ABSTRACT
The entrance complex, transition state, and exit complex for the title reaction have been investigated using the CCSD(T) method with correlation consistent basis sets up to cc-pVQZ. The stationary point geometries for the reaction are related to but different from those for the water monomer reaction HCl + OH → Cl + H2O. Our most important conclusion is that the hydrogen-bonded water molecule removes the classical barrier entirely. For the endothermic reverse reaction Cl + (H2O)2, the second water molecule lowers the relative energies of the entrance complex, transition state, and exit complex by about 4 kcal/mol. The title reaction is exothermic by 17.7 kcal/mol. The entrance complex HCl⋯OH·(H2O) is bound by 6.9 kcal/mol relative to the separated reactants. The classical barrier height for the reverse reaction is predicted to be 16.5 kcal/mol. The exit complex Cl⋯(H2O)2 is found to lie 6.8 kcal/mol below the separated products. The potential energy surface for the Cl + (H2O)2 reaction is radically different from that for the valence isoelectronic F + (H2O)2 system.
ACKNOWLEDGMENTS
The research in China was supported by the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2012), the Research Fund for the Doctoral Program of Higher Education (Grant No. 20104407110007), and the National Natural Science Foundation of China (NNSFC) (Grant No. 20973066). The research at the University of Georgia was supported by the U.S. Department of Energy, Basic Energy Sciences, Chemical Sciences Division, Gas Phase Chemical Physics Program.
