TNT and DNT are important explosives used as base charges of landmines and other explosive devices. They are often combined with RDX in specific explosive formulations. Their detection in vapor phase as well as in soil in contact with the explosives is important in landmine detection technology. The spectroscopic signatures of nitroaromatic compounds in neat forms: crystals, droplets, and recrystallized samples were determined by Raman Microspectroscopy (RS), Fourier Transform Infrared Microscopy (FTIR) and Fiber Optics Coupled -Fourier Transform Infrared Spectroscopy (FOC-FTIR) using a grazing angle (GA) probe. TNT exhibits a series of characteristic bands: vibrational signatures, which allow its detection in soil. The spectroscopic signature of neat TNT is dominated by strong bands about 1380 and 2970 cm -1 . The intensity and position of these bands were found remarkably different in soil samples spiked with TNT. The 1380 cm -1 band is split into a number of bands in that region. The 2970 cm -1 band is reduced in intensity and new bands are observed about 2880 cm -1 . The results are consistent with a different chemical environment of TNT in soil as compared to neat TNT. Interactions were found to be dependent on the physical source of the explosive. In the case of DNT-sand interactions, shifts in vibrational frequencies of the explosives as well as the substrates were found.
2,4,6-Trinitrotoluene is a high explosive used in manufacturing landmine, bombs, and other explosive devices. It has been the main source of contamination in groundwater, soil as a result of intentional or accidental releases at many places around the world. Crystallization of TNT in soil from TNT/methanol solutions was carried out and characterized using vibrational spectroscopy. TNT exhibits a series of characteristic bands that allow its detection when in soil. The spectroscopic signatures of neat TNT and TNT in soil samples were determined with Raman Microspectroscopy and Fourier Transform Infrared (FTIR) Microscopy. The spectroscopic signature of neat TNT is dominated by strong bands about 1380 and 2970 cm -1 . The intensity and position of these bands are found remarkably different in soil samples spiked with TNT. The 1380 cm -1 band is split into a number of bands in that region. The 2970 cm -1 is reduced in intensity and new bands are observed at about 2880 cm -1 . The results are consistent with a different chemical environment for TNT in soil as compared to neat TNT. Further measurements are required to fully understand the spectroscopic signature of TNT in soil samples. Its detection in soil is essential in landmine detection technology, and could address the improvement of the devices in the mentioned technology.
The Raman vibrational frequencies in the finger print region (700-1600 cm −1 ) have been calculated for 2,4-dinitrotoluene, 2,6-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT). The Raman vibrational intensities and frequencies for these molecules have been calculated using B3LYP Density Functional Theory method with 6-311+G** and Sadlej's medium-sized polarized basis sets (Sadlej pVTZ). The normal mode assignments in the finger print region were carried out by Normal Coordinate Analysis, where localized and de-localized coordinates were used to facilitate an accurate description of the vibrational modes. The Raman intensities were calculated from the Raman scattering cross sections using the ab initio calculated Raman scattering activities. Comparison of these intensities using different basis sets indicates that the Sadlej pVTZ basis sets increase the calculated intensities for the NO 2 symmetric stretching and bending frequencies by more than 15 % relative to 6-311+G** basis. The potential energy distribution for the symmetric and asymmetric NO 2 stretches indicates that 2-NO 2 and 6-NO 2 couple strongly in 2,6-DNT and 2,4,6-TNT, while 2-NO 2 and 4-NO 2 groups couple weakly in 2,4-DNT. These findings suggest that the coupling strength of 2-NO 2 , 6-NO 2 and 4-NO 2 groups can be used to distinguish between dinitro and trinitro toluenes.
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