Ultrafast Reaction Dynamics of Nitro-Organic Molecular Cations

Shock initiation of energetic materials produces cations and anions that can contribute to the initial endothermic chemical reactions leading to detonation. Despite their potential importance, these transient charged species are difficult to detect in detonation experiments and often ignored in molecular dynamics modeling of shocked energetic materials. The pump-probe technique of femtosecond time-resolved mass spectrometry (FTRMS) and complementary theoretical calculations can unravel initial unimolecular dissociation reactions of transient cationic species on femtosecond-picosecond timescales. Here, we report the insights gained into sub-picosecond reaction timescales from FTRMS measurements and quantum chemical modeling for three ionized energetic molecules: nitromethane cation, multiply charged para-nitrotoluene cations, and ethylene glycol dinitrate (EGDN) cation. Each of these cationic species undergoes one or more decomposition reactions within hundreds of femtoseconds.