Laser spectroscopy of molecular LiHe: The 3dp2Π2transition

The rotationally resolved absorption spectrum of the 3d ${}_{}{}^2{}_{}{}^{}\mathit{p}$ ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$ transition in molecular LiHe has been measured. For each of three isotropic variants ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_{}^3{}_{}{}^{}$He, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_{}^4{}_{}{}^{}$He, and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}_{}^4{}_{}{}^{}$He, six vibrational transitions have been observed from the lower 2p ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$(v’ ’=0,1) electronic state to the upper 3d ${}_{}{}^2{}_{}{}^{}\mathrm{\Delta }$(v’=0,1,2,3) electronic state. Analysis of the observed spectra has yielded values for the well depth and equilibrium separation of 1020(20) ${\mathrm{cm}}^{\mathrm{-}1}$ at 3.37(3)${\mathit{a}}_0$ for the 2p ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }$ state and 610(20) at 3.52(2)${\mathit{a}}_0$ for the 3d ${}_{}{}^2{}_{}{}^{}\mathrm{\Delta }$ state. Details of our analysis and our experimental technique are presented.