Transition of the Rydberg series from the spectroscopic to the united atom region in LiH

Abstract

The behaviours of Rydberg states are studied using the multi-reference configuration interaction method for the 20 excited electronic states in the four-electron molecular system, LiH, which are greatly different from those in molecular systems with fewer electrons. The electronic structure of LiH is characterized by low-lying doubly excited states at small R but none at R > 0.7a0. The transition from the doubly excited configuration-dominant states to the singly excited configuration-dominant states is found to take place in a narrow range of R. The Rydberg series at small R and in the spectroscopically observable region are different because of the distinct natures of the two regions. The transition of the doubly excited interlopers 2p2 1Dσ and 2p2 1Dδ at small R into singly excited Rydberg states in the spectral region is studied. Sharp mirror peaks in the dipole moment curves at the avoided crossing points are explained by non-adiabatic coupling.