Theoretical Studies On Reaction Mechanisms And Rate Constants Of Several HFEs With OH Radical Reaction

Hydrofluoroethers (HFEs) have been the third generation alternatuvel compounds to CFCs and are used in various industrial applications. However, they may be evaluated as possible greenhouse gases because of absorption in the terrestrial infrared radiation. So assessing its atmospheric chemistry and environmental impact is necessary by determining its atmospheric lifetime. Detailed investigations on the reaction mechanisms and kinetics of HFEs are very important to control atmospheric pollutions.By the quantum chemistry theory, the mechanisms and dynamics studies of reactions of CH₂FCF₂OCHF₂/ CH₂FOCH₂F/CF₃CH₂OCH₃ + OH have been carried out theoretically. These reactions are described as: CH₂FCF₂OCHF₂ + OHâ†'products CH₂FOCH₂F + OHâ†'products CF₃CH₂OCH₃ + OHâ†'productsThe important and valuable results in this work are summarized as follows:1. Theoretical Studies on the Mechanisms and Dynamics of OH Radicals with CH₂FCF₂OCHF₂ and CH₂FOCH₂F. The geometries, frequencies of all the stationary points were carried out at the B3LYP/6-311G(d,p), BH&H-LYP/6-311G(d,p) and MP2(full)/6-311G(d,p) levels. In this work we studied the potential energy surface information(including optimized geometries, harmonic vibrational frequencies and the single-point energy calculations of the stationary points), the reaction enthalpies (ΔH _r,298⁰ ) and reaction gibbs free energiesΔG_r,298⁰ . Also, the heoretical prediction of the rate constants, the temperature dependence of branching ratios are provided. Moreover, standard enthalpies of formation of CH₂FCF₂OCHF₂,CHFCF₂OCHF₂,CH₂FCF₂OCF₂,CH₂FOCH₂Få'ŒCHFOCH₂F radical are estimated theoretically using group-balanced isodesmic reactions. The rate constants calculated by canonical variational transition state theory with small-curvature tunneling (CVT/SCT) correction are consistent with the available experimental values. The result of rate constant calculations in over the temperature range of 220-2000K show that the rate constants of two reactions have positive temperature dependence. The three-parameter Arrhenius expressions are as follows (in units of cm3 molecule^-1 s^-1): k₁ = 1.62×10^-20 T^2.75 exp(^-1011/T); k₂ = 3.40×10^-(21) T^3.04 exp(-384/T)。2. Theoretical Studies on the Potential Energy Surfaces and Thermodynamics of CF₃CH₂OCH₃ with Radicals. The geometries, frequencies of all the stationary points were carried out at the MP2/6-311G(d,p) and BH&H-LYP/6-311G(d,p) levels. The single-point energy calculations for the stationary points were carried out at BMC-CCSD andBMC-QCISD level by using the MP2/6-311G(d,p) and BH&H-LYP/6-311G(d,p) optimized geometries. Moreover, the reaction enthalpies (ΔH _r,298⁰ ), reaction gibbs free energiesΔG_r,298⁰ , and standard enthalpies of formation of CF₃CH₂OCH₃, CF₃CHOCH₃ and CF₃CH₂OCH₂ estimated theoretically using group-balanced isodesmic reactions carried out at several different levels.