Reinvestigation of the Gas-Phase Structure of RDX Using Density Functional Theory Predictions of Electron-Scattering Intensities

Abstract

Density functional calculations at the B3LYP/6-31G* level are used to generate electron-diffraction intensity curves for six conformers of hexahydro-1,3,5-trinitro-s-triazine (RDX). These are compared with an experimental curve (Shishkov, I. F.; Vilkov, L. V.; Lolonits, M.; Rozsondai, B. Struct. Chem. 1991, 2, 57) for which a structural model of gas-phase RDX was proposed. The calculations were done to investigate possible causes of the discrepancies between the theoretical structures and the molecular model proposed by Shishkov et al. The results show that alternative structures to that proposed from experiment can reproduce the measured intensities. Also, barriers to interconversion between the conformers were calculated to investigate the possibility of rapid interconversion at the temperature of the experiment (433 K). Barriers range from 1.5 to 5 kcal/mol, suggesting that measurements of RDX in the gas phase might reflect a dynamically averaged structure that represents contributions from the individual conformers.

Nuclear fukui functions and the deformed atoms in molecules representation of the electron density: Application to gas‐Phase RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐ triazine) electronic structure and decomposition

“…Therefore, gas-phase RDX has probably the three lowest energy conformers-AAE, AAA, and AEE-interconverting among each other. The same energy ordering and similar relative energies were previously obtained by other researchers [13,25].…”

“…Frequency calculations confirmed the minimum character of each structure. Comparisons with previous calculations provided further confirmation of the converged geometries [25]. Single-point calculations for the cation and anion of each conformer, using the optimized ground state geometry, were carried out at the same calculation level.…”

Ab initio study of coherent anti-Stokes Raman scattering (CARS) of the 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) explosive

“…The conformations differ by the arrangement of the nitro groups relative to the ring atoms of the RDX molecule. It was shown that the most stable conformer in gas phase was the one belonging to the C 3m point group, namely the AAA conformer [32][33][34]. The spectra presented in the present work are obtained for this conformer (see Fig.…”

“…[32]. The conformations differ by the arrangement of the nitro groups relative to the ring atoms of the RDX molecule.…”

Hyper Raman spectra calculated in a time-dependent Hartree–Fock method

“…In our recent work [11], we found that the RDX molecule with AAA conformer [24][25][26] is the most stable one among six different possible molecular conformations. In fact, test calculations on a different conformer showed significant changes in the spectra, …”