Rotational Relaxation of Molecular Nitrogen

Abstract

A supersonic free jet was probed to obtain a direct measure of the rotational relaxation time (τr) of nitrogen. Definition of an effective collision cross section (πσr2) for translational—rotational energy exchange in terms of τr, yields a πσr2 for nitrogen that increases with decreasing temperature faster than the viscosity cross section. Comparison of the experimental πσr2 with values obtained using thermal-conductivity data and the theory of Mason and Monchick yields good agreement.