Ultrafast dynamics in superexcited states of phenol

We observe three-photon ionization photoelectron spectra of phenol in a mol ecular beam. After excitation by the first photon to the S-1 electronic sta te, a second photon lifts the molecule to a set of superexcited molecular s tates at an energy of 9 eV, which is 0;5 eV above the ionization energy. Ph otoelectron spectra are obtained by ionizing the molecule with a third phot on. The spectra show prominent Rydberg series with delta = 0.32 and delta = 0.80, as well as several other series. Time-delayed photoelectron spectra are obtained from two-color ionization experiments. These spectra are analy zed by eliminating underlying contributions from competing ionization proce sses, and by referencing all decays to a set of particularly persistent pho toelectron peaks. A kinetic picture emerges that invokes an ultrafast conve rsion of the initially excited, optically bright, superexcited valence stat e to a set of vibrationally excited Rydberg states, on a femtosecond time s cale. Further dynamical processes among the Rydberg states proceed on a pic osecond time scale.