Selective bond scission in forming NO2 from NO3- in γ-irradiated crystals of urea nitrate, diglycine nitrate, and monoglycine nitrate as studied by electron spin resonance

The controlling factors of selective bond breakage in forming NO2 from NO3- in irradiated crystals of the title compounds have been studied by using a single-crystal ESR technique. The results indicate that the NO2 radical with one particular orientation is formed in any of these crystals as a result of scission of a particular N-O bond of NO3-. From a comparison of the hyperfine coupling and g tensors with the crystallographic data, it was clarified that the oxygen atom participating in the strongest hydrogen bond is preferentially detached to form NO2. Such a selective formation of NO2 is interpreted in terms of the reaction scheme in which NO2 is formed by protonation of the primary anion radical NO32- followed by dissociation of OH-, where the proton transfer across the strongest hydrogen-bonding path triggers the selective reaction