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A: Spectroscopy, Molecular Structure, and Quantum Chemistry
New High Pressure Phases of Energetic Material TEX: Evidence from Raman Spectroscopy, X-ray Diffraction and First Principles Calculations Rajitha Rajan, Ravindran Ramamoorthy Thoguluva, Venkatesan Vaidyanathan, Srihari Velaga, Krishan Kumar Pandey, Sharat Chandra, Karuna Kara Mishra, and Anuj A Vargeese J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b04868 • Publication Date (Web): 27 Jun 2018 Downloaded from http://pubs.acs.org on June 29, 2018
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The Journal of Physical Chemistry
New High Pressure Phases of Energetic Material TEX: Evidence from Raman Spectroscopy, X-ray Diffraction and First Principles Calculations Rajitha Rajan^, T. R. Ravindran^*, V. Venkatesan**, V. Srihari#, K. K. Pandey#, Sharat Chandra^, Karuna Kara Mishra^†, Anuj A. Vargeese‡ ^Materials Science Group, HBNI, Indira Gandhi Centre for Atomic Research, Kalpakkam- 603102, India ** Research & Innovation Centre, DRDO, 5th Floor, IIT Madras Research Park, Taramani, Chennai- 600 113, India # High pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai- 400085, India ‡ Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Telangana State, Hyderabad- 500 046, India ABSTRACT: Samples of energetic material TEX (C6H6N4O8) are studied using Raman spectroscopy and X-ray diffraction (XRD) up to 27 GPa pressure. There are clear changes in the Raman spectra and XRD patterns around 2 GPa related to a conformational change in the TEX molecule, and a phase transformation above 11 GPa. The molecular structures and vibrational frequencies of TEX are calculated by density functional theory based Gaussian 09W and CASTEP programs. The computed frequencies compare well with Raman spectroscopic results. Mode assignments are carried out using Vibrational Energy Distribution Analysis program, and also visualized in the Materials Studio package. Raman spectra of the high pressure phases indicate that the sensitivity of these phases is more than that of the ambient phase.
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INTRODUCTION
Energetic materials release hundreds of kilojoules of energy per mole in micro to nano seconds under appropriate stimuli such as impact, heat, and shock. Such materials can be broadly classified into explosives, propellants, and pyrotechnics. Explosives are further classified as primary or secondary. Primary explosives are more sensitive to external stimuli and generate a short and strong shock wave on initiation whereas secondary explosives need a strong stimulus in the form of a shock wave from a primary explosive to detonate1. Detonation process generates high pressures of the order of 40 GPa and temperatures of ∼5000 K2, resulting in phase transformations including decomposition of the parent phase. The physics and chemistry of shockwaves leading to explosive reactions and the extent of sensitivity of explosives are extensively explored, and continue to be hot areas of research3. Mechanical energy is known to be conveyed to low energy intermolecular vibrations and thereafter transferred to high energy internal modes through multiphonon up-pumping processes4-9. Low energy lattice phonons (
