Valence in the Rydberg/continuum region in molecular inner-shell spectroscopy

Abstract

The core-to-valence, especially core-to-σ*, excitation is sometimes obscure in molecular soft X-ray absorption spectra. The potential energy curve (PEC) of the core-to-σ* state is repulsive for the bond elongation; on the other hand, the PECs of the core ionized state and the core-to-π* state are bound and the core-to-Rydberg states are almost parallel to the PEC of the core ionized state. Thus, the σ* state can have interactions with the Rydberg and continuum states, and even with the π* state in some cases, around the Franck–Condon region. Using schematic PECs, we have discussed, where the σ* state is located in the 1s photoabsorption spectra of N 2, O 2, CH 3F, and C 2H 2, and how we know evidence for the σ* state in the 1s photoabsorption spectra of CH 4.