Electron-impact excitation of Li II: A model study of wave-function and collisional approximations and of resonance effects.

Abstract

Results are presented of five-state close-coupling and distorted-wave calculations for electron-impact excitation of Li ii from the ground state to the four n=2 states (2 ${}^{3}$S, 2 ${}^{1}$S, 2 ${}^{3}$${P}^{o}$, 2 ${}^{1}$${P}^{o}$) for energies below the ionization threshold. Sensitivity of the results to scattering approximation, target wave functions, and resonance effects is examined. The spin-allowed transitions are found to be much more sensitive to scattering approximation and to the choice of target wave functions than are the spin-forbidden transitions. Resonances contribute noticeably to both spin-allowed and spin-forbidden transitions, but rather more strongly to the latter. Good quantitative agreement is obtained with measurements of the 1 ${}^{1}$S\ensuremath{\rightarrow}2 ${}^{3}$${P}^{o}$ cross section, and of the positions of the lowest 1s3l3l' resonances.