The Detection of Energetic Materials by Laser Photoacoustic Overtone Spectroscopy

Abstract

Laser-based sensors offer high sensitivity and species selectivity with real-time capabilities for monitoring the vapors of some energetic materials. However, the extremely low vapor pressure of many solid energetic materials under ambient conditions impedes these sensors. In this paper, we report on a novel technique based on laser photoacoustic overtone spectroscopy to detect and differentiate solid 1,3,5-trinitrotoluene (TNT), 1.3.5-trinitro-1,3,5-triazacyclohexane (RDX), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) in real time at ambient conditions. A tunable, near-infrared laser excites the target compound in the spectral region between 5800 to 6100 cm−1, and a microphone monitors the sound that they generate by non-radiative, collisional de-excitation processes. The photoacoustic signals result from first-overtone and combination absorptions of the energetic material's C–H vibrations, and the collisional processes enhance the signal at atmospheric pressure. The spectra reveal features that are unique to each measured material and these features can serve as a fingerprint for that material. We report the effects of laser energy and wavelength on signal intensity and estimate a detection limit for these compounds.

Predicting Solubility of Military, Homemade, and Green Explosives in Pure and Saline Water using COSMO‐RS

“…The aqueous solubility is also important for explosive detection; a primary transport mechanism for vapors from buried explosives or landmines is upward advection due to evaporation of soil water [10]. Accurate solubility data, including the effects of inorganic salts in saline environments, are needed to understand the fate, extraction, and detection of these compounds [1,10,13,[17][18][19][20][21].…”

Comprehensive Infrared Study of Tetryl, Dinitrotoluene, and Trinitrotoluene Compounds

“…When comparing the present results to data reported by literature in similar papers, 48,49 some differences emerge from the comparison; nevertheless we found a complete agreement among LPAS, IR, and calculated frequencies in our results. The LPAS overtone spectroscopy of TNT published in a recent paper 50 was performed in the 6000 cm −1 region, and this does not allow a direct comparison with our LPAS data.…”

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

“…Photoacoustic spectroscopy is selective (characteristic rotational and vibrational absorption) and sensitive (~1 ng TNT [204]), and can be used without sample preparation. It is also advantageous because it is not sensitive to light scattering caused by the substrate, but only to absorption of optical radiation [204].…”

“…It is also advantageous because it is not sensitive to light scattering caused by the substrate, but only to absorption of optical radiation [204]. However, care must be taken to ensure there are not interferences from other substances including atmospheric gases [205], other explosives, and background noise [206].…”