Doped rare gas clusters up to completion of first solvation shell, CO 2 -(Rg) n , n = 3-17, Rg = Ar, Kr, Xe.

Spectra of rare gas atom clusters containing a single carbon dioxide molecule are observed using a tunable mid-infrared (4.3 µm) source to probe a pulsed slit jet supersonic expansion. There are relatively few previous detailed experimental results on such clusters. The assigned clusters include CO 2 -Ar n with n = 3, 4, 6, 9, 10, 11, 12, 15, and 17, and CO 2 -Kr n and CO 2 -Xe n with n = 3, 4, and 5. Each spectrum has (at least) a partially resolved rotational structure, and each yields precise values for the shift of the CO 2 vibrational frequency (ν 3 ) induced by the nearby rare gas atoms, together with one or more rotational constants. These results are compared with theoretical predictions. The more readily assigned CO 2 -Ar n species tend to be those with symmetric structures, and CO 2 -Ar 17 represents completion of a highly symmetric (D 5h ) solvation shell. Those not assigned (e.g., n = 7 and 13) are probably also present in the observed spectra but with band structures that are not well-resolved and, thus, are not recognizable. The spectra of CO 2 -Ar 9 , CO 2 -Ar 15 , and CO 2 -Ar 17 suggest the presence of sequences involving very low frequency (≈2 cm -1 ) cluster vibrational modes, an interpretation which should be amenable to theoretical confirmation (or rejection).