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

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 S0 and S1 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.