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Theoretical Studies on Reaction Mechanisms and Rate Constants of Several HFEs with OH Radical Reaction

Author: SongGuiCai
Tutor: PanXiuMei
School: Northeast Normal University
Course: Physical and chemical
Keywords: Reaction Mechanism Radical Reactions Potential Energy Surface Group-balanced Isodesmic Reactions Rate Constants
CLC: O643.12
Type: Master's thesis
Year: 2011
Downloads: 20
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Abstract


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 + OH→products CH2FOCH2F + OH→products CF3CH2OCH3 + OH→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 energiesΔGr,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,CH2FOCH2F和CHFOCH2F 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 T2.75 exp（-1011/T）; k2 = 3.40×10-（21） T3.04 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 energiesΔGr,2980 , and standard enthalpies of formation of CF3CH2OCH3, CF3CHOCH3 and CF3CH2OCH2 estimated theoretically using group-balanced isodesmic reactions carried out at several different levels.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Chemical kinetics > The mechanism and kinetics of chemical reactions
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