Wave Packet Movements near the Conical Intersection between Two Excited Potential Surfaces May Create Observable Molecular Oscillations

A femtosecond pump-probe experiment is performed on tetrakis(dimethylamino)ethylene. The evolution resulting from the pi-pi(*) excitation of the CC double bond corresponds to movement along a single adiabatic potential surface with deformation along several coordinates and passage near a conical intersection. Surprisingly, this movement excites the umbrella mode of the amino groups, resulting in a measurable oscillation regime.