Simulating Relaxation Channels of CO₂ in Clathrate Nano-cages

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

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

The energy levels of CO₂ in the small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using pairwise atom-atom interaction potentials. In the s cage, the centre of mass of CO₂ oscillates with small amplitudes, asymmetrically about the cage center with harmonic frequencies around 100 cm^-1. In the l cage, oscillations are anharmonic with large amplitude motions in a plane parallel to the hexagonal faces of the cage and the corresponding frequencies are calculated to be 55 cm^-1 and 30 cm^-1. Librational harmonic frequencies are calculated at 101.7 cm^-1 and 56.0 cm^-1 in the s cage and at 27.9 cm^-1 and 46.4 cm^-1 in the l cage. Results show that the coupling between the CO₂ molecule and the nano-cage is quite different for the low frequency translational, rotational or librational modes and the high frequency vibrational modes, which consequently leads to different relaxation channels.

Domains: Materials Science [cond-mat.mtrl-sci]

Pierre-Richard Dahoo, R. Puig, Azzedine Lakhlifi, Constantin Meis, J.D. Gale. Simulating Relaxation Channels of CO₂ in Clathrate Nano-cages. Journal of Physics: Conference Series, 2016, 738, pp.012072. ⟨10.1088/1742-6596/738/1/012072⟩. ⟨insu-01322154⟩