Accurate Vibrational Frequencies of Borane and Its Isotopologues.

Vibrational transitions of borane and its isotopologues ((11)BH3, (11)BD3, (10)BH3, and (10)BD3) have been obtained from state-specific vibrational configuration interaction calculations. Explicitly correlated coupled-cluster calculations, CCSD(T)-F12a, with additional corrections for high-order terms of the coupled-cluster expansion, i.e., CCSDT(Q), were used to determine multidimensional potential energy surfaces. Additional contributions due to core-valence interactions, scalar relativistic effects, and such arising from the diagonal Born-Oppenheimer correction were accounted for in the one-dimensional terms within the expansion of the potential energy surface. From these, anharmonic vibrational spectra were obtained, which are in excellent agreement with experimental data. Mean absolute deviations from gas phase measurements were found to be in the sub-wavenumber regime.