Propagation of sound in water. A molecular-dynamics study

Fluctuation phenomena occurring in a system of 216 water molecules, studied by molecular dynamics at 1 g cm^-3 and 10 ^∘{}C, indicate that (i) transverse currents persist in the form of propagating collective coordinates even for a wavelength of about 20 {}, with indications that the same will happen for much longer wavelengths. The velocity of propagation is 1.05 ×{} 10⁵ cm sec^-1. In the region of 20 {} the lifetime of the fluctuation appears to increase linearly with increasing wavelength. (ii) Density fluctuations at 20 {} are found to be propagating but only marginally; the corresponding velocity of sound is 1.8 ×{} 10⁵ cm sec^-1. (iii) The spectrum of density fluctuations exhibits a secondary maximum at a much higher frequency than the normal frequency of sound propagation and it is suggested that experiments should be directed to the region of this "high-frequency sound."