Surface-induced dissociations of hyperthermal ions at self -assembled monolayer surfaces
Abstract
Ion/surface collisions in hyperthermal energy (1–100 eV) regime unleash a variety of chemically relevant processes. In this energy range, the most of the activation barrier for chemical interactions are overcome, while the energy is not too excessive for chemically important processes. In this thesis, the energetics and mechanisms of the ion/surface reactions are studied from a fundamental viewpoint. As the first effort to understand the collision process, the portion of the translational energy of the projectile that is made available to the system is studied with n-butylbenzene molecular ion, a thermometer ion that has a pair of competing reactions that are sensitive to the internal energy of the ion. This method also provided a better understanding about the instrumental factors. Analytical application of this ion/surface collision was also studied with the isomeric bromotoluene molecular cation systems as the example. Large internal energy deposition made possible by surface-induced dissociation (SID) allowed better isomer discrimination compared to collision-induced dissociation (CID) and electron ionization (EI). A transhalogenation reaction was observed when the bromotoluene isomers collided with the fluorinated self-assembled monolayer (F-SAM) surfaces. Thiophene molecular cation abstracted hydrogen and methyl radicals from the surface where H• and CH 3• are available. The reaction was believed to occur via the sputtered proton mechanism, where the proton sputtered as the projectiles are neutralized at the surface, derivatize the neutralized projectile. The extent of hydrogen abstraction by the projectiles was correlated with the proton affinities and gas phase basicities of the neutral precursors, inspired by the kinetic method for thermochemical measurements in gas phase. It showed good correlation but the method needs more refinement.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.