The UV photolysis of NO2- produces NO● and ●OH radicals. The latter is a highly reactive species that is also produced through water radiolysis. The ●OH radicals then can undergo further reaction with remaining NO2- in solution to produce ●NO2 and OH-, which is a diffusion controlled reaction and can be impacted by solution structure and rheological properties. The production of NO●, ●OH, and ●NO2 radicals are investigated in aqueous solutions of high alkalinity and high ionic strength as a function of alkali cation speciation utlizing nitromethane as a spin trap for EPR spectroscopy. Comparisons of the radical production as a function of ionic strength and alkali cation identity indicate a cation effect for all three radical species. Through complementary investigations with multinuclear single pulse direct excitation NMR spectroscopy and pulsed field gradient NMR diffusometry, cation controlled solution structures and NO2- solvation are determined to alter the initial yields of NO● and ●OH radicals, as well as alter the reactivity of NO2- towards ●OH, impacting the production of ●NO2. The implications of these findings for complex solutions subjected to ionizing radiation are presented.

Cation effects on the evolution of radicals from the UV photolysis of aqueous nitrite solutions

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