Infrared spectroscopy of molecular ions and ion-solvent clusters

Citation

Choi, Jong-Ho (1995) Infrared spectroscopy of molecular ions and ion-solvent clusters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/x6dv-j487. https://resolver.caltech.edu/CaltechETD:etd-09252007-091111

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Studies to elucidate details of ion-molecule interactions at the molecular level are of extreme importance for understanding the solvation process and ion-molecule reactions in clusters and in the condensed phase. In the quest of this purpose, infrared predissociation spectroscopy has been applied to three ionic systems. Infrared spectra of mass-selected clusters NO[superscript +](H2O)n showed that the smaller clusters (n=1-3) were complexes of H2O ligands bound to a nitrosonium ion NO[superscript +] core. In the n = 4 cluster, we found evidence for the onset of an intracluster reaction that formed HONO. From an analysis of the spectrum, we concluded that the n = 5 cluster rearranged to form H3O[superscript +](H2O)3(HONO), i.e., an adduct of the reaction products. This study provides clear evidence for the intracluster rearrangement reaction NO[superscript +](H2O)n[...]H3O[superscript +](H2O)n-2(HONO) at n[...]4. Infrared spectroscopic results on NO2[superscript +](HOX)(X=H,D,[superscript 35]Cl,[superscript 37]Cl) clusters showed a remarkable similarity in the chemistry of protonated nitric acid and chlorine nitrate, and two types of isomers were observed. The structure of the ground-state isomer is an ionmolecule complex, NO2[superscript +](HOX), and the second most stable isomer is a covalently bound species, (OH)(OX)NO[superscript +]. We found evidence for an IR photon-induced isomerization reaction. These spectroscopic results were quite consistent with the predictions of ab initio theory, and may provide important clues to the heterogeneous reaction mechanism involved in the depletion of stratospheric ozone. The first infrared spectroscopic observations of gas-phase hydrated chloride clusters, [...], led to crucial suggestions concerning the structures of halide-water systems. In [...], the water forms a nearly linear hydrogen bond with the chloride ion, and in [...] and [...], the water ligands hydrate the chloride ion asymmetrically, but do not form a hydrogen bond with each other. The observed results for n = 1 and 2 showed good agreement with correlated ab initio calculations. In the n = 4 cluster, the probed structure was the one in which one [...]-bonded water ligand forms a hydrogen bond to an adjacent water ligand. In [...], a liquid-phase-like broad spectrum was observed with several peaks still apparent.

Thesis Files