Lattice Vibrations of the Solids N2, CO2, and CO

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Abstract
The far‐infrared absorptions of the solids N2, CO2, and CO have been investigated. Two bands were observed for each solid below 100 cm−1 and the spectrum observed for CO2 is in good agreement with that reported previously. The frequencies for N2 have been found to be in good agreement with calculations based on the theory described by Walmsley and Pople. The absorption intensities have been calculated from the theory described in the preceding paper. The experimental values available for the intensities are uncertain to within a factor of 3 and the calculated and measured values agree well within this limit. It is concluded that the intensity theory has been shown to be valid to better than within a factor of 2 but a more precise test is contingent on the availability of more accurate experimental measurements. From the lack of agreement between calculated and observed intensity ratios between the absorption bands of the same substance, it is concluded that the quadrupole—quadrupole term is not adequate to describe the angle‐dependent part of the intermolecular potential.