Infrared spectroscopy of Ne–12C18O2 and Xe–12C18O2: Change in the CO2 intramolecular potential by formation of rare gas–CO2 complexes

High-resolution infrared spectra of Ne–12C18O2 and Xe–12C18O2 have been observed in the ν3 band (2314 cm−1) region of 12C18O2 by diode laser absorption spectroscopy of a pulsed molecular beam. The vibrational band origins and rotational constants for these complexes are obtained. The observed shifts of the ν3 band origin for Rg–CO2 (Rg = Ne, Ar, Kr, Xe) with respect to that of CO2 exhibit a systematic 16O–18O isotope effect excepting a significant deviation for Ne–CO2 from a regular trend. This apparent anomaly is interpreted in terms of a change in the intramolecular potential function of CO2 caused by complex formation.