Ground state normal mode analysis: Linking excited state dynamics and experimental observables

Aspects of the photoinduced ring opening reaction of cyclohexadiene with subsequent relaxation to cZc-hexatriene or back to cyclohexadiene are investigated theoretically. In this ultrafast reaction the S-1 state plays a central role, providing the possibility for the molecule to rapidly decay from the excited to the ground state via multiple conical intersections. To better understand the dynamics of the molecule on its way toward the product states, we perform a normal mode analysis of its vibrations in the vicinity of two prominent conical intersections and find several eigenmodes to characterize its motion. This raises hope that our findings could lead to an experimental scheme of detection for the wave packet motion in the hot product states by a time resolved transient absorption measurement. In the end this might be useful in designing an input signal for an optimal control experiment to selectively steer the molecule through a specific conical intersection and influence the product yield. (C) 2001 American Institute of Physics.