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 D-0= 3.13 eV and an FeS electron affinity of 1.70 eV. The ground state of FeS is (5)Sigma(+), 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. (c) 2007 Elsevier B.V. All rights reserved.