Electronic and Structural Evolution of Monoiron Sulfur Clusters, FeSn- and FeSn (n = 1−6), from Anion Photoelectron Spectroscopy

Abstract

We report a photoelectron spectroscopic investigation of a series of monoiron−sulfur clusters FeSn- (n = 1−6) at various photon energies. Vibrationally resolved spectra were measured for FeS- and FeS3-. A wealth of electronic structure information was obtained for FeS and were tentatively assigned, yielding a 5Δ ground state for FeS and a 7Σ+ and a 5Δ excited state at 0.675 and 1.106 eV above the ground state, respectively. Franck−Condon factor simulations were performed for the vibrationally resolved 5Δ ground state and the 5Δ excited state, yielding an Fe−S bond length of 2.18 and 2.29 A for the anion ground state and the 5Δ excited state, respectively, as well as a vibrational temperature of 180 K for the anion. The electron affinities (EA's) of FeSn were measured to be 1.725 ± 0.10, 3.222 ± 0.009, 2.898 ± 0.008, 3.129 ± 0.008, 3.262 ± 0.010, and 3.52 ± 0.02 eV for n = 1−6, respectively. A significant EA increase was only observed from FeS to FeS2, whereas all larger species FeSn (n = 3−6) possess EA's...