Fine and magnetic hyperfine structure in the A 2Π and X 2∑+ states of yttrium monoxide

A molecular beam optical and rf–optical double resonance spectroscopic study of numerous vibrational components in the A2Π3/2–X2∑+ subband of gas phase YO has been performed. The fine and magnetic hyperfine parameters for v=0–4 of the X2∑+ state have been determined. The observed strong vibrational dependence of the spin–rotation parameter γ(X2∑+) is proposed to arise from a perturbation from two as yet unobserved low-lying 2Π states coming from a three open-shell configuration. The magnetic hyperfine parameters for the X2∑+ state can be interpreted in terms of a single unpaired electron model. An estimate for the A2Π excited state dipolar parameter has been established.