Potential infrared relaxation channels calculated for CO2 clathrate hydrates

The infrared bar-spectrum of a single carbon dioxide molecule encapsulated in nano-cage clathrate hydrate is determined using the LD (Lakhlifi-Dahoo) extended site inclusion model successfully applied to analyze the spectra of CO2 isotopologues isolated in rare gas matrices. Trapping is energetically more favorable in clathrate structure of type sI than sII. CO2 exhibits hindered orientational motions (librational motions) around its equilibrium configurations in the small and large nano-cages. The orientation transitions are weak, and the spectra are purely vibrational. In the static field inside the cage, the doubly degenerate bending mode nu(2) is blue shifted and split. From the scheme of the calculated energy levels for the different degrees of freedom, which is comparable to that of CO2 in rare gas matrices, if is conjectured that infrared excited CO2 will rather relax radiatively. Non-radiative channels can be analyzed by binary collision model. (C) 2016 Elsevier Ltd. All rights reserved.