Communication: Transfer ionization in a thermal reaction of a cation and anion: Ar+ with Br− and I−

We present experimental evidence that reactions of argon cations Ar+ with the halogen anions Br− and I− do not occur exclusively by mutual neutralization, but also produce the cations Br+ or I+ ions by transfer ionization (TI). The experiments were carried out in flowing-afterglow plasmas at gas temperatures between and 300 and 500 K, and employed a variant of the Variable Electron and Neutral Density Attachment Mass Spectrometry method. The measured TI rate coefficients are 1.9 ± 0.6 × 10−9 cm3 s−1 and 1.1 ± 0.30.8× 10−9 cm3 s−1 for the Br− and I− reactions, respectively. We find that the TI rate coefficients decline with temperature as T−0.5 to T−1. No indication of TI was found in the reaction with Cl−, where it is endoergic