[en] The near-normal incidence spectral reflectance of deuterium oxide at 27 ⁰C has been measured in the spectral range 6800--350 cm^-1. Kramers-Kronig phase shift analysis has been applied to measured reflectance to obtain values of the real and imaginary parts of the complex index of refraction N (ν) = n (ν) + ik (ν). The results are compared in detail with the corresponding optical constants of ordinary water at 27 ⁰C. In general, the D₂O absorption bands are narrower and less intense than the corresponding bands in ordinary water