Kinetic parameters for the reaction of OH radical with cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF: Hybrid meta DFT and CVT/SCT/ISPE calculations

A dual-level direct dynamic method is employed to estimate the addition and hydrogen abstraction rate coefficients for the reactions of cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF with hydroxyl radicals (OH) using variational transition state theory (VTST) with interpolated single-point energies (ISPE) at CCSD(T)/cc-pVTZ//M06-2X/6-31+G(d,p) level of theory. The rate coefficients of cis-CHF=CHCHF2, trans-CHFHCHF2, CF2=CHCHF2 and CF2=CHF + OH reactions were computed using Canonical Variational Transition state Theory (CVT) with Small Curvature Tunneling (SCT) in the temperature range of 200-400 K. It was found that the contribution of abstraction reactions toward the overall reaction to be insignificant, and hence negligible in comparison to the addition reactions in the studied temperature range of 200-400 K. The total rate coefficient for cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF + OH reactions were calculated to be 6.83 x 10(-13), 3.17 x 10(-12),5.43 x 10(-13) and 2.22 x 10(-13) cm(3) molecule(-1) s(-1), respectively at 298 K. The atmospheric life times of cis-CHF=CHCHF2, trans-CHF=CHCHF2CHF, CF2=CHCHF2 and CF2=C=CHF are estimated to be 16,3.4, 21 and 57 days respectively at 277 K. The global warming potentials (GWPs) of title molecules at the time horizons of 20, 100 and 500 years were computed using the rate coefficients and radiative forcing values obtained in this study. Since these title molecules show significantly lower GWPs than many hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs), it is conclude that these hydrofluoroolefines (HFOs) may be possible replacements to HFCs in many industrial applications. (C) 2015 Elsevier B.V. All rights reserved.