Defense Date

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dr. James Terner

Abstract

In this dissertation, the ion mobility technique is used to determine the structures of small acetylene cluster ions, (C2H2)1-3+, mass-selected from the largest ever reported ionized acetylene clusters. The technique is also used to characterize the reaction of acetylene clusters with water in an effort to elucidate thermochemistry and kinetics of some interesting ion-molecule reactions suspected to occur in interstellar clouds and other interplanetary bodies.A combination of ion mobility measurements, collision induced dissociation (CID), and theoretical calculations are used to provide the most conclusive evidence for the frequently hypothesized trimerization of ionized acetylene to form the benzene ion. The results also provide evidence for the isomerization of the acetylene dimer ion, (C2H2)2+, to form the cyclobutadiene and vinylacetylene ions.Investigation of the reactions of acetylene radical ions (C2H2∙+) with water reveals competing kinetics for two primary, C2H4O∙+ and C2H3O+, and a secondary, H+(H2O)n, product with an overall reaction rate coefficient of 2.0 × 10-11 cm3s-1. By comparing experimentally observed reactions to theoretically (G3MP2) predicted thermochemistry, the C2H4O∙+ ion is suggested to be the ethenolium ion (vinyl alcohol ion, CH2CHOH∙+) and the C2H3O+ ion is suggested as either the 1-hydroxy-ethenylium (CH2COH+) or cyclic 2H-oxirenium (c-CH2CHO+) ion. Investigation of the temperature dependence of the equilibrium constant for the association reaction (C2H2)3 + + (H2O)n-1 ↔ (C2H2)3∙+(H2O)n using the van't Hoff plot revealed binding energies and reaction entropies identical to those recently published for the benzene+/water system thus providing even more evidence for the formation of benzene ions from ionized acetylene clusters.We also provide a density functional (UB3LYP/Wachters+ f) investigation of Fe+, Co+, and Ni+(C2H2)n clusters (where n = 1-3) to supplement mass spectrometric analysis of the acetylene-solvated cations. For the Co+(C2H2)n clusters, the mass spectrum revealed an intriguing behavior of oscillating magic numbers which we suspect to be the consequence of a Co+-mediated polymerization reaction to form covalent Co+CnHn complexes. The UB3LYP/Wachters+f predicted barrier and exothermicity for the initial step of the proposed trimerization reaction are 25.4 and 101.4 kcal/mol respectively. Our results suggest the efficiency of this reaction is facilitated by cooperative interactions and favorable orientations of acetylenes in the cluster.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2008

Included in

Chemistry Commons

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