Mutual neutralization of atomic rare-gas cations (Ne+, Ar+, Kr+, Xe+) with atomic halide anions (Cl-, Br-, I-).

We report thermal rate coefficients for 12 reactions of rare gas cations (Ne⁺, Ar⁺, Kr⁺, Xe⁺) with halide anions (Cl^-, Br^-, I^-), comprising both mutual neutralization (MN) and transfer ionization. No rate coefficients have been previously reported for these reactions; however, the development of the Variable Electron and Neutral Density Attachment Mass Spectrometry technique makes it possible to measure the difference of the rate coefficients for pairs of parallel reactions in a Flowing Afterglow-Langmuir Probe apparatus. Measurements of 18 such combinations of competing reaction pairs yield an over-determined data set from which a consistent set of rate coefficients of the 12 MN reactions can be deduced. Unlike rate coefficients of MN reactions involving at least one polyatomic ion, which vary by at most a factor of ∼3, those of the atom-atom reactions vary by at least a factor 60 depending on the species. It is found that the rate coefficients involving light raregas ions are larger than those for the heavier rare-gas ions, but the opposite trend is observed in the progression from Cl^- to I^-. The largest rate coefficient is 6.5 × 10^-8 cm³ s^-1 for Ne⁺ with I^-. Rate coefficients for Ar⁺, Kr⁺, and Xe⁺ reacting with Br₂^- are also reported. [ABSTRACT FROM AUTHOR]