Gas phase recombination of hydrogen and deuterium atoms

Rate constants for the reaction $\mathrm{H+H+M}\to {\mathrm{H}}_2+\mathrm{M}$ , 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 ${\text{8.1 ± 0.4 × 10}}^{\text{−33}}{\text{,\hspace{0.17em}7.0 ± 0.4 × 10}}^{\text{−33}}$ , and ${\text{9.2 ± 0.6 × 10}}^{\text{−33}}\hspace{0.17em}{\mathrm{cm}}^6\hspace{0.17em}{\mathrm{molecules}}^{\text{−2}}·{\sec }^{\text{−1}}$ at 298°K for M = H₂, He, and Ar, respectively; these values rising to ${\text{18.5 ± 2.2 × 10}}^{\text{−33}}{\text{,\hspace{0.17em}12.0 ± 1.5 × 10}}^{\text{−33}}$ , and ${\text{27.4 ± 4.6 × 10}}^{\text{−33}}\hspace{0.17em}{\mathrm{cm}}^6\hspace{0.17em}{\mathrm{molecules}}^{\text{−2}}·{\sec }^{\text{−1}}$ at 77°K. For the equivalent deuterium atom process with D₂ as the third body, the rate constants are ${\text{6.1 ± 0.3 × 10}}^{\text{−33}}\hspace{0.17em}{\mathrm{cm}}^6\hspace{0.17em}{\mathrm{molecules}}^{\text{−2}}·{\sec }^{\text{−1}}$ at 298°K and ${\text{15.1 ± 1.0 × 10}}^{\text{−33}}\hspace{0.17em}{\mathrm{cm}}^6\hspace{0.17em}{\mathrm{molecules}}^{\text{−2}}·{\sec }^{\text{−1}}$ at 77°K. These values are compared with previous experimental measurements and with recent theoretical calculations.