Direct dynamics simulations of the unimolecular dissociation of dioxetane: Probing the non-RRKM dynamics

In a previous UB3LYP/6-31G* direct dynamics simulation, non-Rice–Ramsperger–Kassel–Marcus (RRKM) unimolecular dynamics was found for vibrationally excited 1,2-dioxetane (DO); [R. Sun et al., J. Chem. Phys. 137, 044305 (2012)]. In the work reported here, these dynamics are studied in more detail using the same direct dynamics method. Vibrational modes of DO were divided into 4 groups, based on their characteristic motions, and each group excited with the same energy. To compare with the dynamics of these groups, an additional group of trajectories comprising a microcanonical ensemble was also simulated. The results of these simulations are consistent with the previous study. The dissociation probability, N(t)/N(0), for these excitation groups were all different. Groups A, B, and C, without initial excitation in the O–O stretch reaction coordinate, had a time lag to of 0.25–1.0 ps for the first dissociation to occur. Somewhat surprisingly, the C–H stretch Group A and out-of-plane motion Group C excitations ...