Spectroscopic and structural proprieties of LiAr and LiAr2 molecules

Abstract

We determined and tried to understand the spectroscopic and structural properties of small LiAr and LiAr2 molecules within a simple model considering LiAr as a result of interaction between a valence electron and a LiAr+ molecular ion. Potential energy curves, spectroscopic constants, and vibrational levels corresponding to the Li(2s, 2p, 3s, and 3p)+Ar dissociation are reported for the LiAr molecule. The depth of the potential well for the X2Σ+ ground state is found to be 50 cm−1 (the corresponding experimental value is (42.5±1.2) cm−1 [1]). Re is determined to be 9.36 a.u. (the experimental value is 9.24 a.u.). For the first excited state A, Re = 4.97 a.u. and De = 993cm −1 (the corresponding experimental values are 4.68 a.u. and (925−40) cm−1, respectively [1]). The spacing between the vibrational levels for the ground and first excited states is in very good agreement with the experiment. For the ground state, the difference between our results and the data of the most recent experiment is about 1 cm−1. The model has been extended to study the LiAr2 molecule in two forms (linear and triangular). We have determined the potential energy surfaces of the states dissociating to Li(2s, 2p)+Ar2 and thus found the triangular form to be more stable as compared to the linear one. We have also calculated the transition energy between the ground state and first excited states of this molecule. The emission spectrum of the Li(2s)+Ar2→Li(2p)+Ar2 transition in both forms redshifts as compared to the Li(2s)→Li(2p) atomic transition.