| Abstract | High resolution spectra of (CO₂)₂-Rg trimers (Rg = Ne, Ar, Kr, and Xe) in the region of the CO₂ ν₃ fundamental (≈2350 cm⁻¹) are reported, using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. These (CO₂)₂-Rg transitions tend to be hidden among stronger spectra due to other species, such as CO₂-Rg and (CO₂)₂. Each trimer consists of a (CO₂)₂ unit which is similar to the free carbon dioxide dimer (planar parallel staggered) plus an Rg atom located out-of-plane on the dimer C2 symmetry axis, but the (CO₂)₂ unit may not remain exactly planar in the dimer. Experimental structures show that the C-Rg bond lengths in the trimers are similar to those in the corresponding CO₂-Rg dimers. As well, the vibrational band origin shifts, relative to (CO₂)₂ itself, are similar to those of CO₂-Rg relative to CO₂. |
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