Recently, terahertz spectroscopy has attracted increasing interest as a probe of organic molecular crystals such as
pharmaceutical compounds and explosives. Terahertz time-domain spectroscopy (THz-TDS) focuses on low-frequency
(10-120 cm<sup>-1</sup>) intermolecular modes that are characteristic of the crystal structure. The prospect of material-specific
identification, combined with the ability of THz light to penetrate many common materials, has lead to an emphasis on
the prospect of a THz-based, standoff explosives detection device. In this presentation, THz spectra of materials
ranging from military-grade explosives to home-made explosive components will be discussed. In addition to the
experimental results, THz spectral assignments will be presented based on solid-state density functional theory
simulations. Finally, the effect of particle size on the observed spectra will also be considered.
We report on the transmission and reflection terahertz (THz) spectra of the high explosives RDX and PETN. These
common military explosives are compared to simulants L-tartaric acid and sucrose, respectively. The use of these
simulants enables researchers to develop many aspects of THz spectroscopy for explosives detection without the need
for live explosives. Further, we discuss the effect of sample preparation on the THz spectrum of RDX and demonstrate
that experiments performed on different terahertz instruments at multiple laboratories show quantitative agreement
between spectra recorded with four different instruments.
We report on THz spectra of RDX obtained from various domestic and international sources. The observed spectral
differences can be traced to the method of RDX manufacture. Depending on the method of manufacture, the resulting
energetic material will contain imperfections within the crystal such as voids, solvent trapped within the voids,
crystalline dislocations, explosive mixtures and co-crystallization of other energetic byproducts. Additionally, neat
energetic material crystallites often range from tens to hundreds of microns. To investigate these phenomena,
transmission and reflection mode THz spectroscopy was performed. The resulting spectral differences are interpreted in
an attempt to identify material and contaminant effects.