Fragment ion-photon coincidence (FIPCO) measurements by electron impact on ethylene and the Monte Carlo simulation of the band shape

Fragment ion-photon coincidence (FIPCO) spectra by controlled electron impact on ethylene have been observed. Several typical band shapes to be observed in the FIPCO spectra have been simulated by Monte Carlo calculations and interpreted on the basis of the lifetimes of light emission and dissociation and of the sequence of emission and dissociation. The correlations between the CH(A-X) emission and the H⁺, CH⁺ and CH₂⁺ ions are observed and verified by the Monte Carlo simulation of the observed band shapes. The average translational energy is estimated to be 0.09 eV for H⁺, 0.35 eV for CH⁺ and 0.04 eV for CH₂⁺. The branching ratios of their ions are also estimated to be 6.6:89.7:3.7 for H⁺:CH⁺:CH₂⁺. On the basis of dissociation limits, the threshold energies in the CH(A-X) excitation function and the translational energies of their ions, it is concluded that the H⁺ and CH₂⁺ ions are produced through sequential dissociations into CH(A)+CH₂(X)+H⁺ and into CH(A)+CH₂⁺(X)+H (n = 1) and that the CH⁺ ion is produced through direct dissociation into CH(A)+CH⁺(X)+H₂(X).