Laser Absorption Spectroscopy of $LaF^{+}$: Accurate Term Energies for the $H^{2}\Pi$, $D^{2}\Phi$, and $X^{2}\Delta$ States

Abstract

The laser absorption spectrum of the $LaF^{+}$ molecular ion has been observed for the first time. Gas phase LaF was obtained by heating a mixture of a 0.2 g of La metal and 0.3 g of $LaF_{3}$ powder to 1900 K. $LaF^{+}$ ions were produced by passing a 25 kHz discharge (80-100W, 0.5A peak current)through the vapor cathode, 138 lines of the $^{2}\Phi_{25}-^{2}\Delta_{15}(0,0)$ band were recorded. This band system was observed previously $^{a}$ in the emission spectrum of $LaF^{-1}$. Accurate term energies are (in $cm^{-1}$):$$T_{a}(H^{2}\Pi_{0.5})=30398.78(5), T_{0}(D^{2}\Phi_{3.5})=17099.24(5), T_{0}(X^{2}\Delta_{2.5})=274.62(5)$$$$T_{0}(H^{2}\Pi_{0.5})=30237.85(5), T_{0}(D^{2}\Phi_{2.5})=16534.738(5), T_{0}(X^{2}\Delta_{1.5})=0.0$$ Ligand field theory models were used to provide the configurational assignment for the $LaF^{-}$ electronic states. The symmetry for the ground state of the $LaF^{-}$ molecular ion has been reassigned as $X^{2}\Delta$.