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 ν2 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, it is conjectured that infrared excited CO2 will rather relax radiatively. Non-radiative channels can be analyzed by binary collision model. •Equilibrium configuration of carbon dioxide molecule trapped in structure I clathrate hydrates is determined.•Shifts of the vibrational frequencies of the CO2 molecule are calculated using contact transformation method.•The orientational motions of the CO2 molecule are studied. The level schemes correspond to librational motions.•The infrared absorption coefficients are calculated and correspond to pure vibrational transitions.