| Abstract | Weakly bound CO₂-Rg₂ trimers are studied by high-resolution (0.002 cm⁻¹) infrared spectroscopy in the region of the CO₂ ν₃ fundamental band (≈2350 cm⁻¹), using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion with an effective rotational temperature of about 2 K. CO₂–Ar₂ spectra have been reported previously, but they are extended here to include Rg = Ne, Kr, and Xe as well as new combination and hot bands. For Kr and Xe, a unified scaled parameter scheme is used to account for the many possible isotopic species. Vibrational shifts of CO₂-Rg₂ trimers are compared to those of CO₂-Rg dimers, and in all cases the trimer shifts are slightly more positive (blue-shifted) than expected on the basis of linear extrapolation from the dimer. Combination bands directly measure an intermolecular vibrational mode (the CO₂ rock) and give values of about 32.2, 33.8, and 34.7 cm⁻¹ for CO₂–Ar₂, –Kr₂, and –Xe₂. Structural parameters derived for CO₂-Rg₂ trimers are compared with those of CO₂-Rg and Rg₂ dimers. Spectra of the mixed trimers CO₂-Rg-He are also reported. |
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