Investigating high-explosives electronic structure and radiation induced decomposition by X-ray Raman scattering

Theory and modeling have long preceded experiment in the fundamental physical and chemical kinetic properties of detonation. This technical gap exists because conventional chemical analytic methods are not easily applied to the rapid processes within the tumultuous dense bulk of the detonation. Hard X-ray core-level spectroscopies give access to local electronic structure within the bulk and are sensitive to the bond nature of the X-ray excited atom. X-ray Raman spectroscopy (XRS), a core-level photon-in/photon-out hard X-ray technique, emerges as a unique tool to address these fundamental questions. XRS provides bulk sensitivity and allows investigating absorption edges of low Z elements with hard X-rays avoiding usual constraints inherent to UV/soft X-ray spectroscopies.

We present X-ray Raman spectra of static high explosives measured at the BL-15 beamline of the Stanford Synchrotron Radiation Lightsource¹, along with ab initio density functional theory calculations. By combining experimental results and theoretical calculations, spectral features and trends observed in the near-edge region of the XRS spectra were analyzed, unambiguously assigning spectral fingerprints to different moieties within the samples².  As an application of the developed experiment-theory methodology, we performed systematic XRS studies on high-explosives for different radiation doses at cryogenic temperatures. Such application may enable distinguishing undetonated systems from transient structures originating from decomposition induced by the intense x-ray radiation beam. Understanding the decomposition mechanisms under static conditions, sets the basis for future time-resolved dynamic studies of high explosives under detonation conditions.

[1] D. Sokaras, D. Nordlund, T.-C. Weng, et al , "A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource", Review of Scientific Instruments 83, 043112 (2012) https://doi.org/10.1063/1.4704458

[2] Paredes-Mellone, O.A., Nielsen, M.H., Vinson, J. et al. Investigating the electronic structure of high explosives with X-ray Raman spectroscopy. Sci Rep 12, 19460 (2022). https://doi.org/10.1038/s41598-022-24066-z