Water-wire clusters: Vibronic spectra of 7-hydroxyquinoline·(H[sub 2]O)[sub 3].

The supersonically cooled 7-hydroxyquinoline·(H[sub 2]O)[sub 3] cluster was investigated by mass- and isomer-selected S[sub 1]←S[sub 0] resonant two-photon ionization and S[sub 1]→S[sub 0] fluorescence spectroscopy. UV(ultraviolet)/UV-holeburning measurements prove that a single cluster isomer is formed, although different tautomers (7-keto- and 7-hydroxyquinoline), rotamers (cis and trans) and isomers (cyclic and water-wire) are possible. Ab initio calculations of structures and vibrations of different tautomers and isomers of this cluster predict that the cis-enol-7-hydroxyquinoline·(H[sub 2]O)[sub 3] "water-wire" cluster is the most stable species. The experimental S[sub 0] and S[sub 1] inter- and intramolecular vibrational frequencies are in good agreement with the calculated harmonic frequencies. S[sub 1]←S[sub 0] excitation leads to contraction of all four hydrogen bonds along the hydrogen bonded water wire, inducing intense intermolecular stretching vibrations of the O-H...O and HO-H...N(quinoline) hydrogen bonds which terminate the water-wire. There are no spectroscopic signs of proton transfer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]