Mutual neutralization of He⁺ with the anions Cl⁻, Br⁻, I⁻, and SF₆⁻

Mutual neutralization (MN) rate coefficients k_MN for He⁺ with the anions Cl⁻, Br⁻, I⁻, and SF₆⁻ are reported from 300 to 500 K. The measured rate coefficients may contain a contribution from transfer ionization, i.e., double ionization of the anion. The large rate coefficient for He⁺ + SF₆⁻ (2.4 × 10⁻⁷ cm³ s⁻¹ at 300 K) is consistent with earlier polyatomic MN results found to have a reduced mass dependence of μ^−1/2. Neutralization of He⁺ by the atomic halides follows the trend observed earlier for Ne⁺, Ar⁺, Kr⁺, and Xe⁺ neutralized by atomic halides, k_MN (Cl⁻) < k_MN (Br⁻) < k_MN (I⁻). Only an upper limit could be measured for the neutralization of He⁺ by Cl⁻. Predictions of the rate coefficients from a previously proposed simple model of atomic–atomic MN results are consistent with the present He⁺–halide rate coefficients. The temperature dependences are modestly negative for Br⁻ and I⁻, while that for SF₆⁻ is small or negligible.