Detailed analysis of shake structures in the KLL Auger spectrum of H2S

Shake processes of different origin are identified in the KLL Auger spectrum of H2S with unprecedented detail. The KLL Auger spectrum is presented together with the S 1s−1 photoelectron spectrum including the S 1s−1V−1nλ and S 1s−12p−1nλ shake-up satellites with V−1 and nλ indicating a hole in the valence shell and an unoccupied molecular orbital, respectively. By using different photon energies between 2476 and 4150 eV to record the KLL Auger spectra two different shake-up processes responsible for the satellite lines are identified. The first process is a shake-up during the Auger decay of the S 1s−1 core hole and can be described by S 1s−1→2p−2V−1nλ. The second process is the Auger decay of the shake-up satellite in the ionization process leading to S 1s−1V−1nλ→2p−2V−1nλ transitions. By combining the results of photoelectron and Auger spectra the involved V−1nλ levels are assigned

A comprehensive study of the vibrationally resolved S 2p −1 Auger electron spectrum of carbonyl sulfide

High-resolution normal Auger-electron spectra of carbonyl sulfide subsequent to S 2p −1 photoionization at photonenergies of 200, 220, and 240 eV are reported along with corresponding photoelectron spectra. In addition, theoretical results are presented that take the core-hole orientation of the various spin-orbit-split and molecular-field-split S 2p −1 states into account. Auger transitions to eight metastable dicationic final states are observed and assigned on the basis of the theoretical results. From Franck- Condon analysis, assuming Morse potentials along the normal coordinates for seven of the observed quasi-stable dicationic final states, information on the potential-energysurfaces is derived and compared with theoretical results from the literature

Postcollision interaction effects in KLL Auger spectra following argon 1s photoionization

Postcollision interaction effects on the Auger decay of a deep core hole are studied both experimentally and theoretically. KL2,3L2,3 decay spectra of the Ar 1s vacancy are measured with high-energy resolution with excess photon energies ranging from 0 to 200 eV above the ionization threshold. Interaction of the Auger electron with the photoelectron and the ion field manifests itself in the Auger spectra as a distortion of the energy distribution of the Auger electron close to threshold. Moreover, recapture of the photoelectron due to energy exchange is dominating in the low-photon-energy range above threshold. The experimental results are compared with calculations based on the semiclassical approach to the postcollision interaction. The energies of the discrete levels and individual recapture cross sections are computed in the Hartree-Fock approximation. Good agreement is found between the calculated and experimental spectra, validating the model used

Simulation of Auger decay dynamics in the hard X-ray regime: HCl as a showcase

Auger decay after photoexcitation or photoemission of an electron from a deep inner shell in the hard X-ray regime can be rather complex, implying a multitude of phenomena such as multiple-step cascades, post-collision interaction (PCI), and electronic state-lifetime interference. Furthermore, in a molecule nuclear motion can also be triggered. Here we discuss a comprehensive theoretical method which allows us to analyze in great detail Auger spectra measured around an inner-shell ionization threshold. HCl photoexcited or photoionized around the deep Cl 1s threshold is chosen as a showcase. Our method allows calculating Auger cross sections considering the nature of the ground, intermediate and final states (bound or dissociative), and the evolution of the relaxation process, including both electron and nuclear dynamics. In particular, we show that we can understand and reproduce a so-called experimental 2D-map, consisting of a series of resonant Auger spectra measured at different photon energies, therefore obtaining a detailed picture of all above-mentioned dynamical phenomena at once

Statistical Properties of Fano Resonances in Atomic and Molecular Photoabsorption

Statistical properties of Fano resonances occurring in photoabsorption to highly excited atomic or molecular states are derived. The situation with one open and one closed channel is analyzed when the classical motion of the excited complex in the closed channel is chaotic. The closed channel subspace is modeled by random matrix theory. The probability distribution of the Fano parameter is derived both for the case of time reversal symmetry (TRS) and broken time reversal symmetry. For the TRS case the area distribution under a resonance profile relevant for low resolution experiments is discussed in detail.Comment: 4 pages, 4 figure

Two-to-one Auger decay of a double L vacancy in argon

We have observed L223−M3 Auger decay in argon where a double vacancy is filled by two valence electrons and a single electron is ejected from the atom. A well-resolved spectrum of these two-to-one electron transitions is compared to the result of the second-order perturbation theory and its decay branching ratio is determined

Ultrafast nuclear dynamics in the doubly-core-ionized water molecule observed via Auger spectroscopy

We present a combined experimental and theoretical study of the Auger-emission spectrum following double core ionization and excitation of gas-phase water molecules with hard-x-ray synchrotron radiation above the O K−2 threshold. We observe an indication of ultrafast proton motion occurring within the 1.5 fs lifetime of the double-core-hole (DCH) states in water. Furthermore, we have identified symmetric and antisymmetric dissociation modes characteristic for particular DCH states. Our results serve as a fundamental reference for state-of-the-art studies of DCH dynamic processes in liquid water both at synchrotron and free-electron-laser facilities

Auger resonant-Raman decay after Xe L-edge photoexcitation

We have investigated resonant Auger decay of xenon following photoexcitation of each of the three L edges under resonant-Raman conditions, which allowed us to characterize several higher Rydberg transitions. Relative intensities for spectator final states reached after L1−, L2−, and L3-edge excitations are studied in detail. Thanks to state-of-the-art experimental arrangements, our results not only reproduce the previously calculated 3d−25d and nd(n>5) state cross sections after L3 excitation, but also allow extracting the 3d−26d spectator state energy position and revealing its resonant behavior, blurred by the insufficient experimental resolution in previous data sets. The 3d−26p and 3d−27p states reached after L1 excitation as well as the 3d−25d and 3d−26d states reached after L2 excitation are also investigated and their relative intensities are reported and compared to ab initio Dirac-Hartree-Fock configuration-interaction calculations. We found the signature of electronic- state-lifetime interference effects between several coherently excited intermediate states, due to large lifetime broadening. Electron recapture processes are also identified above all three photoionization thresholds

Argon as a showcase

Electronic-state–lifetime interference is a phenomenon specific for ionization of atoms and molecules in the hard-x-ray regime. Using resonant KL2,3L2,3 Auger decay in argon as a showcase, we present a model that allows extracting the interference terms directly from the cross sections of the final electronic states. The analysis provides fundamental information on the excitation and decay processes such as probabilities of various decay paths and the values of the dipole matrix elements for transitions to the excited states. Our results shed light on the interplay between spectator, shake-down, and shake-up processes in the relaxation of deep core-hole states