The influence of pressure on the infrared spectra of hydrogen-bonded solids. V. The formation of Fermi resonance 'windows'

Abstract

Measurements have been made of the influence of pressure to 40 kbar on the infrared spectra of the normal and X-deuterated forms of seven solid compounds which have strong X-H...Y hydrogen bonds and whose spectra show very broad and intense X-H stretching bands at low frequencies. For two of the compounds, isonicotinic acid and nicotinic acid, compression causes the smooth transformation of superimposed absorption bands into Fermi resonance 'windows', or 'Evans holes'. The effect probably arises from increased overlap of the wave functions for in-plane ring-bending vibrations and X-H stretching vibrations.