Spectroscopic identification of carbon dioxide clusters: (CO2)6 to (CO2)13

In spite of wide interest in CO(2) clusters, only dimers and trimers have previously been assigned to specific infrared bands. Here, transitions for clusters with 6-13 molecules are identified in the ν(3) region (～2350 cm(-1)). Spectra are observed in a supersonic jet (T ～ 2.5 K) using a tunable laser probe, and analyzed with the aid of cluster calculations based on a widely-used model potential. Vibrational origins show blue-shifts significantly larger than predicted by resonant dipole interactions.