화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.103, No.49, 10470-10476, 1999
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-photon resonance-enhanced photoionization coupled with photoelectron spectroscopy. 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 or 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 excited electronic state of the ion ((A) over tilde). In comparison, ionization via the longer-lived S-1 state using 275 nm pulses generates slightly more (A) over tilde ions. We interpret the relative intensities of the (A) over tilde state signals as a reflection of configuration interactions in the 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 produces 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 the 6a vibration. This suggests that the S-2 state has a geometrical structure that is displaced from the ground state along the 6a coordinate. No vibrational structure could be resolved in the (A) over tilde ion spectrum obtained by ionization via either S-2 or S-1.