Infrared spectra of (CO2)2 – Rg trimers, Rg = Ne, Ar, Kr, and Xe

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