We report infrared spectra of phenol－(H2O)n (~20 ≦ n ≦ ~50) in the OH stretching vibrational region. Phenol－(H2O)n forms essentially the same hydrogen bond (H-bond) network as that of the neat water cluster, (H2O)n+1. The phenyl group enables us to apply the scheme of infrared－ultraviolet double resonance spectroscopy combined with mass spectrometry, achieving the moderate size selectivity (0 ≦ Δn ≦ ~6). The observed spectra show clear decrease of the free OH stretch band intensity relative to that of the H-bonded OH band with increasing cluster size n. This indicates increase of the relative weight of four-coordinated water sites, which have no free OH. Corresponding to the suppression of the free OH band, the absorption peak of the H-bonded OH stretch band rises at ~3350 cm－1. This spectral change is interpreted in terms of a signature of four-coordinated water sites in the clusters.
