PHOTODECOMPOSITION OF NITRITE AND UNDISSOCIATED NITROUS-ACID IN AQUEOUS-SOLUTION

Quantum yields of phenol and nitrate, produced by photodecomposition i n aqueous solutions of NO2- and HNO2 in the presence of benzene as sca venger for OH radicals, have been determined as a function of waveleng th between 280 and 390 nm. The production of phenol was used to calcul ate primary OH quantum yields. For NO2- photolysis at pH 6 Phi(1)(OH) was found to decrease with increasing wavelength from 0.069 +/- 0.008 at 280 nm to 0.022 +/- 0.004 at 390 nm, in agreement with previous dat a. The OH quantum yield Phi(2)(OH) for the photolysis of HNO2 at pH 2 was essentially constant over the entire wavelength range with Phi(2) = 0.35 +/- 0.02 (2 sigma). Quantum yields for NO3- are comparable in m agnitude to those of phenol, indicating that NO as primary product is largely oxidized to nitrate. The most likely conversion processes are reactions of NO with O-2(-) (pH 6), the latter resulting from the oxid ation of benzene, to form peroxynitrous acid, which undergoes thermal decomposition, and of NO2 with HO2 (pH 2) to form peroxynitric acid, w hich reacts further with HNO2. The rate of NO3- production decreases w ith time in the photolysis of NO2-, whereas it increases in the photol ysis of HNO2, and these features remain unexplained.