Study of phenol–water complexes using frequency- and time-resolved pump–probe photoionization

Abstract

Two-color multiphoton ionization has been used to study phenol–water complexes containing one phenol and one, two, and three water molecules. Photoionization efficiency spectra show that phenol–(H2O) possesses a sharp ionization threshold, giving an adiabatic ionization potential of 63 980 cm−1 (1300 cm−1 lower than previously reported). This is followed by a vibrational progression in the ion of about 240 cm−1 that has been assigned to the hydrogen bond stretching motion. Spectra obtained with the ionization wavelength set so as to avoid fragmentation of the complexes have resulted in a reassignment of the S1 state spectra of phenol–(H2O)2 and phenol–(H2O)3. Spectra taken with the ionization laser delayed by 300 ns reveal that both phenol–(H2O)2 and phenol–(H2O)3 lose two water molecules after intersystem crossing from the vibrationless level of the S1 state. However, it is known that the triplet species obtained from phenol–(H2O)3 is much longer lived than that obtained from phenol–(H2O)2. This large difference in the triplet lifetimes provides clues as to the nature of the bonding in the parent complexes.