Photochemistry of molecules relevant to the atmosphere: photodissociation of nitric acid in the gas phase.

This Minireview gives an account of the photochemical decay of nitric acid HNO3 in the gas phase, which has been well investigated under bulk and molecular-beam conditions. Due to the importance of this molecule in atmospheric chemistry, attention was paid to the irradiation regions around 300 and 200 nm, where solar photolysis of HNO3 is expected to be particularly efficient. While the low-energy region is characterized by the products OH and NO2, the high-energy region gives rise to a variety of photochemical decay pathways, dominated by channels which lead to the products HONO + O in different electronic states.