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

摘要

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 > 0.7a(0). 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 2p(2) D-1(sigma) and 2p(2) D-1(delta) 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.