Electron-Atom Collision Effects in Mercury Vapor

Abstract

In a recent paper', the author described an experiment in which he measured the energy losses sustained by slow-speed electrons passing through mercury vapor. It is the purpose of the present paper t'; review the -.ar ious phenomena associated with such losses, and to attempt to correlate those which seem to have a common explanation. In most experiments of this nature, a hot cathode or other source of electrons is surrounded by a grid, by means of which the electrons; may be given any desired amount of energy (measured in volts of accelerating potential). During or immediately following this acceleration, the electrons are made to pass through mercury vapor maintained at a pressure varying from 0.001 mm to several mms with different methods. The rest of the experimental setup varies widely with the purpose in view, and may be of either an electrical or an optical nature, or both. The phenomema observed fall into three classes: those relating to the atom, to the radiations given out by the atom, and to the impinging electron. The atom may exhibit electronegative properties when a valence electron is displaced from its normal position to one more remote from the nucleus, as a result of an impact with an electron; but if one or more valence electrons are entirely ejected from the atom, the latter becomes a positive ion. The potentials at which the rate of production of negative ions receives a sudden increase or decrease were determined by Nielsen', and are given in Table I.