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

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.