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25 September 2007 Ab initio calculation of Raman vibrational signatures of 2,4-dinitrotoluene, 2,6-dinitrotoluene and 2,4,6-trinitrotoluene
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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 Sadlejs 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 NO2 symmetric stretching and bending frequencies by more than 15 % relative to 6-311+G** basis. The potential energy distribution for the symmetric and asymmetric NO2 stretches indicates that 2-NO2 and 6-NO2 couple strongly in 2,6-DNT and 2,4,6-TNT, while 2-NO2 and 4-NO2 groups couple weakly in 2,4- DNT. These findings suggest that the coupling strength of 2-NO2, 6-NO2 and 4-NO2 groups can be used to distinguish between dinitro and trinitro toluenes.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jairo Castillo-Chara, César Manrique-Bastidas, Nairmen Mina, Miguel E. Castro, and Samuel P. Hernández-Rivera "Ab initio calculation of Raman vibrational signatures of 2,4-dinitrotoluene, 2,6-dinitrotoluene and 2,4,6-trinitrotoluene", Proc. SPIE 6756, Chemical and Biological Sensors for Industrial and Environmental Monitoring III, 67560G (25 September 2007);

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