Knowledge Bank

For each of the $X~3B1$, $a~1A1$, and $b~1B1$ electronic states of the $BH2-$ 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 $a~$ and $b~$ states were such that the surfaces remain degenerate at all linear configurations. For the $X~$ state the rotation-vibration energies were calculated from the surface using the $MORBIDa$ Hamiltonian, and for the $a~$ and $b~$ states the rovibronic energies were calculated using the $RENNERb$ Hamiltonian. For the $X~$ state we obtain $rc=1.2034\backslash AAc=129.5$ and a barrier to linearity of $2226cm-1$. The vibrational wavenumbers are determined to be $v1=2353$ $cm-1$, $v2=883$ $cm-1$ and $\nu 3=2498$ $cm-1$. For the $a~$-state we determine $rc=1.2369\backslash AA,\alpha c=105.7\circ$, a barrier height to linearity of $6071cm-1$ and the vibrational wavenumbers $v1=2070$ $cm-1$, $v2=986$ $cm-1$, and $\nu 3$ = $2059cm-1$. For the $b~$-state we determine $rc=1.1936\backslash AA,\alpha e=135.9\circ$, a barrier height to linearity of $1069cm-1$ and the vibrational wavenumbers $\nu 1=2399$ $cm-1$, $\nu 2=915$ $cm-1$, and $\nu 3$ = $2591cm-1$. The most interesting result we obtain is that the singlet-triplet splitting $T0(a~-1A1$) is only $153cm-1$ for $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}BH2-$. Hence singlet-triplet perturbations will significantly affect all levels of the ground state.