| Computational chemistry has been very useful to study the properties of explosives and molecular interactions between explosives and different types of soils. In this work, we used a computational treatment to calculate the properties of 2,4,6-trinitrotoluene (TNT) and its interactions with clay minerals such as kaolinite. In the first part, we performed a geometry optimization, vibrational analysis and solvation effect on the TNT molecule. In the second part, the intermolecular interaction energy, and the vibration frequencies were calculated for the complex of TNT and the siloxane surface of kaolinite. These calculations were made in order to determine the spectroscopic signature of TNT and the possible changes when the TNT interacts with water and soil. The results obtained for the first part show two lower energy conformers for TNT (Cs and Cl). Comparison of the calculated energy of the two structures using several basis sets reveals that, the lowest-energy geometry for the TNT structure corresponds to Cs symmetry with B3LYP/6-311+G** level of theory and basis set, respectively. Experimental IR spectra of TNT are presented and assigned assisted by theoretical spectra obtained using the B3LYP/6-311+G** level of theory and basis set, respectively. In the second part, the results provide information about the interaction energy of TNT on soil environments. The binding energy between the TNT and the siloxane surface was -38 kJ/mol, obtained with MP2/6-31+G(d) level of theory and basis set, respectively. The calculated interaction has their minimal at a separation between the two systems of 3.5 A. The theoretical IR spectra of the interaction was obtained with DFT/B3LYP method and the 6-31+G(d) basis set. The spectra calculated predicted a shifting effect in NO2 bands, due to the interaction. The frequency shifts were compared and confirmed with experimental spectra obtains with IR spectroscopy. |
