Hydrogen-bonded phenol-acid clusters studied by vibrational resolved laserspectroscopy and ab initio calculations - I. Formic acid

The hydrogen-bonded complexes of phenol with one and two molecules of formi c acid are studied by resonant two-photon ionization, IR-UV double-resonanc e spectroscopy, dispersed fluorescence spectroscopy and ab initio calculati ons at the Hartree-Fock level. The shifts of the electronic spectra, the in termolecular vibrations in the S-0 and S-1 states and the calculated bindin g energies point to cyclic arrangements for both phenol(formic acid), and p henol(formic acid)(2). Phenol is involved in two hydrogen bonds acting as p roton donor to the carboxylic group of the acid and as proton acceptor. The stable (formic acid), dimer opens to allow insertion of a phenol molecule and formation of a cyclic phenol(formic acid)(2) structure. (C) 1999 Elsevi er Science B.V. All rights reserved.