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).

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Fragment ion-photon coincidence (FIPCO) spectra by 120 eV electron impact on carbon tetrafluoride (CF 4 ) have been observed, in which optical emission in the 200-600 nm region has been detected. Only the CF + 3 fragment has been found in the FIPCO spectra, demonstrating that the dissociative doubleionization process producing a pair of CF + 3 and F + is negligible in the correlation with the optical emission. This finding was already known from photon-impact experiments, but such a process was expected to play an important role in the ultraviolet-visible emission by electron impact on CF 4 . The translational energy distribution of CF + 3 has also been estimated on the basis of the highresolution FIPCO spectra and their Monte Carlo simulation. The magnitude of the mean translational energy of CF + 3 has been explained together with earlier results obtained through threshold photoelectron-photoion coincidence experiments by considering the Franck-Condon region in the transition among the neutral ground state of CF 4 and its ionic A, C and D states.

Fragment ion-photon coincidence (FIPCO) spectra by 120 eV electron impact on acetylene, C 2 H 2 , have been observed. Correlated detection of CH(A-X) emission and H + and C + ions, as well as between the CH + ion and its own emission, was observed and verified with the help of Monte Carlo simulation of the band shapes observed. The translational energy distribution of the H + ion is determined to be 1000 ± 150 K (0.13 ± 0.02 eV). Those for CH + and C + are 0.25 and 0.15 eV, respectively; the former translational energy accompanies a Gaussian distribution with a full-width at half-maximum (FWHM) of 0.2 eV, whereas the latter FWHM is 0.15 eV. A strong C 2 H + n (n = 0, 1) band is also observed in the FIPCO spectra and ascribed to dissociative processes following light emission from C 2 H + and C 2 H + 2 . Similar experiments have been carried out at 350 eV electron impact energy, to examine the dissociative processes accompanying the light emission caused by the ionization of a C 1s electron. No significant difference is observed between the FIPCO spectra at 120 and 350 eV impact energy.

Fragment ion-photon coincidence (FIPCO) spectra by 120 eV electron impact on trifluoromethane (CHF3) have been observed, in which optical emission in the 200-600 nm region has been detected. The CF3+, CHF2+, CF2+ and CF+ ions were observed in the FIPCO spectra. The kinetic energy distributions of these ions were estimated on the basis of the Monte Carlo simulation of their observed band shapes. Considering the total kinetic energy release in the dissociation processes producing CF3+ and CHF2+, we have concluded that the production of CF3+ and CHF2+ follows the D-B and D-C emissions of the parent ion, respectively. The CF2+ and CF+ ions were correlated with the Balmer emission from the excited hydrogen atom. These dissociation processes producing CF2+ and CF+ take place after the excitation to singly charged superexcited states of CHF3.