Mechanism of formation of triatomic molecules in atomic combination reactions. Part 1.—Formation of ClNO and ClCO in reactions of atomic chlorine

Abstract

The kinetics of reaction of ²P ground-state chlorine atoms with nitric oxide and with carbon monoxide have been investigated at various temperatures and at total pressures near 1 mm Hg. The reaction of Cl with NO involved a simple third-order combination reaction as the primary step forming nitrosyl chloride, [graphic omitted] The overall reaction can be considered as a nitric oxide-catalyzed removal of chlorine atoms, analogous to the reactions of O and H with nitric oxide. For the third bodies MHe, Ar, O₂, N₂, Cl₂ and SF₆, the values for k_1n at 293°K were, respectively, (3.5±0.5), (2.9±0.5), (3.9±0.5), (3.5±0.5), (3.4±0.5), and (3.5±0.5) 10¹⁶ cm⁶ mole^–2 sec^–1. Over the temperature range 270–620°K, negative Arrhenius activation energies (kcal mole^–1) were found for k_1n as follows, E_a=(–1.1±0.1)[Ar], (–0.7±0.2)[Cl₂], and (–1.2±0.2)[SF₆].

The reaction between chlorine atoms and carbon monoxide was much slower than the nitric oxide reaction. At 195°K, the kinetics were explained on the basis of two reactions, [graphic omitted] At higher temperatures the rate of removal of Cl by CO was greatly diminished, and the kinetics became more complex. Under these conditions, contribution by the thermal dissociation of ClCO is appreciable. The results are consistent with a value of about 7 kcal mole^–1 for the heat of dissociation of the ClCO radical. The rate constant k_1c(for MAr) at 300°K was 10^(14.5±0.3) cm⁶ mole^–2 sec^–1, and reaction (1c) had an Arrhenius activation energy of about –2 kcal mole^–1.