Retro-Diels−Alder Femtosecond Reaction Dynamics

In this communication, we present our first femtosecond (fs), real-time studies of the retro-Diels-Alder reactions of norbornene (NB) and norbornadiene (NBD), products of the cycloaddition of cyclopentadiene with ethylene and acetylene, respectively. The reaction path, together with transition state (TS) structures, is displayed in Figure 1 (bottom). The experiments were designed with the following considerations in mind. First, the reactions were studied in a molecular beam in order to isolate the elementary processes, free of solvent perturbations. Second, we examined the dynamics of the reaction from a well-defined initial geometry, a precursor of Diels-Alder products.