Theory of Electron Diffusion Parallel to Electric Fields. II. Application to Real Gases

The theoretical analysis of the preceding paper is extended to include inelastic collisions. The resulting theory is then used to obtain values for the diffusion coefficient ${D}_{L}$, which is appropriate for electrons diffusing parallel to an electric field. Theoretical values of $\frac{{D}_{L}}{\ensuremath{\mu}}$ are compared with values of $\frac{{D}_{T}}{\ensuremath{\mu}}$ as a function of $\frac{E}{N}$ for the gases helium, argon, hydrogen, deuterium, nitrogen, oxygen, carbon dioxide, water vapor, carbon monoxide, krypton, and xenon; $\ensuremath{\mu}$ is the electron mobility, ${D}_{T}$ is the diffusion coefficient for electron diffusion perpendicular to the electric field, $E$ is the electric field strength, and $N$ the number density of the gas. A comparison is also made between theoretical values of $\frac{{D}_{L}}{\ensuremath{\mu}}$ and the available experimental values of this quantity. Experimental differences that have been observed between ${D}_{L}$ and ${D}_{T}$ of the order of a factor of seven in argon and a factor of two in helium, hydrogen, and nitrogen are satisfactorily explained.