The structure optimization, Hessian calculation, and all SP calculations were all carried out using the Turbomole program. Computing the fully coupled six-mode PES for the reduced salicylaldimine system is an immense task, and we will accordingly represent the PES with restrictions in the included mode-couplings. We construct a MCR consisting of all one-mode (6) and two-mode combinations (15) and we further add all three-mode combinations including the TS mode (10). This is obtained through including MCs using Eq.( ) with w m = 1 for all modes except the TS mode for which w m = 0. This keeps the number of MCs at a manageable level (31) while giving a high coupling level for the TS mode. This MCR is used both in the TD-ADGA calculation and in the reference PES.