Hydrogen atom abstraction from HOOOCl by chlorine atom and OH radical

Gas-phase reactions of HOOOCl with both Cl atom and OH radical are investigated using ab initio methods. The structures of all reactants, products, intermediates, and transition states have been optimized and characterized with the quadratic configuration interaction (QCISD) method. The overall mechanism for the Cl + HOOOCl and OH + HOOOCl reaction is the formation of HCl + O2 + ClO and H2O + O2 + ClO, respectively. The rate-limiting step in each reaction is the abstraction of hydrogen from HOOOCl by either Cl or OH radicals and the barrier height is predicted to be 1.9 kcal mol−1 and 8.1 kcal mol−1 for abstraction by Cl atom and OH radical, respectively. Since both barriers for hydrogen abstraction are high, the reaction is suggested to be slow. These results also suggest that an atmospheric removal mechanism for HOOOCl may result from reaction with Cl atoms rather than with OH radicals, and that photolysis of HOOOCl may be the major removal mechanism for the intermediate.

A description of H-abstraction from the HOOOCl, intermediate of the ClO + HO2 reaction, gives reaction enthalpies of −29.0 and −47.6 kcal mol−1, and barriers of 1.9 and 8.1 kcal mol−1 when the reaction partner is Cl or OH. The viability of a channel for Cl to ClO conversion is suggested.Figure optionsDownload as PowerPoint slide