Quantitative dynamics of paradigmatic SN2 reaction OH- + CH3F on accurate full-dimensional potential energy surface

The bimolecular reaction between OH- and CH3F is not just a prototypical S(N)2 process, but it has three other product channels. Here, we develop an accurate full-dimensional potential energy surface (PES) based on 191 193 points calculated at the level CCSD(T)-F12a/aug-cc-pVTZ. A detailed dynamics and mechanism analysis was carried out on this potential energy surface using the quasi-classical trajectory approach. It is verified that the trajectories do not follow the minimum energy path (MEP), but directly dissociate to F- and CH3OH. In addition, a new transition state for proton exchange and a new product complex CH2F-center dot center dot center dot H2O for proton abstraction were discovered. The trajectories avoid the transition state or this complex, instead dissociate to H2O and CH2F- directly through the ridge regions of the minimum energy path before the transition state. These non-MEP dynamics become more pronounced at high collision energies. Detailed dynamic simulations provide new insights into the atomic-level mechanisms of the title reaction, thanks to the new chemically accurate PES, with the aid of machine learning. Published under an exclusive license by AIP Publishing.

Automated summary

In this study, an accurate full-dimensional potential energy surface (PES) was developed, and the non-minimum energy path (MEP) dynamics of the reaction between OH- and CH3F were revealed through dynamic simulations, uncovering new proton exchange and proton abstraction product channels, providing new insights into the mechanism of the reaction.