Kinetic studies of reactions of hydrogen atoms with HCl, Cl2 and NOCl, and chlorine atoms with H2 and NOCl

Abstract

Rate constants for the reaction pair [graphic omitted] have been measured from 295 to 425 K under pseudo-first-order conditions ([HCl]₀/[H]₀ and [H₂]₀/[Cl]₀≫ 1) using the discharge-flow-resonance-fluorescence technique. The rate constants followed the Arrhenius expressions: k_f=(2.01 ± 0.3)× 10^–11 exp [–(1790 ± 140)/T], k_r=(6.00 ± 0.5)× 10^–11 exp [–(2470 ± 100)/T].

The ratio of these rate constants agrees with the thermodynamic equilibrium constant, suggesting that the complicating wall effects and secondary H-atom reactions observed in previous discharge-flow studies of these reactions have been eliminated.

Similar kinetic studies at room temperature of the reactions: [graphic omitted] gave the rate constants: k₂=(1.70 ± 0.26)× 10^–11 cm³ molecule^–1 s^–1, k₃=(1.82 ± 0.27)× 10^–11 cm³ molecule^–1 s^–1, k₄=(7.2 ± 2.4)× 10^–11 cm³ molecule^–1 s^–1. The values for k₂ and k₃ are in excellent agreement with those reported by previous discharge-flow–resonance-fluorescence studies. The value for k₄ is approximately a factor of two larger than the only other direct determination.