Spectroscopic study on hydrogen-bonding and charge resonance interactions in aromatic cluser ions

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The purpose of this project is to investigate hydrogen bonding interaction in clusters involving an aromatic molecule as a chromophor. We have constructed an apparatus for pulsed field ionization (PFI)-ZEKE photoelectron spectroscopy. The structure and hydrogen bonding interaction in neutral clusters have been compared with those in cluster cations where the hydrogen bonding interaction competes with the charge resonance interaction. We have observed the electronic spectra of 5-hydroxytropolone-CO_2/H_2O and 9-hydroxyphenalenone-CO_2/H_2O clusters, and clarified the effects of intermolecular interaction on proton tunneling combined with multidimensional potential calculations. Three structural isomers have been clearly identified in 4-aminobenzonitrile-H_2O. The PFI-ZEKE spectrum of one isomer, where the oxygen atom of water is hydrogen-bonded to the amino proton, has been successfully observed. We have investigated stable structures and intermolecular interaction in the aniline dimer cation, benzene-aniline hetero-dimer cation, and benzene-benzylalcohol hetero-dimer cation. In the aniline dimer ion and benzene-aniline ion, the hydrogen-bonding interaction is predominant and no charge resonance interaction occurs, whereas the charge resonance interaction has been observed in the benzene-benzylalcohol dimer ion. The intermolecular interaction in the clusters ions has been correlated to the stable structures obtained by ab initio and density functional theory calculations. We have shown that the hydrogen bonding interaction is very sensitive to charge densities on the constitute atoms of the chromophor.