The infrared spectrum of isotopically diluted potassium hydrogen bifluoride. Doubling of the HF stretching and of the v3 + v1 band

Abstract

Infrared spectra (of mulls in Nujol and Fluorolube and discs in potasium iodide) have been obtained for crystalline KDF2 of higher deuterium content (c. 97.5%) than used by previous workers. This made possible an unambiguous identification of the bands of KHF2 as a solid solute in KDF2. HF stretching (v3) is split into a doublet with separation c. 52 cm-1, and the combination band v3 + v1 has a doublet separation of c. 64 cm-1. For 1.5% KDF2 in KHF2 the splitting of v3 of DF2- is too small to produce two separate bands. The splitting is attributed to the interconversion doubling which Ketelaar erroneously believed to have detected in 1941. Arguments previously put forward against the F-...HF structure are shown not to take into account the increasing tendency of the anionic dipoles to adopt an ordered arrangement as the temperature is lowered. ��� KHF2 and KDF2 have also been examined in solid solution in potassium halides and in water. Narrow v3 bands are obtained in KCl and KBr, but broad ones, as in crystalline KHF2, in KI and in water.