title: FRAGMENT ION-PHOTON COINCIDENCE (FIPCO) STUDY OF DISSOCIATIVE IONIZATION ACCOMPANYING LIGHT EMISSION BY ELECTRON IMPACT ON ETHYLENE AND ACETYLENE authours: Kenji Furuya, Kouichiro Maruyama, Eri Koto, Takeshi Ueda, Akihiro Matsuo, and Teiichiro Ogawa affiliations: Kyushu University, Kasuga, Fukuoka 816-8580, Japan summary: Fragment ion-photon coincidence (FIPCO) spectra of ethylene and acetylene have been observed by 120 eV electron impact. To explain the shapes of the coincidence bands, Monte Carlo simulation has been carried out. As a result, it is found that there are correlations between the CH(A-X) emission and the H+, CH+ and CH2+ ions in the ethylene case. In addition, the branching ratios and translational energy distributions of their ions are determined. In the acetylene case, the CH(A-X) emission is found to be correlated with the H+ and C+ ions.