The pure rotational spectrum of TiS (X 3Δ r) at submillimeter wavelengths

Abstract

The pure rotational spectrum of TiS in its X 3Δ r ground state has been measured using millimeter–wave direct-absorption techniques in the frequency range of 313–425 GHz. This free radical was created by the reaction of titanium vapor, produced in a high-temperature Broida-type oven, with H 2S. Eight to ten rotational transitions were recorded for the main titanium isotopologue, 48TiS, in the v = 0 and v = 1 levels, as well as for the v = 0 state of 46TiS, observed in natural abundance ( 48Ti: 46Ti = 74:8). All three Ω components were observed in almost every recorded transition, with no evidence for lambda-doubling. The data were fit with a Hund’s case(a) Hamiltonian, and rotational, spin–orbit, and spin–spin constants were determined, as well as equilibrium parameters for 48TiS. Relatively few fine structure parameters were needed for the analysis of TiS ( A, A D, and λ), unlike other 3d metal species. The rotational pattern of the three fine structure components suggests the presence of a nearby excited 1Δ state, lying ∼3000 cm −1 higher in energy. From the equilibrium parameters, the dissociation energy for TiS was estimated to be ∼5.1 eV, in reasonable agreement with past thermochemical data.