Line Shape of the OD Absorption in the Infrared Spectrum of Partially Deuterated Water

Abstract

SHARP OH bands have recently been reported in partially deuterated solid alcohols which have been attributed to the absence of intermolecular coupling¹. We wish to call attention to the remarkable change in band shape for the uncoupled OD oscillator of HDO in H₂O on freezing. We have measured the infrared absorption of the OD band near 2,500 cm⁻¹ in dilute solutions of D₂O in H₂O in conditions where the wings of the band can be observed for at least 250 cm⁻¹ on either side of the absorption maximum. The spectra were digitally recorded and band shapes subjected to numerical analysis. The OD band of ice is sharp (31 cm⁻¹ wide at half-peak height) and Lorentzian for at least twelve half-widths and exhibits no asymmetry in this range. With melting, the band broadens (half-width of 150 cm₋₁) and is Gaussian in shape for two half-widths. At 4° C no asymmetry is seen; however, at higher temperatures asymmetry appears on the low frequency side of the band. Our high temperature data appear to be in good agreement with those of Falk and Ford².