Product distribution in the photolysis of s-cis butadiene: A dynamics simulation

In this paper, we report the results of nonadiabatic molecular dynamics computations on s-cis butadiene. Our objective was to understand the complex mechanism of the photolysis of this hydrocarbon through the analysis of an ensemble of trajectories computed with the hybrid MMVB method. Within the limitations of our computational strategy (the initial conditions and the limitations of the MMVB potential), our results suggest that some of the experimentally observed photoproducts, such as s-trans butadiene, bicyclobutane, and Z,Z- butadienes (obtained by irradiating substituted E,E-butadienes) are exclusively formed through "dynamic paths" defined by certain subsets of trajectories that lie far from conventional minimum energy paths. In particular, concurrent double bond isomerization (e.g., Z,Z-->E,E isomerization) seems to be achieved by decay of a "dynamically locked intermediate", a metastable excited-state species.