Femtosecond multiphoton ionization photoelectron spectroscopy of the S-2 state of phenol

We investigated the short-lived St ((1)A(1)) state of phenol using two-phot on resonance-enhanced photoionization coupled with photoelectron spectrosco py. Spectra were obtained by exciting the S-2 state with femtosecond laser pulses at various wavelengths near 207 nm and ionizing with pulses at 207 o r 414 nm. The spectra feature a strong transition to the ground electronic state of the ion ((X) over tilde) and a very weak transition to the first e xcited electronic state of the ion ((A) over tilde). In comparison, ionizat ion via the longer-lived S-1 state using 275 nm pulses generates slightly m ore (A) over tilde ions. We interpret the relative intensities of the (A) o ver tilde state signals as a reflection of configuration interactions in th e intermediate S-2 and S-1 states. Time-delayed ionization experiments, as well as experiments with different laser pulse durations, suggest that the S-2 state has a lifetime between 150 and 350 fs. Ionization via S-1 produce s a vibrationally resolved photoelectron spectrum, while ionization via S-2 leads to a highly congested spectrum. The envelope of the latter spectrum extends over more than 1 eV and features a long progression, probably in th e 6a vibration. This suggests that the S-2 state has a geometrical structur e that is displaced from the ground state along the 6a coordinate. No vibra tional structure could be resolved in the (A) over tilde ion spectrum obtai ned by ionization via either S-2 or S-1.