The influence of a high magnetic field on the viscosity of diamagnetic gases of linear, symmetric and asymmetric top molecules is studied within the frame-work of the kinetic theory based on the Waldmann-Snider equation. The quadratic Zeeman effect associated with the anisotropic magnetic susceptibility is taken into account in addition to the usual linear Zeeman splitting.A viscous flow in a polyatomic gas gives rise to a collision-induced alignment of the molecular rotational angular momentum. The alignment, in turn, affects the value of the viscosity. Hence application of an external field has an influence on the transport coefficient if the alignment is appreciably altered by the field-induced motion of the rotational angular momentum of a molecule between two successive collisions. This phenomenon, known as the Senftleben-Beenakker effect 2 , has been studied extensively both experimentally and theoretically for gases of paramagnetic and diamagnetic linear and symmetric top molecules in the presence of a magnetic field 2 , and for polar gases of symmetric top molecules in the presence of an electric field 2 . If the relevant field Hamiltonian is of dipolar type (1st order Zeeman and Stark effects) the fieldinduced change of the transport coefficients depends on the magnitudes of the magnetic and electric fields H and E and on the pressure of the gas via H/P and E/P. Polar gases of linear ^-molecules in the presence of an electric field (2nd order Stark effect) where an E 2 /P dependence can be expected have been treated theoretically 3 but no measurements have been reported so far.In this note, theoretical expressions derived from the Waldmann-Snider equation 4 are presented for the magnetic-field-induced change of the viscosity of diamagnetic gases in the presence of strong magnetic fields. The quadratic (2nd order) Zeeman effect associated with the anisotropic molecular susceptibility is taken into account in addition to the usual linear (1st order) Zeeman effect. The quadratic term is of particular importance for heavier (organic) molecules 5 . Linear, symmetric and asymmetric top molecules are treated.Reprint requests to Dr. S. Hess, Institut für Theoretische Physik der Universität Erlangen-Nürnberg, D-8520 Erlangen, Glückstraße 6.
Waldmann-Snider Equation and Field HamiltonianThe nonequilibrium state of a polyatomic gas is characterized by the distribution function (operator) f (t,X,p,J...) where p and hJ are the linear and rotational angular momenta and the dots stand for additional operators specifying the internal state of a molecule. The average ( W) of an operator W(p,J,.. The 2nd, 3rd and 4th term in Eq. (1) describe the change of due to the free flight, to the internal motion, and to the binary collisions of the molecules. For diamagnetic molecules in the presence of a strong magnetic field H = Hh(hh = l) the Hamiltonian can be written as 5 -C^hJ-hCzHzjihJJh (2) where 777 denotes the symmetric traceless part of a tensor. The coefficients Ct and C2 which, in general, depend on the internal quan...