Theoretical study of the kinetics and mechanism of the decomposition of trifluoromethanol, trichloromethanol, and tribromomethanol in the gas phase

Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of unimolecular and water-accelerated decomposition of the halogenated alcohols CX3OH (X = F, Cl, and Br) into CX2O and HX. The calculations show that reactions of the unimolecular decomposition of CX3OH are of no importance under atmospheric conditions. A considerably lower energy pathway for the decomposition of CX3OH is accessible by homogenous reactions between CX3OH and water. It is shown that CX3OH + H2O reactions proceed via the formation of intermediate complexes. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes. The calculated values of the second-order rate constants are of 2.5x10(-21), 2.1x10(-19) and 1.2x10(-17) cm(3)molecule(-1)s(-1) at 300 K for CF3OH + H2O, CCl3OH + H2O, and CBr3OH + H2O, respectively. The theoretically derived atmospheric life-times of the CX3OH molecules indicate that the water-mediated decomposition reactions CX3OH + H2O may be the most efficient process of CF3OH, CCl3OH, and CBr3OH loss in the atmosphere.