INFRARED-SPECTRA OF NITRIC AND HYDROCHLORIC-ACID HYDRATE THIN-FILMS

The mono-, di-, and trihydrates of nitric acid have been prepared as thin crystalline films and characterized by their distinctive infrared spectra. The infrared spectra of the mono- and trihydrates have been found to be significantly different than previously reported, to the extent that the published spectra are of questionable use. The spectrum of the dihydrate of HNO3, which has not been reported previously, differs sharply from that of the other hydrates primarily because of effects indicative of a much more severely distorted nitrate ion. Infrared spectra are also reported for the tetra- and hexahydrate of HCl. The spectrum of tetrahydrate largely duplicates existing data but is included for comparison with the previously unpublished spectrum of the hexahydrate. Sharp O-D stretching bands of dilute HOD in the hexahydrate are indicative of proton ordering within the network of the waters of hydration and a affirm the view based on X-ray data that, unlike the highest crystalline hydrate of HClO4, the structure does not mimic that of the classical clathrate hydrates.