– conical intersection in trans-butadiene: ultrafast dynamics and optical spectra

Abstract The potential-energy functions of the 1 1 B u and 2 1 A g excited valence states of trans-butadiene have been characterised by the CASPT2 method. Based on these ab initio data, a vibronic-coupling model describing the conical intersection of the 1 1 B u and 2 1 A g states has been constructed. UV resonance-Raman and absorption spectra have been calculated, employing the time-dependent approach. The time-dependent wave-packet calculations reproduce the expected ultrafast (≈30 fs) radiationless decay of the optically bright 1 1 B u state into the dark 2 1 A g state.

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