  Chemiluminescence in 1,2-dioxetane occurs through a thermally activated
decomposition reaction into two formaldehyde molecules. Both ground-state and
nonadiabatic dynamics (including singlet excited states) of the decomposition
reaction have been simulated, starting from the first O-O bond-breaking
transition structure. The ground-state dissociation occurs between t = 30 fs
and t = 140 fs. The so-called entropic trap leads to frustrated dissociations,
postponing the decomposition reaction. Specific geometrical conditions are
necessary for the trajectories to escape from the entropic trap and for
dissociation to be possible. The singlet excited states participate as well in
the trapping of the molecule: dissociation including the nonadiabatic
transitions to singlet excited states now occurs from t = 30 fs to t = 250 fs
and later. Specific regions of the seam of the S0/S1 conical intersections that
would "retain" the molecule for longer on the excited state have been
identified.
