Infrared spectra of (CO$_2$)$_2$-Rg trimers, Rg = Ne, Ar, Kr, and Xe

TL;DR

This study reports high-resolution infrared spectra of (CO$_2$)$_2$-Rg trimers with Rg = Ne, Ar, Kr, Xe, revealing structural and vibrational details using laser spectroscopy in a supersonic jet expansion.

Contribution

First high-resolution spectra of (CO$_2$)$_2$-Rg trimers in the CO$_2$ nu3 region, providing insights into their structures and vibrational shifts compared to dimers.

Findings

C-Rg bond lengths are similar to CO$_2$-Rg dimers.

Vibrational band shifts are comparable to those in CO$_2$-Rg dimers.

Trimers have a similar structural motif with the Rg atom out-of-plane.

Abstract

High resolution spectra of (CO$_2$)$_2$-Rg trimers (Rg = Ne, Ar, Kr, and Xe) in the region of the CO2 nu3 fundamental (~2350 cm$^{-1}$) are reported, using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. These (CO$_2$)$_2$-Rg transitions tend to be hidden among stronger spectra due to other species, such as CO$_2$-Rg and (CO$_2$)$_2$. Each trimer consists of a (CO$_2$)$_2$ unit which is similar to the free carbon dioxide dimer (planar parallel staggered) plus an Rg atom located out-of-plane on the dimer C$_2$ symmetry axis, but the (CO$_2$)$_2$ 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 CO$_2$-Rg dimers. As well, the vibrational band origin shifts, relative to (CO$_2$)$_2$ itself, are similar to those of CO$_2$-Rg relative to CO$_2$.