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We have studied the ultrafast dissociation of the H2S molecule upon S 2p3/2→6a1 inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron–ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A 3Π and c 1Π states by the S++H fragmentation mechanism. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy and Auger spectroscopy studies of gas-phase hexamethyldisiloxane (HMDSO) are presented. The photodissociation of this molecule is studied using various experimental coincidence techniques. We compare the fragmentation pathways observed after core ionization followed by Auger decay and after valence double photoionization of the molecule. A strongly selective production of the doubly charged tetramethyldisiloxane ion is observed in the low binding-energy regions. Theoretical calculations are carried out to tentatively explain the stability of the produced dication. [ABSTRACT FROM AUTHOR]

Auger decay spectra of CO subsequent to O 1s ionization with 549.85 eV photons, i.e. close to the top of the shape resonance, are presented. Their comparison with the normal Auger spectrum recorded at a photon energy well above the shape resonance reveals distinct features. In particular, in the energy region of the O 1s-1→b1Πand O 1s-1→a1Σ+ Auger transitions which are well known to consist of vibrational progressions, additional narrow lines are revealed by the spectra recorded at 549.85 eV. In a detailed fit analysis of these Auger spectra it was possible to show that the newly found lines do not exhibit the expected distortions caused by post-collision interaction. This observation identifies these lines as caused by a different mechanism, such as resonant Auger decay processes of doubly excited states. The transitions are assigned using energy and intensity arguments in combination with complementary angular distribution measurements for the Auger electrons. [ABSTRACT FROM AUTHOR]

Abstract: The present work aims at characterizing short-lived core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the resonance in the binding energy region 15–19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the , and final states. This is explained by (1) the variation in the C–O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the intermediate states can be predicted in analogy with e.g. the N2, CO2 and N2O molecules. [Copyright &y& Elsevier]

Abstract: Auger spectra from the decay of core-ionized N2 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 420eV. 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 fine 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. [Copyright &y& Elsevier]

A four-element conical electron lens has been developed in view of its integration to a double toroidal electron energy analyzer (DTA) dedicated to Auger electron-ion coincidence measurements. The lens design, using electron trajectory numerical simulations, was entirely guided by the perspective of analyzing energetic electrons with high resolution in the multicoincidence regime. The design, construction, and experimental characterization stages of this electron optics system are described in this article. Emphasis is put on the importance of third generation synchrotron radiation sources when performing such multicoincidence experiments. [ABSTRACT FROM AUTHOR]

A Doppler-type shift in the kinetic energy of atomic Auger electrons emitted after fast dissociation of O[sub 3] molecules is observed. The resonant Auger spectrum from the decay of repulsive core-excited states reflects both the early molecular ozone decay and that from excited dissociation fragments. The kinetic energy of the fragment is manifested as an energy shift of the atomic Auger lines when the measurement is made under certain conditions. We report measurements of the energy-split atomic fragment emission lines arising from dissociation on a time scale comparable to the core-hole lifetime. For the O 1s–σ[sup *] states the kinetic energy release amounts to several electron volts. We report measurements for excitation of both the terminal and central oxygen 1s electrons. A simple kinematic model for extracting a lower limit for the kinetic-energy release is presented and is compared with the result of a Born–Haber cycle, which may be seen as an estimate of the maximum energy release. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High-resolution Auger spectroscopy applied under resonant Auger Raman conditions is shown to be a powerful tool for characterizing complex potential energy surfaces in core-excited systems. Using the example of N[sub t] 1s[sup -1]π[sup *]→X˜[sup 2]Π resonant Auger transition in nitrous oxide we emphasize the interplay between the nuclear motion and the electronic decay. We show how the choice of excitation energy allows selection of core-excited species of different geometries. The nuclear dynamics of these species are mapped by measuring the resonant Auger decay spectra. In addition to the changes in vibrational structure observed for the resonant Auger decay spectra, a strong influence of nuclear motion on the electronic decay is revealed, inducing the so-called “dynamical Auger emission.” The experimental results are supported by ab initio quantum chemical calculations restricted to a linear geometry of the core-excited state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A new experimental setup for measurement of the angular distributions of energy selected Auger electrons emitted from fixed in space molecules is presented. The system is based on two identical ion detectors with a small angular acceptance placed at 0° and 90° relative to the polarization axis of the incident radiation, and a high luminosity double-toroidal electron analyzer combined with position sensitive detection. This setup allows selection of the molecular alignment for σ and π ionization channels simultaneously and provides an energy and ejection angle measurement of the outgoing electron. The performance in terms of energy and angular resolution, as well as the calibration procedure, are discussed. Sample results obtained on the carbon monoxide ionized above the C 1s threshold are presented. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High-resolution, angle-resolved resonant Auger electron spectra of the NO molecule in the regions of both N and O 1s→2π core electron excitations are presented. A large number of vibrational final states are resolved due to high energy resolution. Calculations based on lifetime vibrational interference (LVI) theory neglecting interference between different electronic intermediate states and between direct and resonant channels have been performed. A comparison between theoretical and experimental spectra shows that LVI theory describes the major spectroscopic features quite well. The same holds for the evolution of the angular averaged partial cross sections with the change of excitation energy. The angular distribution of particular vibrational final states are, however, not described successfully with LVI calculations at the present level of sophistication. A theoretical analysis supports that one reason for this deviation is electronic state interference. [Copyright &y& Elsevier]