INFRARED-SPECTRA OF SOLID FILMS FORMED FROM VAPORS CONTAINING WATER AND NITRIC-ACID

Infrared spectra have been recorded at 188 K for crystalline mono- and trihydrates of nitric acid formed by vapor deposition. In addition, spectra of fully deuterated forms of these same compounds have been obtained. These spectra have been interpreted in terms of the known ionic structures of the hydrates and the known spectra of oxonium and nitrate ions. Two other less stable solids were formed, a molecular hydrogen-bonded HNO3.H2O complex, stable only at temperatures below 120 or 150 K, and a substance thought to be a crystalline mixture of trihydrate and ice which sometimes formed from water-rich vapors and which upon pumping and/or warming could be converted into crystalline trihydrate. While these four substances appear to be the four species recently reported by Ritzhaupt and Devlin, we disagree with their allocation of structures to two of them. In particular, we disagree with their claims that a stable dihydrate exists. The relevance of the results to the stratospheric "ozone hole" problem is discussed.