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Title page for ETD etd-04042003-172408


Type of Document Dissertation
Author Papantonakis, Michael Robert
Author's Email Address michael.papantonakis@vanderbilt.edu
URN etd-04042003-172408
Title Mechanisms of Ablation and Ion Formation in Infrared Laser Mass Spectrometry
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Dr. Richard F. Haglund, Jr. Committee Chair
Dr. David Hercules Committee Member
Dr. Richard Caprioli Committee Member
Dr. Thomas Kephart Committee Member
Dr. William Gabella Committee Member
Keywords
  • MALDI
  • Free-electron laser
  • infrared
  • ion formation
  • ablation
  • mass spectrometry
Date of Defense 2003-03-28
Availability unrestricted
Abstract
The studies described in this work take advantage of a unique infrared light source that allowed the exploration of previously uninvestigated vibrational modes and excitation densities, plus other laser systems that allowed us to compare the importance of pulse duration and electronic excitation in the ultraviolet. Results from several experiments were compared to current models of ion formation, allowing us to observe their applicability to our systems. One experiment assembled the most extensive range of excitation conditions to date to challenge the contribution of primary excitation events to the final ion yield. Despite the vastly different charged species and densities necessarily created, the results showed qualitatively similar spectra in all cases. We therefore concluded that the similarity of mass spectra alone offers a poor or incomplete picture from which to determine the operative mechanisms for ion formation, and that the observed ions are likely formed in the expanding plume. A second set of experiments utilized vibrational excitation of an intrinsic mode of a sample, eliminating the need for addition of an exogenous matrix. From a practical point of view, this represents a promising new approach to the analysis of complex mixtures. From a mechanistic point of view, the optical and thermal properties of the material, which control the degree of vibrational or electronic excitation upon irradiation, were found to determine the ablation pathways, which subsequently determines the ion formation process. This degree of excitation density, which determines whether ion formation occurs under conditions of thermodynamic equilibrium or kinetic control, may or may not determine the efficiency of ion production, depending on the particular vibrational mode under consideration.
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  Chapter1.pdf 91.35 Kb 00:00:25 00:00:13 00:00:11 00:00:05 < 00:00:01
  Chapter2.pdf 298.38 Kb 00:01:22 00:00:42 00:00:37 00:00:18 00:00:01
  Chapter3.pdf 407.29 Kb 00:01:53 00:00:58 00:00:50 00:00:25 00:00:02
  Chapter4.pdf 605.29 Kb 00:02:48 00:01:26 00:01:15 00:00:37 00:00:03
  Chapter5.pdf 375.01 Kb 00:01:44 00:00:53 00:00:46 00:00:23 00:00:02
  Chapter6.pdf 62.65 Kb 00:00:17 00:00:08 00:00:07 00:00:03 < 00:00:01
  Front_Matter.pdf 104.51 Kb 00:00:29 00:00:14 00:00:13 00:00:06 < 00:00:01

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