Photochemical decomposition of energetic materials: observation of aryl benzyloxy nitroxide and aryl benzyl nitroxide radicals in solutions of 1,3,5-trinitrobenzene and toluene and their deuteriated analogues at 200 K

: Electron spin resonance spectroscopy is used to probe the photodecomposition of 1,3,5-trinitrobenzene (TNB) in toluene. The photodecomposition is conducted at 200 K with solutions containing TNB and toluene along with solutions containing their deuterated analogues. Primary radicals observed in the decomposition have structures consistent with 3,5- dinitrophenyl benzyloxy nitroxide moieties. These radicals are proposed to be precursors to 3,5-dinitrophenyl benzyl nitroxide radicals previously observed in both photochemical and thermal decomposition. The aryl bezyloxy nitroxide radicals appear to decompose into 3,5-dini-trophenyl benzyl nitroxide radicals (secondary radicals) after the samples are allowed to remain at 200 K for extended time periods or after the solutions are warmed to 290 K. The secondary radicals observed in the study exhibit a temperature dependence involving the benzyl hydrogens adjacent to the nitroxide functionality. These hydrogens become magnetically inequivalent at low temperature, which may be attributed to the presence of different conformers of the aryl benzyl nitroxide species. Spectroscopic parameters for all the radicals observed are reported along with a proposed reaction scheme for the decomposition event. Reprints.