Rotational and hyperfine analysis of the [formula omitted] (0,0) band of TaO.

[Display omitted] • The previously unassigned D 2 Π 1 / 2 - X 2 Δ 3 / 2 transition of TaO has been fully analyzed. • D 2 Π 1 / 2 state rotational, Λ-doubling, and hyperfine constants have been determined. • Wide hyperfine splittings are present that arise mostly in the upper state. • The predominant hyperfine interaction is from the Λ-doubling d parameter. The D 2 Π 1 / 2 - X 2 Δ 3 / 2 transition of TaO has been analyzed for the first time by recording a laser excitation spectrum of its (0,0) band, which lies near 696 nm. This band was first observed many years ago by Cheetham and Barrow (Trans. Faraday Soc. 63 (1967) 1835–1845), who did not undertake an analysis due to the dense rotational structure. The spectrum displays broad hyperfine structure arising from the 181Ta nucleus that is well resolved at the Doppler-limited resolution of the experiment. The data were fitted using an effective Hamiltonian expressed in a Hund's case (c) basis, confirming the upper state symmetry as 2 Π 1 / 2 and yielding an accurate set of molecular constants describing its rotational and hyperfine structure. [ABSTRACT FROM AUTHOR]