Electric field Senftleben-Beenakker effects

Abstract

The transport properties of a dilute gas of polar molecules in the presence of a static homogenous electric field are obtained using as a starting point a form of the Waldmann-Snider transport equation. This transport equation differs from the simpler form found for the magnetic field analogue because of the non-diagonality of the electric dipole moment operator, and hence of the density matrix, in the internal energy. A closed equation for the diagonal part alone is derived. There is a marked difference between the behaviour of symmetric top molecules and linear Σ-molecules: the changes in the transport coefficients due to the application of the electric field occur at much higher field values for the latter, which also have a functional dependence on E 2/ p rather than on E/ p as for symmetric top molecules. It is found that these Senftleben-Beenakker effects have, for linear molecules, saturation values very different from their magnetic field analogues while, for symmetric top molecules, the electric and magnetic saturation values coicide to a good approximation. Furthermore, a cross effect between the heat-flux vector and the pressure tensor occurs only in the case of symmetric top molecules.