Investigations on the Structure of Fluid Methane by Neutron Diffraction Experiments

Abstract

High pressure neutron diffraction experiments on a mixture of CH4 and CD4 as well as on pure deuterated methane CD4 were performed at three supercritical states. The structure factor was determined at three different densities at a temperature of T = 370K. The intra- and intermolecular structure was determined from the structure factor. The results from pure CD4 are in very good agreement with former neutron diffraction experiments. The experiments on the isotopic mixture allowed the direct determination of the pair correlation function of the molecular centres. The results of the diffraction experiments are presented in this paper.

A Refined Intermolecular Interaction Potential for Methane: Spectral Analysis and Molecular Dynamics Simulations

“…temperature T = 370 K and pressure P = 51~77 MPa (density r = 0.216~0.340 g/cm 3 ). [51][52] As we can see from the comparison of the calculated data with the experiment, the overall agreement is very good. On the other hand, our previous MP2 potential produces poorer results as compared with the present one.…”

“…One is a phase point far from the triple point but close to the melting line 50 while the other is a supercritical point. [51][52] A schematic plot of these phase points is shown in Figure 3. In the experiment of Habenschuss et al, 50 X-ray diffraction data were obtained directly and analyzed using the molecular scattering factors through Fourier transform to obtain the carbon-carbon correlation functions.…”

“…35 In the experiments of Kreitmeir et al, high pressure neutron scattering experiments on mixtures of CD 4 and CH 4 and on pure CD 4 were obtained at supercritical states. [51][52] The structural information was then retrieved from the structure factors. Figure 5 presents the simulated CD 4 and CH 4 radial distribution functions at the supercritical phase point with Fig .…”

Structural Analysis of Molecular Materials Using the Pair Distribution Function

“…With respect to their geophysical roles in both terrestrial and even Martian environments, molecular anions including sulfate and perchlorate solvation have been investigated. − PDFs were also recently used to identify the formation of adsorbed and hydrated layers around nanoparticles in suspension . While not discussed further here, it it worth noting that an additionally large body of work has also focused on the molecular states in other liquids ,, such as hydrocarbons, − their derivatives, − ionic liquids, − and acids. , …”