Abstract
The Li 1s core excitation spectra in LiH was studied by means of x-ray Raman scattering (XRS) spectroscopy in a wide range of momentum transfers q. The analysis of the near-edge region of the measured spectra in combination with q-dependent ab initio calculations of XRS spectra based on the Bethe–Salpeter equation (BSE) reveals that the prominent peak at the excitation onset arises from two main contributions, namely a pre-edge peak associated to a p-type core exciton and strong transitions to empty states near the bottom of the conduction band, which is in contrast to previous experimental studies that attributed that feature to a single excitonic peak. The p-like angular symmetry of the core exciton is supported by BSE calculations of the relative contributions to the XRS spectra from monopole and dipole transitions and by the observed decrease of its normalised intensity for increasing momentum transfers. Higher energy spectral features in the measured XRS spectra are well reproduced by BSE, as well as by real-space multiple-scattering calculations.
Highlights
Lithium hydride is the simplest heteronuclear compound; it crystallises in the simple rock-salt structure and in the unit cell it has only four electrons, which have s-like character in a picture of essentially ionic bonding between Li+ and H−
The analysis of the near-edge region of the measured spectra in combination with q-dependent ab initio calculations of x-ray Raman scattering (XRS) spectra based on the Bethe–Salpeter equation (BSE) reveals that the prominent peak at the excitation onset arises from two main contributions, namely a pre-edge peak associated to a p-type core exciton and strong transitions to empty states near the bottom of the conduction band, which is in contrast to previous experimental studies that attributed that feature to a single excitonic peak
We reported an experimental and theoretical study of the Li 1s core excitation spectra in LiH using XRS spectroscopy and calculations based on the real space multiple scattering (RSMS) and BSE methods, as implemented in the FEFF and OCEAN codes, respectively
Summary
Lithium hydride is the simplest heteronuclear compound; it crystallises in the simple rock-salt structure and in the unit cell it has only four electrons, which have s-like character in a picture of essentially ionic bonding between Li+ and H−. This simplicity has led the use of LiH as a benchmark to probe different theoretical approaches for electronic structure calculations [1]. Based on similarities with the absorption spectrum of LiF, a prominent peak at the onset of the reflectance spectrum was attributed to a transition from the Li+ 1s level to a n = 1 coreexciton state associated with the p-like conduction band. Prominent peaks observed in the photoelectron yield spectrum [13] and in the electron energy-loss spectrum (EELS) [14] at
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