Rotational Relaxation of Molecular Nitrogen

Abstract

A supersonic free jet was probed to obtain a direct measure of the rotational relaxation time (τ_r) of nitrogen. Definition of an effective collision cross section (πσ_r²) for translational—rotational energy exchange in terms of τ_r, yields a πσ_r² for nitrogen that increases with decreasing temperature faster than the viscosity cross section. Comparison of the experimental πσ_r² with values obtained using thermal‐conductivity data and the theory of Mason and Monchick yields good agreement.