| Title: | K-edge absorption spectra of isoelectronic gaseous hydrides: a combination of atomic and molecular channels |
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| Authors: | ID Hauko, Robert, Univerza v Mariboru (Author)
ID Padežnik Gomilšek, Jana, Univerza v Mariboru (Author)
ID Kodre, Alojz, Univerza v Ljubljani (Author)
ID Arčon, Iztok, UNG (Author)
ID Aquilanti, Giuliana, Elettra (Author) |
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| Files: |
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| Language: | English |
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| Work type: | Not categorized |
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| Typology: | 1.12 - Published Scientific Conference Contribution Abstract |
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| Organization: | UNG - University of Nova Gorica
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| Abstract: | The fine detail in the x-ray absorption spectra in the energy region of absorption edges
provides the insight into the mechanism of inner-shell photoexcitation: in particular in spectra of
free atoms or simple molecules, the simplest being gaseous hydrides [1-2].
Measured K edge absorption spectra of hydrides of 3p (PH3, H2S in HCl) and 4p (GeH4,
AsH3, H2Se, HBr) elements, and published data of 2p hydrides (CH4, NH3, H2O, HF) as well as
SiH4 [3-6] and the noble gases at the end of the isoelectronic series (Ne, Ar, Kr) are compared to
the respective calculated spectra, obtained by atomic HF86, GRASP codes [7] and molecular
DFT (Density functional theory) ORCA code [8]. For a clearer view of intraatomic processes,
the weak and simple structural (XAFS) signal of the molecule is removed from the spectra.
Among the spectral features below the continuum limit, those with the lowest energy
belong to the transition of the core electron to the lowermost free orbitals with the molecular
character. They are, as a rule, wider than the transitions to the higher orbitals with prevailing
atomic character. The theoretical description with DFT code without specific adaptations is
sufficient for a qualitative picture of the pre-edge structure. The fine structure immediately above
the K edge stems from the coexcitation of valence electrons. We have proved that the
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. This process is markedly
different from coexcitations of more tightly bound electrons [9].
In the collection of consecutive and homologous data, analyzed by a common procedure,
the reaction channels can be identified with better precision and reliability than in analysis of
individual spectra. Our analysis showed that the energies and probabilities of single-electron
transitions into the molecular orbitals are 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 atomic orbitals the influence of the molecular field
is negligible. |
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| Keywords: | hidridi, rentgenska spektroskopija, XAFS |
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| Year of publishing: | 2018 |
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| Number of pages: | 1 |
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| PID: | 20.500.12556/RUNG-4277 |
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| COBISS.SI-ID: | 5221115 |
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| NUK URN: | URN:SI:UNG:REP:KTTTRQAZ |
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| Publication date in RUNG: | 12.09.2018 |
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| Views: | 4751 |
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| Downloads: | 0 |
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