The molar absorptivity of dilute HDO in water and in aqueous NaCl solutions was determined at temperatures between 10 and 85° in the spectral region from 4000 to 2000 cm−1.The infrared band profiles for the OH and OD stretching fundamentals are single-peaked and devoid of shoulders, in contrast to the high-frequency shoulders recently observed in the Raman spectrum. It is shown that such shoulders do not contradict a single-peaked distribution of OH oscillators with respect to inter-molecular geometry. Absence of resolvable sub-bands in the spectrum of HDO in concentrated salt solutions indicates a wide distribution of ion–H2O interactions, akin to the distribution of H2O–H2O interactions in water.