High-Pressure Studies of Trimethylsilane Azide by Raman Scattering and Synchrotron X-ray Diffraction

We have reported the high-pressure behavior of energetic material trimethylsilane azide ((CH₃)₃SiN₃, TMSiN₃) by in situ Raman scattering and synchrotron angle-dispersive X-ray diffraction (ADXRD) measurements in diamond anvil cells with a pressure up to ∼40 GPa at ambient temperature. The analyses of Raman spectra showed two liquid-liquid phase transitions at 0.13 and 7.9 GPa. The XRD results verified that TMSiN₃ remained in a liquid state throughout the phase transitions. In the pressure range of 0.13-2.6 GPa, the distortion of the Si-C₃ bond and the shortening of the bond between azide group and silicon atom lead to the first phase transition. The second transition is ascribed to the rotation of methyl group at 7.9 GPa. With further compression, the azide groups become increasingly asymmetric, and completely amorphous at 33.8 GPa. This paper is useful to understand the behavior of azide group and the molecular structural evolution of organic azide under high pressure. The unique high-pressure behavior of the azide group in TMSiN₃ may be useful for improving in the formation of the polynitrogen compound with azides.