Imaging dynamics of chemical reaction between F- and CH3Cl

Halogenated hydrocarbons play a very important role in organic synthesis both as solvents and as reaction intermediates. The bimolecular nucleophilic substitution (SN2) is one of the most common processes of these compounds. The reaction type is of fundamental importance in physical organic chemistry due to its underlying simplicity, nevertheless its reaction dynamics has not been understood in complete detail. In the past, understanding of the reaction dynamics relied heavily on chemical trajectory simulations. However, advancements in the cross beam scattering and velocity map imaging (VMI) techniques in the previous decade have led to new insights into the reaction dynamics from measurements of correlated energy and angle differential cross sections.

The simplest case of a nucleophilic substitution reaction consists of a methyl halide colliding with a mono atomic nucleophile. Using a crossed beam setup and a velocity map imaging spectrometer, our group has extensively studied exothermic SN2 reaction systems. We have performed experiments on the SN2 reaction of fluoride ion with methyl chloride at six different relative collision energies ranging from 0.6 eV to 3.0 eV. The direct SN2 pathway is the dominant channel at high energy with an increasingly strong contribution from the complex mediated channel at lower energies. We have also investigated the effect of deuteration on the reaction dynamics by performing the experiment with CD3Cl at a single collision energy of 1.2 eV and looking for the relative importance of the direct and complex mediated channels.

In this talk, I shall present the imaging technique in detail and highlight some important observations.  A comparison of the present results with previous studies by our group on similar systems like, fluoride ions on methyl iodide and chloride ions on methyl iodide will provide better understanding of the reaction dynamics of SN2 reactions