Infrared spectroscopy of Kr–12C18O2: Change in the CO2 intramolecular potential by complex formation and isotope effect on the vibrationally averaged intermolecular geometry

The high-resolution infrared spectrum of Kr–12C18O2 has been observed in the ν3 band (2314 cm−1) region of 12C18O2 with diode laser absorption spectroscopy of pulsed molecular beam. The vibrational band origin of Kr–12C18O2 corresponding to the ν3 mode of 12C18O2 shows a shift of Δν0 = −0.86510(30) cm−1 with respect to that of 12C18O2. The geometrical parameters of the T-shaped ground-state average structure are determined to be RKrC = 3.6204(11) Å and ΘKrCO = 83.51(10)°. The change in the CO2 intramolecular potential upon complex formation is derived from the observed red shift Δν0, and the isotope effects on RKrC and ΘKrCO are reproduced by ab initio calculation.