K-edge absorption spectra of gaseous hydridesIztok Arčon
, Jana Padežnik Gomilšek
, Robert Hauko
, Alojz Kodre
, Giuliana Aquilanti
, 2018, objavljeni povzetek znanstvenega prispevka na konferenci
Opis: X-ray absorption spectra in the energy region of absorption edges reveal fine details of the
mechanism of inner-shell photoexcitation: in particular in spectra of free atoms or simple
molecules, the simplest being gaseous hydrides [1-2]. In a collection of data from consecutive
and homologous elements, analyzed by a common procedure, the reaction channels can be
identified with better precision and reliability than in analysis of individual spectra.
Absorption spectra of the hydrides of 3p elements (PH3, H2S in HCl) were measured at the
XAFS beamline of the Elettra synchrotron in Trieste: a new type of adjustable absorption cell
for measurement of noxious gases at room temperature and at low photon energies was
developed for the purpose. For the analysis, data from an earlier experiment on 4p hydrides
(GeH4, AsH3, H2Se, HBr), and published data of 2p hydrides (CH4, NH3, H2O, HF) [3-4] as
well as SiH4 and the noble gases concluding the isoelectronic series (Ne, Ar, Kr) were
adopted. The spectra are compared to respective calculated spectra, obtained by atomic HF86,
GRASP codes and molecular DFT (Density functional theory) ORCA code .
Our analysis of the pre-edge structures showed that the energies and probabilities of singleelectron
transitions into the lowermost orbitals with the molecular character were strongly
affected by the symmetry of the molecule, essentially in the same way in 3p and 4p
homologues, but not in 2p homologues with a stronger influence of the core charge. In
transitions to higher orbitals with prevailing atomic character the influence of the molecular
field is negligible.
The fine structure immediately above the K edge stems from the coexcitation of valence
electrons. These coexcitations can be explained as a two-step process: the inner-shell
photoeffect followed by the shake-up of a valence electron predominantly to a free atomic
orbital. The process is markedly different from coexcitations of more tightly bound electrons
. The results of relative shake-up probabilities can be compared to results of emission
spectroscopies, the probabilities of double excitation to bound states show a correlation with
the dissociation probability of the molecule.
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Povzetek najdenega: ... večelektronske vzbuditve, hidridi, rentgenska absorpcijska spektroskopija...
Ključne besede: večelektronske vzbuditve, hidridi, rentgenska absorpcijska spektroskopija
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