Kinetic parameters for the reaction of OH radical with cis-CHFCHCHF2, trans-CHFCHCHF2, CF2CHCHF2 and CF2CCHF: Hybrid meta DFT and CVT/SCT/ISPE calculations

Abstract

A dual-level direct dynamic method is employed to estimate the addition and hydrogen abstraction rate coefficients for the reactions of cis-CHFCHCHF2, trans-CHFCHCHF2, CF2CHCHF2 and CF2CCHF 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-CHFCHCHF2, trans-CHFCHCHF2, CF2CHCHF2 and CF2CCHF + 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-CHFCHCHF2, trans-CHFCHCHF2, CF2CHCHF2 and CF2CCHF + OH reactions were calculated to be 6.83 × 10−13, 3.17 × 10−12, 5.43 × 10−13 and 2.22 × 10−13 cm3 molecule−1 s−1, respectively at 298 K. The atmospheric life times of cis-CHFCHCHF2, trans-CHFCHCHF2CHF, CF2CHCHF2 and CF2CCHF 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 hydrofluoro-olefines (HFOs) may be possible replacements to HFCs in many industrial applications.