Ultrafast energy flow in the wake of solution-phase bimolecular reactions

Vibrational energy flow into reactants, and out of products, plays a key role in chemical reactivity, so understanding the microscopic detail of the pathways and rates associated with this phenomenon is of considerable interest. Here, we use molecular dynamics simulations to model the vibrational relaxation that occurs during the reaction CN+c-C6H12 -> HCN+c-C6H11 in CH2Cl2, which produces vibrationally hot HCN. The calculations reproduce the observed energy distribution, and show that HCN relaxation follows multiple timescales. Initial rapid decay occurs through energy transfer to the cyclohexyl co-product within the solvent cage, and slower relaxation follows once the products diffuse apart. Re-analysis of the ultrafast experimental data also provides evidence for the dual timescales. These results, which represent a formal violation of conventional linear response theory, provide a detailed picture of the interplay between fluctuations in organic solvent structure and thermal solution-phase chemistry.