| Résumé | 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 CO₂–Arₙ with n = 3, 4, 6, 9, 10, 11, 12, 15, and 17, and CO₂–Krₙ and CO₂–Xeₙ 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 (ν₃) 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–Arₙ species tend to be those with symmetric structures, and CO₂–Ar₁₇ represents completion of a highly symmetric (D₅ₕ) 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–Ar₉, CO₂–Ar₁₅, and CO₂–Ar₁₇ 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). |
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