Insight into the chemistry of TNT during shock compression through ultrafast absorption spectroscopies

Abstract

Thin films of trinitrotoluene (TNT) were shock compressed using the ultrafast laser shock apparatus at Los Alamos National Laboratory. Visible (VIS) and mid-infrared (MIR) transient absorption spectroscopies were simultaneously performed to probe for electronic and vibrational changes during shock compression of TNT. Three shock pressures (16 GPa, 33 GPa, and 45 GPa) were selected to observe no reaction, incipient reaction, and strongly developed reactions for TNT within the experimental time scale of <250 ps. Negligible absorption changes in MIR or VIS absorptions were observed at 16 GPa. At 33 GPa, MIR absorptions in the 3000 cm−1–4000 cm−1 range were observed to increase during the shock and continue to increase during the rarefaction, in contrast to the VIS absorption measurements, which increased during the shock and almost fully recovered during rarefaction. At 45 GPa, both VIS and MIR absorptions were strong and irreversible. The intense and spectrally broad MIR absorptions were attributed to short lived intermediates with strong, spectrally broad absorptions that dominate the spectral response. The MIR and VIS absorption changes observed at 33 GPa and 45 GPa were credited to shock induced chemistry, most likely including the formation of a very broad hydrogenic stretch feature. The results from these experiments are consistent with the chemical mechanisms that include O–H or N–H formation such as CH3 oxidation or C–N homolysis.

Shock Pressure Dependence of Hot Spots in a Model Plastic-Bonded Explosive

“…Most current reactive models are calibrated against macro-scale experiments measuring bulk PBX behavior where the behavior of individual hot spots must be inferred rather than measured, or experiments at pressures and temperatures far below detonation. ,, On the microscale, ultrafast spectroscopic shock techniques approach measuring reaction kinetics with picosecond resolution although short shock durations (<1 ns) and spatially averaged integration currently limit their ability to address energy localization at the microstructure. − …”

Developing Reaction Chemistry Models from Reactive Molecular Dynamics: TATB

“…While the later time (and lower pressure) reactions in propellant combustion flame structures can be well-studied, the initial processes in the condensed phase are more conjectural [8][9][10][11]. The direct observation of reaction processes in solid materials, particularly under shock-loading, has proven to be quite difficult, being frustrated by optical constraints and the rapid reaction rates at appropriate conditions [18][19][20]. The limited chemical information available is currently insufficient to develop or test multistep models.…”

Mode-Selective Vibrational Energy Transfer Dynamics in 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) Thin Films

“…While there is rich literature investigating shockwave-induced processes in reactive and inert solids (see refs − for recent examples), little experimental work exists − on fundamental vibrational dynamics in solid, neat EMs that shed light on VET through strongly coupled, delocalized vibrational modes. Much of the existing VET research is performed in EM mimics and model systems (e.g., liquid nitromethane , ) or solvated energetics (see refs − for examples), where the importance of phonon-mediated long-range interactions that form the basis for a complete picture of VET in EMs is not captured, leading to observed dynamics that are not representative of the dynamics in solid EMs. , Furthermore, the molecular conformation of solvated energetics can be different from that in extended EM solids, resulting in differences in the nature of intermolecular interactions and vibrational coupling.…”