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

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.