A Note on the Longitudinal Diffusion of Electrons in Argon

It has been shown both experimentally and theoretically that the diffusion of electrons subject to the influence of an applied electric field is often significantly different in directions parallel and normal to the electric field (Wagner, Davis, and Hurst 1967; Parker and Lowke 1969; Lowke and Parker 1969; Skullerud 1969). Lowke and Parker (1969) showed that the ratio of the diffusion coefficients (DL parallel to the electric field and DT normal to the field) is particularly sensitive to rapid variations with energy of the momentum transfer cross section of the electrons. It is to be expected therefore that for electrons in argon the Ramsauer?Townsend minimum in the momentum transfer cross section at energies of ~ 0·3 eV will have a marked influence on the value of DL.