HYDROGEN-BONDING IN METAL-ION SOLVATION - VIBRATIONAL SPECTROSCOPY OFCS-6) IN THE 2.8 MU-M REGION((CH3OH)(1)

The vibrational spectroscopy of cesium ions solvated by methanol has b een obtained in the 2.8 mu m region, using a tunable infrared laser an d a triple quadrupole mass spectrometer. The cluster ions are generate d by the collision between the ion and a preformed methanol cluster. T he resulting nascent ion cluster is stabilized by evaporative cooling prior to spectroscopic study. The vibrational spectra of the OH stretc h, in Cs+(CH3OH)(1-6), reveal the onset of hydrogen-bond formation wit h as few as three molecules in the first solvent shell, for a subset o f the mass-selected cluster ions. Prominent infrared features have bee n observed near 3665 cm(-1), for methanol molecules individually compl exed to the ion, and near 3520, 3415 and 3345 cm(-1) corresponding to methanols complexed to the ion and participating in hydrogen bonds. St ructural interpretations of these features are made by comparison with vibrational spectra of neutral methanol clusters. There is clear evid ence that more than one structural isomer exists for clusters with thr ee to five solvent molecules. The variations in the OH stretching freq uency contain far more structural information than previous spectrosco pic studies of the CO stretch. Whereas the former experiments revealed the size of the solvent shell and differences between the environment s in the solvent shells, structural variations within the first solven t shell are now observable. The balance between electrostatic interact ions (ion-solvent) and hydrogen bonding (solvent-solvent) can be exami ned at the molecular level, which should be extremely useful in develo ping accurate new, computationally efficient, interaction potentials.