Energy-Dependence Measurement of the CH4++CH4=CH3+CH5+ Reaction Cross Section

From measurements of primary and secondary ions produced by electron bombardment of methane gas in a special mass-spectrometer ion source, analysis yields values of the cross sections for the ion—molecule reaction CH4++CH4=CH3+CH5+. The source is designed to be free of magnetic discrimination, between primary and secondary ion intensities, which has been shown to be prevalent in conventional machines. The cross section is found to be essentially independent of collision energy over the range 3–18 eV, the value being (5.0±0.2)×10−16 cm2. The present result is not in accord with the slow-ion theory of Gioumousis and Stevenson, but suggests the influence of the repulsive as well as attractive part of the potential in the reaction mechanism.