The pure rotational spectrum of TiS (X3Δr) at submillimeter wavelengths

The pure rotational spectrum of TiS in its X3Δr 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 H2S. 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, AD, 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.