Torsional potential energy surfaces and vibrational levels in trans

Quantum chemical calculations of vibrational frequencies of Stilbene were followed by the computation of the potential energy surface for the two rotors related to the single bonds. By the flexible model approach applied to the computed surface we have confirmed previous assignment of mode 37 and determined frequency of the elusive mode 48. The same analysis was performed not only for the ground, but also for the excited electronic state. The shape of the potential energy surface in S0 is in agreement with that of styrene and the barrier height obtained from the fitting in S1 is increased with respect to S0, a