The properties of liquid nitrogen

Measurements are reported of the nitrogen-nucleus spin-lattice relaxation time, T 1, in liquid nitrogen 14N2 and liquid nitrogen 15N2 along the liquid-vapour coexistence line from 77·3 K up to the critical temperature and for the fluid at the critical density up to 145 K. Values of the molecular reorientational correlation time, τ Q , and the molecular angular momentum correlation time, τ sr , are determined. The values of τ Q and τ sr and the relation between them are discussed in terms of various theories of molecular reorientation in molecular liquids. The values of τ Q and τ sr are also compared with those predicted by computer simulation methods. It is concluded that the molecular reorientation in liquid nitrogen is not by classical reorientational diffusion except possibly at temperatures near the triple point. It is suggested that at higher temperatures the reorientation is on average by rather large angles and that the process may be quantum mechanical to some extent. (For paper I in this series see reference [8].)