Complete line shape for the impact, static, and the intermediate regions

Line shapes are calculated for the resonance broadening of an excited level through the dipole–dipole interaction. The calculations are based on two main approximations: (1) two body collisions and (2) straight classical path for the translational motion. The results are valid over the complete region extending from the impact to the static regimes. It is shown that, under suitable conditions, the incomplete collisions can give rise to (a) a splitting of the line at the center and (b) nonlinear density dependence of the line width.