AN AB INITIO CALCULATION OF $BH^{-}_{2}$ ROVIBRONIC ENERGIES: A VERY SMALL SINGLET-TRIPLET SPLITTING
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Date
1996
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Publisher
Ohio State University
Abstract
For each of the $\tilde{X}^{3}B_{1}$, $\tilde{a}^{1}A_{1}$, and $\tilde{b}^{1}B_{1}$ electronic states of the $BH^{-}_{2}$ molecular ion we have calculated over 50 ab initio points on the potential energy surfaces using the MRD-CI method for all eight electrons. Analytical functions were fitted through the points for each state, and the functions for the $\tilde{a}$ and $\tilde{b}$ states were such that the surfaces remain degenerate at all linear configurations. For the $\tilde{X}$ state the rotation-vibration energies were calculated from the surface using the $MORBID^{a}$ Hamiltonian, and for the $\tilde{a}$ and $\tilde{b}$ states the rovibronic energies were calculated using the $RENNER^{b}$ Hamiltonian. For the $\tilde{X}$ state we obtain $r_{c} = 1.2034 \AA c = 129.5$ and a barrier to linearity of $2226 cm^{-1}$. The vibrational wavenumbers are determined to be $v_{1} = 2353$ $cm^{-1}$, $v_{2} = 883$ $cm^{-1}$ and $\nu_{3} = 2498$ $cm^{-1}$. For the $\tilde{a}$-state we determine $r_{c} = 1.2369 \AA, \alpha_{c} = 105.7^{\circ}$, a barrier height to linearity of $6071 cm^{-1}$ and the vibrational wavenumbers $v_{1} = 2070$ $cm^{-1}$, $v_{2} = 986$ $cm^{-1}$, and $\nu_{3}$ = $2059 cm^{-1}$. For the $\tilde{b}$-state we determine $r_{c} = 1.1936 \AA, \alpha_{e} = 135.9^{\circ}$, a barrier height to linearity of $1069 cm^{-1}$ and the vibrational wavenumbers $\nu_{1} = 2399$ $cm^{-1}$, $\nu_{2} = 915$ $cm^{-1}$, and $\nu_{3}$ = $2591 cm^{-1}$. The most interesting result we obtain is that the singlet-triplet splitting $T_{0} (\tilde{a}^{-1}A_{1}$) is only $153 cm^{-1}$ for $^{11}BH^{-}_{2}$. Hence singlet-triplet perturbations will significantly affect all levels of the ground state.
Description
$^{a}$P. Jensen, J. Mol. Spectrosc. 128, 478-501(1988). $^{b}$P. Jensen, M. Brumm, W. P. Kraemer, and P. R. Bunker, J. Mol. Spectrosc. 171, 31-57 (1995); M. Kolbuszewski, P. R. Bunker, W. P. Kramer, G. Osmann, and P. Jensen, Mol. Phys. in press.
Author Institution: FB 9 - Theoretische Chemie, Bergische, Universit\""{a}t - Gesamthochschule Wuppertal; STEACIE Institute for Molecular Sciences, National Research Council of Canada
Author Institution: FB 9 - Theoretische Chemie, Bergische, Universit\""{a}t - Gesamthochschule Wuppertal; STEACIE Institute for Molecular Sciences, National Research Council of Canada