Investigating the electronic states of BaOH by V-type double resonance spectroscopy and ab initio calculations: Further evidence of perturbation from the state

Abstract: A single band belonging to the band system has been rotationally analyzed for each of the two isotopologues, BaOH and BaOD, using high-resolution V-type optical–optical double resonance spectroscopy. BaOH and BaOD molecules were synthesized in a Broida-type oven. High-resolution spectra were recorded by monitoring the dip in fluorescence of the transition excited by a single-mode ring dye laser (pump laser), whilst a single-mode Ti:Sapphire laser scanned the corresponding transition. The observed spectra resemble a typical transition, believed to emanate from single or triple quanta of the bending vibration in the 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 state. Previous analyses of the 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 state. Although the newly observed state bands have not been conclusively assigned a specific spin state, the derived Ω-doubling constants show significant character, further indicating strong interactions between the and 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 , , , , , and states have been characterized by means of multireference configuration interaction calculations using the MOLPRO software. Calculated vertical term energies show relatively good agreement with existing optical data. [Copyright &y& Elsevier]