Haycraft, James J.; Stevens, Lewis L.; and Eckhardt, Craig J., "The elastic constants and related properties of the energetic material cyclotrimethylene trinitramine (RDX) determined by Brillouin scattering" (2006 The acoustic phonons of cyclotrimethylene trinitramine ͑RDX͒ have been studied using Brillouin scattering. The analysis of the acoustic-phonon velocities allowed determination of the complete stiffness tensor for this energetic material. The results are compared to other recent experimental and theoretical determinations of the RDX elastic constants, bulk moduli, and shear moduli. The observed ordering of elastic constants, C 11 Ͼ C 22 Ͼ C 33 , is qualitatively associated with a ͑001͒ cleavage plane and molecular packing. This interpretation is further corroborated by the linear compressibilities plotted in three crystallographic planes, and a comparison to recent theoretical and experimental hydrostatic compression studies on RDX. Finally, the elasticity of RDX is compared to a recently published report on the beta polymorph of cyclotetramethylene tetranitramine's elasticity, and is related to several proposed mechanisms for detonation initiation.

The single-crystal, polarized, Raman spectra for cyclotrimethylene trinitramine ͑RDX͒ have been studied at room temperature and pressure over the region of 5 -3400 cm −1 . While the observed Raman bands agree well with a previous Raman study, this work provides a consistent interpretation of the Raman spectra by assignment of fundamental modes, overtones, and combination bands. A total of 56 internal vibrations were observed, 36 of which were labeled as fundamental molecular vibrations. In addition, all 24 lattice optical phonons are identified. All six possible polarizations were probed to obtain the A g , B 1g , B 2g , and B 3g symmetry modes for both the lattice and molecular modes. Finally, the importance of these phonons for coupling with "doorway" Raman-active modes of RDX is discussed in relation to proposed mechanisms for detonation initiation.

The acoustic phonons of the epsilon polymorph of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.0(5,9).0(3,11)] dodecane (epsilon-CL-20) have been studied using Brillouin scattering spectroscopy. Analysis of the acoustic phonon velocities allowed determination of the complete stiffness tensor for this energetic material. The results are compared to a theoretical determination of the epsilon-CL-20 elastic constants, bulk moduli, and shear moduli. The observed ordering of elastic constants, C(22)>C(33)>C(11), is noted to be different from other nitramine energetic materials. Finally, the elasticity of epsilon-CL-20 is compared to recently published reports on cyclotrimethylene trinitramine's (RDX) elasticity and the beta polymorph of cyclotetramethylene tetranitramine's (beta-HMX) elasticity.

The single-crystal polarized Raman spectra for cyclotetramethylenetetranitramine, -polymorph ( -HMX), are reported over the region of 10 to 3150 cm -1 . While the agreement with previous Raman studies is quite good, a consistent interpretation of the Raman spectra is provided through assignment of fundamental modes, overtones, and combination bands. This affords the first assignment of all six Raman-active optical phonons of -HMX. It was found that three A g symmetry librations are accidentally degenerate with three B g optical phonons. The importance of these phonons for coupling with "doorway" Raman-active modes of -HMX is discussed in relation to proposed vibrational mechanisms for the initiation of detonation.