Hot Atom Reactions in the HBr–Br2, DBr–Br2 Systems

Abstract

Reactions of photochemically generated hot hydrogen atoms have been studied in HBr–Br₂ systems at 185 and 229 nm and in DBr–Br₂ systems at 185 nm. Kinetic analysis furnishes k₃/k₂—the rate coefficient ratio for the reactions $$\mathrm{H}*{\mathrm{+Br}}_2\leftarrow {\displaystyle {lim}^3}\mathrm{HBr+Br}$$ and $$\mathrm{H}*\mathrm{+HBr}\leftarrow {\displaystyle {lim}^2}{\mathrm{H}}_2\mathrm{+Br}.$$ At 185 nm for HBr, $k_3{\mathrm{/k}}_2\text{=4.11± 0.16}$ , while at 229 nm $k_3{\mathrm{/k}}_2\text{=5.48± 0.22}$ . For DBr at 185 nm the ratio is $\text{5.07± 0.12}$ . Complementary trajectory calculations have been performed on a semiempirical potential‐energy surface. The results of these calculations suggest that the observed variations in k₃/k₂ arise primarily because the reaction cross section for Process (3) varies strongly with energy in the hot atom regime and is different for the HBr and DBr systems.