Resonant Auger decay study of core-excited OCS (original) (raw)
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Multi-Coincidence Studies of Fragmentations of Core Excited OCS Molecules
Acta Physica Polonica A, 1997
Molecular fragmentation following photon excitation of core electrons from K shells of C and O and L shell of S atoms forming the OCS molecule was studied. Emerging photoelectrons and charged fragments were detected in coincidence. Application of time-of-flight spectroscopy together with triple coincidence photoelectron-photoion-photoion, double coincidence photoelectron-photoion and photoion-photoion techniques allow a detailed insight into the geometry and the dynamics of the de-excitation processes and an unambiguous assessment of all fragmentation channels of highly excited molecules. Such studies are of major interest in fundamental research and they are relevant also in environmental, biological and technological investigations.
Quasi two-step dissociation effects observed in the core excited OCS molecule
Studies of the decay dynamics following carbon 1s and sulfur 2p electron excitations of the OCS molecule using the photoelectron–photoion–photoion coincidence method and a synchrotron radiation source are presented. A Monte Carlo code is utilized to interpret the data obtained, which together with previous measurements including branching ratios, kinetic energy distributions and ionic b-parameters give new information on the dynamics of three-body dissociation processes. The results indicate that the instantaneous and sequential dissociation models should be replaced by quasi two-step models. q 1998 Elsevier Science B.V.
The Journal of Chemical Physics, 2012
Global three dimensional potential energy surfaces and transition dipole moment functions are calculated for the lowest singlet and triplet states of carbonyl sulfide at the multireference configuration interaction level of theory. The first ultraviolet absorption band is then studied by means of quantum mechanical wave packet propagation. Excitation of the repulsive 2 1 A state gives the main contribution to the cross section. Excitation of the repulsive 1 1 A state is about a factor of 20 weaker at the absorption peak (E ph ≈ 45 000 cm −1 ) but becomes comparable to the 2 1 A state absorption with decreasing energy (35 000 cm −1 ) and eventually exceeds it. Direct excitation of the repulsive triplet states is negligible except at photon energies E ph < 38 000 cm −1 . The main structure observed in the cross section is caused by excitation of the bound 2 3 A state, which is nearly degenerate with the 2 1 A state in the Franck-Condon region. The structure observed in the low energy tail of the spectrum is caused by excitation of quasi-bound bending vibrational states of the 2 1 A and 1 1 A electronic states. The absorption cross sections agree well with experimental data and the temperature dependence of the cross section is well reproduced.
Resonant Auger decay of the core-excited C^{*}O molecule in intense x-ray laser fields
Physical Review A, 2011
The dynamics of the resonant Auger (RA) process of the core-excited C * O(1s −1 π * , v r = 0) molecule in an intense X-ray laser field is studied theoretically. The theoretical approach includes the analogue of the conical intersections of the complex potential energy surfaces of the ground and 'dressed' resonant states due to intense X-ray pulses, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The light-induced non-adiabatic effect of the analogue of the conical intersections of the resulting complex potential energy surfaces gives rise to strong coupling between the electronic, vibrational and rotational degrees of freedom of the diatomic CO molecule. The interplay of the direct photoionization of the ground state and of the decay of the resonance increases dramatically with the field intensity. The coherent population of a final ionic state via both the direct photoionization and the resonant Auger decay channels induces strong interference effects with distinct patterns in the RA electron spectra. The individual impact of these physical processes on the total electron yield and on the CO + (A 2 Π) electron spectrum are demonstrated.
Influences from the C1sshape resonance on the vibrational progression in the Auger decay of CO
Physical Review A, 1998
Auger decay from the C 1s core-ionized state of CO has been studied with vibrational resolution both at the C 1s shape resonance and far above. Variations in the vibrational intensity distribution with photon energy are observed. This observation is explained solely by the modified vibrational envelope of the core-ionized intermediate state at the shape resonance maximum, as demonstrated in a numerical simulation. This implies that the temporary trapping of the photoelectron at the shape resonance does not significantly affect the deexcitation process. Thus the deexcitation step is described by the Franck-Condon principle even at the shape resonance. The angular anisotropy of the Auger decay at the shape resonance has also been studied with vibrational resolution. Weak dependence upon the final state and no detectable influence from the vibrational quanta is observed. ͓S1050-2947͑98͒03409-X͔
“Hidden” vibrations in CO: Reinvestigation of resonant Auger decay for the C 1 s→ π* excitation
We report an experimental investigation of higher vibrational levels (ЈϾ2) of the C 1s→* excitation in CO utilizing resonant Auger electron spectroscopy. These vibrational states are not readily seen in a total yield absorption spectrum, whereas they are shown to be discernable in a partial electron yield spectrum. Furthermore, the nature of the spectator part between E Bin ϭ26.5 and 30 eV, being subject of an ongoing debate, is discussed on the grounds of the presented experimental data. The experiments indicate that the formally used adiabatic framework for the multitude of close lying 2 ⌸ potential curves is inappropriate, but that a diabatic treatment can be used for the interpretation of the spectra.
Physical Review A, 2002
We report an experimental investigation of higher vibrational levels (ЈϾ2) of the C 1s→* excitation in CO utilizing resonant Auger electron spectroscopy. These vibrational states are not readily seen in a total yield absorption spectrum, whereas they are shown to be discernable in a partial electron yield spectrum. Furthermore, the nature of the spectator part between E Bin ϭ26.5 and 30 eV, being subject of an ongoing debate, is discussed on the grounds of the presented experimental data. The experiments indicate that the formally used adiabatic framework for the multitude of close lying 2 ⌸ potential curves is inappropriate, but that a diabatic treatment can be used for the interpretation of the spectra.
We report new measurements of the decay of the core-excited O 1s -1 g 3 ⌸ u state in molecular oxygen under Auger resonant Raman conditions. The spectral features are interpreted with the aid of ab initio calculations using standard lifetime-vibrational interference, and in some cases, employing a model in which the bond-length dependence of the Auger transition rates is taken into account. By analyzing a series of Augerdecay spectra using different excitation energies, several instances of fixed kinetic energy are pointed out in the spectra; the nondispersive behavior arises from the decay between two potentials that are essentially parallel.
Spin-forbidden shake-up states of OCS molecule studied by resonant photoelectron spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2004
Resonant photoionization of OCS at the sulfur 2p 3/2 → 4 * resonance is observed. The spectra show three satellite structures between B (2) and C (2) valence-ionized states. Based on ab initio theoretical calculations, these satellites are assigned to 4 , 2 , and 2 shake-up-like satellites with three open shells, where the shake-up electron occupies the 4 * orbital. The transition to the spin-forbidden 4 state arises from strong singlet-triplet mixing via the spin-orbit coupling in the intermediate sulfur 2p-4 * excited state. In order to understand the observed satellite intensities, matrix elements for the Auger-like two-electron process from the intermediate sulfur 2p→ 4 * excited states to the final valence-ionized states are analytically derived.