Two-electron excitations and one-electron multiple-scattering resonances in the x-ray absorption of solid neon.

Abstract

The local and partial density of states of the conduction band of solid neon in a large energy interval has been extracted from the analysis of the K-edge x-ray-absorption near-edge structure (XANES) spectrum by using a full multiple-scattering method. The absorption cross section for one-electron transitions from the Ne 1s level to the conduction-band final states in the solid Ne is predicted by first principles. The absorption cross section is described as due to an atomic factor and to a structure factor determined by the local and partial density of states for a large cluster formed by about 80 atoms. The experimental spectrum is obtained by describing the final state in the fully relaxed potential in the presence of the core hole. The exciton peak at threshold is shown to be due to the lowest unoccupied valence state pushed down in the bound-state region by the core hole. In the 100-eV XANES energy range the single-scattering approximation fails to predict the XANES of solid Ne indicating that the full multiple-scattering approach is required. The present analysis allows us to identify strong two-electron excitations 1${\mathit{s}}^{2}$2${\mathit{s}}^{2}$2${\mathit{p}}^{6}$\ensuremath{\rightarrow}1${\mathit{s}}^{1}$2${\mathit{s}}^{2}$2${\mathit{p}}^{5}$${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{i}}$${\mathit{p}}^{2}$ in the energy range of 30 eV above the K edge, involving monopole 2p\ensuremath{\rightarrow}\ensuremath{\varepsilon}p transitions to the lowest valence states at energy \ensuremath{\varepsilon}. The intensity of the two-electron excitations is found to be so strong that it should be considered in standard extended x-ray-absorption fine-structure--XANES data analysis for local structure investigation.