Product energy deposition of CN plus alkane H abstraction reactions in gas and solution phases

In this work, we report the first theoretical studies of post-transition state dynamics for reaction of CN with polyatomic organic species. Using electronic structure theory, a newly developed analytic reactive PES, a recently implemented rare-event acceleration algorithm, and a normal mode projection scheme, we carried out and analyzed quasi-classical and classical non-equilibrium molecular dynamics simulations of the reactions CN + propane (R1) and CN + cyclohexane (R2). For (R2), we carried out simulations in both the gas phase and in a CH2Cl2 solvent. Analysis of the results suggests that the solvent perturbations to the (R2) reactive free energy surface are small, leading to product energy partitioning in the solvent that is similar to the gas phase. The distribution of molecular geometries at the respective gas and solution phase variational association transition states is very similar, leading to nascent HCN which is vibrationally excited in both its CH stretching and HCN bending coordinates. This study highlights the fact that significant non-equilibrium energy distributions may follow in the wake of solution phase bimolecular reactions, and may persist for hundreds of picoseconds despite frictional damping. Consideration of non-thermal distributions is often neglected in descriptions of condensed-phase reactivity; the extent to which the present intriguing observations are widespread remains an interesting question. (C) 2011 American Institute of Physics. [doi:10.1063/1.3595259]