DOI
https://doi.org/10.25772/HXRN-6A70
Defense Date
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Dr. Katharine Tibbetts
Second Advisor
Dr. Sally Hunnicutt
Third Advisor
Dr. Supathorn Phongikaroon
Fourth Advisor
Dr. Vladimir Sidorov
Fifth Advisor
Dr. Dusan Bratko
Abstract
Energetic materials and the unimolecular dissociation dynamics attributed to their initiation and subsequent bimolecular detonation have been a subject of interest for defense agencies such as the Department of Defense (DoD) for decades. The timescale in which these initial dynamics exist ranges from several picoseconds to dozens of femtoseconds, necessitating equally fast time-resolved experiments to capture and characterize these events. Our lab specializes in one such laser-based technique: femtosecond time-resolved mass spectrometry (FTRMS). FTRMS is an essentially nondiscriminatory pump-probe laser technique with nearly infinite modifications via pulse shaping, intensity, and wavelength modulation that can readily examine previously undefined dissociation pathways in energetic species, all while maintaining high mass resolution. The pump-probe experiments ionize the molecule and then induce selective fragmentation by populating electronic excited states. Measuring the resulting dissociation products will increase overall comprehension of the chemical reaction mechanisms and the timescales under which they operate. Not only have we FTRMS to probe dynamics of energetic molecules such as explosive simulants on the several dozen femtosecond timescale, but we also applied these same dynamics to quantify the composition of mixtures of nitrotoluene isomers. Finally, we have built a front-loading chamber that utilizes separate femtosecond desorption and postionization lasers to overcome the dependence on sample volatility. Various metals have been ablated and gases introduced to the chamber to both provide preliminary data as well as for optimization of ion collection and optics alignment. The end goal is to empirically capture the elusive initiation precursor ions of explosive molecules such as TNT, RDX, TATB, and HMX.
Rights
© Shane L McPherson 2023
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
8-11-2023
Included in
Analytical Chemistry Commons, Computational Chemistry Commons, Physical Chemistry Commons