Intermediates, dynamics and potential energy surfaces of gas phase ion-molecule reactions

Fundamental energetic and dynamical properties of gas-phase ion-molecule reactions were studied using both experimental and theoretical methods. Experimental results were obtained using Fourier transform ion cyclotron resonance (FT-ICR) spectrometry, and infrared multiple photon (IRMP) activation. Statistical reaction rate theories (RRKM theory) and ab-initio quantum calculations were used to aid in the interpretation of experimental results.; The experimental characterization of the potential energy surfaces for two classes of gas-phase reactions, S{dollar}sb{lcub}rm N{rcub}{dollar}2 substitution and carbonyl addition-elimination, was accomplished through the synthesis and characterization (chemically and photochemically) of reactive intermediates. Intermediates were shown conclusively to be unsymmetrical ion-molecule complexes, and no evidence for stable, covalent adducts was found. These experiments provided direct evidence for a double minimum potential energy surface for the bimolecular reactions. The non-observation of covalent tetrahedral adducts in the carbonyl addition-elimination reactions is noteworthy, given the importance of tetrahedral adducts in solution-phase reactions of carbonyl compounds. Angular momentum differences between the bimolecular and photo-induced reactions were shown to have important consequences for the efficiency of product formation.; The S{dollar}sb{lcub}rm N{rcub}{dollar}2 reaction of cyanide ion (CN{dollar}sp-{dollar}) with chloroacetonitrile (NCCH{dollar}sb2{dollar}Cl) was studied using equilibrium, kinetic, photochemical, and theoretical techniques. An intermediate in the near thermoneutral proton transfer reaction, (NC){dollar}sb2{dollar}CH{dollar}sp-{dollar} + HCl {dollar}to{dollar} (NC){dollar}sb2{dollar}CH{dollar}sb2{dollar} + Cl{dollar}sp-{dollar}, was formed in two distinct and widely separated energy regimes above the thresholds for either reaction channel and the energy dependence of the branching ratio for dissociation was determined and was qualitatively consistent with a statistical RRKM model. The uncommon observation that the post-S{dollar}sb{lcub}rm N{rcub}{dollar}2-substitution complex accessed multiple channels was used to explore the dynamics of dissociation processes for ion-molecule complexes, which was applied to the formulation of a general picture for gas-phase S{dollar}sb{lcub}rm N{rcub}{dollar}2 reactions.; The observation of a post-substitution proton transfer reaction was also used to determine the relative contributions of competing reaction channels in the reactions of ambident nucleophiles with acetyl chlorides. For the reaction of acetone enolate and the cyanomethide (NCCH{dollar}sb{lcub}2sp-{rcub}{dollar}) ions, reaction with trifluoroacetyl chloride proceeds predominantly by carbon attack.