The optimized structures of several complexes of phosphorus containing compounds and CO2 in the gas phase were determined theoretically. The Gaussian 03 computer software package was used to perform the ab initio computations, including Hartree-Fock (HF/6-31+G(d)) and density functional theory (B3LYP/6-31+G(d)). At the same level of calculation, the binding energy between CO2 and phosphorus containing compounds was calculated. The binding energies for CO2-trialkyl phosphate complexes increased with the number of alkyl groups attached to the phosphorus. Harmonic infrared frequencies were calculated for the CO2 bending mode (v(2)) in the various complexes. The appearance of a second peak in the CO2 bending mode (v(2)) at lower wavenumber verified the strong interaction between CO2 and phosphorus containing compounds. The results of the ab initio computations were in good agreement with data previously reported. (c) 2005 Elsevier B.V. All rights reserved.