Oscillations in the H₂ + Cl₂ reaction: Experimental measurements and numerical simulation

Thermokinetic oscillations during the reaction between hydrogen and chlorine are reported when reaction takes place under semibatch operation. Up to 10 oscillations were observed in a single experiment, and temperature excursions greater than 200 K were measured directly by a thermocouple. The reaction was performed in nonadiabatic conditions by the relatively slow admission of hydrogen to the chlorine already present in the reaction vessel. Total reactant pressures in the range 40-80 Torr were investigated at vessel temperatures between 600 and 650 K. The oscillations were found to exist in a closed region of parameter space determined by the rate of supply of the hydrogen and the vessel temperature. The theoretical background to the existence of the oscillations is derived, and numerical calculations based on established kinetics for the H₂ + Cl₂ reaction are presented to relate the experimental observations to these principles. Phase relationships between the molecular reactants, free-radical intermediates, and the reactant temperature are explored.