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

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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 7Li40Ar and 6Li40Ar 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∑.