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Spectroscopy and photodissociation of solvated multiply charged ions

Kieron P Faherty, University of Massachusetts - Amherst

Abstract

Solvated transition metal solvent cluster ions were generated by electrospray ionization and their spectroscopy and photo dissociation dynamics have been studied by laser photofragment spectroscopy. Solvation of Co 2+ by water and methanol has been examined by studying Co2+ (H2O)n and Co2+(CH3OH) n (n = 4–7). ^ An electrospray ionization reflectron time-of-flight mass spectrometer (ESI-RTOFMS) was developed to produce gas phase transition metal solvent cluster ions. This system couples with a Nd:YAG pumped dye laser to produce a unique mass spectrometry-laser photodissociation system. This instrument was compared to ESI-mass spectrometers in the literature. It shows a mass resolution (m/Δm) of 250 and a detection limit of 480 pmol. The instrument compares favorably to existing analytical instrumentation and several improvements are suggested. ^ Hydrated cluster ions, Co2+(H2O)n (with n = 4–7), have been generated by electrospray ionization and studied by laser photofragment spectroscopy. The similarity between the spectrum of gas-phase Co2+(H2O)6 and the absorption spectrum of aqueous cobalt (II) suggests that Co2+(H2 O)6 (aq) is responsible for the room-temperature solution absorption spectrum. The observed photodissociation spectrum of Co 2+(H2O)4 is similar to new bands that appear in aqueous cobalt(II) at high temperatures and have been assigned to Co 2+(H2O)4 (aq) in the literature. The hexahydrate dissociates by loss of one or two water molecules, whereas the heptahydrate dissociates by loss of two or three water molecules. In both cases, loss of two water molecules is the preferred dissociation pathway. The tetrahydrate dissociates either by simple loss of water or by charge separation to form CoOH+(H2O)2 and H3O +, with charge separation being the preferred dissociation channel. ^ Methanolic cluster ions, Co2+(CH3OH)n (with n = 4–7), show behavior similar to that of the hydrated clusters. The gas phase spectra display similar shifts from the solution absorption spectra, but absorb more strongly than the corresponding hydrated clusters. The hexamethanol cluster dissociates via loss of one or two methanol molecules; the heptamethanol cluster dissociates via loss of one, two or three methanols. The tetramethanol cluster primarily dissociates by a charge separation mechanism similar to that observed in the hydrated clusters, forming Co(OCH3) +(CH3OH)2 and H+(CH3OH); dissociation by simple loss of methanol is a minor channel. ^

Subject Area

Chemistry, Analytical|Chemistry, Physical

Recommended Citation

Kieron P Faherty, "Spectroscopy and photodissociation of solvated multiply charged ions" (January 1, 2004). Doctoral Dissertations Available from Proquest. Paper AAI3118295.
http://scholarworks.umass.edu/dissertations/AAI3118295

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