Defense Date


Document Type


Degree Name

Doctor of Philosophy



First Advisor

Dr. Katharine Tibbetts


Chemists have sought to control molecular dissociation with lasers for decades. Effective control of unimolecular dissociation was only achieved with the development of high-intensity ultrashort pulsed lasers and coherent control techniques that operate on timescales faster than vibrational energy redistribution. In view of this, our lab has specialized in the study of polyatomic radical cations using femtosecond time-resolved mass spectrometry (FTRMS). The interest in radical cations stems from the fact that they are highly reactive species that contribute to many physical, chemical, and biological processes. For instance, radical cations participate in shock initiation of detonated energetic materials used as explosives and propellants. In this regard, we have studied some nitroaromatic radical cations commonly used as models for energetic materials. We discuss some results involving the dynamics of vibrational wave packets and rearrangement/fragmentation pathways.

Concerning vibrational wave packet dynamics, we employed computational chemistry to predict the most efficient probe wavelength for our experimental measurements on nitrobenzene cation demonstrating the feasibility and convenience of this approach. We also investigated pump-probe control schemes to manipulate fragmentation product yields in p-nitrotoluene (PNT) cation.

Finally, we investigated the dissociation dynamics and fragmentation pathways of o-nitroaniline, a model compound for the military explosive 2,4,6-triamino-1,3,5-trinitrobenzene (TATB). This model seems to capture the hydrogen bonding features that lead to energetically unfavorable rearrangement/fragmentation pathways in TATB. We expect that our experimental and computational results provide insights into the inherent stability of this molecule that explains the low sensitivity (and therefore relatively high safety) of TATB as an explosive.


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