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. 2023 Jan 16;28(2):904.
doi: 10.3390/molecules28020904.

Probing the Potential Energy Profile of the I + (H2O)3 → HI + (H2O)2OH Forward and Reverse Reactions: High Level CCSD(T) Studies with Spin-Orbit Coupling Included

Xinyuan Zhang  1 , Xiaoting Chen  1 , Yan Lin  1 , Yan Meng  1 , Guoliang Li  1 , Yaoming Xie  2 , Henry F Schaefer 3rd  2
Affiliations

Probing the Potential Energy Profile of the I + (H2O)3 → HI + (H2O)2OH Forward and Reverse Reactions: High Level CCSD(T) Studies with Spin-Orbit Coupling Included

Xinyuan Zhang et al. Molecules. .

Abstract

Three different pathways for the atomic iodine plus water trimer reaction I + (H2O)3 → HI + (H2O)2OH were preliminarily examined by the DFT-MPW1K method. Related to previous predictions for the F/Cl/Br + (H2O)3 reactions, three pathways for the I + (H2O)3 reaction are linked in terms of geometry and energetics. To legitimize the results, the "gold standard" CCSD(T) method was employed to investigate the lowest-lying pathway with the correlation-consistent polarized valence basis set up to cc-pVQZ(-PP). According to the CCSD(T)/cc-pVQZ(-PP)//CCSD(T)/cc-pVTZ(-PP) results, the I + (H2O)3 → HI + (H2O)2OH reaction is predicted to be endothermic by 47.0 kcal mol-1. The submerged transition state is predicted to lie 43.7 kcal mol-1 above the separated reactants. The I···(H2O)3 entrance complex lies below the separated reactants by 4.1 kcal mol-1, and spin-orbit coupling has a significant impact on this dissociation energy. The HI···(H2O)2OH exit complex is bound by 4.3 kcal mol-1 in relation to the separated products. Compared with simpler I + (H2O)2 and I + H2O reactions, the I + (H2O)3 reaction is energetically between them in general. It is speculated that the reaction between the iodine atom and the larger water clusters may be energetically analogous to the I + (H2O)3 reaction. The iodine reaction I + (H2O)3 is connected with the analogous valence isoelectronic bromine/chlorine reactions Br/Cl + (H2O)3 but much different from the F + (H2O)3 reaction. Significant difference with other halogen systems, especially for barrier heights, are seen for the iodine systems.

Keywords: CCSD(T) computations; atom–molecule reactions; iodine atom; potential energy profile; water trimer.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Figure 1
Figure 1
Stationary points on the lowest-energy potential energy profile of the I + (H2O)3 reaction. The distances and relative energies are given in angstroms and kcal mol−1, respectively.
Figure 2
Figure 2
Comparison of the potential energy profiles for the I + (H2O)3, I + (H2O)2 and I + H2O reactions.
Figure 3
Figure 3
Comparison of the potential energy profiles for the I + (H2O)3 (black), Br + (H2O)3 (brown), Cl + (H2O)3 (green) and F + (H2O)3 (red) reactions. The PP is only used for the bromine and iodine atoms.
See this image and copyright information in PMC

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