Knowledge Bank

Sub-Doppler infrared spectra of $Ne-CO2,Ar-CO2$, and $Kr-CO2$ have been recorded near 3613 and $3715cm-1$, in the region of the $2\nu 20+\nu 3/\nu 1+\nu 3$ Fermi diad of $CO2$. using an optothermal molecular-beam color-center laser spectrometer. In addition, pulsed-nozzle Fourier-transform microwave spectra are reported for the ground vibrational states of the complexes. The infrared and microwave spectra are consistent with T-shaped complexes as shown originally by Steed, Dixon, and $Klemperer1$ for $Ar-CO2$. The infrared band origins for the Ar and Kr complexes are red shifted, from that of free $CO2$, by 1.09 and $0.95cm-1$ for $Ar-CO2$ and by 1.97 and $1.76cm-1$ for $\mathrm{<mrow\; data-mjx-texclass="ORD">84</mrow>}Kr-CO2$. For $Ne-CO2$, blue shifts of 0.15 and $0.19cm-1$ are observed. The lower Fermi components are free of perturbations, whereas the upper components of $Ar-CO2$ and $Kr-CO2$ are perturbed. For $Ar-CO2$ the perturbation is strong. shifting the positions of the observed Q-branch lines of the $Ka=1\leftarrow 0$ subband by as much as 500 MHz.