Population relaxation of highly rotationally excited molecules at collisions

Collisional energy transfer between highly rotationally excited molecules and bath gas is considered as a stochastic process occurring in energy space. An exact solution to master equation for the population density is given in terms of simple analytical formulas for weak and strong collisions. The strong collisions are shown to manifest themselves in the distribution pattern composed of maxima and minima in the energy dependence of population density. This effect is explained in detail on physical grounds. The bulk averages of rotational energy moments and energy transfer moments are calculated analytically.