Femtosecond Multiphoton Ionization Photoelectron Spectroscopy of the S2 State of Phenol

We investigated the short-lived S2 (1A1) state of phenol using two-photon resonance-enhanced photoionization coupled with photoelectron spectroscopy. Spectra were obtained by exciting the S2 state with femtosecond laser pulses at various wavelengths near 207 nm and ionizing with pulses at 207 or 414 nm. The spectra feature a strong transition to the ground electronic state of the ion (X) and a very weak transition to the first excited electronic state of the ion (A). In comparison, ionization via the longer-lived S1 state using 275 nm pulses generates slightly more A ions. We interpret the relative intensities of the A state signals as a reflection of configuration interactions in the intermediate S2 and S1 states. Time-delayed ionization experiments, as well as experiments with different laser pulse durations, suggest that the S2 state has a lifetime between 150 and 350 fs. Ionization via S1 produces a vibrationally resolved photoelectron spectrum, while ionization via S2 leads to a highly congested spe...