Molecular Rotational Dynamics in Mixed CH4-CO2 Hydrates: Insights from Molecular Dynamics Simulations

BR Cladek and SM Everett and MT McDonnell and MG Tucker and DJ Keffer and CJ Rawn, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 26251-26262 (2019).

DOI: 10.1021/acs.jpcc.9b06242

The impact of guest molecule composition on the rotational dynamics in CH4, CO2, and mixed CH4-CO2 gas hydrates is investigated with classical molecular dynamics simulations. Rotational autocorrelation functions are calculated for the guest and host molecules in each hydrate composition from simulation trajectories at 10, 40, 190, and 270 K. Analysis of these functions for each molecule is further decomposed into cage type for each CH4 and CO2 guest and cage face for the H2O host. CH4 becomes more constrained, and CO2 gains freedom in the mixed guest systems. Mixing guest species in gas hydrates alters the intermolecular interaction environment, impacting the rotational motion of the guest molecules. This effect is also seen in the host lattice H2O molecules, as evidence of molecular rotations is seen in the CO2 hydrate at 270 K during longer simulations.

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