Adiabatic approach for ultrafast quantum dynamics mediated by simultaneously active conical intersections

In ultrafast photoinduced reactions often more than one conical intersection is involved. We present an adiabatic approach which allows to treat the evolution towards and the transfer via two simultaneously accessible conical intersections (CoIns). The feasibility of quantum dynamical investigations in the adiabatic representation is demonstrated for a prototype system, namely the photoinduced ring opening of 1,3-cyclohexadiene (CHD). We find a branching of the wavepacket already in the excited state followed by a subsequent branching upon return to the ground state. The latter is different for the two intersections and depends on the location and topology. (C) 2001 Elsevier Science B.V. All rights reserved.