SPECTROSCOPY AND STRUCTURE OF SOLVATED ALKALI-METAL IONS

Vibrational pre-dissociation spectroscopy combined with mass spectrome try has been used to obtain the infrared spectra of mass-selected clus ter ions. The onset of new spectroscopic features, as a function of so lvent number, had been shown to correspond to specific structural chan ges such as the filling of solvent shells and the formation of hydroge n bonds. These small finite systems offer a number of advantages over traditional solution-based measurements and perhaps are the most usefu l way to test current theoretical calculations and models. Whereas the rmodynamic properties, derived from high-pressure mass spectrometry me asurements, give some indication of solvent shell size, vibrational sp ectra suggest a more complex picture. When combined with recent infrar ed studies of size-selected neutral clusters, considerable detail of t he solvent structure about the ion can be obtained. The solvation of t he alkali-metal ions Na+ and Cs+ by a number of solvents, including wa ter, will be discussed. Future directions and applications will be pre sented.