Atmospheric chemistry of CF3(CX2)2CH2OH: rate coefficients and temperature dependence of reactions with chlorine atoms and the subsequent pathways of alkyl and alkoxy radicals (X = H, F)

Abstract

The atmospheric and kinetic properties of CF₃(CX₂)₂CH₂OH (X = H, F) with chlorine atoms were studied by density functional and canonical variational transition state theories in conjunction with the small-curvature tunneling correction. The minimum energy path was obtained by the CCSD(T)/6-311++G(d,p)//B3LYP/6-311G(d,p) method. The H-abstraction channel from the –CH₂O– group was found to be the dominant channel, whereas that from the –OH site of the title reactions may be negligible because of the high barrier. All rate constants computed within 200–1000 K are in reasonable agreement with the available experimental values. The degradation mechanism of CF₃(CX₂)₂CH₂OH is discussed. The subsequent pathways of the CF₃(CX₂)₂C˙HOH and CF₃(CX₂)₂C(O˙)HOH radicals were studied. The atmospheric lifetime and global warming potentials (GWPs) of CF₃(CX₂)₂CH₂OH were computed, and it is shown that fluorine substitution may increase the lifetime and GWPs. It is also indicated that fluorine substitution may decrease the reactivity. The reaction enthalpies and reaction Gibbs free energies for all relevant reactions were discussed. The rate coefficient expressions for the title reactions obtained are k_T1 = 5.75 × 10⁻¹⁷T^2.26 exp(428.02/T) and k_T2 = 1.30 × 10⁻¹⁷T^1.96 exp(67.40/T) per cm³ per molecule per s.