Infrared Spectroscopy of Chromophore-Labeled Water Clusters Phenol-(H2O) n (n < ~50)

Abstract

To analyze hydrogen bond network structures consisting of tens of water molecules, we measured moderately size-selective IR spectra of large, labeled water clusters phenol-(H2O) n in the OH stretch region. The observed spectral features were analyzed in terms of hydrogen bond ring size motifs and coordination numbers of water molecules. The detailed analyses of the free OH band indicated that the observed low-frequency shift originates from the cooperativity of hydrogen bonds and the structural development from the highly strained 4-membered ring motif to the more relaxed 5- and 6-membered ring motifs. The suppression of free OH band intensity with an increase of n represents the increase of the abundance of 4-coordinated waters. We expect that the present characterization method of hydrogen bond networks may be applicable to more complicated, condensed phase water.