Measured cross section for the formation of H+2 by fast proton impact on methane

Abstract

The classical theory of ion–molecule rearrangement collisions proposed by Bates, Cook, and Smith for the capture cross section for the formation of H+2 in the reaction H++CH4→CH3+H+2 was confirmed. Measurements at incident proton energies of 70, 85, 100, and 150 eV gave cross sections peaking sharply at scattering angles (laboratory coordinates) of about 46° as predicted. Typical values of the total cross section are 2.0×10−21 cm2 at 70 eV and 7.6×10−22 cm2 at 100 eV, a factor of 30 less than the theoretical values, which are believed to represent upper limits to the cross section. The asymmetrical shape of the differential cross section is consistent with that predicted by a classical construction method described by Gillen, Mahan, and Winn.