Highly resolved UV spectroscopy of clusters: isotope substitution studies of hydrogen-bonded phenol·water Original Research Article

We present highly resolved UV spectra of the S1←S0 000 band in monodeuterated phenol and its cluster with D2O. An analysis of the rotational fine structure of the electronic transitions by correlation automated rotational fitting (CARF) yields the rotational constants for the respective electronic ground and excited states. From the rotational constants the rS position of the monomer oxygen hydrogen, the docking position of the water molecule, is calculated using Kraitchmanʹs equations for monosubstitution. We calculate the cluster structure by an iterative calculation based on Kraitchmanʹs symmetric disubstitution equations. We find a value of 1.87(14) Å for the HPhenol–OWater distance in the hydrogen bond in S0 and a shortening to 1.82(23) Å in S1. Furthermore, we investigate the torsional motion caused by the hindered rotation of the water moiety around the bonding axis. In contrary to the phenol·H2O in the phenol-OD·D2O spectra only one torsional sub-band caused by the hindered rotation of the water moiety is found. Therefore, the difference between the tunnel splittings in S0 and S1 is below the experimental resolution and smaller than 100 MHz.