NO3 Radical: “Soft” Lattice Preparation and Pure ESR Spectrum at 88°K

Abstract

The NO₃ radical is generated by the direct photolysis of ceric ammonium nitrate in aqueous nitric acid solutions. When produced in aqeuous HONO₂–HOClO₃ mixtures frozen to form a good glass or “soft” lattice at 88°K, the pure ESR spectrum of NO₃ is uncomplicated by lattice distortions. Under these conditions we found the radical to be planar with true axial symmetry having the following computed parameters: $g_{\Vert }\text{\hspace{0.17em}=\hspace{0.17em}2.0041\hspace{0.17em}±\hspace{0.17em}0.0003}$ , $\text{g⊥\hspace{0.17em}=\hspace{0.17em}2.0207\hspace{0.17em}±\hspace{0.17em}0.0003}$ , and $\mathrm{\sigma (}\frac{1}{2}{\mathrm{\Delta H}}_{\mathrm{pp}}\text{)\hspace{0.17em}=\hspace{0.17em}5.16}\mathrm{Oe}$ . Some problems of NO₃ photochemistry are explained. The use of this technique to generate a variety of more stable free radicals is discussed. The first comparative evidence is given that radicals with nearly equal electron affinities, such as OH and NO₃, nevertheless show unique and selective reactivity differences toward the same substrates.