The influence of nuclear spins on the transport properties of molecular gases and application to HD

Coupling between the angular momentum J and the nuclear spins of a molecule modifies those contributions to the transport properties of a molecular gas which arise from the macroscopic orientational polarization. This (low pressure) effect is studied in detailfor molecular HD at low temperature (J = 1 states). Because the rotational quantum numbers are low (J = 1), a quantum treatment is essential and moreover be classical motion of J differs significantly from simple precession: the “nutation” of J being also important. This nutation gives rise to significant phase randomization of the angular-momentum polarizations at zero field, and to a field effect on the axial polarizations which are in addition to the usual field effects on nonaxial polarizations.