High-resolution laser spectroscopy of LiAr: Spectroscopic parameters and interaction potentials of the $A 2∏$ and the $B 2∑$ states

The absorption spectrum of the LiAr molecule has been recorded with high resolution using a supersonic beam and applying the method of laser-induced fluorescence. Altogether, about 1400 absorption lines due to the transitions $A 2∏←X 2∑$ and $B 2∑←X 2∑$ of the two isotopomers ⁷$Li40Ar$ and ⁶$Li40Ar$ could successfully be assigned. The spectroscopic parameters of vibration and rotation, of spin-orbit splitting, and of λ-type doubling have been obtained for vibrational levels 5–10 of $A 2∏$ and 0–3 of $B 2∑.$ Using the observed rovibrational energies as input data the interatomic potentials of both electronic states have been determined in form of analytical functions by means of a fully quantum-mechanical method of approach. For the equilibrium values we get $Re=2.50(8)$ Å, $De=957(30) cm−1$ for $A 2∏$ and $Re=6.24(5)$ Å, $De=33.8(1.0) cm−1$ for $B 2∑.$