Femtosecond dynamics of retro Diels-Alder reactions: the concept of concertedness

Using femtosecond-resolved mass spectrometry in a molecular beam, we report real-time studies of the retro Diels-Alder reactions of cyclohexene, norbo rnene and bicyclo[2,2,2]oct-2-ene. The experimental results and theoretical calculations elucidate the influence of conical intersections on ground-st ate reaction trajectories. We address the issue of concertedness on the act ual time scale of the nuclear motion. (C) 1999 Elsevier Science B.V. All ri ghts reserved.