Collision broadening and relaxation of the resonance lines of lithium and sodium in helium gas

Abstract
The interaction potentials of the low-lying states of the molecules LiHe and NaHe are calculated by a model potential method and used in the impact approximation to derive the widths and the shifts of the lithium and sodium resonance lines in helium gas. The widths are about three times larger than those given by the conventional van der Waals broadening formula. Expressions are obtained for the cross sections for fine-structure and depolarizing transitions in the elastic approximation. The resulting cross sections are in satisfactory agreement with experimental data and with more elaborate calculations.