Thermal decomposition of HCl measured by ARAS and IR diode laser spectroscopy

Abstract

The thermal decomposition of HCl behind shock waves was studied by time-dependent concentration measurements of both the decomposition product H, as well as the initial reactant HCl. The experiments were performed in mixtures containing 1.4 to 3800 ppm HCl diluted in argon in the temperature range 2500K≤ T ≤ 4600K. In the first series of experiments H atoms were measured by applying the ARAS technique (Atomic Resonance Absorption Spectroscopy). In the second series of experiments an infrared diode laser was rapidly tuned to the (0–1) P7 vibrational-rotational line of HCl and the resulting absorption profiles were evaluated in terms of concentrations of the initial reactant. From both the concentration profiles of H and HCl, a rate coefficient of the reaction H C I + A r ⇌ H + C I + A r , k 1 = 9.0 * 10 13 exp ⁡ ( − 44000 K T ) c m 3 m o l s was determined. Based on a proposed reaction mechanism, rate coefficients of secondary reactions of H and HCl with the initial reactant were estimated.