Simulating Relaxation Channels of CO2 in Clathrate Nanocages

[摘要] The energy levels of CO2in 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 CO2oscillates 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-1and 30 cm-1. Librational harmonic frequencies are calculated at 101.7 cm-1and 56.0 cm-1in the 5 cage and at 27.9 cm-1and 46.4 cm-1in the l cage. Results show that the coupling between the CO2molecule 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.

[发布机构] LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC Univ. Paris 06, CNRS, Guyancourt; F-78280, France^1;CHAIR Materials Simulation and Engineering, UVSQ, Université Paris Saclay, Versailles Cedex; 78035, France^2;Institut UTINAM-UMR 6213 CNRS, Université de Franche-Comté, Observatoire de Besançon, Besançon Cedex; 25010, France^3;INSTN- CEA, Université Paris Saclay, Gif-sur-Yvette; 91191, France^4;Nanochemistry Research Institute, Curtin Institute for Computation, Department of Chemistry, Curtin University, PO Box U1987, Perth; WA; 6845, Australia^5

[效力级别] 数学

[关键词] Atom-atom interaction;Born-Oppenheimer approximation;Harmonic frequency;High-frequency vibrational modes;Large-amplitude motion;Librational modes;Relaxation channels;Small amplitude