Water-chain clusters: vibronic spectra of 7-hydroxyquinoline·(H2O)n, n=1–4

Mass- and isomer-selected S1←S0 resonant two-photon ionization spectra of the series of supersonically cooled 7-hydroxyquinoline·(H2O)n, n=1–4 clusters are reported. These represent a series of hydrogen-bonded “water-chain” clusters, strung between the –O–H group and the N atom of the aromatic molecule. The vibronic spectra of n=2 and 4 clusters are strongly overlapped with the n=3 spectrum, and are identified for the first time; all exhibit large red-shifts (≈2000 cm−1). The n=2 and 3 clusters form solely water-chain clusters, while n=4 exists as water-chain clusters and as three other isomers, as shown by UV/UV laser-holeburning.