Ab initio studies of ClO[sub x] reactions. VII. Isomers of Cl[sub 2]O[sub 3] and their roles in the ClO+OClO reaction.

The mechanism for the reaction ClO+OClO has been investigated by ab initio molecular orbital and transition state theory calculations. Nine stable isomers of Cl[sub 2]O[sub 3] (including optical isomers) are located at the B3LYP/6-311+G(3df ) level. The transition states between pairs of isomers are explored and the stability of the isomers and their dissociation mechanisms are discussed. The relative stability predicted by the modified Gaussian-2 (G2M) method at the G2M//B3LYP/6-311+G(3df ) level is ClOCl(O)O>ClOOOCl(C[sub 2])>ClOOOCl(C[sub s])>ClClO[sub 3](C[sub 3v])>cyc-ClOOCl(O)>ClOOClO. The formation of ClOCl(O)O is dominant at low temperatures, taking place barrierlessly with the second and third order rate constant, k[sub 1][sup ∞]=3.0×10[sup -10] cm[sup 3] molecule[sup -1] s[sup -1] and k[sub 1][sup 0]=1.1×10[sup -17] T[sup -5.5] exp(-398/T) cm[sup 6] molecule[sup -2] s[sup -1] in the temperature range of 200–400 K for N[sub 2] as the third-body. Over 500 K, formation of ClOO+ClO becomes dominant and ClOCl+[sup 1]O[sub 2] is also competitive. Their overall rate constants can be given by k[sub ClOO]=1.0×10[sup -22] T[sup 2.8] exp(-78/T) and k[sub ClOCl]=9.6×10[sup -22] T[sup 2.4] exp(-1670/T)cm[sup 3] molecule[sup -1] s[sup -1], respectively, in the temperature range of 500–2500 K. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]