Quantum dynamics calculations on a model surface based on CASPT<sub>2</sub>//CASSCF calculations are carried out to probe the traversal
of a wave packet through an extended seam of conical intersection
during the light-induced Wolff rearrangement of diazonaphtoquinone.
The reaction is applied in the fabrication of integrated circuits.
It consists of nitrogen elimination and ring rearrangement to yield
a ketene. After excitation, the wave packet relaxes and reaches the
extended seam. A fraction of the wave packet decays to the ground
state at a region of the seam connected to a carbene intermediate,
while the remaining part decays at a region leading to the ketene.
The passage of the wave packet through the extended seam explains
the competition between concerted ketene formation and a stepwise
mechanism involving a carbene. The two primary photoproducts are formed
in the first 100 fs of the simulation, in agreement with recent ultrafast
spectroscopy measurements
