121. Probing the Reaction Mechanisms Involved in the Decomposition of Solid 1,3,5-Trinitro-1,3,5-Triazinane (RDX) by Energetic Electrons

Santosh Kumar Singh, Cheng Zhu, Vasant Vuppuluri, Steven F. Son, and Ralf I. Kaiser, Journal of Physical Chemistry A, (2019) DOI: 10.1021/acs.jpca.9b08695

The decomposition mechanisms of RDX have been explored over the past decades, but as of now, a complete picture on these pathways has not yet emerged as evident from the discrepancies in proposed reaction mechanisms and the critical lack of products and intermediates observed experimentally. This study exploited a surface science machine to investigate the decomposition of solid-phase RDX by energetic electrons at a temperature of 5 K. The products formed during the irradiation were monitored online and in situ via infrared and UV-VIS spectroscopy, and products subliming in the temperature programmed desorption phase were probed with a reflectron time-of-flight mass spectrometer coupled with a soft photo-ionization at 10.49 eV (ReTOF-MS-PI). The infrared spectroscopy revealed the formation of water (H2O), carbon dioxide (CO2), dinitrogen oxide (N2O), nitrogen monoxide (NO), formaldehyde (H2CO), nitrous acid (HONO) and nitrogen dioxide (NO2). ReTOF-MS-PI identified 38 cyclic and acyclic products arranged into, e.g., dinitro, mononitro, mononitroso, nitro-nitroso, and amines species. Among these molecules, 21 products such as N-methylnitrous amide (CH4N2O), 1,3,5-triazinane (C3H9N3) and N-(aminomethyl)methanediamine (C2H9N3) were detected for the first time in laboratory experiments; mechanism based on gas phase and condensed phase calculations were exploited to rationalize the formation of the observed products. The present studies reveal a rich, unprecedented chemistry in the condensed phase decomposition of RDX, which is significantly more complex than the unimolecular gas phase decomposition of RDX thus leading us closer to an understanding of the decomposition chemistry of nitramine-based explosives.