I + (H2O)2 ↿HI + (H2O)OH Forward and Reverse Reactions. CCSD(T) Studies Including Spin–Orbit Coupling

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• 作者：Hui Wang ; Guoliang Li ; Qian-Shu Li ; Yaoming Xie ; Henry F. Schaefer III
• 刊名：Journal of Physical Chemistry B
• 出版年：2016
• 出版时间：March 3, 2016
• 年：2016
• 卷：120
• 期：8
• 页码：1743-1748
• 全文大小：335K
• ISSN：1520-5207

文摘

The potential energy profile for the atomic iodine plus water dimer reaction I + (H₂O)₂ → HI + (H₂O)OH has been explored using the “Gold Standard” CCSD(T) method with quadruple-ζ correlation-consistent basis sets. The corresponding information for the reverse reaction HI + (H₂O)OH → I + (H₂O)₂ is also derived. Both zero-point vibrational energies (ZPVEs) and spin–orbit (SO) coupling are considered, and these notably alter the classical energetics. On the basis of the CCSD(T)/cc-pVQZ-PP results, including ZPVE and SO coupling, the forward reaction is found to be endothermic by 47.4 kcal/mol, implying a significant exothermicity for the reverse reaction. The entrance complex I···(H₂O)₂ is bound by 1.8 kcal/mol, and this dissociation energy is significantly affected by SO coupling. The reaction barrier lies 45.1 kcal/mol higher than the reactants. The exit complex HI···(H₂O)OH is bound by 3.0 kcal/mol relative to the asymptotic limit. At every level of theory, the reverse reaction HI + (H₂O)OH → I + (H₂O)₂ proceeds without a barrier. Compared with the analogous water monomer reaction I + H₂O → HI + OH, the additional water molecule reduces the relative energies of the entrance stationary point, transition state, and exit complex by 3–5 kcal/mol. The I + (H₂O)₂ reaction is related to the valence isoelectronic bromine and chlorine reactions but is distinctly different from the F + (H₂O)₂ system.