Experimental Determinations of Charge Transfer Cross Sections and Secondary Electron Emission by Ion Bombardment

Abstract

The method utilized by the authors for determining charge transfer cross sections has been improved and applied to symmetric and unsymmetric reactions involving the inert gases, N₂, H₂, CH₄, C₂H₄, C₂H₆, and C₃H₈. The cross sections were found to be about 20% higher than the values previously reported. The discrepancy can be explained by the fact that in previous experiments cross sections were determined from net charge measurements without taking full account of the secondary electrons impinging on the plate where the charge transfer ions were collected. As expected from adiabatic hypothesis, the reactions involving mixtures of gases having nearly equal ionization potentials were found to have maximum cross sections for low‐energy ions. The interaction distances were calculated from the observed ion energy for which the cross sections are a maximum. The method described here can be utilized to determine the secondary electron emission from a metal surface due to ion bombardment. Such determination has been made for a brass surface. Relating the variation of emission with the ion mass and energy, it is found that the emission varies inversely as the square root of the ion mass.