Combined effect of small- and large-angle scattering collisions on a spectral line shape

•Line profiles are developed with account of soft and hard collisions.•Main types of intermolecular interaction were taken into account.•A criterion for the analysis of a spectral line narrowing was proposed.•Two types of line narrowing were considered.

Algebraic approximations for line profiles calculated on the basis of quantum-mechanical collision integral kernels for dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole intermolecular interaction potentials were obtained. In derivation of the profiles velocity-changing collisions of molecules with scattering on small and large angles also with the speed-dependence of collision relaxation constants have been taken into account. It was shown that the relative contribution of small-angle collisions into the frequency of elastic velocity-changing collisions is much more pronounced for long-range potentials. A sensitive criterion for analysis of a line narrowing was proposed and tested.