Fig. 2.

PESs and nuclear wave packet snapshots during photoisomerization. (A) PESs of the S₁ and S₀ electronic states in the two-dimensional nuclear space. The nuclear wave packet starts in S₁ at the cis structure (0° torsion), assuming impulsive excitation. It reaches the CoIn at around 90° torsion and 140° of CNN bending at 90 fs. A vibronic coherence emerges in the course of the nonadiabatic passage. The wave packet bifurcates, and in the S₀ state, significant parts have reached the trans geometry at 170 fs. Periodic boundary conditions are employed along torsion in the excited state, while absorbing the wave packet at 180° torsion in the ground state due to having reached the product minimum. The complete movie is provided as electronic supplement (Movie S1). (B) Electronic state populations and coherence magnitude during the process. The nuclear wave packet relaxes from S₁ (yellow) to S₀ (green). The amount that has reached the trans geometry is drawn in red. Other parts of the wave packet exit the nuclear grid at CNN angles larger than 180°, a process that is not further captured or investigated. The coherence magnitude becomes nonvanishing at the CoIn passage starting from around 90 fs, after which it stays significant for 100 fs and then slowly decays.