The exothermic HCl + OH·(H2O) reaction: removal of the HCl + OH barrier by a single water molecule.
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.
MOE Key Laboratory of Theoretical Chemistry of the Environment, Center for Computational Quantum Chemistry, South China Normal University, Guangzhou 510006, China.
Guoliang
G
Li
MOE Key Laboratory of Theoretical Chemistry of the Environment, Center for Computational Quantum Chemistry, South China Normal University, Guangzhou 510006, China.
Hui
H
Wang
MOE Key Laboratory of Theoretical Chemistry of the Environment, Center for Computational Quantum Chemistry, South China Normal University, Guangzhou 510006, China.
Qian-Shu
QS
Li
Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Yaoming
Y
Xie
Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Henry F
HF
Schaefer
D006851:Hydrochloric Acid / Q000737:chemistry*; D006860:Hydrogen Bonding; D006878:Hydroxides / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D006878:Hydroxides; D014867:Water; C031356:hydroxide ion; D006851:Hydrochloric Acid