| Popis: |
A single band belonging to the A′2Δ- X2Σ+ 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 B2Σ+- X2Σ+ transition excited by a single-mode ring dye laser (pump laser), whilst a single-mode Ti:Sapphire laser scanned the corresponding A′2Δ-X2 Σ+ transition. The observed spectra resemble a typical 2Π-2Σ transition, believed to emanate from single or triple quanta of the bending vibration in the A ′2Δ 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 2Σ+ state. Previous analyses of the A2Π-X2Σ+ 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′2Δ state. Although the newly observed A′2Δ state bands have not been conclusively assigned a specific spin state, the derived Ω-doubling constants show significant 2Π1/2 character, further indicating strong interactions between the A2Π and A ′2Δ 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 D′2Σ+, D2Σ+, C2Π, B2Σ+, A2Π, A′2Δ and X2Σ+ 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. © 2011 Elsevier Inc. All rights reserved. |
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