Ultrafast Internal Conversion Dynamics of 2-Chloropyridine by Femtosecond Time-Resolved Photoelectron Imaging

Ultrafast internal conversion dynamics of 2-chloropyridine were studied by femtosecond time-resolved photoelectron imaging spectroscopy coupled with time-resolved mass spectroscopy. The ultrafast internal conversion from the second excited state (S-2) to the first excited state (S-1) via an adjacent conical intersection within (162 +/- 5) fs was clearly observed from the time-dependence of the photoelectron spectra. The subsequent deactivations involved the coupling of S-2/S-0 (the ground state) and S-1/S-0 conical intersections, which occurred on a timescale of about (5.5 +/- 0.3) ps, and led to the internal conversion to the ground state from the S-2 and S-1 states.