The Experts below are selected from a list of 159 Experts worldwide ranked by ideXlab platform

Alexander M. Bradshaw - One of the best experts on this subject based on the ideXlab platform.

  • Conformational and nuclear dynamics effects in molecular Auger spectra: fluorine core-hole decay in CF4
    Journal of Physics B: Atomic Molecular and Optical Physics, 2014
    Co-Authors: Tiberiu Arion, Ralph Püttner, Volker Ulrich, Silko Barth, Toralf Lischke, Alexander M. Bradshaw, Osamu Takahashi, Marko Förstel, Uwe Hergenhahn
    Abstract:

    In a molecular Auger Spectrum information on the decaying state is implicitly ensemble-averaged. For a repulsive core-ionized state, for example, contributions from all parts of its potential curve are superimposed in the Auger Spectrum. Using carbon tetrafluoride (CF4, tetrafluoromethane), we demonstrate for the first time that these contributions can be disentangled by recording photoelectron–Auger electron coincidence spectra with high energy resolution. For the F K-VV Spectrum of CF4, there are significant differences in the Auger decay at different intermediate state (single core hole) geometries. With the help of calculations, we show that these differences result primarily from zero-point fluctuations in the neutral molecular ground state, but are amplified by the nuclear dynamics during Auger decay.

  • Separating the Vibrationally Resolved Auger Decay Channels for a CO Core Hole State
    Physical review letters, 2008
    Co-Authors: Volker Ulrich, Silko Barth, Sanjeev Joshi, Toralf Lischke, Alexander M. Bradshaw, Uwe Hergenhahn
    Abstract:

    The K-VV Auger Spectrum of carbon monoxide (CO) excited by C 1s photoionization has been investigated with a novel electron-electron coincidence setup. The energy resolution is sufficiently high to resolve the vibrational energy levels of the core-ionized intermediate state and of most dicationic final states in the two-dimensional electron energy map. We demonstrate how the influence of vibrational states on a molecular Auger Spectrum can be accessed experimentally without the constraint of averaging over all intermediate state energies.

  • The C 1s Auger decay Spectrum of the molecule: the effects of vibrational fine structure, double excitations and shake-up transitions
    Journal of Physics B: Atomic Molecular and Optical Physics, 1996
    Co-Authors: Antti Kivimäki, M. Neeb, B. Kempgens, H. M. Köppe, Alexander M. Bradshaw
    Abstract:

    Auger electron spectra of the methane molecule have been measured at various photon energies below and above the C 1s threshold. At energies corresponding to the higher Rydberg resonances the resonant Auger Spectrum approaches the normal Auger Spectrum both in form and peak position. Deviations from this trend are observed, however, when the core-to-Rydberg transition is accompanied by the excitation of vibrational modes. Auger spectra measured at the continuum resonance around 303 eV excitation energy display new decay features, which allows this resonance to be assigned to core-hole double excitations. Furthermore, above the C 1s threshold the satellite Auger features arising from the lowest shake-up initial states are identified.

Francesco Tarantelli - One of the best experts on this subject based on the ideXlab platform.

  • Ultrafast X-ray Auger probing of photoexcited molecular dynamics
    Nature communications, 2014
    Co-Authors: Brian K. Mcfarland, Francesco Tarantelli, John D Bozek, J. P. Farrell, S. Miyabe, A. Aguilar, Nora Berrah, Christoph Bostedt, Philip H. Bucksbaum, J.-c. Castagna
    Abstract:

    Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger Spectrum as a function of photoexcitation--X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger Spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger Spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.

  • Radiationless decay in the region of the 2t2g and 4eg resonances in SF6.
    The Journal of chemical physics, 2011
    Co-Authors: Paola Bolognesi, Francesco Tarantelli, Patrick O'keeffe, Antti Kivimäki, Vitaliy Feyer, Loriano Storchi, L Avaldi
    Abstract:

    The S 2p Auger Spectrum of SF(6) has been studied in the region of the 2t(2g) and 4e(g) resonances. The partial Auger spectra due to the ionization of the 2p spin-orbit components and of a shake-up satellite state have been measured selectively by tuning the photon energy and using the Auger electron-photoelectron coincidence technique. A detailed analysis of the Auger Spectrum has also been performed using the Green's function-based second-order algebraic diagrammatic construction method.

  • Theory of wave packet dynamics: resonant Auger Spectrum of HF
    Journal of Electron Spectroscopy and Related Phenomena, 1998
    Co-Authors: Elke Pahl, Lorenz S. Cederbaum, Hansdieter Meyer, Francesco Tarantelli
    Abstract:

    Abstract The time-dependent theory of wave packet dynamics accompanying the excitation and decay in the molecular Auger process is reviewed and applied to the resonant Auger Spectrum of HF. When the core-excitation is performed by an energetically non-selective source (`broad-band' excitation), many intermediate states are populated during the excitation process and their decay gives many interplaying contributions within the same energy region. To interpret the Spectrum we have carried out a detailed theoretical study of all the decaying and final electronic states involved. In order to restrict the number of participating decaying states, narrow-band excitation has to be performed, so that only one intermediate decaying state is populated. We have studied in detail one particular transition between purely repulsive potential curves, where we show the effects introduced by the energetically selective excitation. By detuning the excitation energy off the resonance, very prominent interference patterns can be found. These explain the quenching of the so-called `atomic lines' and the surprising new features which appear in the case of small detuning towards higher excitation energies. The effects discussed are shown to be of a general nature. The description in the time-dependent picture allows for a novel and deeper understanding of the underlying mechanisms of these effects since the physically relevant quantities can be traced on the real time scale of the process.

  • adiabatic and nonadiabatic effects of nuclear dynamics in spectra of decaying states Auger Spectrum of hf
    Journal of Chemical Physics, 1996
    Co-Authors: Elke Pahl, L S Cederbaum, Hansdieter Meyer, D Minelli, Francesco Tarantelli
    Abstract:

    An all ab initio calculation of the Auger Spectrum of HF is presented which includes the effects introduced by nuclear dynamics. The involved potential curves of the core‐ionized decaying state and the dicationic final states are computed by CASSCF. On these curves, the wave‐packet dynamics is performed in an exact manner. Special attention is paid to the transition to the 1Π(2σ−1,1π−1) final state where an avoided crossing between this state and a satellite state is found within the region of decay. By vibronic coupling, the satellite gains intensity which influences the shape of the Spectrum. The experimental Spectrum is very well reproduced.

Sören Svensson - One of the best experts on this subject based on the ideXlab platform.

  • The influence of the σ resonance on the Auger decay of core-ionized molecular nitrogen
    Chemical Physics Letters, 2008
    Co-Authors: Stacey Ristinmaa Sörensen, Olle Björneholm, Catalin Miron, R. Feifel, M. N. Piancastelli, Sören Svensson
    Abstract:

    Auger spectra from the decay of core-ionized N-2 have been studied as a function of the exciting photon energy. Discrete features appear in the Auger Spectrum when the photon energy is tuned to the shape-resonance region at 420 eV. The Auger spectra for two final dicationic states are studied; simulations of the contributions from the decay of the gerade and ungerade core-hole states are made based on a Franck-Condon picture including life time vibrational interference. We are able to reproduce the vibrational. ne structure in the Auger Spectrum using a model where the coherent sum of the decay channels from the vibrationally-excited states are treated separately for the gerade and ungerade states.

  • The x‐ray excited Auger electron Spectrum of NO and potential curves and photodissociation of the NO2+ ion
    The Journal of Chemical Physics, 1992
    Co-Authors: Lars G. M. Pettersson, L. Karlsson, A. Naves De Brito, Nestor Correia, M. P. Keane, Mats Larsson, L. Broström, Sven Mannervik, Sören Svensson
    Abstract:

    A study of the NO2+ ion by means of Auger spectroscopy, fast ion beam laser spectroscopy and ab initio calculations is reported. The photon induced Auger Spectrum of NO was recorded. Potential curves for a number of electronic states of NO2+ were calculated by the complete active space SCF method in order to facilitate an analysis of the Auger Spectrum. A photoabsorption Spectrum of NO2+ was observed by means of photofragment kinetic energy spectroscopy and assigned to the A 2Π←X 2Σ+ transition. The two different experimental methods both give a value of 38.6 eV for the appearance energy of NO2+, which is entirely consistent with recent photoionization and double charge transfer results.

  • Comment on the NVV Auger electron Spectrum of the HI molecule
    Journal of Physics B: Atomic Molecular and Optical Physics, 1991
    Co-Authors: L. Karlsson, Sören Svensson, P. Baltzer, A. Naves De Brito, Nestor Correia, Björn Wannberg
    Abstract:

    The implications for the NVV Auger Spectrum of HI of the recent high resolution studies of the I 4d photoelectron Spectrum of HI are discussed. It is found that ligand field splitting must be considered in the interpretation of the Auger Spectrum. However, vibrational structure is definitively present in the Auger Spectrum and could possibly explain the apparent discrepancies concerning linewidths between the photoelectron and Auger electron spectra.

Uwe Hergenhahn - One of the best experts on this subject based on the ideXlab platform.

  • Conformational and nuclear dynamics effects in molecular Auger spectra: fluorine core-hole decay in CF4
    Journal of Physics B: Atomic Molecular and Optical Physics, 2014
    Co-Authors: Tiberiu Arion, Ralph Püttner, Volker Ulrich, Silko Barth, Toralf Lischke, Alexander M. Bradshaw, Osamu Takahashi, Marko Förstel, Uwe Hergenhahn
    Abstract:

    In a molecular Auger Spectrum information on the decaying state is implicitly ensemble-averaged. For a repulsive core-ionized state, for example, contributions from all parts of its potential curve are superimposed in the Auger Spectrum. Using carbon tetrafluoride (CF4, tetrafluoromethane), we demonstrate for the first time that these contributions can be disentangled by recording photoelectron–Auger electron coincidence spectra with high energy resolution. For the F K-VV Spectrum of CF4, there are significant differences in the Auger decay at different intermediate state (single core hole) geometries. With the help of calculations, we show that these differences result primarily from zero-point fluctuations in the neutral molecular ground state, but are amplified by the nuclear dynamics during Auger decay.

  • Separating the Vibrationally Resolved Auger Decay Channels for a CO Core Hole State
    Physical review letters, 2008
    Co-Authors: Volker Ulrich, Silko Barth, Sanjeev Joshi, Toralf Lischke, Alexander M. Bradshaw, Uwe Hergenhahn
    Abstract:

    The K-VV Auger Spectrum of carbon monoxide (CO) excited by C 1s photoionization has been investigated with a novel electron-electron coincidence setup. The energy resolution is sufficiently high to resolve the vibrational energy levels of the core-ionized intermediate state and of most dicationic final states in the two-dimensional electron energy map. We demonstrate how the influence of vibrational states on a molecular Auger Spectrum can be accessed experimentally without the constraint of averaging over all intermediate state energies.

John D Bozek - One of the best experts on this subject based on the ideXlab platform.

  • Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
    Journal of Physics B: Atomic Molecular and Optical Physics, 2015
    Co-Authors: Alvaro Sanchez-gonzalez, John D Bozek, Christoph Bostedt, T. Barillot, R. J. Squibb, Přemysl Kolorenč, Marcus Agåker, Vitali Averbukh, Michael J. Bearpark, S. Bruce
    Abstract:

    We report the first measurement of the near oxygen K-edge Auger Spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant Auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge Auger Spectrum and an assignment of Auger decay channels is performed.

  • Ultrafast X-ray Auger probing of photoexcited molecular dynamics
    Nature communications, 2014
    Co-Authors: Brian K. Mcfarland, Francesco Tarantelli, John D Bozek, J. P. Farrell, S. Miyabe, A. Aguilar, Nora Berrah, Christoph Bostedt, Philip H. Bucksbaum, J.-c. Castagna
    Abstract:

    Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger Spectrum as a function of photoexcitation--X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger Spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger Spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.

  • xenon n4 5oo Auger Spectrum a useful calibration source
    Journal of Electron Spectroscopy and Related Phenomena, 2002
    Co-Authors: T X Carroll, T. D. Thomas, John D Bozek, E Kukk, V Myrseth, Leif J Saethre, Karoline Wiesner
    Abstract:

    Abstract In the xenon N 4,5 OO Auger Spectrum there are 19 prominent lines ranging in kinetic energy from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this Spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin–orbit splitting of the xenon 4d lines is determined to be 1979.0±0.5 meV.