  Pump-probe photoionization has been used to map the relaxation processes
taking place from highly vibrationally excited levels of the S2 state of
azulene, populated directly or via internal conversion from the S4 state.
Photoelectron spectra obtained by 1+2[prime] two-color time-resolved
photoelectron imaging are invariant (apart from in intensity) to the pump-probe
time delay and to the pump wavelength. This reveals a photoionization process
which is driven by an unstable electronic state (e.g., doubly excited state)
lying below the ionization potential. This state is postulated to be populated
by a probe transition from S2 and to rapidly relax via an Auger-like process
onto highly vibrationally excited Rydberg states. This accounts for the time
invariance of the photoelectron spectrum. The intensity of the photoelectron
spectrum is proportional to the population in S2. An exponential energy gap law
is used to describe the internal conversion rate from S2 to S0. The vibronic
coupling strength is found to be larger than 60$\pm$5 $\mu$eV.
