Volume II/20 provides critically evaluated data on free molecules, obtained from infrared spectroscopy and related experimental and theoretical investigations. The volume is divided into four subvolumes, A: Diatomic Molecules, B: Linear Triatomic Molecules, C: Nonlinear Triatomic Molecules, D: Polyatomic Molecules. Subvolume B2 contains data for CO2 (OCO) and has been split into two parts. Subvolume II/20 B2° has dealt exclusively with the normal isotopic species of carbon dioxide 12C16O16O. The present part ß deals with thirteen isotopic varieties of CO2. Subvolume B3 containing data for N2O, and further subvolumes are in preparation.