The microscopic dynamics of four prototype systems (water, ammonia, nitrogen, and neon) across the critical temperature has been investigated by means of high-resolution inelastic x-ray scattering. The experimental line shape has been described using a model based on the memory function formalism. Two main relaxations, the thermal and the structural one, were observed in all the investigated systems. We found that the microscopic mechanism driving the structural relaxation clearly changes, being mainly governed by intermolecular bond rearrangements below the critical temperature and by binary collisions above it. Moreover, we observed that the relative weight of the thermal relaxation systematically increases on approaching the critical temperature, thus allowing for the observation of a transition from an adiabatic to an isothermal regime of sound propagation. Finally, we found the presence of an additional instantaneous relaxation, likely related to the coupling between collective vibrational modes and intramolecular degrees of freedom.

High frequency dynamics in liquids and supercritical fluids: A comparative inelastic x-ray scattering study / F., Bencivenga; A., Cunsolo; M., Krisch; G., Monaco; Ruocco, Giancarlo; F., Sette. - In: THE JOURNAL OF CHEMICAL PHYSICS. - ISSN 0021-9606. - 130:6(2009), p. 064501. [10.1063/1.3073039]

High frequency dynamics in liquids and supercritical fluids: A comparative inelastic x-ray scattering study

RUOCCO, Giancarlo;
2009

Abstract

The microscopic dynamics of four prototype systems (water, ammonia, nitrogen, and neon) across the critical temperature has been investigated by means of high-resolution inelastic x-ray scattering. The experimental line shape has been described using a model based on the memory function formalism. Two main relaxations, the thermal and the structural one, were observed in all the investigated systems. We found that the microscopic mechanism driving the structural relaxation clearly changes, being mainly governed by intermolecular bond rearrangements below the critical temperature and by binary collisions above it. Moreover, we observed that the relative weight of the thermal relaxation systematically increases on approaching the critical temperature, thus allowing for the observation of a transition from an adiabatic to an isothermal regime of sound propagation. Finally, we found the presence of an additional instantaneous relaxation, likely related to the coupling between collective vibrational modes and intramolecular degrees of freedom.
2009
acoustic wave propagation; ammonia; liquid structure; liquid-liquid transformations; neon; nitrogen; vibrational modes; water; x-ray scattering
01 Pubblicazione su rivista::01a Articolo in rivista
High frequency dynamics in liquids and supercritical fluids: A comparative inelastic x-ray scattering study / F., Bencivenga; A., Cunsolo; M., Krisch; G., Monaco; Ruocco, Giancarlo; F., Sette. - In: THE JOURNAL OF CHEMICAL PHYSICS. - ISSN 0021-9606. - 130:6(2009), p. 064501. [10.1063/1.3073039]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/83514
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