Ionization, excitation, and chemical reaction in uniform electric fields II-The energy balance and energy efficiencies for the principal electron processes in hydrogen

Abstract

In a previous communication, Part I, Emeléus, Lunt, and Meek* have discussed the rate of an electron collision process, ionization, in a uniform electrical field. In this paper we elaborate their analysis and extend it to five other types of electron collision processes. The discharge conditions now postulated are those of a swarm of electrons moving through a gas under the influence of a uniform electric field so that the system is in a steady state, the current density being sufficiently low so that the stationary concentration of all products of electron collisions (ions and excited particles) is negligible compared with that of the gas molecules in the ground state. Such conditions are realized with considerable exactitude in the uniform positive column. This is of particular importance because in such a discharge the rates of the various types of electron collisions contemplated in the present theory are sufficiently large to enable comparisons to be made between experiment and the predictions of the theory. There are many experiments, notably those of Townsend* and Langmuir, relating to the conditions now postulated which show the velocities of the electrons in the swarm are distributed at random about a mean, and that the mean velocity greatly exceeds that of the gas molecules (or atoms) in which the swarm moves; in a given gas the average electron energy, V electron-volts, has been shown by Townsend and his collaborators to be a function of X p -1, the ratio of the electric field to the gas pressure. In addition to this random motion, there is a relatively small drift motion of the swarm in the direction of the uniform field X ; the drift velocity, W cm. sec.-1, in a given gas is also a function of X p -1, and its magnitude determines the rate at which electrons gain energy from the field, and also the magnitude of the (drift) current carried by the ionized gas.