243 research outputs found
Angular distribution of Auger electrons from fixed-in-space and rotating C 1sâ2Ï photoexcited CO: Theory
Deep-core photoionization of krypton atoms below and above the 1s ionization threshold
Electronic relaxation of atomic Kr below and above the 1s ionization threshold is investigated experimentally using hard x-ray photoelectron spectroscopy. The experimental results are interpreted with the aid of relativistic Dirac-Fock calculations. The 1s orbital core-hole lifetime is extracted and the satellite's structures accompanying the photoelectron main line are assigned. Auger spectra recorded below and above the K edge are also investigated. In particular, the Auger cascade originating from vacancies of different origin in the L shell is analyzed in great detail. Competition between radiative KL versus nonradiative KLL Auger emission is emphasized
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 1sâ1 photoelectron spectrum including the S 1sâ1Vâ1nλ and S
1sâ12pâ1nλ shake-up satellites with Vâ1 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 1sâ1 core hole and can be described by S 1sâ1â2pâ2Vâ1nλ. The second process
is the Auger decay of the shake-up satellite in the ionization process leading
to S 1sâ1Vâ1nλâ2pâ2Vâ1nλ transitions. By combining the results of
photoelectron and Auger spectra the involved Vâ1nλ levels are assigned
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
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
Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-ray FEL
We have performed X-ray two-photon photoelectron spectroscopy (XTPPS) using
the Linac Coherent Light Source (LCLS) X-ray free-electron laser (FEL) in order
to study double core-hole (DCH) states of CO2, N2O and N2. The experiment
verifies the theory behind the chemical sensitivity of two-site (ts) DCH states
by comparing a set of small molecules with respect to the energy shift of the
tsDCH state and by extracting the relevant parameters from this shift.Comment: 11 pages, 2 figure
Subfemtosecond Control of Molecular Fragmentation by Hard X-Ray Photons
Tuning hard x-ray excitation energy along Cl 1sâÏâ resonance in gaseous HCl
allows manipulating molecular fragmentation in the course of the induced
multistep ultrafast dissociation. The observations are supported by
theoretical modeling, which shows a strong interplay between the topology of
the potential energy curves, involved in the Auger cascades, and the so-called
core-hole clock, which determines the time spent by the system in the very
first step. The asymmetric profile of the fragmentation ratios reflects
different dynamics of nuclear wave packets dependent on the photon energy
Two-to-one Auger decay of a double L vacancy in argon
We have observed L223âM3 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 Kâ2 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
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