Rate coefficients for the attachment reactions of electrons with c-C7F14, CH3Br, CF3Br, CH2Br2and CH3I determined between 200 and 600K using the FALP technique

Abstract

The rate coefficients, beta , for the attachment reactions of electrons with c-C₇F₁₄, CH₃Br, CF₃Br, CH₂Br₂ and CH₃I have been determined under truly thermal conditions at temperatures in the range 200-600K using the flowing afterglow/Langmuir probe technique. The beta values (in units of CM³ s^-1) at 300K are 6.8*10^-8, 6*10^-12, 1.6*10^-8, 9.3*10^-8 and 1.2*10^-7 respectively. The beta for all of the reactions increase with temperature and approach the theoretical maximum value of beta at high temperatures. From Arrhenius plots, activation energies for the reactions have been determined to be 40, 300, 80, 50 and 25 meV respectively. All of the reactions, except for that with c-C₇F₁₄ (for which electron attachment is apparently non-dissociative), proceed by exoergic dissociative attachment producing halogen atomic negative ions. The data are compared with previous data where these are available.