Infrared spectra of the (N2)2 and N2–Ar van der Waals molecules

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Abstract
Spectra of the weakly bound van der Waals molecules (N2)2 and N2 –Ar have been studied in the 2250–2450 cm−1 region corresponding to the N2 monomer vibrational frequency. The experiments were performed on equilibrium gas samples at low temperatures (77–90 K) using a long path length (154 m) cell and a Fourier transform infrared spectrometer. The spectra appear as relatively weak fine structure on top of the broad, diffuse, collision-induced fundamental band of nitrogen. The structure due to (N2)2 is extremely weak, and resembles that seen in earlier low-resolution work by Long et al. [Chem. Phys. 2, 485 (1973)], except that a new Q branch feature is detected here near the band center. On the other hand, the structure due to N2 –Ar is much more prominent, varied, and sharp than that of (N2)2, showing far greater detail than did a previous low-resolution study by Henderson and Ewing [Mol. Phys. 27, 903 (1974)]. Existing calculations are not adequate to utilize the information carried in the N2 –Ar spectrum, but in the future it should be possible to refine our knowledge of the intermolecular potential for this system by using these results.