A comparative study of ion activation processes in mass spectrometry

Stevan Roy Horning, Purdue University

Abstract

This thesis examines and compares several ion formation and activation techniques used in mass spectrometry, including, charge exchange, collision-induced dissociation, surface-induced dissociation, electron-induced decomposition, and photodissociation. Fragmentation recorded for the molecular ion of the organic molecule, limonene, is used to compare the energy transfer associated with each of these activation techniques. In a second experiment, the distribution $P(\epsilon)$ of internal energies deposited into an ion upon activation is determined using a simple thermochemical procedure based on the appearance energies from a series of decarbonylation reactions from metal carbonyl ions. $P(\epsilon)$ distributions of tungsten hexacarbonyl molecular ions following collisional activation at electron and kiloelectron volt energies were compared for several atomic, diatomic and polyatomic target gases. The difference in energy deposition at the two collision energies was attributed to different mechanisms (electronic and vibrational excitation) of activation. Kiloelectron volt angle-resolved collision-induced dissociation (ARMS) experiments were performed on tungsten hexacarbonyl and iron pentacarbonyl molecular ions at small scattering angles ($<$2.5$\sp\circ$) at 1.5, 2 and 3 keV collision energies. The average internal energy deposited into the ion increased by more than 5 eV as the scattering angle ($\theta$) is raised from 0 to 2.5$\sp\circ$. The average internal energy also increased with the kinetic energy of the ion ($E$) and the mass of the target. The $P(\epsilon)$ distributions acquired upon collisional activation for ions scattered through small angles upon 3 keV collision are bimodal in shape. the lower energy component in the distribution is thought to be due to electronic excitation, while the higher energy component is associated with a vibrational excitation mechanism. $P(\epsilon)$ distributions were also determined for tungsten hexacarbonyl ions formed by charge exchange with singly and doubly charged rare gas ions. The energy transferred varied with the recombination energy of the ion. A large fraction of the kinetic energy of the rare gas ion was also transferred during charge exchange at energies between 2 and 10 eV. Charge exchange between doubly charged rare gas ions and tungsten hexacarbonyl resulted in the formation of doubly charged ions. Singly charged ions were also recorded due to a single electron transfer from the doubly charged rare gas ion. Kinetic energy release measurements for reaction between doubly charged transition-metal ions and tungsten hexacarbonyl showed that the average energy released by the reactants upon transfer of a single electron is approximately 2 eV.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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