Reactions of atomic hydrogen with hydrogen chloride and nitrosyl chloride

The kinetics of reaction of hydrogen chloride with atomic hydrogen have been investigated in a discharge-flow system at total pressures near 1 mm Hg, and from 195 to 373°K. The rate of removal of hydrogen atoms was first-order in [H] and [HCl], H+HCl→H2+Cl. (1) The rate constant k1 is satisfactorily represented by the expression k1=(3.5±1.5)× 1011T½ exp [(–2900±300)/RT] cm3 mole–1 sec–1, in this temperature range. Combination of these data with values found for k1 at higher temperatures shows that all the results can be fitted satisfactorily either (i) by a simple collision theory temperature-dependence, k1=(6.2±3.5)× 1011T½ exp [(–3100±400)/RT] cm3 mole–1 sec–1, with a steric factor of about 0.025, or (ii) by various models for the transition complex HHCl, where the temperature-dependence has a more complex form. The correlation of the data for k1 with the simple Arrhenius expression A exp (–E/RT) is not satisfactory. The best fit of the data is to two semi-empirical, linear models proposed by Bigeleisen et al.3 for the HHCl transition complex, in which there is strong H—H bonding, and to a triangular model, but the limits of experimental error do not rule out several other models. The reaction of hydrogen atoms with nitrosyl chloride was both stoichiometric, H+NOCl→NO+HCl (2) and very rapid, k2 > 1 × 1012 cm3 mole–1 sec–1 at 300°K. The reaction can be used as a gas phase titration for the measurement of hydrogen atom concentrations.