GAS-PHASE CLUSTER ION VIBRATIONAL SPECTROSCOPY OF NA-7)((CH3OH)(2)

The vibrational spectra of Na+(CH3OH)(2-7) in the 2.7-3.0 mu m region have been measured using a LiNbO3 optical parametric oscillator and a triple-quadrupole molecular beam apparatus. The cluster ions are forme d by the impact of a sodium ion with a preformed methanol cluster. Fre quency shifts of the methanol O-H stretch are used to identify both th e onset of hydrogen-bond formation and the nature of the hydrogen-bond ed species in the cluster ions, permitting the microscopic characteriz ation of the solvation process. Methanol molecules associated with the cluster ion, but not acting as proton donors in a hydrogen bond, abso rb in the 3660-70 cm(-1) region, while bands due to hydrogen-bonded sp ecies have been observed at similar to 3515, 3420, and 3350 cm(-1). Th e onset of hydrogen-bond formation is nominally first observed for Na(CH3-OH)(4), with more extensive hydrogen bonding observed for Na+(CH3 OH)(5-7). An assessment of the influence of the sodium ion on the meth anol vibrational frequencies can be made through comparison with the s pectra of Cs+(CH3OH)(1-5) and (CH3OH)(2-3). The effect of the electros tatic interaction, between either the sodium or cesium ion and the met hanol solvent, is primarily reflected by the onset and extent of hydro gen-bond formation as opposed to the magnitude of vibrational spectros copic shifts.