Spectroscopy of Lithium Boride, a HEDM Candidate Molecule

Abstract

Calculations are reported on the spectroscopy of lithium boride (LiB) in support of experimental efforts in the High Energy Density Matter (HEDM) program at the Air Force's Phillips Laboratory. Internally contracted multireference configuration-interaction calculations employing extended one-particle basis sets and state-averaged complete-active-space self-consistent-field wave functions are carried out for the electronic states dissociating to separated-atom limits below about $30000 cm^{-1}$, where the zero of energy refers to the ground-state atoms $(Li {^{2}}S + B {^{2}}P)$. Included in this energy range are states dissociating to $Li (2p) ^{2}S + B {^{2}P}, Li (3s) {^{2}S} + B {^{2}P}$, and $Li (2s) {^{2}S} + B (2p^{2}) {^{4}P}$. The $X^{3}\Pi$ state of the molecule, with $D_{e} = 9872 cm^{-1}$ and $r_{e} = 4.06a_{0}$, is lower in energy than the $(1) {^{1}}\Sigma^{+}$ state $(D_{e} = 7940 cm^{-1}$ and $r_{e} = 4.52 a_{0})$ by $1932 cm^{-1}$. Also dissociating to ground-state atoms, the $(1) {^{1}\Pi}$ state exhibits a significant minimum, with $D_{e} = 3627 cm^{-1}$ and $r_{e} = 4.17 a_{0}$. Potential-energy curves, transition moments, and spectroscopic constants are reported for the upper and lower states involved in transitions that might be particularly relevant to observing LiB in emission spectra from a corona-excited supersonic expansion.