High-frequency longitudinal and transverse dynamics in water
- Dipartimento di Fisica and INFM, Universita di Roma 'La Sapienza', I-00185, Rome (Italy)
- European Synchrotron Radiation Facility, Boite Postal 220, F-38043 Grenoble (France)
- Institut Laue-Langevin, BP 156, F-38043 Grenoble (France)
High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor S(Q,{omega}) of liquid water have been performed for wave vectors Q between 4 and 30 nm{sup -1} in distinctly different thermodynamic conditions (T=263-420 K; at, or close to, ambient pressure and at P=2 kbar). In agreement with previous inelastic x-ray and neutron studies, the presence of two inelastic contributions (one dispersing with Q and the other almost nondispersive) is confirmed. The study of their temperature and Q dependence provides strong support for a dynamics of liquid water controlled by the structural relaxation process. A viscoelastic analysis of the Q-dispersing mode, associated with the longitudinal dynamics, reveals that the sound velocity undergoes a complete transition from the adiabatic sound velocity (c{sub 0}) (viscous limit) to the infinite-frequency sound velocity (c{sub {infinity}}) (elastic limit). On decreasing Q, as the transition regime is approached from the elastic side, we observe a decrease of the intensity of the second, weakly dispersing feature, which completely disappears when the viscous regime is reached. These findings unambiguously identify the second excitation to be a signature of the transverse dynamics with a longitudinal symmetry component, which becomes visible in S(Q,{omega}) as soon as the purely viscous regime is left.
- OSTI ID:
- 20641338
- Journal Information:
- Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Vol. 71, Issue 1; Other Information: DOI: 10.1103/PhysRevE.71.011501; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-651X
- Country of Publication:
- United States
- Language:
- English
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