A Study of the Heterogeneous Reaction between Dinitrogen Pentaoxide and Chloride Ions on Low-Temperature Thin Films

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 2 h -N 2 O 4 . When nitryl chloride is co-deposited with either water or HCl/water mixtures, infrared spectra indicative of solid D 2 h -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.