Direct imaging of the ultrafast internal conversion in isolated piperidine

Schematic energy diagrams of piperidine. The pump laser (400nm) prepares the S1 state and S2 state. Due to ultrafast internal conversion (IC), this state converts to the higher S2 state with lower vibrational energy. Here, 1st and 2nd are corresponding to the first and second photoelectron bands. The timescales for S1/S2 IC and S2/S0 IC are marked 62fs and 184fs, respectively.