Spectra of CO2-Rg2 and CO2-Rg-He trimers (Rg = Ne, Ar, Kr, and Xe): Intermolecular CO2 rock, vibrational shifts and three-body effects

Weakly bound CO2-Rg(2) trimers are studied by high-resolution (0.002 cm(-1)) infrared spectroscopy in the region of the CO2 nu(3) fundamental band (approximate to 2350 cm(-1)), using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion with an effective rotational temperature of about 2 K. CO2-Ar-2 spectra have been reported previously, but they are extended here to include Rg = Ne, Kr, and Xe as well as new combination and hot bands. For Kr and Xe, a unified scaled parameter scheme is used to account for the many possible isotopic species. Vibrational shifts of CO2-Rg(2) trimers are compared to those of CO2-Rg dimers, and in all cases the trimer shifts are slightly more positive (blue-shifted) than expected on the basis of linear extrapolation from the dimer. Combination bands directly measure an intermolecular vibrational mode (the CO2 rock) and give values of about 32.2, 33.8, and 34.7 cm(-1) for CO2-Ar-2, -Kr-2, and -Xe-2. Structural parameters derived for CO2-Rg(2) trimers are compared with those of CO2-Rg and Rg(2) dimers. Spectra of the mixed trimers CO2-Rg-He are also reported.

Automated summary

Weakly bound CO2-Rg(2) trimers were studied using high-resolution infrared spectroscopy, and their vibrational shifts were compared to those of CO2-Rg dimers. The findings suggest that the trimer shifts are slightly more positive than expected.