Viscosity and thermal conductivity of polar gases in an electric field

Abstract

The influence of an electric field on the viscosity and thermal conductivity of gases of polar molecules has been investigated both theoretically and experimentally. The two different methods to solve the kinetic equation for polar symmetric top molecules, i.e. the perturbative method, employed by Mikhaǐlova and Maksimov, and the variational method, employed by Levi, McCourt and Tip, have both been refined. The improved methods now yield the same result: the field dependence of the electric effect is essentially the same as obtained by Mikhaǐlova and Maksimov whereas the terms contributing to the effect are essentially those given by Levi, McCourt and Tip. Measurements on the viscosity coefficient η 3 and the thermal conductivity coefficient λ″ are described. The hot-wire method which has been used for the thermal conductivity measurements is thoroughly discussed. The experimental results extend to the linear molecule NO, the oblate symmetric top molecules: NF 3, CHF 3, CHCl 3, N(CH 3) 3, the prolate symmetric top molecules: CH 3F, CH 3Br, CH 3CN and the slightly asymmetric top molecules: CH 3NH 2, C 2H 5Cl, C 2H 5CN, CH 3NO 2. The data for η 3 are in direct agreement with the improved theory, taking one term into account. The behaviour of λ″ can also be explained on the basis of the improved theory, but generally two terms have to be taken into account, including one term due to non-invertible collisions. The cross sections derived from the η 3 data agree with the cross sections obtained from nonresonant absorption.