LASERSPECTROSCOPY OF THE $B^{2}\Sigma$ STATE OF LiAr

Abstract

The rovibrational structure of the transition $B^{2}\Sigma\leftarrow X^2\Sigma$ of LiAr has been investigated by means of high-resolution laser spectroscopy using a supersonic beam for production of the $molecules^{a}$. About 100 absorption lines could successfully be assigned for each isotopomer $^{7}LiAr$ and $^{6}LiAr$ providing in addition the vibrational numbering of the observed levels $v = 0\ldots 3$ of the $B^{2}\Sigma$ state. The analysis of the experimental observations was complicated by the occurrence of perturbations between rovibrational levels of the $B^{2}\Sigma$ and of the $A^{2}\Pi$ state which have not been taken into account, up to now. For the $B^{2}\Sigma$ interaction potential we used a Morse-van der Waals potential as an analytical expression reproducing the observed energy levels with an error margin of $0.015cm^{-1}$. The van der Waals parameter $C_{6}$ was fixed to its theoretical value. Our preliminary results for the $B^{2}\Sigma$ state of $^{7}LiAr$ are $R_{c} = 6.24(5)$ {\AA} and $D_{c} = 33.8(2.0)cm^{-1}$.