Theoretical study of population sharing between n=2 levels in the Li++He collision

Abstract

Presents a theoretical study of the relative populations of Sigma and Pi states associated with Li*(n=2)+He+ and Li++He*(n=2) products that are formed in Li++He collisions at keV energies. A half-collision model is considered where the (1s sigma 22p sigma 2p pi ) 1 Pi molecular state is assumed to be prepared initially (as a result of a primary 2p sigma -2p pi rotational coupling step) and the population-sharing processes occur as the collisional system breaks apart. The corresponding calculations involve six-state and twelve-state atomic-like diabatic representations and are carried out using the impact parameter method. the differential electron capture probability and the Stokes' parameters for Li*(22P) and He*(21P) excitations are determined. The calculated alignment angles gamma (Li,He) and shape parameters are slowly oscillating functions of the collision energy. The differences between the results for Li and He are discussed in terms of the various electron transition mechanisms. Qualitative agreement between theory and experiment is found for gamma (Li) but the comparison for gamma (He) is disappointing.