Ultrafast dynamics through conical intersections and intramolecular vibrational energy redistribution in styrene.

We report a femtosecond time-resolved photoelectron spectroscopy (TRPES) investigation of internal conversion in the first two excited singlet electronic states of styrene. We find that radiationless decay through an S(1)/S(0) conical intersection occurs on a timescale of ∼4 ps following direct excitation to S(1) with 0.6 eV excess energy, but that the same process is significantly slower (∼20 ps) if it follows internal conversion from S(2) to S(1) after excitation to S(2) with 0.3 eV excess energy (0.9 eV excess energy in S(1)).