Formation and dissociation of doubly ionized methane

Abstract

Translational energy spectra of H− ions arising from double charge transfer to 1.5–7.0 keV protons from methane have been recorded and interpreted as the single and double ionization spectra of CH4. The excited states of CH++4 are not resolved, but a large broad peak of 4 eV half-width is observed, starting at around 35 eV, with a long tail extending to 44 eV. The peak maximum is at 38.6 eV. Four dissociation reactions of CH2+4 have been observed using photoion–photoion coincidence techniques with Heii light. All the principal discrepancies in comparisons between the experimental and theoretical work on CH2+4 can now be reconciled.

Cross Sections for Electron Collisions with Methane

“…Formation of unstable dications, CH 2+ 4 , in photoionization of CH 4 has already been observed by Fournier et al 97 According to their measurements, the dication formed from 44 eV photon impact decays preferentially into (CH us to evaluate quantitatively the contribution from multiple ionization into the experimental cross sections. Knowing that half of the H + ions observed experimentally at 100 eV come from double ionization, we can roughly estimate the counting ionization cross section in methane by subtracting half of the recommended H + cross section from the recommended total (=gross) cross section,…”

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

“…However, the kinetic energy of 3.7 eV for protons emitted after double-ionization states turns out to be much smaller than the result in Ref. [15]. Gluch et al measured the KED of protons from the dissociation of methane in electron impact reactions [9]; they found the first two groups in the proton KED as Latimer et al observed.…”

Probing dissociative molecular dications by mapping vibrational wave functions

“…As DCT is a charge-transfer reaction due to collision with a medium-energy ion beam, it is believed to result in a truly vertical transition to the dication [16][17][18]. On the other hand, an influence of the nuclear dynamics in the core-ionized state on Auger spectra is well known.…”

“…The dicationic states of this molecule, in particular the ground state, have attracted considerable interest. Methods for their investigation include Auger decay [13,14], charge stripping spectroscopy (see the critical review in [15]), double charge transfer [16][17][18], photoelectron-ion-ion coincidence spectroscopy [19], photoelectron-photoelectron coincidence spectroscopy [20], coincidence spectroscopy of Auger electrons and ions [21][22][23], and quantum chemical calculations [15,[23][24][25][26]. The four lowest dicationic states actually possess a potential-energy surface with a local minimum [23], i.e., CH 2+ 4 can be metastable.…”