493 research outputs found
Ultrafast molecular three-electron collective auger decay
No full textA new class of many-electron Auger transitions in atoms was initially proposed over 40 years ago\footnote{G.N. Ogurtsov et al., Sov. Phys. Tech. Phys. 15, 1656 (1971) and V.V. Afrosimov et al., JETP Lett. 21, 249 (1975).}, but the first tentative evidence for its real existence was only adduced by Lee et al.\footnote{I. Lee, R. Wehlitz, U. Becker and M. Ya. Amusia, J. Phys. B: At. Mol. Opt. Phys. 26, L41 (1993).} in 1993, on the basis of the resonant Auger spectrum of Kr. Using a multi-electron coincidence technique with synchrotron radiation, we unambiguously showed very recently that the transition suggested by Lee et al. in Kr really does take place, but with a rather small branching ratio\footnote{J.H.D. Eland, R.J. Squibb, M. Mucke, S. Zagorodskikh, P. Linusson, and R. Feifel, New J. Phys. 17, 122001 (2015).}. Related inter-atomic three-electron transitions in rare gas clusters were recently predicted by Averbukh and Kolorenč\footnote{V. Averbukh and P. Kolorenč, Phys. Rev. Lett. 103, 183001 (2009).} and demonstrated by Ouchi et al.\footnote{T. Ouchi et al., Phys. Rev. Lett. 107, 053401 (2011).}.
From consideration of the energy levels involved it seems that the basic three-electron process could occur in molecules too, wherever a double inner-valence shell vacancy lies at a higher energy than the molecular triple ionisation onset. Experiments on CHF reveal for the first time the existence of this new decay pathway there\footnote{R. Feifel et al., Phys. Rev. Lett. 116, 073001 (2016).}, and calculations show that despite its three-electron nature, its effective oscillator strength is orders of magnitudes higher than in atoms, allowing an efficient competition with both molecular dissociation and two-electron decay channels on the ultrafast time scale. The dramatic enhancement of the molecular three-electron Auger transition can be explained in terms of a partial breakdown of the molecular orbital picture of ionisation. We predict that the collective decay pathway will be significant in a wide variety of heteroatomic molecules ionised by extreme UV and soft X-rays, particularly at Free-Electron-Lasers where double inner-shell vacancies can be created efficiently by two-photon transitions.Made available in DSpace on 2017-01-26T21:39:43Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
Ultrafast molecular three-electron collective Auger Decay [Elektronisk resurs]
No full textA new class of many-electron Auger transitions in atoms was initially proposed over 40 years ago, but the first tentative evidence for its real existence was only adduced by Lee et al. in 1993, on the basis of the resonant Auger spectrum of Kr. Using a multi-electron coincidence technique with synchrotron radiation, we unambiguously showed very recently that the transition suggested by Lee et al. in Kr really does take place, but with a rather small branching ratio\footnote{J.H.D. Eland, R.J. Squibb, M. Mucke, S. Zagorodskikh, P. Linusson, and R. Feifel, New J. Phys. 17, 122001 (2015).}. Related inter-atomic three-electron transitions in rare gas clusters were recently predicted by Averbukh and Kolorenč\footnote{V. Averbukh and P. Kolorenč, Phys. Rev. Lett. 103, 183001 (2009).} and demonstrated by Ouchi et al.\footnote{T. Ouchi et al., Phys. Rev. Lett. 107, 053401 (2011).}. From consideration of the energy levels involved it seems that the basic three-electron process could occur in molecules too, wherever a double inner-valence shell vacancy lies at a higher energy than the molecular triple ionisation onset. Experiments on CH3 F reveal for the first time the existence of this new decay pathway there\footnote{R. Feifel et al., Phys. Rev. Lett. 116, 073001 (2016).}, and calculations show that despite its three-electron nature, its effective oscillator strength is orders of magnitudes higher than in atoms, allowing an efficient competition with both molecular dissociation and two-electron decay channels on the ultrafast time scale. The dramatic enhancement of the molecular three-electron Auger transition can be explained in terms of a partial breakdown of the molecular orbital picture of ionisation. We predict that the collective decay pathway will be significant in a wide variety of heteroatomic molecules ionised by extreme UV and soft X-rays, particularly at Free-Electron-Lasers where double inner-shell vacancies can be created efficiently by two-photon transitions
Three-electron collective Auger decay in CH3F
No full textWe report on experimental and theoretical study of collective Auger decay of double inner-valence vacancy in fluoromethane, in which two electrons simultaneously fill the vacancies and a third electron is ejected to continuum. Calculations predict the respective lifetime of the double vacancy state to be in the femtosecond range, typical for two-electron Auger decay. Measured electron spectra indirectly support this rather surprising result
An experimental and theoretical study of double photoionization of CF4 using time-of-flight photoelectron-photoelectron (photoion-photoion) coincidence spectroscopy
No full textSingle photon double ionization of C F4 has been studied by means of a time-of-flight photoelectron-photoelectron coincidence technique, which has very recently been extended towards ion detection, with energy analysis for the electrons and mass analysis for the ions. The complete single photon double ionization electron spectrum of C F4 up to a binding energy of ∼51 eV is presented and discussed, also with the aid of accurate ab initio Green's function calculations. From ion detection in coincidence with the ejected electrons, we derive fragmentation pathway-selected double ionization electron spectra of C F4. From the same data we extract the yield of each doubly charged ion or ion pair as a function of the double ionization energy. © 2006 American Institute of Physics
Counter-matched nested exposure case-control design: Making information ascertainment worth the effort - Supplementary Materials
No full textThe R code for data generation and exemplary functions to perform and evaluate both NECC sampling designs are available at the GitHub page of the corresponding author (https://github.com/JanFeifel) (Publicly available upon publication)
Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation
No full textThe fragmentation pattern of the peptide model system, N-methylacetamide, is investigated using ion time-of-flight (TOF) spectroscopy after resonant K-shell excitation. Corresponding near-edge X-ray absorption fine structure (NEXAFS) spectra recorded at high resolution at the C1s, N1s and O1s edges are presented. Analysis of the ion TOF data reveals a multitude of fragmentation channels and dissociation pathways. Comparison between the excitation of six different resonances in the vicinity of the C1s, N1s and O1s edges suggests evidence for site-selective bond breaking. In particular the breaking of the peptide bond and the N-C-alpha bond show a clear correlation with resonant excitation at the N1s edge. Also, stronger tendencies towards site-selective bond breaking are found for the generation of single ions compared with ion pairs. Analysis of angular distributions of ions from breakage of the peptide bond yields a fragmentation time of <400 fs
Core level ionization dynamics in small molecules studied by x-ray-emission threshold-electron coincidence spectroscopy
No full textX-ray-emission threshold-electron coincidence spectroscopy has been applied to N2, O2, and N2O. The main
features of the spectra can be interpreted as conventional core level threshold electron spectra, free from
postcollision interaction effects. The relative cross sections for adiabatic ionization of close-lying core hole
states and vibrational substates are presented. The results are compared to theoretical predictions and state-ofthe-
art photoelectron spectra and are discussed in terms of direct threshold ionization and core vacancy
rearrangement processes
NEXAFS and XPS studies of nitrosyl chloride
No full textThe electronic structure of nitrosyl chloride (ClNO) has been investigated in the gas phase by X-ray photoelectron (XPS) and
Near Edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Cl 2p, Cl 2s, N 1s and O 1s edges in a combined experimental and theoretical study. The theoretical calculations at different levels of approximation predict ionization potential values
in good agreement with the experimental data and allow to assign the main features of the absorption spectra. An unexpected
failure of the density functional model is observed, however, for the calculation of the Cl 2s binding energy and related to a large
self-interaction error. Largely different photoabsorption cross section patterns are experimentally observed in core excitations
from the investigated quantum shells (n = 1,2). This finding is confirmed by the oscillator strength distributions calculated at
the different absorption edges; in the case of the n = 2 shell the bands below the threshold are extremely weak and most of the
absorption intensity is due to excitations in the continuum
Soft x-ray NEXAFS and XPS studies of nitrosyl choride
No full textThe gas-phase ClNO molecule has been studied theoretically and experimentally by XPS (X-ray Photoelectron Spectroscopy) and NEXAFS (Near Edge X-ray Absorption Fine Structure) spectroscopy, at the Cl 2p, Cl 2s, N 1s and O 1s edges. The comparison of the measured and computed NEXAFS spectra reveal a clear localization of the LUMO (Lowest Unoccupied Molecular Orbital) along the N–O bond, suggesting that by selective core electron excitation to the LUMO, the cleavage of this bond could preferentially be activated
NEXAFS spectroscopy and site-specific fragmentation of N -methylformamide, N,N -dimethylformamide, and N,N -dimethylacetamide
No full textNear-edge X-ray absorption fine-structure (NEXAFS) spectra measured at the C, N, and O K-edges
for three molecules containing the amide moiety, N-methylformamide (HCONHCH3), N,Ndimethylformamide
(HCON(CH3)2), and N,N-dimethylacetamide (CH3CON(CH3)2) are presented.
These molecules have similar structures and differ by the number of methyl groups located at the
molecular ends. The fragmentation of these molecules after resonant excitation at different K-edge
resonances is also investigated, using a 3D-ion imaging time-of-flight spectrometer. A comparison
between the molecules with respect to the relative contributions of the fragments created upon
excitation at distinct resonances reveals site-specific fragmentation. Further information about the
character of the core-excitation and dissociation process is obtained from the angular distributions of
the ion fragments
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