IONIC MECHANISMS FOR HETEROGENEOUS STRATOSPHERIC REACTIONS AND ULTRAVIOLET PHOTOABSORPTION CROSS-SECTIONS FOR NO2+, HNO3, AND NO3- IN SULFURIC-ACID

We present room temperature photo-absorption cross sections between 180 and 340 nm for potassium nitrate dissolved in sulfuric acid-water solutions of 0, 80, and 96% sulfuric acid by mass. Other investigators have obtained ultraviolet absorption spectra for similar solutions above 220 nm, and there is a large literature on the spectra, species, and nitration reactions in sulfuric acid solutions. The predominant nitrogen-containing species are the nitrate anion (NO3-) in pure water or dilute sulfuric acid solutions, molecular nitric acid (HNO3) in 80% sulfuric acid, and the nitronium ion (NO2+) in 96% sulfuric acid. Upon reviewing the literature involving these species, we consider elementary ionic and molecular reactions in mechanisms of stratospheric heterogeneous catalysis. We formulate a general mechanism for acid catalyzed reactions, with examples that convert inactive HCl and ClNO3 into photochemically active ClNO2, ClNO, Cl2, HOCl, and ClO, and we show that reactions forming all of these products are thermodynamically allowed.