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

Fragment ion-photon coincidence (FIPCO) spectra by controlled electron impa ct on ethylene have been observed. Several typical band shapes to be observ ed in the FIPCO spectra have been simulated by Monte Carlo calculations and interpreted on the basis of the lifetimes of light emission and dissociati on and of the sequence of emission and dissociation. The correlations betwe en the CH(A-X) emission and the H+, CH+ and CH2+ ions are observed and veri fied 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+ an d 0.04 eV for CH2+. The branching ratios of their ions are also estimated t o 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 translationa l energies of their ions, it is concluded that the H+ and CH2+ ions are pro duced through sequential dissociations into CH(A) + CH2 (X) + H+ and into C H(A) + CH2+; (X) + H (n = 1) and that the CH+ ion is produced through direc t dissociation into CH(A) + CH+(X) + H-2 (X).