On the photochemistry of aqueous nitrate solutions excited in the 195-nm band

The photochemistry of aqueous nitrate solutions excited in the high-energy (195-nm) ππ* band of the ion is investigated using steady-state and flash-irradiation techniques. The formation of hydroxyl radicals is demonstrated by observing the absorption of characteristic transients formed by the reaction of OH (or O^-) with CO₃^2-, CNS^-, and O₂. The formation of pernitrite is also investigated and found to be unaffected by [NO₂^-], [NO₃^-], [O₂], and [CH₃CH₂OH]. The flash technique enables the determination of the dissociation constant of pernitrous acid, yielding pK_a = 6.0 ± 0.3. A third photochemical path, the evolution of O₂ and the stoichiometric formation of NO₂^-, is also investigated. The effect of various solutes on the yields of molecular oxygen is analyzed. The results appear to be inconsistent with a mechanism involving intermediate oxygen atoms.