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 deals with thirteen isotopic varieties of CO2. Subvolume B3 containing data for N2O, and further subvolumes are in preparation.