Dissociative charge-transfer reactions of Ar+ with fluoromethanes at thermal energy

Abstract

A flowing-afterglow apparatus coupled with a low pressure chamber has been used to measure product ion distributions and rate constants in the charge-transfer reactions of Ar+ with CHnF4−n (n=1–3) at thermal energy. Near-resonant dissociative charge transfer followed by loss of H and/or F are major product channels observed. In the Ar+/CH3F reaction, CHF+ and CH2+ ions, which are either absent or very weak in He(i) photoionization, are also found as minor products. The product ion distributions suggest that the Ar+/CHnF4−n (n=1–3) reactions proceed dominantly through near-resonant charge transfer. The total rate constants are 1.7±0.6, 1.9±0.7, and 2.0±0.6×10−9 cm3 s−1 for CH3F, CH2F2, and CHF3, respectively. These values are in reasonable agreement with those predicted from the average dipole orientation (ADO) theory, being independent of the existence of ionic states with favorable Franck–Condon factors for ionization.