Highly resolved UV spectroscopy of clusters: isotope substitution studies of hydrogen-bonded phenol-water

We present highly resolved UV spectra of the S-1 <-- S-0 0(0)(0) band in mo nodeuterated phenol and its cluster with D2O. An analysis of the rotational fine structure of the electronic transitions by correlation automated rota tional fitting (CARF) yields the rotational constants for the respective el ectronic ground and excited states. From the rotational constants the r(s) position of the monomer oxygen hydrogen, the docking position of the water molecule, is calculated using Kraitchman's equations for monosubstitution. We calculate the cluster structure by an iterative calculation based on Kra itchman's symmetric disubstitution equations. We find a value of 1.87(14) A ngstrom for the H-Phenol-O-Water distance in the hydrogen bond in S-0 and a shortening to 1.82(23) Angstrom in S-1. Furthermore, we investigate the to rsional motion caused by the hindered rotation of the water moiety around t he bonding axis. In contrary to the phenol . H2O in the phenol-OD . D2O spe ctra only one torsional sub-band caused by the hindered rotation of the wat er moiety is found. Therefore, the difference between the tunnel splittings in S-0 and S-1 is below the experimental resolution and smaller than 100 M Hz. (C) 1998 Elsevier Science B.V. All rights reserved.