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7765300 
Journal Article 
EPR-SPECTRA OF PHOTOCHEMICAL NO2 FORMATION IN MONOCYCLIC NITRAMINES AND HEXANITROHEXAAZAISOWURTZITANE 
Pace, MD 
1991 
1 
Journal of Physical Chemistry
ISSN: 0022-3654 
95 
15 
5858-5864 
English 
WOS:A1991FY38800028 
NO2 radicals produced by ultraviolet light are studied in three condensed-phase nitramines; cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), and hexanitrohexaazaisowurtzitane (HNIW), a newly developed nitramine. Electron paramagnetic resonance (EPR) spectroscopy is used to measure NO2 radical concentrations in polycrystalline samples of each nitramine and to analyze NO2 conformations in single crystals of HNIW. The results show that HNIW has a quantum yield of formation of NO2 radicals that is 1 order of magnitude greater than either RDX or HMX. Trapped NO2 radical sites in an HNIW single crystal are analyzed at 77 K before (I) and after (II) annealing at 298 K. For (I) the nitrogen hyperfine couplings and g values are Ax = 5.7 mT, Ay = 5.8 mT, Az = 7.0 mT and gx = 2.0062, gy = 1.9952, gz = 2.0020. For (II) the values are Ax = 4.9 mT, Ay = 5.4 mT, Az = 7.0 mT and gx = 2.0057, gy = 1.9927, gz - 2.0017. EPR spectral line shapes indicate different motional correlation times of I and II at 77 K. At 298 K stabilization of NO2 radicals in the α-polymorph of HNIW is attributed to trapping of NO2 in clathrate regions of the HNIW crystallites.