Investigating CH₄ Thermal Activation in Clathrate Nanocages

Azzedine Lakhlifi (1) , Pierre-Richard Dahoo (2, 3) , Constantin Meis (2, 4) , Julian D. Gale (2, 5)

1 UTINAM - Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
2 UVSQ - Université de Versailles Saint-Quentin-en-Yvelines
3 PLANETO - LATMOS
4 INSTN - Institut National des Sciences et Techniques Nucléaires
5 CIC - Curtin Institute for Computation

The energy levels of methane molecule trapped, at low temperature, in small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using the Extended Lakhlifi-Dahoo model based on pairwise atom-atom effective interaction potentials. In the s cage, the center of mass of CH4 exhibits a slightly asymmetrical 3D oscillation motion with small amplitude around the cage center. Two methods were used to calculate the frequencies of such a motion: a 3D harmonic treatment and a 1D Discrete Variable Representation (DVR) treatment in the X, Y and Z directions. They give approximately the same values of, respectively, 133 cm-1, 108 cm-1 and 120 cm-1. In the l cage, the oscillations are anharmonic and characterized by large amplitude motions with frequencies of 63 cm-1, 52 cm-1 and 47 cm-1. In the s and l nano-cages, the molecule exhibits strongly perturbed rotational motion. The rotational level schemes are quite different from that of the molecular free rotational motion, and for each nano-cage, the obtained levels are described as combination of the free rotation levels.

Domains: Theoretical and/or physical chemistry; Chemical Physics [physics.chem-ph]

Azzedine Lakhlifi, Pierre-Richard Dahoo, Constantin Meis, Julian D. Gale. Investigating CH₄ Thermal Activation in Clathrate Nanocages. Journal of Physics: Conference Series, 2017, 6th International Conference on Mathematical Modelling in Physical Sciences (IC-MSQUARE 2017), 28–31 August 2017, Pafos, Cyprus, 936 (1), pp.012071. ⟨10.1088/1742-6596/936/1/012071⟩. ⟨insu-01576471⟩