Density dependence of structure of supercritical carbon dioxide along an isotherm

Abstract

Neutron diffraction experiments for supercritical CO2 have been carried out over a wide range of Q (0.018≤Q≤30 Å−1) at ρ*=ρ/ρc=1.5, 1.2, 0.77, and 0.34 along an isotherm at 310 K (T*=T/Tc=1.02). The measurement enabled us to obtain quantitatively reliable radial distribution functions of the fluid including both short-ranged structure and long-ranged density fluctuation. The structure factor and radial distribution function showed the structural change from the attraction-predominant gaslike structure to the repulsion-predominant liquidlike one with increasing fluid density. With respect to the long-ranged structure, almost linear Ornstein–Zernike–Debye plots were obtained for S(Q) of the fluids at all densities. A plot of correlation length against reduced density seems to have a maximum at the critical density. A ratio, α(r), of the density fluctuation produced by the correlation within r to that to the infinity presented a new aspect of the density fluctuation. Molecular dynamics simulation has also been performed in order to investigate a molecular basis of the experimental radial distribution functions. The calculated GN(r)’s were in good agreement with experimental ones at each density. In laboratory space, a variety of orientational coordination structures are almost equally found in the fluid at all densities examined, while T-shaped structure is preferentially present in polar-angle space.

The Structure of Carbon Dioxide around Naphthalene Investigated using H/D Substitution in Neutron Diffraction

“…Using this as a justification, we compare our supercritical CO 2 data with published neutron data, molecular dynamics simulations, RISM calculations, and Monte Carlo simulations 5 performed at pressures and temperatures different from those used in our experiments, but at a very similar density. The main features of the measured intermolecular CO 2 structure compared to published neutron 18 and molecular dynamics simulation curves are in good agreement, whereas the RISM and Monte Carlo simulations are in approximate agreement (see Figure 4). …”

Vibrational Lifetimes and Spectral Shifts in Supercritical Fluids as a Function of Density: Experiments and Theory

“…One might speculate that there is a specific interaction between CO 2 and W(CO) 6 . Supercritical CO 2 tends to from T-shaped structures with the oxygen of one CO 2 coordinated with the carbon of another CO 2 , forming a T. 70 It is possible that CO 2 has a tendency to coordinate with the oxygens of W(CO) 6 in the same manner. Such a specific interaction could modify the density dependence of the vibrational lifetime.…”

A first principles approach to the electronic properties of liquid and supercritical CO2

“…Recent researches also emphasize the interest in the combination of subcritical and supercritical CO 2 with ionic liquids 6 which may lead to the design of sophisticated multiphasic reaction environments. 6 Numerous investigations on the structure, [9][10][11][12][13][14][15][16][17][18][19] dynamics, 9,17 Raman spectrum, [20][21][22][23] and thermochemical properties 24-31 of CO 2 were reported. A very recent work discusses the absorption of CO 2 in a protic ionic liquid.…”