High-Pressure Vibrational Spectroscopy of Energetic Materials:  Hexahydro-1,3,5-trinitro-1,3,5-triazine

Abstract

Vibrational spectroscopy has been used to investigate the room-temperature high-pressure phases of the energetic material hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The pressure-induced alterations in the spectral profiles were studied in a compression sequence to 30.2 GPa using Raman spectroscopy and to 26.6 GPa using far-infrared spectroscopy. At pressures near 4.0 GPa, several changes become immediately apparent in the Raman spectrum, such as large frequency shifts, mode splittings, and intensity changes, which are associated with a phase transition from alpha-RDX to gamma-RDX. Our study extends the kinetic stability of gamma-RDX to pressures near 18.0 GPa. Evidence for a new phase was found at pressures between 17.8 and 18.8 GPa and is based on the appearance of new vibrational bands and associated changes in intensity patterns. The new phase has vibrational characteristics that are similar to those of beta-RDX, suggesting the two polymorphs share a related crystal structure.

Pressure-Induced Phase Transition in Hydrogen-Bonded Supramolecular Adduct Formed by Cyanuric Acid and Melamine

“…The blue shift observed for external modes is to be expected since the strength of the interactions between the adjacent molecules should increase with the reduction of intermolecular distances. [41][42][43][44] At the same time, the intensity of the mode at 152 cm -1 reduced significantly with the increase of pressure. Furthermore, an abrupt change in the spectrum shape, which can be visualized as evidence for the pressureinduced phase transition, was observed at about 4.4 GPa.…”

Density functional theory calculations of anisotropic constitutive relationships in alpha-cyclotrimethylenetrinitramine

“…2 The hydrostatic equation of state ͑EOS͒ of RDX at room temperature was obtained by Olinger et al 3 and Yoo et al 4 Both experiments 3,4 found a phase transition from ␣-RDX to ␥-RDX near 4 GPa. Subsequently, Raman spectroscopy has been employed for a detailed investigation of RDX at pressures up to about 4 GPa by Ciezak et al 6 and Dreger and Gupta, 7 who found features in the spectra that are associated with the phase transition at this pressure. Very recently, the structure of the ␥ polymorph has been reported by Davidson et al 8 using a combination of x-ray and neutron diffraction.…”

Monitoring the α→β solid–solid phase transition of RDX with Raman spectroscopy: A theoretical and experimental study

“…In the solid-state, RDX exists in five polymorphic phases, termed a [1,2], b [3,4], c [5][6][7][8], d [9] and e [10]. Previous works have established a phase as the st form at room temperature, where the six-membered ring RDX molecules posses essentially C s symmetry with two of the NO 2 groups axial and the third equatorial with respect to the triazine ring [11,12].…”