INTERACTIONS OF α-RDX WITH THE SILOXANE SITE SURFACE: A COMPUTATIONAL MODELING APPROACH

摘要

Interactions of a-RDX, with the basal siloxane surface of the clay mineral kaolinite has been perform in our laboratory using the Gaussian 03 computational package. The low energy conformation of α-RDX (89.1 kcal/mol) was used to carry out the interaction with the clay mineral using the Hartree Fock (HF), DFT, DFT∥HF, MP2, and MP2∥HF levels of theory in order to determine the orientation, the types of bonds reacting between the two molecules and the adsorption as well. The results point out that the nitro group in pseudo-equatorial position interacts with the siloxane surface. DFT∥HF level and Basis Set Superposition Error (BSSE) corrected MP2∥HF were perform to obtain the binding energies (E_b) and the contribution of dispersion interaction to the binding energies (DE_b). The E_b using DFT∥HF level of theory between those molecules fluctuate in a range of 38 to 51 kJ/mol once we applied the BSSE correction at different basis sets. Furthermore the results indicates a decrease in the Eb/BSSE (DFT∥HF) of ～13 kJ/mol when polarization functions are added. The calculated binding energy of the RDX-siloxane surface complex is ～57 kJ/mol using MP2∥HF/6-31+G (d) model chemistry. Studies of theoretical IR spectra of the interaction were obtained with DFT∥HF methods and the 6-31+G(d) basis set with a small molecular model (single tetrahedra). The calculation predicted a band shift effect in the region of 1200-1800 cm~(-1), due to interactions of the α-RDX with the siloxane surface.