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A new extended theory of electron transport in dense gases is presented. It is shown that positive and negative density effects can be explained in terms of a single unifying theory. The agreement between theory and experiment is extremely good over a wide range of pressure and temperature in gases with a negative effect, such as He and H2. Some further improvements of the theory in gases with elevated polarizability seem to be necessary for a better quantitative agreement with experimental data, even if the agreement in Ar makes us confident that the proposed theoretical approach can be correct. In the light of our unifying theory, previous theoretical models are analyzed and it is shown that almost all can be obtained under special conditions.

Calculations have been made of the effect of absorbing electrodes on a continuous stream of electrons travelling in a gas in a uniform electric field. The effective electron drift and diffusion coefficients become a complex function of position, so that the electron density distribution is no longer given by the solution of the electron continuity equation using the usual equilibrium drift velocity and either the transverse or the longitudinal diffusion coefficients appropriate to the applied electric field and gas pressure. Calculations for a momentum transfer cross-section proportional to electron speed indicate an increase of the average electron energy of about a factor of two at the anode. Predictions using Monte Carlo methods and solutions of the Boltzmann transport equation are in good agreement. Monte Carlo calculations are also applied to predict the influence of absorbing boundaries on the Townsend-Huxley experiment (1974). Predicted current ratios compared with ratios obtained from a solution of the continuity equation lie between ratios obtained using both isotropic and conventional transverse and longitudinal diffusion coefficients.

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