Deducing anharmonic coupling matrix elements from picosecond time-resolved photoelectron spectra: application to S(1) toluene at low vibrational energy.

The 6a(1) + 10b(1)16b(1) Fermi resonance in S(1) toluene is studied through picosecond time-resolved photoelectron spectroscopy. Our time and energy resolution, together with the necessary stability to monitor dynamics for many hundreds of picoseconds, enable new and unexpected insight into the dynamics and identity of the prepared wavepacket, and the determination of the coupling matrix elements responsible for those dynamics. In particular we are able to determine the influence of the torsional motion of the methyl group on the dynamics; this motion has long been implicated as an effective accelerator of IVR processes.