Vibrational Spectroscopy Study of β and α RDX Deposits

Abstract

Deposits of β and α RDX on glass substrates have been examined with optical and Raman microscopy. The measurements reveal significant differences in the morphology and Raman spectra of β and α RDX. Structures that resemble an island, as well as scattered particles, are observed in white light images of β RDX. Well-defined crystals are observed in white light images of α RDX. The spectroscopic signature of these forms of RDX has marked differences in Raman frequencies and relative intensities. The transition from β to α RDX is driven by the amount of RDX deposited. There is a close agreement between measured and calculated vibrational frequencies for β and gas-phase RDX. A poor correlation is found between measured and predicted Raman intensities and depolarization ratios for β and gas-phase RDX, respectively. These differences lead us to conclude that the properties of β and gas phase RDX are markedly different, despite the similarities in the vibrational frequencies.

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“…(3) and the average difference in assigned peaks in spectral range 0-4270 cm -1 is about 2 cm -1 . Standoff spectrum of C4 is in a good agreement with the spectrum obtained by other authors [5][6][7][8][9] and the average difference in assigned peaks in spectral range 0 -4270 cm -1 is about 2 cm -1 . One of the aims of the study is to study the influence of integration time and laser power on Raman cross section and to determine the integration time and laser power at which the optimal signal to noise (S/N) ratio is achieved for standoff Raman spectra.…”

Standoff Raman Spectroscopic Detection of Explosive Molecules

“…The peak shape at the region from 2900 to 3100 cm −1 convinced that the our RDX sample was α polymorph, which was known to be the most stable form in the room tempertaure. 12 The HMX sample was also measured at confocal Raman microscope. The result was shown in Figure 4(c).…”

Hyperspectral microscopy of explosives particles using an external cavity quantum cascade laser

“…For example, formation of RDX α-and β-crystalline phases has been observed to depend on the amount of RDX deposited from solutions onto surfaces, and different infrared spectral properties have been observed for the two phases. 26 The examples of explosives particles and residues in this manuscript are not intended to present a comprehensive study of particle size and sample preparation techniques for explosives detection; however, similar applications of the hyperspectral microscopy technique would be valuable for future systematic studies of the dependence of the infrared spectrum on particle morphology. For the examples presented in this manuscript, two sample preparation methods were used.…”