Anomalous Isotopic Frequency Ratio of the Stretching (N + H) Vibrations in Ion Pairs

Abstract
Earlier, when investigating H-complexes of the RO-H…BR1 type in solutions 1–3 and crystalline state 4, the isotopic shift for frequencies of the stretching vibrations (OH) at substitution of H for D was shown to systematically decrease with increased strength of the H-bond. In strong H-complexes, the (OH) and (OD) bands in the i.r. spectra have a complex structure: depending on the strength of the H-complex in a wide range of frequencies (3000–1000 cm−1), several submaxima caused by a Fermi-resonance interaction of the fundamental tone of (OH) with combinations and overtones in the bending vibrations of R-O-H were observed 1–5. Hence, the frequencies and intensities of the (OH) and (OD) bands in strong H-complexes should be considered as corresponding to the gravity centre ( °) and overall intensity (A°) of all the