Abstract
High level coupled-cluster theory, with spin-orbit coupling evaluated via the Breit-Pauli operator in the interacting-states approach, is used to investigate the OH radical reaction with Cl2 and the subsequent reaction HOCl + Cl. The entrance complex, transition state, and exit complex for both reactions have been determined using the CCSD(T) method with correlation consistent basis sets up to cc-pV6Z. Also reported are CCSDT computations. The OH + Cl2 reaction is predicted to be endothermic by 2.2 kcal/mol, compared to the best experiments, 2.0 kcal/mol. The above theoretical results include zero-point vibrational energy corrections and spin-orbit contributions. The activation energy (Ea) of the OH + Cl2 reaction predicted here, 2.3 kcal/mol, could be as much as 1 kcal/mol too high, but it falls among the four experimental Ea values, which span the range 1.1-2.5 kcal/mol. The exothermicity of the second reaction HOCl + Cl → HCl + ClO is 8.4 kcal/mol, compared to experiment 8.7 kcal/mol. The activation energy for latter reaction is unknown experimentally, but predicted here to be large, 11.5 kcal/mol. There are currently no experiments relevant to the theoretical entrance and exit complexes predicted here.
Highlights
With the manufacture of chlorine-containing compounds, such as ethylene dichloride and chlorinated solvents, chlorine as a waste gas enters the atmosphere in large quantities
The correlation-consistent polarized valence basis sets of Dunning, Kendall, Harrison, Woon, and Peterson, including cc-pVDZ, ccpVTZ, cc-pVQZ, and cc-pV5Z are employed to optimize the structures of the reactants, entrance complex, transition states, exit complex, and the products.[16−19] The stationary points are characterized by harmonic vibrational frequency analyses with the CCSD(T)/cc-pVQZ method
The intrinsic reaction coordinate (IRC)[20,21] method in Gaussian 0922 is used with the M05/DZP DFT method[23] to confirm that the transition states connect the designated entrance and exit complexes, where the DZP basis sets are the Huzinaga−Dunning double-ζ plus polarization Gaussian sets.[24,25]
Summary
With the manufacture of chlorine-containing compounds, such as ethylene dichloride and chlorinated solvents, chlorine as a waste gas enters the atmosphere in large quantities. The chemistry of the chlorine oxides, including ClO, play an important role in atmospheric chemistry.[1] At the same time, the OH radical plays a widely recognized important role in both atmospheric and combustion chemistry,[2] and its interactions with chlorine are important. In this context, the OH + Cl2 → products reaction has been the subject of both experimental and theoretical studies. Their reaction energies for different OH + Cl2 → HOCl + Cl pathways were obtained from density functional theory and the QCISD method
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