Origin of Ultrasonic Absorption in Heavy Water

Hall's theory of structural relaxation is applied to explain the excess ultrasonic absorption in D₂O. Two states, one characterized by higher volume and lower energy (icelike structure) and the other characterized by lower volume and higher energy (close-packed structure) are assumed to be available to each molecule of D₂O. The occurrence of a density maximum ρₘₐₓ at 11.2^∘{}C and a static compressibility minimum β0 min at about 75^∘{}C favors a two-state model for D₂O. The absorption coefficient is calculated with three trial values of β_∞ (16×{}10^-12, 17×{}10^-12, and 18×{}10^-12 cm²/dyn). It is found that with β_∞=17×10^-12 cm²/dyn, Hall's theory agrees very well with the experimental results.