Mutual neutralization of H+ and D+ with the atomic halide anions Cl-, Br-, and I-

Mutual neutralization (MN) rate constants k(MN) for the reactions of H+ and D+ with the atomic halide anions Cl-, Br-, and I- were measured using the variable electron and neutral density attachment mass spectrometry technique in a flowing afterglow Langmuir probe apparatus. At 300 K, the rate constants for each reaction studied are on the order of 10(-8) cm(3) s(-1). A trend for the rate constants of the systems in this work, k(MN) (Cl-) < k(MN) (Br-) < k(MN)(I-), is consistent with prior studies of rare gas cation with atomic halide anion MN. A recent theoretical study involving ab initio quantum mechanical treatment of the H+ + Cl- and D+ + Cl- reactions reported rate constants significantly lower than the rates reported here. A previously proposed empirical model that predicts atom-atom k(MN) as a simple function of the total reaction exothermicity shows good agreement with the newly measured rate constants.