MOLECULAR-DYNAMICS SIMULATIONS OF RING INVERSION IN RDX

Molecular dynamics simulations, using the finite volume method of Murr ell and co-workers [J. Chem. Phys. 94, 3908 (1991)], have been carried out to study conformational changes in hexahydro-1,3,5-trinitro-1,3,5 -triazine (RDX) in isolation and in dense Xe gas. The configurational distributions for RDX in a Xe bath and in the gas-phase are markedly d ifferent. The results show that as the solvent concentration increases , the concentration of RDX molecules in the boat conformation increase s by a factor of about 4. The rate constant for the chair-->boat ring inversion was calculated as a function of the xenon concentration [Xe] . The rate constant obeys Lindemann behavior at low concentrations, i. e., it increases with increasing solvent density. At [Xe] approximatel y 6.2 mol dm-3, the rate constant reaches a maximum (Kramer's turnover ) and becomes a decreasing function of the solvent concentration. For [Xe] above 16.2 mol dm-3, the rate constant again increases as a funct ion of the solvent density.