Infrared spectroscopy of (12C18O2)2 and isotope effect on the vibrationally averaged structure of (CO2)2

The high-resolution infrared spectrum of (12C18O2)2 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 (12C18O2)2 corresponding to the ν3 mode of 12C18O2 shows a blue shift of 1.62362(19) cm−1 with respect to that of 12C18O2. The geometrical parameters of the slipped parallel ground-state structure are RCC = 3.5947(11) Å and θCCO = 57.97(7)°. By calculating vibrational wavefunctions on ab initio potentials for four intermolecular degrees of freedom, the isotope effect on RCC is found to arise mainly from in-plane tilting.