Molecules in high spin states: The millimeter and submillimeter spectrum of the MnS radical (X 6Σ+)

Abstract

The pure rotational spectrum of MnS (v=0) in its X 6Σ+ ground state has been recorded using millimeter and submillimeter direct absorption techniques in the range 160–502 GHz. MnS was synthesized in the gas phase by the reaction of manganese vapor and CS2 in a high-temperature Broida-type oven. Fourteen rotational transitions for this radical were measured, each consisting of six fine-structure components. In the lower rotational lines, hyperfine structure, arising from the Mn55 nuclear spin of 5/2, was also resolved in each spin component. These data were analyzed using a case (b) Hamiltonian, and rotational, fine structure, and hyperfine parameters determined for MnS. In the analysis, the third-order correction to the spin-rotation interaction, γS, and the fourth-order spin–spin coupling term, θ, were found necessary for an acceptable fit. The hyperfine constants determined suggest that MnS is more covalent than MnO, but more ionic than MnH. There additionally appears to be considerable sdσ hybridization in molecular orbital formation for this molecule. Bond lengths of the 3d transition-metal sulfides were compared as well, and those of MnS, CuS, and TiS do not follow the trend of their oxide analogs. This result indicates that there are significant bonding differences between transition-metal sulfides and transition-metal oxides.