Cavity ring down absorption spectroscopy of the BΣ-XΣ transition of YO

The absorption spectrum of the (2, 0) and (2, 1) bands of the B²Σ⁺-X²Σ⁺ transition of YO between 442 and 478 nm were recorded using laser vaporization/reaction with free-jet expansion and cavity ring down laser absorption spectroscopy. Local rotational perturbations have been found for both spin components of the v = 2 level of the B²Σ⁺ state. The observed perturbations could be ascribed to a degenerate perturbing state interacting with the B²Σ⁺ state. Least-squares fit of the observed upper state term values yielded molecular constants for the v = 2 level of the B²Σ⁺ state and the perturbing ²Π state. Earlier ab initio calculations J. Chem. Phys. 89 (1988) 2160] indicated that the C²Π state is nearby, it is plausible that the C²Π state is the perturbing state.