High-resolution laser spectroscopy of BaOH and BaOD: Anomalous spin-orbit coupling in the A˜2Πstate

The A˜2Π(000)-X˜2Σ+(000) transition of BaOD has been rotationally analyzed using laser excitation spectroscopy. BaOD molecules were synthesized through the reaction of Ba atoms with D2O in a Broida-type oven. Rotational and fine structure parameters determined for the A˜2Π(000) state of BaOD yielded a spin-orbit coupling constant A significantly different from the corresponding value for BaOH (∼605.8 cm−1 versus 560.1 cm−1). Λ-doubling constants for the A˜2Π state were observed to be in poor agreement with the predictions of the pure precession model for the interaction between the A˜2Π and the B˜2Σ+ states in BaOD. Explanations for the unusual spin-orbit splitting and apparent failure of the pure precession and unique perturber models in BaOH and BaOD are discussed, with particular reference to possible global and local perturbations arising from vibrationally excited bands of the A˜′2Δ state.