Reactions of chlorine atoms and hydroxyl radicals with trichloroethanol: a mechanistic and kinetic study |
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| Authors: | Li Wang Song Liu Jing-lai Zhang |
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| Institution: | (1) Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, People’s Republic of China; |
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| Abstract: | The multi-channel reactions (1) CCl3CH2OH+Cl→ products and (2) CCl3CH2OH+OH→ products have been investigated by using the dual-level direct dynamics method. Two reaction channels, i.e., methylene-
and hydroxyl-hydrogen abstraction, are identified for each reaction. The optimized geometries and frequencies of the stationary
points are calculated at the B3LYP/6-311G(d,p) and MP2/6-311G(d,p) levels. Higher-level energies are obtained at the MC-QCISD
and G3(MP2) levels based on the B3LYP and MP2 geometries, respectively, as well as by the CCSD(T)/6-31G(d)+CF method using
the B3LYP geometries. Complexes with energies lower than those of the reactants are located at the entrance of each reaction
channel. The rate constants for each reaction channel are evaluated by using the canonical variational transition state theory
(CVT) incorporating the small-curvature tunneling (SCT) correction in a temperature range of 200–2000 K at the MC-QCISD//B3LYP/6-311G(d,p)
level. The agreement of the calculated rate constants and experimental values for two reactions is seen to be remarkably good.
Theoretical results indicate that in a low temperature range, the branching ratio to the hydroxyl-H-abstraction channel for
both reactions is found negligible. The reactions proceed practically via methylene-H-abstraction yielding the products of
CCl3CHOH+HCl and CCl3CHOH+H2O, respectively; while for reaction of CCl3CH2OH+Cl, hydroxyl-H-abstraction channel appears to be probable with the increase of temperature. The enthalpies of formation
for the CCl3CH2OH, CCl3CHOH, and CCl3CH2O species are evaluated via isodesmic reactions at several levels. |
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