Theoretical studies on kinetics, mechanism and thermochemistry of gas-phase reactions of CF3CHFCF2OCF3 with OH radicals and Cl atoms and fate of alkoxy radical at 298 K

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF3CHFCF2OCF3 with OH radicals and Cl atoms using M06-2X/6-31+G(d,p) level of theory. The energetic calculations were refined by using aug-cc-pVTZ basis set. Our calculations reveal that OH-initiated hydrogen abstraction is thermodynamically and kinetically more facile than that from the Cl-initiated hydrogen abstraction. Using group-balanced isodesmic reactions, the standard enthalpies of formation (ΔHf°) for species and bond dissociation energies for CH bond are also reported. The ΔHf° for CF3CHFCF2OCF3 and •CF(CF3)CF2OCF3 species calculated from M06-2X/6-31+G(d,p) results are −523.15 and −471.65 kcal mol−1, respectively. The rate constants evaluated by canonical transition state theory (CTST) are found to be 1.22 × 10−15 and 3.40 × 10−17 cm3 molecule−1 s−1 which are in a reasonable agreement with the available experimental data of (1.43 ± 0.28) × 10−15 and (4.09 ± 0.42) × 10−17 cm3 molecule−1 s−1, respectively, for OH and Cl-initiated hydrogen abstraction reactions. The atmospheric life time of CF3CHFCF2OCF3 is estimated to be 38.5 years. The atmospheric fate of the alkoxy radical, CF3CF(O•)CF2OCF3 is also investigated for the first time using same level of theory.