Infrared photodissociation spectroscopic studies on the solvation of metal cations
Carnegie, Prosser DeVane
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Metal cation water complexes are generated by a laser vaporization of a metal rod coupled to a supersonic expansion. The ions are then analyzed with infrared photodissociation (IR-PD) spectroscopy in a reflectron time-of-flight mass spectrometer (RTOF). The monohydrated complexes are first studied to understand the effects the metal cation has on the water ligand. The OH stretching frequencies of the water ligand are shown to red shift from those of molecular water. The red shift results from interplay between electrostatic and covalent bonding characteristics that differ for each metal. Interesting binding characteristics appear when the vibrational spectra of the noble metal cation water complexes are obtained. The spectrum for Au(H2O)Ar2 reveals that the relativistic effects from this metal lead to significantly larger covalent type bonding than the other noble metals. The study of the solvation of metal cations progresses in the analysis of larger solvated species. V(H2O)n complexes present spectra showing the vanadium cation prefers a coordination of four waters. After the coordination of vanadium is satisfied waters begin to bind in the second solvation sphere. As the number of waters in the complex increases the formation of large hydrogen bonded networks appear in the vibrational spectrum. The results from this large scale study are compared with those of other systems to discuss the different features involved in each system. Finally, the study describes the characteristics of doubly charged metal cations with water. These complexes more accurately depict bulk solutions, where transition metals are present in higher oxidation states. The relative shifts and the intensities in the frequencies measured elucidate the bonding in these complexes. The above studies serve to fully understand the solvation of metal cations from small to large sizes.