A theoretical study on the low-lying electronic states of the Li2H molecule

The structures and properties of the ground and low-lying excited states of Li2H have been investigated by ab initio calculation. The UMP2-optimized geometry of ground-state Li2H is in agreement with experiment. Properties of the excited 2B2 and 2A2 states have been predicted, based on UMP2-optimized structures, which are consistent with previous theoretical calculations. However, there is a larger difference between UMP2-optimized and Vezinʹs experimental structure of the excited 2B1 state. A careful MRSDCI study of the 2B1 potential energy surface predicts that the structure observed by Vezin et al. is a stable geometry with ionic state character while the geometry obtained by UMP2 optimization is another stable structure with covalent character. The bonding between H and Li atoms is of partial covalent character in the 2A1 state, but ionic in the 2B2 and 2A2 states.