Reaction rates and energy distributions among reaction products for the H+Cl2 and Cl+H2 reactions

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Abstract
Rate coefficients have been calculated for the bimolecular exchange reactions of H with Cl2 and Cl with H2. Three‐dimensional classical trajectories of the collision dynamics of these reactions have been calculated using London–Eyring–Polanyi–Sato (LEPS) potential energy surfaces. The results of this trajectory study are as follows. For the H+Cl2 reaction at room temperature, the relative rate coefficients for formation of HCl into specific vibrational states are: k (v′=1) =0.01, k (v′=2) =0.65, [k (v′=3) =1.0], k (v′=4) =0.10, and k (v′=5) ?0. The symbol v′ indicates the product HCl vibrational state. The relative rate coefficient k (v′=2)/k (v′=3) has a slight temperature dependence, and the other relative rate coefficients k (v′≠2)/k (v′=3) are temperature dependent. The mean fraction (?v′=Ev′/ Etotal and ?J′=EJ′/Etotal) of the total energy entering vibration plus rotation is ?v′+?J′= (0.46+0.05) =0.51. For the Cl+H2 (v=0) reaction, ?v′+?J′= (0.37+0.16) =0.53; and for Cl+H2(v=1), ?v′+?J′ = (0.57+0.11) =0.68. Both Cl+H2 reactions exhibit efficient conversion of reaction energy into internal excitation of the product HCl molecule. A smaller fraction of reaction energy becomes relative translational energy in the Cl+H2(v=1) reaction than in the Cl+H2(v=0) reaction. The reaction Cl+H2 is greatly enhanced by increased vibrational energy in the reagent molecule H2. The Cl+H2(v=1) reaction generates an inverted population of HCl(v′=1) molecules that can, under proper conditions, produce lasing from the v′=1 to v=0 transition. Temperature‐dependent rate coefficients are provided for many reactions that have not been measured experimentally.