The potential energy of the N20 molecule in the zeolite NaA has been calculated from the evaluation of its electrostatic, dispersion, and repulsion components for different positions and orientations of the molecule. We thus obtain the positions and depths of the potential wells. The potential barriers to translation and rotation are very high and the molecule performs librational and translational oscillations inside the well, the frequencies of which have been calculated. We also evaluate the lifetime of the adsorption and the time of residence of the molecule in the well. The observed far-infrared spectra may account for the calculated frequencies. As regards the vibrational spectrum, the splitting of v1 is interpreted by the two possible orientations of the molecule N2O: the profile of the v3 band and its variation with temperature can be explained by the frequency distribution due to translation.

A theoretical model of vibrational dephasing with motional narrowing by the librational motions of the molecules in their liquid cages is proposed and tested on the infrared ν6 degenerate fundamental of liquid methyl iodide and perdeutero methyl iodide over a temperature range of −190 to + 40 °C. The theory, which does not require artificial separation of vibrational and orientational coordinates, is particularly applicable to associated and sterically hindered liquids.

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