Hydrogen-bonded phenol–acid clusters studied by vibrational resolved laser spectroscopy and ab initio calculations: I. Formic acid

Abstract

The hydrogen-bonded complexes of phenol with one and two molecules of formic acid are studied by resonant two-photon ionization, IR–UV double-resonance spectroscopy, dispersed fluorescence spectroscopy and ab initio calculations at the Hartree–Fock level. The shifts of the electronic spectra, the intermolecular vibrations in the S 0 and S 1 states and the calculated binding energies point to cyclic arrangements for both phenol(formic acid) 1 and phenol(formic acid) 2. Phenol is involved in two hydrogen bonds acting as proton donor to the carboxylic group of the acid and as proton acceptor. The stable (formic acid) 2 dimer opens to allow insertion of a phenol molecule and formation of a cyclic phenol(formic acid) 2 structure.