The elastic constants ofD2Oice have been measured between 0° and −140°C. From these data and the elastic constants ofH2Oice, the molecular force constants—Kfor change of bond length andGfor change of 0⋯0⋯0 angle—have been calculated.KandGshow a similar temperature dependence as the elastic constants; their absolute values enlarge on deuteration. For comparison, values ofKandGcalculated from infrared data are given.