Defense Date
2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Dr. Katharine Tibbetts
Abstract
Shock initiation of energetic materials produces cations and anions that can contribute to initial endothermic chemical reactions which lead to detonation. Hence, knowledge of the initial dissociation pathways of ionized energetic molecules is important for advancing the understanding of initiation mechanisms and meeting longstanding goals of the Department of Defense. Despite their potential importance, these transient charged species are difficult to detect in detonation experiments and are often ignored in molecular dynamics modeling of shocked energetic materials. However, the technique of pump-probe femtosecond time-resolved mass spectrometry (FTRMS) paired with complementary theoretical calculations can be used to elucidate initial unimolecular dissociation reactions of energetic materials on the femtosecond-picosecond timescales.
In this work, the results of three FTRMS studies on the isomers of nitrotoluene, model compounds for the secondary high explosive trinitrotoluene (TNT), are reported. Here, we have successfully quantified isomers in mixture, induced selective fragmentation to manipulate fragmentation patterns, and explored the lifetimes of multiply charged cations produced under high-intensity laser shock conditions. FTRMS is inherently a gas phase technique and as a result, cannot investigate secondary high explosives themselves due to their low vapor pressures. To combat this limitation, a novel laser desorption and postionization FTRMS instrument was constructed wherein solid samples of TNT, RDX, HMX, etc. can be desorbed into the gas phase for FTRMS measurements. The latter portion of this work reports the current efforts to optimize this instrument towards its intended goals of detecting intact parent molecular ions of secondary high explosives and elucidating their initial dissociation pathways for the first time.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
4-5-2024