Spectroscopic detection of the hydrogen bond isotope effect in KHF 2

A small decrease in the frequency of the Raman active symmetric stretching mode of the bifluoride ion in crystalline potassium bifluoride on deuteration has been observed. This is interpreted in terms of a contraction of the hydrogen bond on deuteration, an effect not previously observed spectroscopically. Some approaches to estimating the magnitude of the contraction are discussed and the results they yield compared.