Computational study on decomposition kinetics of CH 3 CFClO radical

Abstract

The present study deals with the decomposition of haloalkoxy radical (CH3CFClO) formed from 1,1-dichloro-1-fluoroethane (HCFC-141b) in the atmosphere. The study is performed using ab-initio quantum mechanical methods. Out of the three plausible pathways of decomposition of the titled species, the one that involved the C–C bond scission and the other occurring via Cl-atom elimination have been considered for detailed study. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at MP2 level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2(MP2) level of theory. The path involving the Cl-elimination is found to be dominant and found to occur with a barrier height of 3.6 kcal mol − 1 whereas the C–C bond scission path proceeds with a barrier of 10.0 kcal mol − 1. The thermal rate constants for the above two decomposition pathways are evaluated using Canonical Transition State Theory (CTST) and these are found to be 2.9 × 108 s − 1 and 4.3 × 105 s − 1 for Cl-elimination and C–C bond scission respectively at 298 K and 1 atm. pressure. The existence of transition states on the corresponding potential energy surface is ascertained by the occurrence of only one imaginary frequency obtained during the frequency calculation. The Intrinsic Reaction Coordinate (IRC) calculation has also been performed to confirm the smooth connection of the TS to the reactant and the products. Computational studies using G2(MP2) methods have been performed to investigate the decompositions channels of CH3CFClO radical formed from HCFC-141b in the atmosphere. The results show that Cl elimination pathway is the dominant one. Rate constants of different channels considered have also been evaluated using Canonical Transition State Theory (CTST).