Fourier transform infrared spectroscopy of molecular clusters: The structure and internal mobility of clustered carbon dioxide

Infrared spectra of supersonic jets of carbon dioxide seeded in helium are reported: Features assignable to clusters were observed for the ν2, ν3, ν1+ν3, and 2ν2+ν3 bands. A detailed study was made of the ν3 band, from which it was concluded that the clusters do not adopt the face-centered cubic crystal structure of solid carbon dioxide. The observed spectra indicate that the cluster geometry is largely determined by pairwise interactions between adjacent molecules. Furthermore, expansions of pure carbon dioxide produced clusters whose spectra indicate motional averaging: such clusters seem to be fluid on a picosecond time scale.