From 1984 to 1996 there was rapid progress in the spectroscopy of CO2 dimers and trimers, but since then little work has appeared. Here we report a number of new high-resolution infrared results. For the dimer, a combination band provides the first experimental intermolecular vibrational frequency, and 13C isotopic spectra clarify the role of resonant and non-resonant vibrational shifts. For the cyclic trimer, a new parallel combination band involving an out-of-plane intermolecular mode is observed, and various 13C isotope results are analysed. In addition to these dimer and trimer results, the spectra also contain features which must be due to larger (CO2) N clusters in the range N ≈ 5–15.
Part of the fundamental band of the CO2 dimer for (12C16O2)2. The simulations use parameters from Table 2, an effective rotational temperature of 3°K, and an assumed Gaussian linewidth of 0.0017 cm-1.