The Diffusion of Electrons in a Gas at Low Temperatures

Abstract

In the absence of an electric field, the state of motion of electrons moving freely among molecules of a gas is one in which the mean energy of agitation Q of an electron is the same as that, Q₀, of a molecule of the gas. It is known, however, that in the presence of an applied uniform electric field Z the steady state of motion is one in which Q exceed's Q₀, and, for a constant gas temperature, Q is a function of Z/n where n is the number of gas molecules in unit volume. Usually the measurements are made at room temperature, generally taken as 288°K, and it is convenient to replace Z/n by Z/p where p is the pressure of the gas in millimetres of mercury. It is of interest, however (Crompton, Huxley, and Sutton 1953), to investigate how the dependence of Q upon Z/n is influenced by the temperature of the gas itself, that is to say, by Q₀. If the dependence of Q upon both Z/n and Q₀ be expressed by some formula Q = f(Z/n, Q₀), then all that is known with certainty about the function f is that when Z/n = 0, Q = Q₀. In view of the absence of any theoretical guidance concerning the dependence of Q upon both Z/n = 0 and Q₀, it was decided to investigate the matter experimentally in two simple diatomic gases, nitrogen and hydrogen.