Origin of Ultrasonic Absorption in Heavy Water

Hall's theory of structural relaxation is applied to explain the excess ultrasonic absorption in ${\mathrm{D}}_2$O. 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 ${\mathrm{D}}_2$O. The occurrence of a density maximum ${\rho }_{max}$ at 11.2°C and a static compressibility minimum ${\beta }_{0 min}$ at about 75°C favors a two-state model for ${\mathrm{D}}_2$O. The absorption coefficient is calculated with three trial values of ${\beta }_{\infty }$ (16×${10}^{-12\mathrm{}}$, 17×${10}^{-12\mathrm{}}$, and 18×${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^2$/dyn). It is found that with ${\beta }_{\infty }=17\mathrm{}\times {10}^{-12\mathrm{}}$ ${\mathrm{cm}}^2$/dyn, Hall's theory agrees very well with the experimental results.