MD SIMULATION OF ROTATIONAL RELAXATION IN LIQUID-NITROGEN - COMPARISON WITH NMR AND RAMAN DATA

A simulation of liquid nitrogen has been performed along the coexisten ce curve. Angular momentum, rotational energy and second-order orienta tional correlation times tau(j), tau(E), tau(theta,2) were calculated. The first and the last were compared with the available data. The res ults for tau(E) were compared with halfwidth data from the isotropic R aman scattering measurements. For the entire coexistence curve, the va lidity of stochastic perturbation theory was shown: omega(Q) tau(E) < 1, where omega(Q) is an average frequency of the Q branch. The rotatio nal contribution to the halfwidth (estimated from the extreme narrowin g formula) decreases with cooling, but does not become less than 25% o f the whole width. The ratio tau(E)/tau(J), varies from 1.7 to 1 in th e region between the critical and the triple points, which is inconsis tent with the Langevin description of the angular momentum relaxation.