High-resolution and symmetry-resolved N and O K-edge absorption spectra of NO

Abstract

High-resolution electron-yield and ‘‘symmetry-resolved’’ ion-yield spectra have been measured at the N and O K edges of a 2Π open-shell molecule, NO. Several Rydberg transitions converging to the 3Π and 1Π ionization thresholds are found. The core-to-valence and core-to-Rydberg transitions are interpreted with the help of ab initio self-consistent-field configuration-interaction and frozen-core calculations for the core-excited states with three open shells. It is found that the equivalent-core model (N*O=O2) breaks down in discussing the state ordering of the three N 1s–2pπ* excited states, 2Δ, 2Σ−, and 2Σ+. It is important to consider explicitly the core hole and the exchange repulsion between the core and π* electrons.