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要旨

The photodynamics of ethylene has been studied by means of ab initio surface-hopping dynamics using extended multireference configuration interaction wavefunctions. At the highest level, the explicit possibility of excited-state CH dissociation and consideration of the Rydberg π−3s state was included into the electronic wavefunction. The initial dynamics is characterised by the torsional motion and the crossing between the bright π−π * state with S 1, the latter having primarily Rydberg character with only a minor contribution of the repulsive valence π−σ * state. Due to back-rotation to planar structures after 17 fs, part of the population flows into the Rydberg states. The lifetime for this fraction of trajectories is significantly longer than that for the valence population. An analysis of the latter population shows that the decay to the ground state proceeds mainly at the pyramidalised conical intersection. Thus, no major qualitative mechanistic changes as compared to previous dynamics simulations are observed for the valence population. In the present work, a decay time of 62 fs was found for the valence population. Simulations performed for ethylene-d4 show a slowdown of the torsional mode. However, since the crossing seam is reached in a more direct way with less torsional oscillations, the excited-state lifetime is almost unchanged as compared to ethylene.