Vibronic Conical Intersection Trajectory Signatures in Wave Packet Coherences.

Conical intersections are ubiquitous in the energy landscape of chemical systems, drive photochemical reactivity, and are extremely challenging to observe spectroscopically. Using two-dimensional electronic spectroscopy, we observe the nonadiabatic dynamics in Wurster's Blue after excitation to the lowest two vibronic excited states. The excited populations relax ballistically through a conical intersection in 55 fs to the electronic ground state potential energy surface as the molecule undergoes an intramolecular electron transfer. While the kinetics are identical on both vibronic energy surfaces, we observe different patterns of coherent oscillations after traversing the conical intersection indicating distinct nonadiabatic relaxation pathways through the conical energetic funnel. These coherences are not created directly by the excitation pulses but are the result of the dynamical trajectories projecting differently on the conical intersection vibrational space. Our spectroscopic data offers a fresh perspective into the complex conical intersection topology and dynamics that emphasizes the critical involvement of the intersection space in dictating the dynamics.