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1.
X-ray absorption spectroscopy set-up for unstable gases: A study of 5p Hydrides
Robert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, 2020, original scientific article

Abstract: An absorption cell is constructed for x-ray absorption spectroscopy of reactive, unstable or hazardous gases at room temperature. In conjunction with in-situ micro-synthesis technique relying on handling the gas in syringes it enabled a first measurement of x-ray absorption spectra in the region of K and L edges for the series of hydrides of 5p elements (SnH4, SbH3, TeH2, HI). The signal-to-noise ratio above 103 was achieved, whereby fine detail is discerned in the spectra, in particular the small sharp features above each absorption edge, testifying of coexcitations of outer electrons in the core photoeffect.
Keywords: X-ray absorption spectroscopy Micro-synthesis absorption cell Gaseous hydrides Multielectron photoexcitations
Published in RUNG: 10.02.2020; Views: 4513; Downloads: 0
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2.
Effects of the molecular potential on coexcitations of valence electrons in the K-shell photoeffect of 3p and 4p elements
Robert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, 2019, original scientific article

Abstract: Photoabsorption spectra of gaseous hydrides of 3p (PH3, H2S, HCl) and 4p elements (GeH4, AsH3 , H2Se, HBr) are measured in the energy region within 50 eV above the K edge, to study coexcitations of valence electrons by photoeffect in the K shell. The analysis of the valence coexcitations is extended to Ar, Kr, and SiH4. Relative probabilities and energies of states in the individual coexcitation channels are recovered by modeling the spectral features with a minimal ansatz based on the features in the contiguous noble gas. The extracted parameters are compared to the results of theoretical calculations for molecules (ORCA code) and free atoms (Hartree-Fock code). The experimental results confirm that the valence coexcitations in the 3p and 4p hydride molecules can be satisfactorily described by a two-step process, with the shake of the outer electron following the excitation of the core electron. The total probability—relative to the K-edge jump—of the shake-up processes shows a steady decrease from 19% in Si to 14% in Cl, and from 15% in Ge to 12% in Br. The experimental values for Ar (12%) and Kr (10%) are in accord with the trend. The dominant contribution is the transition to quasiatomic orbitals, in contrast with the deeper coexcitation channels in hydride molecules where transition to molecular orbitals prevails.
Keywords: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT
Published in RUNG: 05.09.2019; Views: 3764; Downloads: 0
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3.
Edge profiles in K shell photoabsorption spectra of gaseous hydrides of 3p elements and homologues
Robert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, original scientific article

Abstract: Photoabsorption spectra of gaseous hydrides of 3p elements (PH3, H2S, HCl) are measured in the energy region of photoexcitations pertaining to K edge. The analysis of the edge profile is extended to hydrides of 4p series (GeH4, AsH3, H2Se, HBr) from an earlier experiment, and to published spectra of 2p hydrides (CH4, NH3, H2O, HF) and noble gases Ar, Kr and Ne and SiH4. The edge profiles are modelled with a linear combination of lorentzian components, describing excitations to individual bound states and to continuum. Transition energies and probabilities are also calculated in the non-relativistic molecular model of the ORCA code, in good agreement with the experiment. Edge profiles in the heavier homologues are closely similar, the symmetry of the molecule governs the transitions to the lowest unoccupied orbitals. In 2p series the effect of the strong nuclear potential prevails. Transitions to higher, atomic-like levels remain very much the same as in free atoms.
Keywords: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT
Published in RUNG: 23.08.2017; Views: 4421; Downloads: 0
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