, E.; Kevan, S. D.; Tonner, B. P.

    1997-04-01

    The development of photoelectron holography has promoted the need for larger photoelectron diffraction data sets in order to improve the quality of real-space reconstructed images (by suppressing transformational artifacts and distortions). The two main experimental and theoretical approaches to holography, the transform of angular distribution patterns for a coarse selection of energies or the transform of energy-scanned profiles for several directions, represent two limits to k-space sampling. The high brightness of third-generation soft x-ray synchrotron sources provides the opportunity to rapidly measure large high-density x-ray photoelectron diffraction (XPD) data sets with approximately uniform k-space sampling. In this abstract, the authors present such a photoelectron data set acquired for Cu 3p emission from Cu(001). Cu(001) is one of the most well-studied systems for understanding photoelectron diffraction structure and for testing photoelectron holography methods. Cu(001) was chosen for this study in part due to the relatively inert and unreconstructed clean surface, and it served to calibrate and fine-tune the operation of a new synchrotron beamline, electron spectrometer and sample goniometer. In addition to Cu, similar 'volume' XPD data sets have been acquired for bulk and surface core-level emission from W(110), from reconstructed Si(100) and Si(111) surfaces, and from the adsorbate system of c(2x2) Mn/Ni(100).

  2. 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

  3. 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.

  4. 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.

  5. Outermost and inner-shell electronic properties of ClC(O)SCH2CH3 studied using HeI photoelectron spectroscopy and synchrotron radiation.

    PubMed

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

    2011-06-02

    A study of valence electronic properties of S-ethyl chlorothioformate (S-ethyl chloromethanethioate), ClC(O)SCH(2)CH(3), using HeI photoelectron spectra (PES) and synchrotron radiation is presented. Moreover, the photon impact excitation and dissociation dynamics of ClC(O)SCH(2)CH(3) excited at the S 2p and Cl 2p levels are elucidated by analyzing the total ion yield (TIY) spectra and time-of-flight mass spectra acquired in multicoincidence mode [photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO)]. The HeI photoelectron spectrum is dominated by features associated with lone-pair electrons from the ClC(O)S- group, the HOMO at 9.84 eV being assigned to the n(π)(S) sulfur lone-pair orbital. Whereas the formation of C(2)H(5)(+) ion dominates the fragmentation in the valence energy region, the most abundant ion formed in both the S and Cl 2p energy ranges is C(2)H(3)(+). Comparison with related XC(O)SR (X = H, F, Cl and R = -CH(3), -C(2)H(5)) species reveals the impact of the alkyl chain on the photodissociation behavior of S-alkyl (halo)thioformates. © 2011 American Chemical Society

  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. 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.

  8. 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.

  9. 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.

  10. Microscopic solvation of NaBO2 in water: anion photoelectron spectroscopy and ab initio calculations.

    PubMed

    Feng, Yuan; Cheng, Min; Kong, Xiang-Yu; Xu, Hong-Guang; Zheng, Wei-Jun

    2011-09-21

    We investigated the microscopic solvation of NaBO(2) in water by conducting photoelectron spectroscopy and ab initio studies on NaBO(2)(-)(H(2)O)(n) (n = 0-4) clusters. The vertical detachment energy (VDE) of NaBO(2)(-) is estimated to be 1.00 ± 0.08 eV. The photoelectron spectra of NaBO(2)(-)(H(2)O)(1) and NaBO(2)(-)(H(2)O)(2) are similar to that of bare NaBO(2)(-), except that their VDEs shift to higher electron binding energies (EBE). For the spectra of NaBO(2)(-)(H(2)O)(3) and NaBO(2)(-)(H(2)O)(4), a low EBE feature appears dramatically in addition to the features observed in the spectra of NaBO(2)(-)(H(2)O)(0-2). Our study shows that the water molecules mainly interact with the BO(2)(-) unit in NaBO(2)(-)(H(2)O)(1) and NaBO(2)(-)(H(2)O)(2) clusters to form Na-BO(2)(-)(H(2)O)(n) type structures, while in NaBO(2)(-)(H(2)O)(3) and NaBO(2)(-)(H(2)O)(4) clusters, the water molecules can interact strongly with the Na atom, therefore, the Na-BO(2)(-)(H(2)O)(n) and Na(H(2)O)(n)···BO(2)(-) types of structures coexist. That can be seen as an initial step of the transition from a contact ion pair (CIP) structure to a solvent-separated ion pair (SSIP) structure for the dissolution of NaBO(2).

  11. 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.

  12. 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

  13. Photoelectron spectroscopy (PES) and photoelectron diffraction (XPD) studies on the local adsorption of cyclopentene on Si(100)

    NASA Astrophysics Data System (ADS)

    Weier, D.; Lühr, T.; Beimborn, A.; Schönbohm, F.; Döring, S.; Berges, U.; Westphal, C.

    2010-09-01

    We investigated the chemical and geometrical characteristics of the system cyclopentene on Si(100) in a combined photoelectron spectroscopy (PES) and photoelectron diffraction (XPD) investigation. In this study synchrotron radiation was applied to achieve a high resolution with high surface sensitivity. Our PES and XPD results show that the cyclopentene reacts with the silicon dimers of the (2 × 1)-reconstructed surface, changing the planar molecule to a diverse tilted molecule after the adsorption.

  14. Determination of atomic hydrogen in hydrocarbons by means of the reflected electron energy loss spectroscopy and the X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Afanas'ev, V. P.; Gryazev, A. S.; Efremenko, D. S.; Kaplya, P. S.; Ridzel, O. Y.

    2016-09-01

    Elastic peaks electron spectroscopy (EPES) is a perspective tool for measuring the hydrogen atomic density in hydrocarbons. It is known that hydrogen elastic peaks overlap inelastic energy loss spectra. This fact complicates the quantitative interpretation of EPES spectra. In this paper, a novel technique based on the joint use of EPES and X-ray photoelectron spectroscopy (PES) is proposed. A key part of the method is the inelastic scattering background subtraction which is performed in two steps. At the first step, differential inelastic scattering cross-sections are retrieved from PES spectra, while at the second step, the retrieved cross-sections are used to remove the inelastic scattering signal from EPES spectra. Both REELS and PES spectra are described on the base of the invariant imbedding method forming a consistent framework for the surface state analysis. A good agreement is obtained between calculated spectra and experimental data.

  15. 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.

  16. 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.

  17. Photoelectron spectroscopy and density functional study of Co(n)C2(-) (n = 1-5) clusters.

    PubMed

    Yuan, Jin-Yun; Xu, Hong-Guang; Zheng, Wei-Jun

    2014-03-21

    ConC2(-) (n = 1-5) cluster anions were investigated using anion photoelectron spectroscopy. The adiabatic detachment energies (ADEs) and the vertical detachment energies (VDEs) of the ConC2(-) (n = 1-5) cluster anions were determined from their photoelectron spectra. Density functional calculations were performed for the ConC2 (n = 1-5) cluster anions and neutrals. Our studies show that the structures of ConC2(-) (n = 1-5) can be described as attaching C2 to the top sites, bridge sites, or hollow sites of the Con clusters. The C2 retains an integral structure unit in the ConC2 (n = 1-5) cluster anions and neutrals, rather than being separated by the Con clusters. The C2 unit in the ConC2 (n = 1-5) cluster anions and neutrals has the characteristics of a double-bond.

  18. Negative ion photoelectron spectroscopy of 2,2'-bithiophene cluster anions, (2T)n- (n = 1 100)

    NASA Astrophysics Data System (ADS)

    Mitsui, M.; Matsumoto, Y.; Ando, N.; Nakajima, A.

    2005-07-01

    Cluster anions of 2,2'-bithiophene, (2T){n}-, were produced up to n ˜ 500 in the gas-phase. The energetics of the excess electron in the (2T){n}- clusters with n =1{-}100 were explored by negative ion photoelectron spectroscopy. When the vertical detachment energies (VDEs) obtained from the photoelectron spectra were analyzed by a plot against n-1/3, it has been revealed that the excess electron trapping level thus extrapolated is located at ˜ 0.8 eV below the conduction band minimum (i.e. LUMO) of the 2T thin film. The large slope of the VDEs vs. n-1/3 plot suggests that the neutral 2T molecules surrounding the anion core take non-planar twisted conformations with permanent dipole moments, resulting in the exceedingly deep trapping of the excess electron in the 2T cluster anions.

  19. Direct Imaging of Transient Fano Resonances in N_{2} Using Time-, Energy-, and Angular-Resolved Photoelectron Spectroscopy.

    PubMed

    Eckstein, Martin; Yang, Chung-Hsin; Frassetto, Fabio; Poletto, Luca; Sansone, Giuseppe; Vrakking, Marc J J; Kornilov, Oleg

    2016-04-22

    Autoionizing Rydberg states of molecular N_{2} are studied using time-, energy-, and angular-resolved photoelectron spectroscopy. A femtosecond extreme ultraviolet pulse with a photon energy of 17.5 eV excites the resonance and a subsequent IR pulse ionizes the molecule before the autoionization takes place. The angular-resolved photoelectron spectra depend on pump-probe time delay and allow for the distinguishing of two electronic states contributing to the resonance. The lifetime of one of the contributions is determined to be 14±1  fs, while the lifetime of the other appears to be significantly shorter than the time resolution of the experiment. These observations suggest that the Rydberg states in this energy region are influenced by the effect of interference stabilization and merge into a complex resonance.

  20. 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.

  1. 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.

  2. Unambiguous observation of F-atom core-hole localization in CF4 through body-frame photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    McCurdy, C. W.; Rescigno, T. N.; Trevisan, C. S.; Lucchese, R. R.; Gaire, B.; Menssen, A.; Schöffler, M. S.; Gatton, A.; Neff, J.; Stammer, P. M.; Rist, J.; Eckart, S.; Berry, B.; Severt, T.; Sartor, J.; Moradmand, A.; Jahnke, T.; Landers, A. L.; Williams, J. B.; Ben-Itzhak, I.; Dörner, R.; Belkacem, A.; Weber, Th.

    2017-01-01

    A dramatic symmetry breaking in K -shell photoionization of the CF4 molecule in which a core-hole vacancy is created in one of four equivalent fluorine atoms is displayed in the molecular frame angular distribution of the photoelectrons. Observing the photoejected electron in coincidence with an F+ atomic ion after Auger decay is shown to select the dissociation path where the core hole was localized almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling CF3+ and F+ atoms elucidates the underlying physics that derives from the Ne-like valence structure of the F(1 s-1 ) core-excited atom.

  3. Unambiguous observation of F-atom core-hole localization in CF4 through body-frame photoelectron angular distributions

    DOE PAGES

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

    2017-01-17

    A dramatic symmetry breaking in K-shell photoionization of the CF4 molecule in which a core-hole vacancy is created in one of four equivalent fluorine atoms is displayed in the molecular frame angular distribution of the photoelectrons. In observing the photoejected electron in coincidence with an F+ atomic ion after Auger decay we see how selecting the dissociation path where the core hole was localized was almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling CF3+ and F+ atoms elucidates the underlying physics that derives frommore » the Ne-like valence structure of the F(1s-1) core-excited atom.« less

  4. 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.

  5. Variable Mixed Orbital Character in the Photoelectron Angular Distribution of NO_{2}

    NASA Astrophysics Data System (ADS)

    Laws, Benjamin A.; Cavanagh, Steven J.; Lewis, Brenton R.; Gibson, Stephen T.

    2017-06-01

    NO_{2} a key component of photochemical smog and an important species in the Earth's atmosphere, is an example of a molecule which exhibits significant mixed orbital character in the HOMO. In photoelectron experiments the geometric properties of the parent anion orbital are reflected in the photoelectron angular distribution (PAD), an area of research that has benefited largely from the ability of velocity-map imaging (VMI) to simultaneously record both the energetic and angular information, with 100% collection efficiency. Photoelectron spectra of NO_{2}^{-}, taken over a range of wavelengths (355nm-520nm) with the ANU's VMI spectrometer, reveal an anomalous jump in the anisotropy parameter near threshold. Consequently, the orbital behavior of NO_{2}^{-} appears to be quite different near threshold compared to detachment at higher photon energies. This surprising effect is due to the Wigner Threshold law, which causes p orbital character to dominate the photodetachment cross-section near threshold, before the mixed s/d orbital character becomes significant at higher electron kinetic energies. By extending recent work on binary character models to form a more general expression, the variable mixed orbital character of NO_{2}^{-} is able to be described. This study provides the first multi-wavelength NO_{2} anisotropy data, which is shown to be in decent agreement with much earlier zero-core model predictions of the anisotropy parameter. K. J. Reed, A. H. Zimmerman, H. C. Andersen, and J. I. Brauman, J. Chem. Phys. 64, 1368, (1976). doi:10.1063/1.432404 D. Khuseynov, C. C. Blackstone, L. M. Culberson, and A. Sanov, J. Chem. Phys. 141, 124312, (2014). doi:10.1063/1.4896241 W. B. Clodius, R. M. Stehman, and S. B. Woo, Phys. Rev. A. 28, 760, (1983). doi:10.1103/PhysRevA.28.760 Research supported by the Australian Research Council Discovery Project Grant DP160102585

  6. 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.

  7. Hard x-ray photoelectron spectroscopy and x-ray standing waves

    NASA Astrophysics Data System (ADS)

    Lee, Tien-Lin

    2006-03-01

    Using the brilliant undulator radiation available from the third generation synchrotron sources, hard x-ray photoelectron spectroscopy (HAXPES) has become an emerging field in the recent years. With the excitation energy used in HAXPES one can benefits from the large mean free path of fast electrons (˜ 5 nm for electrons of 6 keV kinetic energy) in probing the bulk electronic properties of materials. For high-resolution studies, photon energy bandwidth narrower than 100 meV is also readily achievable in the hard x-ray range with crystal monochromators. In addition, working with hard x-ray offers the possibility for combining photoelectron spectroscopy with x-ray standing wave (XSW) method. With the high spatial resolution from XSWs, this unique combination can provide site-specific, chemical and electronic information for studying surfaces, buried interfaces, thin films and bulk crystals. In this talk, I will briefly mention some HAXPES experiments detecting electrons up to 14.5 keV [1,2]. I will then sketch the principle of combining XSWs with HAXPES and present results from some recent applications using this combination: (1) chemical state-specific surface structure determination with core-level photoemission, (2) site-specific valence x-ray photoelectron spectroscopy and (3) XSW imaging with core-level photoemission. [1] S. Thiess, C. Kunz, B.C.C. Cowie, T.-L. Lee, M. Renier, and J. Zegenhagen. Solid State Communications 132, 589 (2004) [2] C. Kunz, S. Thiess, B.C.C. Cowie, T.-L. Lee, and J. Zegenhagen, Nuclear Instruments and Methods A 547, 73 (2005).

  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. Global, Collisional Model of High-Energy Photoelectrons

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Moore, T. E.; Liemohn, M. W.; Jordanova, V. K.; Fok, M.-C.

    1996-01-01

    A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) has been extended to three dimensions by including transport due to vector E x vector B and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater then 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectrons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.

  10. 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.

  11. 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.

  12. 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 ≃ 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.

  13. 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.

  14. Simulated Photoelectron-Based Imaging of Localized Surface Plasmons with Attosecond Resolution

    NASA Astrophysics Data System (ADS)

    Prell, James; Borja, Lauren; Gandman, Andrey; Whitmore, Desire; Neumark, Daniel; Leone, Stephen

    2013-03-01

    Simulations of proposed photoelectron streaking experiments in the presence of an oscillating plasmon field are presented. The results indicate that localized surface plasmon dephasing can be imaged with attosecond resolution using electron time-of-flight (TOF) or velocity map imaging (VMI) techniques. In the simulation, localized surface plasmons are excited in metal nanoparticles by a few-cycle infrared or visible laser pulse. Using time-delayed single, isolated attosecond x-ray pulses, electrons are photoemitted from the metallic nanoparticles and streaked by both the plasmon and laser electric fields. The effects of these two fields in the streaking spectra and images can be separated so that the temporal evolution of the plasmon electric field can be directly extracted. The plasmon electric field induces a broadening of the photoelectron speed distribution with an envelope directly proportional to that of the plasmon dipole moment. Plasmon-induced oscillation of the angular distribution in VMI is predicted to report the spatial distribution of the plasmon electric field for nanoparticles with high aspect ratios. The simulations indicate that these techniques can be used to map plasmon dynamics with unprecedented temporal resolution.

  15. 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.

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

    PubMed

    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. © 2011 American Institute of Physics

  17. 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.

  18. 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.

  19. 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.

  20. 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.