Cationic double K-hole pre-edge states of CS2 and SF6

Abstract

Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS₂ and SF₆ with a double hole in the K-shell and one electron exited to a normally unoccupied orbital have been obtained. The spectra are interpreted with the aid of a high-level theoretical model giving excellent agreement with the experiment. The results shed new light on the important distinction between direct and conjugate shake-up in a molecular context. In particular, systematic similarities and differences between pre-edge states near single core holes investigated in X-ray absorption spectra and the corresponding states near double core holes studied here are brought out.

Figure 1

Schematic illustration of the two channels contributing to single photon K ⁻² V processes. The red (green) arrows represent the direct (conjugate) path. The curved arrows correspond to photo-excitation processes. The straight arrows correspond to shake processes.

Figure 2

Experimental (lower panel) and theoretical (upper panel) K ⁻² V spectrum of C^*S₂. The theoretical spectrum is based on DFT/B3LYP binding energies (see Table 1). The main peaks are illustrated by electronic iso-density plots. Red lines: direct contributions; green lines: conjugate contributions; black curve: incoherent sum of direct and conjugate contributions.

Figure 3

Experimental sulphur K ⁻² V spectrum of CS₂.

Figure 4

Experimental (lower panel) and theoretical (upper panel) sulphur K ⁻² V spectra of SF₆. Red lines reflect the direct contributions and green lines reflect conjugate contributions. The black curve represents an incoherent sum of the direct and conjugate contributions.

Figure 5

Experimental (lower panel) and theoretical (upper panel) K ⁻² V spectra of ${\mathrm{SF}}_6^{⁎}$. The position of the theoretical low-lying band is set to 1476.04 eV (see Table 1, HF-MP2).