Photoelectron spectra of FeS− explained by a CASPT2 ab initio study

Potential energy curves for the ground states for FeS and FeS−, and of several low-lying electronic states that are responsible for the FeS− photoelectron spectrum, are calculated at the CASPT2 level. Our computational approach predicts a dissociation energy D0 = 3.13 eV and an FeS electron affinity of 1.70 eV. The ground state of FeS is 5Σ+, in agreement with a previous CASSCF/ACPF study but in disagreement with a very recent investigation of the microwave spectrum. New assignments of the photoelectron spectrum of FeS− are presented.