Issue 4, 2017

High-level ab initio potential energy surface and dynamics of the F + CH3I SN2 and proton-transfer reactions

Abstract

Bimolecular nucleophilic substitution (SN2) and proton transfer are fundamental processes in chemistry and F + CH3I is an important prototype of these reactions. Here we develop the first full-dimensional ab initio analytical potential energy surface (PES) for the F + CH3I system using a permutationally invariant fit of high-level composite energies obtained with the combination of the explicitly-correlated CCSD(T)-F12b method, the aug-cc-pVTZ basis, core electron correlation effects, and a relativistic effective core potential for iodine. The PES accurately describes the SN2 channel producing I + CH3F via Walden-inversion, front-side attack, and double-inversion pathways as well as the proton-transfer channel leading to HF + CH2I. The relative energies of the stationary points on the PES agree well with the new explicitly-correlated all-electron CCSD(T)-F12b/QZ-quality benchmark values. Quasiclassical trajectory computations on the PES show that the proton transfer becomes significant at high collision energies and double-inversion as well as front-side attack trajectories can occur. The computed broad angular distributions and hot internal energy distributions indicate the dominance of indirect mechanisms at lower collision energies, which is confirmed by analyzing the integration time and leaving group velocity distributions. Comparison with available crossed-beam experiments shows usually good agreement.

Graphical abstract: High-level ab initio potential energy surface and dynamics of the F− + CH3I SN2 and proton-transfer reactions

Supplementary files

Article information

Article type
Edge Article
Submitted
04 Jan 2017
Accepted
15 Feb 2017
First published
17 Feb 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2017,8, 3164-3170

High-level ab initio potential energy surface and dynamics of the F + CH3I SN2 and proton-transfer reactions

B. Olasz, I. Szabó and G. Czakó, Chem. Sci., 2017, 8, 3164 DOI: 10.1039/C7SC00033B

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