Differential cross sections for the dissociative single and double excitations resulting in H(2p) formation in electron-CH_4 collisions at 80 eV incident electron energy

摘要

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-CH_4 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.