Gas phase recombination of hydrogen and deuterium atoms

Abstract

Rate constants for the reaction H+H+M → H2 + M, with M = H2, He, and Ar were measured over the temperature range 77–298°K. Hydrogen atoms were produced by thermal dissociation and absolute atom concentrations were measured through use of a self-balancing, isothermal catalytic probe detector. The specific rate constants were 8.1 ± 0.4 × 10−33, 7.0 ± 0.4 × 10−33, and 9.2 ± 0.6 × 10−33 cm6 molecules−2 · sec−1 at 298°K for M = H2, He, and Ar, respectively; these values rising to 18.5 ± 2.2 × 10−33, 12.0 ± 1.5 × 10−33, and 27.4 ± 4.6 × 10−33 cm6 molecules−2 · sec−1 at 77°K. For the equivalent deuterium atom process with D2 as the third body, the rate constants are 6.1 ± 0.3 × 10−33 cm6 molecules−2 · sec−1 at 298°K and 15.1 ± 1.0 × 10−33 cm6 molecules−2 · sec−1 at 77°K. These values are compared with previous experimental measurements and with recent theoretical calculations.