The pure rotational spectrum of TiF (X 4Φr): 3d transition metal fluorides revisited

Abstract

The pure rotational spectrum of TiF in its X 4Φr (v=0) ground state has been measured using millimeter/sub-millimeter wave direct absorption techniques in the range 140–530 GHz. In ten out of the twelve rotational transitions recorded, all four spin–orbit components were observed, confirming the Φr4 ground state assignment. Additional small splittings were resolved in several of the spin components in lower J transitions, which appear to arise from magnetic hyperfine interactions of the F19 nucleus. In contrast, no evidence for Λ-doubling was seen in the data. The rotational transitions of TiF were analyzed using a case (a) Hamiltonian, resulting in the determination of rotational and fine structure constants, as well as hyperfine parameters for the fluorine nucleus. The data were readily fit in a case (a) basis, indicating strong first order spin–orbit coupling and minimal second-order effects, as also evidenced by the small value of λ, the spin–spin parameter. Moreover, only one higher order term, η, the spin–orbit/spin–spin interaction term, was needed in the analysis, again suggesting limited perturbations in the ground state. The relative values of the a, b, and c hyperfine constants indicate that the three unpaired electrons in this radical lie in orbitals primarily located on the titanium atom and support the molecular orbital picture of TiF with a σ1δ1π1 single electron configuration. The bond length of TiF (1.8342 Å) is significantly longer than that of TiO, suggesting that there are differences in the bonding between 3d transition metal fluorides and oxides.