Doped rare gas clusters up to completion of first solvation shell, CO2-(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 mu m) source to probe a pulsed slit jet supersonic expansion. There are relatively few previous detailed experimental results on such clusters. The assigned clusters include CO2-Ar-n with n = 3, 4, 6, 9, 10, 11, 12, 15, and 17, and CO2-Kr-n and CO2-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 CO2 vibrational frequency (nu(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 CO2-Ar-n species tend to be those with symmetric structures, and CO2-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 CO2-Ar-9, CO2-Ar-15, and CO2-Ar-17 suggest the presence of sequences involving very low frequency (asymptotic to 2 cm(-1)) cluster vibrational modes, an interpretation which should be amenable to theoretical confirmation (or rejection).

Automated summary

Spectra of rare gas atom clusters containing a single carbon dioxide molecule have been studied using a mid-infrared source. The results provide precise values for the vibrational frequency shift of CO2 induced by the nearby rare gas atoms. The assignments and structures of the clusters are compared with theoretical predictions.