Mechanism of the gas-phase decomposition of trifluoro-, trichloro-, and tribromomethanols in the presence of hydrogen halides.

Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of the decomposition of trifluoro-, trichloro-, and tribromomethanols. The high-pressure limiting rate coefficients k(diss,∞) for the thermal dissociation of CF(3)OH, CCl(3)OH, and CBr(3)OH were calculated using the conventional transition state theory. The results of potential surface calculations show that in the presence of the hydrogen halides HX (X = F, Cl, and Br), considerably lower energy pathways are accessible for the decomposition of CF(3)OH, CCl(3)OH, and CBr(3)OH. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes with the formation of pre- and post-reaction adducts. The presence of hydrogen halides considerably decreases the energy barrier for the bimolecular decomposition of the alcohols CF(3)OH, CCl(3)OH, and CBr(3)OH. Results of this study indicate that hydrogen halides can considerably accelerate the homogeneous decomposition of perhalogenated methanols when they are present in the reaction area at sufficiently high concentrations. However, the atmospheric concentrations of hydrogen halides are too small for efficient removal of atmospheric CF(3)OH, CCl(3)OH, and CBr(3)OH.