Mode-dependent anharmonic coupling between OH stretching and intermolecular vibrations of the hydrogen-bonded clusters of phenol

IR absorption spectra of the OH stretching vibration (v(OH)) and its combination band with the intermolecular vibrations (v(int)) of jet-cooled phenol-H2O and phenol-CH3OH clusters in the S-1 state were measured by fluorescence detected IR depletion spectroscopy (FDIRS). A remarkable mode dependence in their anharmonic couplings was observed: (1) The v(OH)(1) v(int)(1) transition showed blue-shift from the v(OH)(1) <-- 0(0) transition when v(int) is the intermolecular stretching vibration (sigma). (2) On the other hand, the transition showed a red-shift when vi,, is the intermolecular wagging mode (beta(2)). The observed shifts and anharmonic constants are discussed on the basis of the adiabatic potential curves which describe the coupling between the high-frequency v(OH) and the low-frequency intermolecular motions. (C) 1998 Elsevier Science B.V. All rights reserved.