Investigation of core-excited quantum yield spectra of high-symmetric boron compounds

Hallmeier, K.H.; Szargan, R.; Meisel, A.; Hartmann, E.; Gluskin, E.

doi:10.1016/0584-8539(81)80148-1

Cited by 21 publications

(21 citation statements)

References 12 publications

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“…Interest in this edge (~195-210 eV) stems mainly from the potential use of borosilicate glasses in the encapsulation of high-level nuclear waste and the need to determine the B coordination in these materials (cf., Peuget et al 2006Peuget et al , 2007. There have been several B K-edge XANES studies of borate and borosilicate minerals (Hallmeier et al 1981;Brydson et al 1988;Sauer et al 1993;Li et al 1995cLi et al , 1996Garvie et al 1995;Kasrai et al 1998;Fleet andMuthupari 1999, 2000;Fleet and Liu 2001). In general, the spectra of In B 2 O 3 ( Fig.…”

Section: (C)mentioning

confidence: 98%

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Henderson

Groot

Moulton

2014

Reviews in Mineralogy and Geochemistry

262

155

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In addition to the XANES region, at higher energies the extended X-ray absorption fine structure (EXAFS) region is found. The spectral shape in the near-edge region is determined by electronic density of states effects and gives mainly information about the electronic properties and the local geometry of the absorbing atom. The EXAFS region is dominated by single scattering events of the outgoing electron on the neighboring atoms, providing mainly information about the local geometric structure around the absorbing site. In this chapter we will focus on XANES. XANES SpectroscopyIn XPS the ground state (Ψ 0 ) is excited to the ground state plus a core hole (c), where the electron (ε) is excited to higher energy, while in XAS the ground state is excited with a coreto-valence excitation (cv). The XPS binding (E B ) is defined as the photon energy (Ω) minus the measured kinetic energy of the electron (E k ) and corrected for the work function (φ):The work function is the minimal energy to emit an electron from the material. In metals the XAS edge energy can be assumed to be equal to the XPS binding energy, because exactly at the XPS binding energy a transition is possible to the lowest empty state. Experimentally the XAS edge energy can be slightly higher than the XPS binding energy, for example if the transition to the lowest empty state is forbidden by selection rules. Single electron excitation approximation and selection rulesIn first approximation XANES can be described as the excitation of a core electron to an empty state. In the Fermi golden rule, the initial state wave function is rewritten as a core wave function and the final state wave function (ε) as a valence electron wave function (ν). This implicitly assumes that all other electrons do not participate in the X-ray induced transition. In this approximation, the Fermi golden rule can be written as:The X-ray absorption selection rules determine that the dipole matrix element is non-zero if the orbital quantum number of the final state differs by one from the initial state (∆L = ± 1, i.e., s → p, p → s or d, etc.) and the spin is conserved (∆S = 0). In the dipole approximation, the shape of the absorption spectrum should look like the partial density of the (∆L = ± 1) empty states projected on the absorbing site, convoluted with a Lorentzian. This Lorentzian broadening is due to the finite lifetime of the core-hole, leading to an uncertainty in its energy according to Heisenberg's principle. The single electron approximation gives an adequate simulation of the XANES spectral shape if the interactions between the electrons in the final state are relatively weak. This is the case for all excitations from 1s core states (K-edges).

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Section: (C)mentioning

confidence: 98%

X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Henderson

Groot

Moulton

2014

Reviews in Mineralogy and Geochemistry

262

155

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“…26 XAS spectra of solid sodium borohydride have been studied previously; However, the spectrum was presented without assignment of the salient spectral features. 27 Boron-containing minerals and glasses have also been studied and the spectral features assigned. [28][29][30][31][32] Trigonally coordinated boron exhibits a sharp pre-edge feature around 194 eV, which is attributed to the transition of an electron from the B 1s core state to the unoccupied B 2p z orbital (oriented perpendicular to the trigonal plane).…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of aqueous borohydride: a potential hydrogen storage medium

Duffin¹,

England²,

Schwartz³

et al. 2011

Phys. Chem. Chem. Phys.

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Borohydride salts have been considered as good prospects for transportable hydrogen storage materials, with molecular hydrogen released via hydrolysis. We examine details of the hydration of sodium borohydride by the combination of X-ray absorption spectroscopy and first principles' theory. Compared to solid sodium borohydride, the aqueous sample exhibits an uncharacteristically narrow absorption feature that is shifted to lower energy, and ascribed to the formation of dihydrogen bonds between borohydride and water that weaken the boron-hydrogen covalent bonds. Water also acts to localize the highly excited molecular orbitals of borohydride, causing transitions to excited states with p character to become more intense and a sharp feature, uncharacteristic of tetrahedral molecules, to emerge. The simulations indicate that water preferentially associates with borohydride on the tetrahedral corners and edges.

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“…The latter feature is unexpected for tetrahedrally coordinated boron according to the concepts proposed by Hallmeier et al 20 and Blau et al?1 We have performed model compound studies in order to further clarify the relationship between B K-edge spectra and local boron coordination. ~.l This spectrum exhibits a broad s-polarized band at 191 eV and a strong, p polarized, low energy peak at 188.6(5) eV.…”

Section: Introductionmentioning

confidence: 61%