Sampling excited state dynamics: influence of HOOP mode excitations in a retinal model.

Zero point energy and classical thermal sampling techniques are compared in semi-classical photodynamics of the pentadienyliminium cation, a minimal retinal model. Using both methods, the effects of vibrational hydrogen-out-of-plane (HOOP) excitations on the photo-reactivity are probed at the ab initio CASSCF level. With 2376 individual trajectories the calculations reveal a clear picture of the relation between the excited state reaction coordinate, surface crossing and product generation. The productivity is strongly coupled with hydrogen torsion and the number of hopping attempts before the molecule finally decays.