Spatial distribution is found for a molecular beam emerging from a cylindrical channel into a vacuum with temperature variation along its surface where heterogeneous processes take place. In the case of an evaporating channel surface the behaviour of the Functions f(theta) (relative number of molecules escaping at the angle theta) and chi(theta) (relative thickness of condensate film on a substrate) are shown to be determined by the character of temperature variation. Thus, these functions have maxima with temperature increasing towards the exit. The distribution of the concentration of admixture molecules in the film is discussed. The results of calculations for a heterogeneous reaction leading to the disappearance of particles show that, with any character of temperature change along the surface, f(theta) is a monotonically decreasing function.