Differential cross sections for the dissociative single and double excitations resulting in H(2p) formation in electron–CH4 collisions at 80 eV incident electron energy

Abstract

The differential cross sections for the dissociative single and double excitations resulting in H(2p) formation with the excitation energy of 19–46 eV in electron–CH4 collisions have been measured as a function of electron scattering angle in the range 4°–48° at 80 eV incident electron energy by means of angle-resolved electron energy-loss spectroscopy in coincidence with detecting Lyman-α photons. This is the first measurement of the differential cross sections for the dissociative double excitations as a function of electron scattering angle in electron–molecule collisions. Their fractions have been compared with those at the optical limit calculated from the density of the dipole oscillator strength for the emission of Lyman-α photons previously measured by our group. The dissociative double excitations in 80 eV electron collisions seem to be brought about in a very different way from those at the optical limit where they arise from the electron correlation in a methane molecule. The differential cross sections have also been discussed in terms of momentum transfer, leading to a universal curve.