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

In ultrafast photoinduced reactions often more than one conical intersectio n is involved. We present an adiabatic approach which allows to treat the e volution 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, na mely the photoinduced ring opening of 1,3-cyclohexadiene (CHD). We find a b ranching of the wavepacket already in the excited state followed by a subse quent branching upon return to the ground state. The latter is different fo r the two intersections and depends on the location and topology. (C) 2001 Elsevier Science B.V. All rights reserved.