Infrared Spectra of Oxonium Halides and the Structure of the Oxonium Ion

Abstract

The monohydrates of the hydrogen halides exist as ionic crystals. The infrared spectra of OH₃F, OH₃Cl, OH₃Br, OH₃I, and OD₃Cl at —195°C showed the four fundamental frequencies expected for a symmetrical pyramid at about 1100 cm^—1 (ν₂), 1700 cm^—1 (ν₄), 2600 cm^—1 (ν₁ or ν₃), and 3200 cm^—1 (ν₁ or ν₃). The high‐frequency bands, which are very broad at —195°C, did not sharpen on cooling to 8°K, indicating that their breadth is caused by some frozen‐in disorder.