Collisional Excitation Transfer between Atoms in Near-Resonant Processes

The cross sections for the excitation transfer between unlike atoms are calculated by the impact parameter method. Approximate formulas for discrete-continuum and discrete-discrete transition probabilities are obtained. The cross section can be obtained by integrating this probability over the impact parameter. The approximate formula is applied to the case of Deuterium-Hydrogen excitation transfer as one of practical examples. Comparisons are made with two other formulas, i. e. Rosen-Zener (R-Z) and Vanishtein-Presnyakov-Sobelman (V-P-S) formulas. The dependence of the cross section on the resonance defect in the discrete-discrete case is also investigated. The agreements among these three formulas are found not very good.