Infrared absorption spectroscopy of Ar–12C18O2: change in the intramolecular potential upon complex formation

An infrared absorption spectrum has been observed and analyzed for an Ar–12C18O2 van der Waals (vdW) complex in the range of 2312–2314 cm−1. The effective structure of the complex derived from the obtained rotational constants is in essential agreement with the structure estimated from that of Ar–12C16O2 based on the isotope effect on the amplitudes of vdW vibrations. The band origin for the Ar–12C18O2 ν4 mode shows a red shift of 0.4567 cm−1 with respect to that for 12C18O2 ν3 mode; the change in the intramolecular potential of CO2 upon complex formation with Ar is determined from the isotope effect on the band-origin shift.