48 research outputs found
The angularly resolved O 1s ion-yield spectrum of O2 revisited
The high-resolution photoabsorption spectrum of O2 below the O 1sÏâ1
ionization threshold has been reanalyzed by using a sophisticated fit
approach. For the vibrational substates of the O 1sÏâ1u(4ââu)3sÏg(3ââu)
Rydberg state Fano lineshapes are observed indicating an interaction with the
O 1sÏâ1g(4ââg)3Ïâu(3ââu) core-to-valence excited state. In the angularly
resolved ion-yield spectrum recorded at 90° relative to the polarization
direction of the synchrotron radiation clear evidence for the O
1sÏâ1g(2ââg)3Ïâu(3ââu) and the O 1sÏâ1u(2ââu)3sÏg(3ââu) state was found. This
observation clearly suggests thatÎ, the projection of total orbital angular
momentum on the molecular axis, is not well separated in the angularly
resolved ion-yield spectrum due to a partial breakdown of the axial-recoil
approximation for these transitions
Recoil lineshapes in hard X-ray photoelectron spectra of large molecules - free and anchored-on-surface 10-aminodecane-1-thiol
Core-level photoelectron spectroscopy of molecules presents unique opportunities but also challenges in the Hard X-ray Spectroscopy (HAXPES) realm. Here we focus on the manifestation of the photoelectron recoil effects in core-level photoemission spectra, using the independent normal-mode oscillators approach that allows to model and investigate the resulting recoil lineshapes for molecules of large sizes with only a slight computational effort. We model the recoil lineshape for N 1s and C 1s photoemission using the 10-aminodecane-1-thiol molecule as an example. It represents also a class of compounds commonly used in creating self-assembled monolayers (SAMs) on surfaces. Attachment of the -SH head group to the surface is modelled here in a simplified way by anchoring the sulfur atom of a single molecule. The effects of the orientation of photoemission in the molecular frame on the recoil lineshape of such anchored molecules are illustrated and discussed as a possible geometry probe. Time-evolution of the recoil excitations from the initial emission site across the entire molecule is also visualized
Cis- and trans-stilbene
Near-edge x-ray absorption fine structure spectra of the cis- and trans-
isomers of stilbene in the gas phase reveal clear differences, which are
analyzed by results from density-functional theory calculations using the
transition potential approach. The differences between the two species also
occur in stilbene adsorbed on Si(100), opening the way towards studying
structural changes in molecules in different surface environments, and
configurational switching in organic molecules on surfaces in particular
SiF4 anomalous behaviour reassessed
The Si 1sâ1, Si 2sâ1, and Si 2pâ1 photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1sâ1 and Si 2sâ1 lifetime broadenings were determined, revealing a significantly larger value for the Si 2sâ1 core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2pâ1 core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2sâ1 core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2pâ1 core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified
A comprehensive study of the vibrationally resolved S 2p â1 Auger electron spectrum of carbonyl sulfide
High-resolution normal Auger-electron spectra of carbonyl sulfide subsequent
to S 2p â1 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 â1 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
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
Argon 1s(-2) Auger hypersatellites
The 1s(-2) Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s(-1)2p(-2)(S-2(e),D-2(e)) and 1s(-1)2s(-1)(S-1)2p(-1)(P-2(o)) are experimentally observed. The lifetime broadening of the 1s(-2) -> 1s(-1)2p(-2)(S-2(e),D-2(e)) states is determined to be 2.1(4) eV. For the used photon energy of h nu = 7500 eV a KK/K ionisation ratio of 2.5(3) x 10(-4) is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained
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
Generalization of the post-collision interaction effect from gas-phase to solid-state systems demonstrated in thiophene and its polymers
We demonstrate experimentally and theoretically the presence of the post-collision interaction (PCI) effect in sulfur KL2,3L2,3 Auger electron spectra measured in the gas-phase thiophene and in solid-state organic polymers: polythiophene (PT) and poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT. PCI manifests itself through a distortion and a blueshift of the normal Auger S KL2,3L2,3 spectrum when S 1s ionization occurs close to the ionization threshold. Our investigation shows that the PCI-induced shift of the Auger spectra is stronger in the solid-state polymers than in the gas-phase organic molecule. Theoretical modeling within the framework of the eikonal approximation provides good agreement with the experimental observations. In a solid medium, two effects influence the interaction between the photoelectron and the Auger electron. In detail, stronger PCI in the polymers is attributed to the photoelectron scattering in the solid, which overcompensates the polarization screening of electron charges which causes a reduction of the interaction. Our paper demonstrates the general nature of the PCI effect occurring in different media
Electron spectroscopy and dynamics of HBr around the Br 1s-1 threshold
A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at approximately equal to 13.482 keV is reported. In detail, the Br 1s(-1) X-ray absorption spectrum, the 1s(-1) photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s(-1) ionization energy as well as on top of the Br 1s(-1)sigma* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s(-1) core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s(-1) single core-hole state as well as of the Br(2s(-2),2s(-1)2p(-1),2p(-2)) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p(-2)sigma* potential energy curve is found to be about -13.60 eV angstrom(-1). The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br