A computational study of the mechanism and kinetics for gas-phase decomposition and reactivity of the C ۴ F ۹OCH۲O radical between ۲۰۰ and ۴۰۰ K

چکیده مقاله

The decomposition processes and reactivity of C 4 F 9OCH2 O• radical formed from C4 F 9OCH3 (HFE-7100) have been studied by density function theory computational methods. All calculations were performed at B3LYP and mPW1PW91 levels of theory with the 6-311G(d,p) basis set. The calculated barrier heights were further improved by QCISD(T)/6-31G(d)//MP2/6-31G(d) methodology to obtain better rate constants. Five possible pathways were investigated: reaction with O 2, reaction with OH radical, C-O bond dissociation, release of H radical and finally rearrangement of the radical and then C-O bond cleavage with energy barriers of 6.35 (6.09) [12.12], 12.85 (16.87) [7.51], 17.05 (21.77) [28.34], 20.3 (20.75) [18.13], 32.60 (31.50) [32.63] and 16.07 (18.73) [20.04] kcal mol -1 , respectively (the values in the parentheses for mPW1PW91 and in the brackets for the QCISD(T) method). Rate constants were calculated by utilising canonical transition state theory in the temperature range of 200–400 K and 1 atm pressure, and Arrhenius diagrams were plotted. The results showed that H elimination and H abstraction pathways are dominant for degradation of C 4 F 9OCH2 O• radical in the atmosphere. A smooth transition from the reactants to products on the corresponding potential energy surface was confirmed by intrinsic reaction coordinate calculations.