Terahertz Spectroscopy of the Explosive Taggant 2,3-Dimethyl-2,3-Dinitrobutane

Abstract

The terahertz spectrum of the crystalline explosive taggant 2,3-dimethyl-2,3-dinitrobutane (C(6)H(12)N(2)O(4)) has been investigated as an alternative means of detecting solid-state explosives. The room-temperature spectrum exhibits two broad absorption features centered at 38.3 and 49.2 cm(-1). Once the sample is cooled to liquid-nitrogen temperatures, the resolution of three additional peaks occurs, with absorption maxima now appearing at 40.1, 47.5, 56.6, 63.9, and 73.6 cm(-1). Solid-state density functional theory simulations, both with and without London force dispersion corrections, have been used for the assignment of the experimental cryogenic THz spectrum to specific molecular motions in the crystalline solid. The B3LYP hybrid density functional paired with the 6-311G(2d,2p) basis set provides an excellent reproduction of the experimental data revealing that the THz spectrum arises from a mixture of intramolecular torsional vibrations localized primarily in the nitro groups and intermolecular lattice vibrations composed of rigid molecular rotations.

First-Principles Calculation of Terahertz Absorption with Dispersion Correction of 2,2′-Bithiophene as Model Compound

“…Organic materials show specific absorption characteristics in the terahertz frequency region (0.1–10 THz), which are important for spectroscopic research and applications such as characterization and identification of explosives, − drugs, − and biological materials. − THz spectroscopy and imaging are also important for identification of defects and inclusions in organic materials. Nonlinear optical organic materials are additionally very important materials for THz wave generation using infrared and near-infrared pump laser sources. , Their figures of merit for THz generation and detection are more than 1 order of magnitude higher compared to their inorganic alternatives, which is due to their high nonlinear optical susceptibilities combined with a low dielectric dispersion from the low-frequency to the optical frequency range.…”

Dielectric Properties of Ethanol and Gasoline Mixtures by Terahertz Spectroscopy and an Effective Method for Determination of Ethanol Content of Gasoline

“…The THz region (0.05–10 THz) exists between microwave and infrared regions, where 1 THz is equivalent to 300 μm, 33.3 cm –1 , or 0.004 eV. THz spectroscopy has been successfully applied in molecular spectroscopy of gases, liquids, , solids, , biological samples (such as DNA and proteins), , and explosives − or in many more areas such as astronomy and communication . Some of the common advantages of the use of time-domain techniques with ultrafast pulses in terahertz spectroscopy can be listed as coherent and fast measurement with high signal-to-noise (S/N) ratio, large spectral bandwidth enabling ultrafast dynamic studies of materials, room temperature measurement capability, determination of complex permittivity through direct measurement of electric field, convenient absorption measurement of both weakly and strongly absorbing materials, no knowledge requirement of optical constants of supportive materials, and also the possibility to obtain experimental data of solvent response to solute at nonideal conditions (high concentrations), which is critically important for correct modeling of mixture solutions.…”

Advances in explosives analysis—part II: photon and neutron methods

“…Likewise, the spectral signatures of explosive mixtures and plastic compositions have been studied [26][27][28][29][30][31][32][33]. Additionally, spectral signatures of homemade explosives and related materials have been analyzed [34][35][36]. Using THz TDS for stand-off detection, where the operator is physically separated from the sample, has also been investigated [25,31].…”