Reflection−absorption infrared spectroscopy (RAIRS) has been employed to investigate the heterogeneous hydrolysis of bromine nitrate (BrONO2) in and on thin ice films between 95 and 185 K. Hydrolysis is observed to occur throughout the temperature range with evidence for two competing mechanisms. At the stratospherically relevant temperature of 185 K, the reaction proceeds by an ionic mechanism to give the hypobromous ion, H2OBr+, and both nitric acid di- and trihydrate. A molecular mechanism is also operative to give hypobromous acid, HOBr, and hydrated nitric acid (HNO3·(H2O) n ). This second route becomes more important under conditions of limited water presence and at lower temperatures. All of the results are compared to analogous studies previously performed on chlorine nitrate (ClONO2).

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When low-temperature thin films of either ionic or covalent dinitrogen pentaoxide, N 2 O 5 , are exposed to gaseous HCl and water, the only products observed in the solid phase by reflection-absorption infrared spectroscopy (RAIRS) are molecular nitric acid and the oxonium ion. Nitryl chloride, ClNO 2 , is not detectable. When dinitrogen pentaoxide is co-deposited with hydrogen chloride and water at 85 K and annealed to 140 K, the resultant RAIR spectra indicate that the film is composed of H 3 O + Cl -, N 2 O 5 , HNO 3 , and D 2h -N 2 O 4 . When nitryl chloride is co-deposited with either water or HCl/water mixtures, infrared spectra indicative of solid D 2h -N 2 O 4 are measured, as well as peaks corresponding to nitrate ions and cis-ClONO (chlorine nitrite). Reaction between ClNO 2 and its isomer, cis-ClONO, is proposed as an explanation for the formation of dinitrogen tetraoxide in both systems. The proposed reaction mechanism for this hydrolysis is extended to the N 2 O 5 /H 2 O/HCl deposits in order to explain the lack of observable ClNO 2 in such thin films.