The action of metastable atoms of helium on a metal surface

Abstract

In the course of a series of experiments on the action of positive ions of helium on a metal surface with which they collided, it was observed that neutral excited atoms of the gas were able to set free large numbers of electrons from the surface. Under appropriate conditions the recombination of helium ions and electrons is able to give very large numbers of these excited atoms, and a process has been developed by which it is possible to obtain an intense beam and study its behaviour under different conditions. The recognition of the existence of metastable states of excited atoms has led to the explanation of many anomalous effects in gaseous discharges, and of some photo synthesised reactions involving a mixture of gases. However, our knowledge of the state is very meagre, and it is still possible to fall into considerable error and uncertainty in measurements which, unknown to the experimenter, involve the formation of excited neutral atoms. Examples of this will be given in the discussion at the end of this paper. Although it has long been recognised that a collision between an excited atom and a metal might well lead to the ejection of an electron from the conductor by a sort of collision of the second kind, yet the magnitude of the effect under appropriate conditions has not been fully appreciated. The part which this type of collision plays in the cathode phenomena of the arc and glow discharges, and the effect which it may have on the characteristics of "probe" collectors, has yet to be determined.