Interfacial chemical reactions, mechanisms and matrix effects in molecular secondary ion mass spectrometry
Abstract
Interfacial chemical reactions, which are induced at solid-gas and liquid-gas interfaces by ion beam bombardment, are examined using molecular secondary ion mass spectrometry (SIMS). Examples of Lewis acid/base, substitution, and reduction reactions are presented. Silver cationization occurs to a greater extent in polycyclic aromatic hydrocarbons that contain a bay region. Alkyl transfer reactions have been studied using carnitine HCl and a number of zwitterionic compounds. A mechanism for this reaction, based on the minimization of the number of charges desorbed into the gas phase, is proposed. Nitrogen-containing heteroaromatic compounds and quinones are hydrogenated in the presence of metals with low work functions. Detailed mechanisms for these reactions are proposed. The extent of reduction of perrhenate salts is dependent upon the alkali or ammonium counterion. Direct comparisons of SIMS and laser desorption (LD) mass spectra have been made using an optical fiber interface to a SIMS instrument. Many of the interfacial reactions observed in SIMS are absent in the LD mass spectra. Kinetic studies of interfacial reactions yield information regarding the area of the surface affected per bombarding particle. Insight into the SIMS mechanism is gained through an examination of the effects of varying the primary ion energy on the extent of fragmentation and on the yield of secondary ions. As the primary ion energy is increased, the secondary ion yield increases but the extent of fragmentation decreases. This effect is observed using both monoatomic and polyatomic primary ions. Matrix effects in SIMS have also been examined. Proton-rich matrices enhance the protonation of neutral molecules and reduce the extent of intermolecular reactions. Matrices can take active roles in intermolecular reactions. For example, nucleophilic matrices are involved in matrix/analyte alkyl transfer reactions and ND$\sb4$Cl acts as a hydrogen-deuterium exchange agent when mixed with organic compounds that contain active hydrogens.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Environmental science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.