Tg. Koch et al., LOW-TEMPERATURE PHOTOCHEMISTRY OF SUBMICROMETER NITRIC-ACID AND AMMONIUM-NITRATE LAYERS, Journal of physical chemistry, 100(27), 1996, pp. 11402-11407
Reflection-absorption infrared spectroscopy has been employed in order
to investigate the low-temperature photochemistry (90-140 K) of thin
films of nitric acid and ammonium nitrate grown in vacuo. Photolysis o
f amorphous nitric acid hydrate, the crystalline dihydrate (NAD) and t
rihydrate (NAT) at lambda > 230 nm resulted in the formation of molecu
lar nitric acid due to rapid protonation of the excited nitrate ion. S
econdary photolysis of HONO2 produced NO2 and NO. If a neat film of mo
lecular, anhydrous nitric acid was irradiated, nitrate and nitronium i
ons were observed. In contrast, ammonium nitrate photolysis at 140 K d
id not result in a proton transfer to produce NH3 and HONO2 but in the
formation of the peroxynitrite ion (ONOO-) as a precursor for NO2-. M
olecular dinitrogen tetraoxide and nitrous oxide were also detected in
the film. Mechanistic details and possible implications for the chemi
stry of the polar atmosphere are discussed.