A new process of negative-ion formation. IV

Abstract

The three previous papers of this series (Arnot and Milligan 1936 b ; Arnot 1937 a, b ) contain an account of experimental work which led the senior author to propose a new process of negative-ion formation. This process is the formation of negative ions at metal surfaces by bombardment of the surface with positive ions, the negative ion being formed by the positive ion capturing two electron from the surface. Further work carried out during the past year, which is described in this paper, has revealed a new variation of the above process. In this latter process the impinging positive ion causes an adsorbed atom on the surface to come off as a negative ion. It is believed that this newer process is essentially similar to the process previously reported, the difference being due merely to the transference of excitation energy from the incident positive ion, after its capture of an electron, to the atom adsorbed on the surface. The discovery of this second effect was made independently by Sloane and Press (1938), although they attribute it to a different process.