High pressure Raman scattering and synchrotron X-ray diffraction studies of benzyl azide

Benzyl azide was investigated by high-pressure Raman scattering spectroscopy and X-ray diffraction technologies. A complete vibrational analysis of benzyl azide was performed by combining the experimental measurements and theoretical calculations using DFT-based scaled quantum chemical approach. The high-pressure Raman spectra and calculation results indicate that benzyl azide underwent a conformational change at 0.67 GPa accompanied by rotation of methylene group and azide group. The frequency of the CH2 bending mode decreases with increasing pressure due to the increase of the C-H···π interactions, which is similar to the role of the hydrogen bond. A liquid to solid phase transition occurred at 2.7 GPa, which was confirmed by the X-ray diffraction measurements. As the pressure reached 25.6 GPa, all the azide group vibrations vanished, indicating that the decomposition pressure of the molecular azide groups in organic azides is lower than that of the azide ions in inorganic azides.