Direct dynamics simulation of dissociation of the [CH3 - I - OH]- ion-molecule complex

Jing Xie, Miranda McClellan, Rui Sun, Swapnil C. Kohale, Niranjan Govind, William L. Hase

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Direct dynamics simulations were used to study dissociation of the [CH3 - I - OH]- complex ion, which was observed in a previous study of the OH- + CH3I gas phase reaction (J. Phys. Chem. A 2013, 117, 7162). Restricted B97-1 simulations were performed to study dissociation at 65, 75, and 100 kcal/mol and the [CH3 - I - OH]- ion dissociated exponentially, in accord with RRKM theory. For these energies the major dissociation products are CH3I + OH-, CH2I- + H2O, and CH3OH + I-. Unrestricted B97-1 and restricted and unrestricted CAM-B3LYP simulations were also performed at 100 kcal/mol to compare with the restricted B97-1 results. The {CH3I + OH-}:{CH2I- + H2O}:{CH3OH + I-} product ratio is 0.72:0.15:0.13, 0.81:0.05:0.14, 0.71:0.19:0.10, and 0.83:0.13:0.04 for the restricted B97-1, unrestricted B97-1, restricted CAM-B3LYP, and unrestricted CAM-B3LYP simulations, respectively. Other product channels found are CH2 + I- + H2O, CH2 + I-(H2O), CH4 + IO-, CH3- + IOH, and CH3 + IOH-. The CH3- + IOH singlet products are only given by the restricted B97-1 simulation and the lower energy CH3 + IOH- doublet products are only formed by the unrestricted B97-1 simulation. Also studied were the direct and indirect atomic-level mechanisms for forming CH3I + OH-, CH2I- + H2O, and CH3OH + I-. The majority of CH3I + OH- were formed through a direct mechanism. For both CH2I- + H2O and CH3OH + I-, the direct mechanism is overall more important than the indirect mechanisms, with the roundabout like mechanism the most important indirect mechanism at high excitation energies. Mechanism comparisons between the B97-1 and CAM-B3LYP simulations showed that formation of the CH3OH - -I- complex is favored for the B97-1 simulations, whereas formation of the HO- - -HCH2I complex is favored for the CAM-B3LYP simulations. The unrestricted simulations give a higher percentage of indirect mechanisms than the restricted simulations. The possible role of the self-interaction error in the simulations is also discussed. The work presented here gives a detailed picture of the [CH3 - I - OH]- dissociation dynamics and is very important for unraveling the role of [CH3 - I - OH]- in the dynamics of the OH-(H2O)n=1,2 + CH3I reactions.

Original languageEnglish (US)
Pages (from-to)817-825
Number of pages9
JournalJournal of Physical Chemistry A
Issue number5
StatePublished - Feb 5 2015

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© 2015 American Chemical Society.


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