Infrared Study of the Crystalline Monohydrates of Nitric, Perchloric, and Sulfuric Acids

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Abstract
The infrared spectra of the solid monohydrates of three strong acids nitric, perchloric, and sulfuric were measured down to 50 cm—1. The last two are completely ionic, viz., H3O+ClO4— and H3O+HSO4—, but the first one always seems to retain a trace of covalent structure, HNO3·H2O. In the three hydrogen-bonded lattices the H3O+ ions have libration frequencies of the order of 700 cm—1 and translation frequencies lying between 120 and 400 cm—1. The frequencies of these lattice modes increase with the strengths of the hydrogen bonds. The deuterated hydrate of sulfuric acid gave only vitreous spectra because of supercooling. Likewise the room-temperature phase of perchloric acid monohydrate showed broad, diffuse absorption bands due to the disordered orientation of the hydronium ions. The pyramidal configuration of the H3O+ ion is confirmed definitely.