Dissociative electron attachment to methylhalides in 3-methylhexane glassy matrix

Dissociative electron attachment reaction to CH₃I, CH₃Cl and CH₃F in a 3-methylhexane glassy matrix was studied by determining the yield of trapped electrons and that of methyl radicals immediately after γ-irradiation at 77 K as a function of the scavenger concentration. The efficiency of conversion from the trapped electrons to the methyl radicals was also studied by photobleaching the trapped electrons. The results obtained are (1) the dissociative electron attachment occurs to CH₃F, for which the gas phase data indicate that the reaction is endothermic by 1·2 eV, during either the γ-irradiation or the photobleaching, and (2) CH₃F is relatively less efficient in scavenging photo-liberated electrons than in scavenging the electrons during the γ-irradiation, whereas CH₃I and CH₃Cl are efficient scavengers for both the electrons. The dependence of the yields of the trapped electrons and the methyl radicals is discussed in terms of the electron-tunneling mechanism and the epithermal electron-scavenging mechanism.