OH Stretching Vibrations of Phenol−(H2O)1 and Phenol−(H2O)3 in the S1 State

OH stretching vibrations of phenol−(H 2 O) n clusters ( n = 1, 3) in the S 1 state have been observed by UV−IR double resonance spectroscopy, where the fluorescence dip induced by the IR excitation was monitored. The spectra were analyzed by comparing with those of the S 0 state reported in a previous work. It was found that a frequency reduction of the phenolic OH stretching vibration and an enhancement of the interactions among the hydrogen bond network in the cluster were much larger in the S 1 state than in the S 0 state, representing the increase in acidity of phenol upon the electronic excitation. The nonradiative process of the vibrationally excited phenol is also discussed based on the fluorescence-dip spectrum of the deuterated phenol in S 1 .