Kinetic study of the reaction of hydrogen atoms with molecular chlorine

Abstract

The reaction of hydrogen atoms with chlorine has been studied in a discharge-flow system using electron spin resonance detection of H-atoms. Chlorine consumption and hydrogen chloride production, measured by on-line mass spectrometry, were much lower than expected. This is explained by the enhanced rate of the reaction H + HCl → H₂+ Cl due to vibrational excitation of the HCl produced in the initial step. Based on a mechanism including this enhanced reaction rate an Arrhenius relation, (4.6 ± 1.3)× 10¹⁰ exp[–(5 940 ± 840) J mol^–1/RT] dm³ mol^–1 s^–1, is obtained for the rate constant of the initial step H + Cl₂→ HCl + Cl over the temperature range 292–434 K.