15min:

J. D. TANDY, J.-G. WANG, P. F. BERNATH, Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK; J. LIÉVIN, Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, CPi 160/09, 50 av F.D. Roosevelt, B-1050 Bruxelles, Belgium.

Two bands for the A^/2 -X^{2 +} transitions of BaOH and BaOD have been rotationally analyzed using high-resolution V-type optical-optical double resonance spectroscopy. BaOH and BaOD molecules were synthesized in a Broida-type oven, using a single mode Ti:Sapphire laser and a single mode dye laser for molecular excitation. The observed spectra mimic a typical ² -^{2 +} transition, believed to emanate from single or triple quanta of the bending vibration in the A^/2 state. Measured rotational lines have been assigned and rotational and fine structure parameters determined through a combined least-squares fit with the millimeter-wave pure rotational data of the X^{2 +} state. Previous analyses of the A² -X^{2 +} transitions of BaOH and BaOD yielded significantly different spin-orbit coupling constants, which were attributed to possible global and local perturbations arising from vibrationally excited bands of the A^/2 state. Although the newly observed A^/2 state bands could not be conclusively designated a specific spin state, the derived -doubling constants also show significant ² character, further indicating a strong interaction between the A² and A^/2 states of BaOH. To validate these conclusions, ab initio calculations have been carried out to further understand the nature of the BaOH excited states. The wavefunctions of the D^{/2 +}, D^{2 +}, C² , B^{2 +}, A² , A^/2 and X^{2 +} states have been optimised with a state averaged multiconfigurational calculation using the MolPro software. Calculated vertical term energies show relatively good agreement with existing optical data.