Chemical dynamics simulations of the monohydrated OH(-)(H2O) + CH3I reaction. Atomic-level mechanisms and comparison with experiment

Jing Xie; Rico Otto; Roland Wester; William L Hase

doi:10.1063/1.4922451

Chemical dynamics simulations of the monohydrated OH(-)(H2O) + CH3I reaction. Atomic-level mechanisms and comparison with experiment

J Chem Phys. 2015 Jun 28;142(24):244308. doi: 10.1063/1.4922451.

Authors

Jing Xie¹, Rico Otto², Roland Wester³, William L Hase¹

Affiliations

¹ Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA.
² Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
³ Institut fur Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25/3, A-6020 Innsbruck, Austria.

PMID: 26133429
DOI: 10.1063/1.4922451

Abstract

Direct dynamics simulations, with B97-1/ECP/d theory, were performed to study the role of microsolvation for the OH(-)(H2O) + CH3I reaction. The SN2 reaction dominates at all reactant collision energies, but at higher collision energies proton transfer to form CH2I(-), and to a lesser extent CH2I(-) (H2O), becomes important. The SN2 reaction occurs by direct rebound and stripping mechanisms, and 28 different indirect atomistic mechanisms, with the latter dominating. Important components of the indirect mechanisms are the roundabout and formation of SN2 and proton transfer pre-reaction complexes and intermediates, including [CH3--I--OH](-). In contrast, for the unsolvated OH(-) + CH3I SN2 reaction, there are only seven indirect atomistic mechanisms and the direct mechanisms dominate. Overall, the simulation results for the OH(-)(H2O) + CH3I SN2 reaction are in good agreement with experiment with respect to reaction rate constant, product branching ratio, etc. Differences between simulation and experiment are present for the SN2 velocity scattering angle at high collision energies and the proton transfer probability at low collision energies. Equilibrium solvation by the H2O molecule is unimportant. The SN2 reaction is dominated by events in which H2O leaves the reactive system as CH3OH is formed or before CH3OH formation. Formation of solvated products is unimportant and participation of the (H2O)CH3OH---I(-) post-reaction complex for the SN2 reaction is negligible.