Theoretical study on the kinetics and mechanism of reactions of halogen atoms with trifluoromethanol

Abstract

Quantum mechanical ab initio calculations have been performed at various levels of theory to study kinetics of the reactions of fluorine, chlorine and bromine atoms with trifluoromethanol. Total energies were improved by using Gaussian-2 (G2) methodology. It is shown that the considered reactions proceed with formation of intermediate complexes. The mechanism of the reactions studied appears to be more complex and may consist of three elementary steps. The heights of the calculated energy barriers explain the differences of the reactivity of F, Cl and Br atoms towards CF3OH. The rate constants and their temperature dependence for the reactions CF3OH + X (k X) and CF3O + HX (kHX) were calculated. The derived analytical expressions kF = 1.7 × 10-11 × (T/300)0.73 × exp(-2,550/T) cm3molecule -1s-1 kCl = 6.5 × 10-12 × (T/300)1.23 × exp(-10,550/T) cm 3molecule-1s-1 kBr = 5.2 × 10-12 × (T/300)1.64 × exp(-15,150/T) cm 3molecule-1s-1 and kHF = 7.2 × 10-13 × (T/300)0.86 × exp(-11, 150/T) cm3molecule-1s-1 kHCl = 1.6 × 10-13 × (T/300)11.36 × exp(-2,200/T) cm 3molecule-1s-1 kHBr = 1.0 × 10-13 × (T/300)1.72 × exp(-200/T) cm 3molecule-1s-1 allow the description of the kinetics of the reactions under investigation. This is of considerable importance for the chemical modelling studies because of the lack of experimental measurements.