Differential cross sections for the dissociative single and double excitations resulting in H(2p) formation in electron–CH₄collisions 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.

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

“…In order to facilitate the following discussion of the results, we first summarize in Table I [20,21]. Since the excitation energies of the two states are higher than the ionization potential of the (1t 2 ) −1 state, the CH 4 molecules in these states are unstable and can decay through the autoionization process.…”

High-resolution (e, 2e + ion) study of electron-impact ionization and fragmentation of methane

“…It thus suggests that the second channel for formation of the CH + 3 may originate from a resonant process through the dissociative autoionization channel via a doubly excited state of the CH 4 molecule, e.g., the (1t 2 ) −2 (3a 1 ) (mo) state. 36 A similar resonant process has been discussed for the case of the H 2 molecule. 35,37 This resonant channel had not been reported in the previous photoionization studies.…”

The relative cross section and kinetic energy distribution of dissociation processes of methane by electron impact

“…Various types of experimental data on the interaction of hydrocarbon molecules with electrons are demanded for understanding the behaviour of such molecules in plasmas. Since Hughes et al made the first measurement [6] of the ionization cross section for CH 4 in 1924 there have been extensive investigations of heavy ion [7,8], electron [9][10][11][12][13][14][15] and photon impact [16,17] ionization for methane. More recently, with the time-of-flight (TOF) mass spectrometry and two-dimensional ion-ion coincidence techniques, the study of multiply ionized molecules provides a method to identify the contributions from different dissociation pathways [9,[18][19][20].…”