Ionization and hydrolysis of dinitrogen pentoxide in low-temperature solids

Solid layers of interest for the chemistry of polar stratospheric clouds ar e investigated. Mixtures of covalent N2O5 and water in various molar ratios are deposited from the vapor phase on a cold 12 K substrate. By repeatedly recording Fourier transform infrared spectra of the samples during gradual warmup to 200 K over a period of several hours the hydrolysis process can be followed. At each concentration the process is found to proceed in sever al distinct steps with sharp temperature thresholds. In samples containing only small amounts of water the covalent N2O5 is first, at around 110 K, co nverted to an ionic nitronium nitrate, and only in a subsequent step does N O2+NO3- react to form nitric acid. (C) 2001 American Institute of Physics.