Computational Studies on Metathetical and Redox Processes of HOCl in Gas Phase. III. Its Self-Reaction and Interactions with HNOx (x = 1−3)

Abstract

The gas-phase redox reactions of HOCl with its self and HNO(x) (x = 1-3) have been studied theoretically by ab initio quantum chemical and statistical mechanical theories. The structures of reactants, intermediate complexes, products, and transition states were optimized at the MPW1PW91/6-311+G(3df,2p) level of theory. The potential energy surface of each reaction was refined at the CCSD(T)/6-311+G(3df,2p) level of theory. The most favorable products are predicted to be ClClO + H(2)O and ClOCl + H(2)O for the HOCl self-reaction (A), H(2)O + Cl + NO for the HOCl + HNO reaction (B), H(2)O + ClNO(2) for the HOCl + HONO-t reaction (C), H(2)O + cis-ClONO for the HOCl + HONO-c reaction (D). For the HOCl + HONO(2) reaction (E), only one dehydration reaction channel was considered to produce H(2)O + ClONO(2). The rate constants of all above five reactions have been predicted at 300-3000 K by the VTST/RRKM theory. The calculation shows that the theoretical rate constants are within the upper limits of experimental results. In addition, we calculated the equilibrium constant for the Cl(2)O + H(2)O --> HOCl + HOCl reaction, which is also in reasonable agreement with experimental data within the error of the available experimental enthalpy change.