The transverse acoustic excitation modes were detected by inelastic x-ray scattering in liquid Ga in the Q range above 9 nm(-1) although liquid Ga is mostly described by a hard-sphere liquid. An ab initio molecular dynamics simulation clearly supports this finding. From the detailed analysis for the S(Q,omega) spectra with a good statistic quality, the lifetime of 0.5 ps and the propagating length of 0.4-0.5 nm can be estimated for the transverse acoustic phonon modes, which may correspond to the lifetime and size of cages formed instantaneously in liquid Ga.

Recently we developed a new microwave spectroscopy technique in the frequency range up to 40 GHz, and measured the static dielectric constant and the dielectric relaxation time for supercritical water. In the present work we report the dielectric properties of heavy water at temperatures and pressures up to 770 K and 59 MPa, respectively. The static dielectric constant of D2O as well as H2O are well described by the Uematsu–Franck formula when the number density instead of the mass density is used as the input parameter. The dielectric relaxation time decreases rapidly with increasing temperature in liquid H2O and D2O and jumps to a large value at the liquid–gas transition. The relaxation time of D2O is longer than that of H2O in the liquid state, and the difference becomes smaller with decreasing density in the gaseous state. For both H2O and D2O the most relevant parameter determining the relaxation time is the temperature at high densities or at low temperatures, and it is the density at low densities or at high temperatures. Based upon the observation that the dielectric relaxation time becomes fairly long in the dilute limit, we have concluded that the dielectric relaxation in the gaseous state is governed by the binary collision of water molecules and explained the relaxation time quantitatively by the collision time. We have extended the interpretation of the dielectric relaxation to the liquid state by taking into account the contribution of bound water molecules that are incorporated in the hydrogen-bond network. Anomalous relaxation at low temperatures is also discussed.

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering spectra of liquid Fe, Cu and Zn. From the analysis of current correlation functions, we concluded that TA excitation modes can experimentally be detected through the quasi-TA branches in the longitudinal current correlation spectra in these liquid metals. The microscopic elastic constants are estimated and a characteristic difference from macroscopic polycrystalline value was found in Poisson's ratio of liquid Fe, which shows an extremely softer value of ∼0.38 compared with the macroscopic value of ∼0.275. The lifetime of the TA modes were determined to be ∼0.45 ps for liquid Fe and Cu and ∼0.55 ps for liquid Zn, reflecting different interatomic correlations between liquid transition metals and non-transition metals. The propagation length of the TA modes are ∼0.85 nm in all of liquid metals, corresponding to the size of icosahedral or similar size of cages formed instantaneously in these liquid metals.

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering (IXS) spectra of liquid Sn. The excitation energies and widths of the TA modes are in good agreement with results of an ab initio molecular dynamics simulation. By comparing current correlation spectra between the experimental and theoretical results quantitatively, we have concluded that the TA modes can be detected experimentally through the quasi-TA branches in the longitudinal current correlation spectra. The lifetime and propagation length of the TA modes were determined to be ~0.7 ps and 0.8-1.0 nm, respectively, corresponding to the size of cages formed instantaneously in liquid Sn.

We have measured optical properties of a mercury wetting film on sapphire under high temperature and high pressure near the liquid-gas critical point of mercury by using a newly developed 45 degrees reflection technique. We have analyzed the experimental data to deduce the density, the thickness, and the coverage of the wetting film quantitatively as functions of pressure and temperature. As a first approximation, we have assumed a slab model for the density profile of the wetting film, and found that the density of the wetting film dslab is much smaller than that of bulk liquid at the liquid-vapor coexistence curve. This result is consistent with the Lifshitz theory, from which we may predict that the sapphire substrate prefers wetting film with density lower than the metal-nonmetal transition. When the temperature is close enough to the prewetting critical temperature Tpw(c), the effective slab density dslab shows a sharp decrease as the pressure approaches the liquid-gas coexistence. This indicates that the slab model is not sufficient to describe the shape of the wetting film, and a smooth variation of the density has to be taken into account. In the prewetting supercritical region, two anomalies are observed in the reflectances. Possible mechanisms of these anomalies are discussed.