Characterization of Ultrafast Decomposition Dynamics in Nitrate Esters

ABSTRACT Ignition of energetic materials initiates chemical reactions on atomic length scales within femtoseconds, making these reactions difficult to investigate experimentally. The technique of femtosecond time‐resolved mass spectrometry (FTRMS) can capture molecular rearrangement and bond‐breaking events in isolated molecules with sub‐50 femtosecond resolution. Coupled with quantum chemical and molecular dynamics computations, the extremely fast temporal resolution of FTRMS enables direct observation of initial unimolecular reaction dynamics that contribute to ignition of energetic materials. This work reports dissociation dynamics for the nitrate esters amyl nitrate (), ethylene glycol dinitrate (EGDN, ), and nitroglycerin (NG, ) following photoionization. Compared to the cation lifetime of 230 fs or longer for amyl nitrate, the EGDN and NG cations decompose on timescales as fast as 40 fs. Moreover, NG cations generally dissociate faster than EGDN cations, with 95% of NG cations dissociating within 60 fs. These trends in the decomposition rates in nitrate ester cations are found to be correlated with the energy released by geometric relaxation upon electron loss.