Longitudinal diffusion coefficients of Li+ and Na+ ions in He, Ne, and Ar: Experimental test of the generalized Einstein relation

Abstract

We have measured, with a drift tube mass spectrometer, the longitudinal diffusion coefficients of Li+ and Na+ ions in He, Ne, and Ar at a gas temperature of 300 °K. The measurements were made as a function of the energy parameter E/N, where E is the electrostatic drift field strength and N is the gas number density in the drift tube. The range of the steady-state, average ionic energy thereby covered extended from close to the thermal value up to 10.1 eV in the case of Li+ in He and a few eV less in the other ion–atom combinations. The experimental data are compared with the results of computations based on three different equations: the original Wannier equation derived for the polarization attraction model, our modification of this equation, and the generalized Einstein relation discussed in the paper immediately preceding this paper [Larry A. Viehland and E. A. Mason, J. Chem. Phys. 63, 2913 (1975)]. The latter relation is superior to the other two in the present application and gives excellent agreement with our experimental data. This is the same conclusion that was reached by Viehland and Mason in their analysis of our data on K+ ions in He, Ne, and Ar.