Hernández Cordero, Neiza M.

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    Ab initio treatment of the RDX-siloxane site surface of clay minerals
    (2006) Hernández Cordero, Neiza M.; Mina, Nairmen; College of Arts and Sciencies - Sciences; Castro, Miguel E.; Hernández Rivera, Samuel P.; Department of Chemistry; Briano, Julio
    The identification of landmines in soil is actually a particular problem around the world. One of the high explosives studied in the past few years is hexahydro-1,3,5-trinitro-s-triazine as well know as RDX. In this work, interactions of RDX with the basal siloxane surface of the clay mineral kaolinite has been perform using computational modeling (Gaussian 03), in order to determine the spectroscopic signature of RDX adsorbed onto clay minerals. In the first part of this work, we performed the optimization geometry and vibrational analysis of three lower-energy conformers. The three lower-energy conformers are distinguished by the arrangement of the nitro groups relative to the triazine ring of the RDX molecule. Two of these conformers have C₃ᵥ symmetry which corresponds to β form, while the third conformer has Cₛ symmetry and corresponds to the α form. The best results, in the optimization of the three conformers were perform using density functional methods (DFT) at the B3LYP/6-311+G (d,p) level of theory. These theoretical calculations were compared to experimental results obtained for the RDX explosive using the FT-IR technique. We also studied the solvation effects on the lowest-energy conformation of RDX molecule. In the second part of this work we used the lowest energy conformation of RDX to carry out the interaction with the siloxane surface. The results point out that the nitro group in pseudo-equatorial position interacts with the siloxane surface. HF, DFT//HF and MP2//HF levels of theory with basis set superposition error (BSSE) correction were perform to obtain the binding energies (E𝘣) and the contribution of dispersion interaction to the binding energies (DE𝘣). The E𝘣 decrease by a factor of ~1.5 once we applied the BSSE correction at different basis sets. Furthermore, the results indicate a decrease in the E𝘣 (~ 13 kJ/mol) when polarization functions (6-31G (d), 6-31G (d,p), 6-311G (d) and 6-311G (d,p)) are added. The calculated binding energy of the RDX-siloxane surface complex is ~ 57 kJ/mol using MP2//HF/6-31+G (d) level of theory and basis set, respectively.