Diffusion and dynamics of noble gases in hydroquinone clathrate channels

In the present work, we study the behavior of the noble gases He, Ne, Ar, and Kr inside a hydroquinone clathrate (HQC) by using all-atom molecular dynamics. Larger elements of the same group were not considered due to their inability to fit inside the HQC cavities. By using the umbrella sampling technique, we have obtained the following inter-cage transition barriers—which are arguably the main factor determining the type of diffusion of the gases—at 310 K and 0.1 MPa: 1192; 2204; 6450; 10 730 kJ mol−1 for the guests He, Ne, Ar, and Kr, respectively. These energy barriers were found to have a linear relation with atomic radii (σ). We have tested this tendency with CH4, due to its intermediate size between Ar and Kr, obtaining a barrier of 8926 kJ mol−1, in excellent agreement with the results for noble gases.