A possible mechanism of relaxation over the rotational sublevels of molecules under conditions of saturation of a vibrational–rotational transition

An analysis is made of rotational relaxation in a molecular system under conditions of saturation of a vibrational–rotational transition. It is shown that for molecules having large dipole moments of vibrational transitions, the rotational relaxation is not due to an "impact" mechanism but to the dipole–dipole interaction between the colliding molecules. On the basis of qualitative concepts, it is established that under certain conditions the relaxation caused by the dipole–dipole interaction may be essentially nondiffusive. An estimate is made of the cross section of the elementary event using the proposed relaxation model for NF₃, CO₂, CF₄, SF₆, and UF₆ molecules. These cross sections are considerably larger than the gas-kinetic cross sections.