Product Identification and Kinetics of Reactions of HCl with HNO_3/H_2SO_4/H_2O Solutions

摘要

The gas-phase products of the reaction between HNO_3/H_2SO_4/H_2O acid solutions and HCl were identified using IR and UV-Vis spectroscopy and chemical ionization mass spectrometry. The major products of the reaction were Cl_2 and ClNO, with quantifiable amounts of ClNO_2 sometimes present. On the basis of quantitative product yield determinations, the overall proposed reaction is 3HCl + HNO_3 → Cl_2 + ClNO + 2H_2O. Kinetic studies were also performed and the reaction was found to follow a second-order rate law: Rate = k[HCl][HNO_3]. On the basis of the products and intermediates observed and the rate law, a mechanism is proposed which involves the NO_2~+ ion as the key reactive species. The rate of the reaction is shown to depend strongly on the total acid concentration of the solution and temperature-dependent studies were also performed. The potential significance of this reaction in connection to stratospheric ozone depletion is evaluated by using the composition and temperature dependence of the rate to estimate the chlorine activation rate at polar stratospheric conditions.