Vibrational Spectra of CO2-Electron Donor−Acceptor Complexes from ab Initio

In this paper, we investigated the 1:1 EDA complexes of CO 2 formed with alcohols, namely, methanol and ethanol (sp 3 O-donating atom), and with acetone (sp 2 O-donating atom) in light of ab initio calculations. The interaction energy and the geometry of the complexes have been evaluated with the Moller−Plesset perturbation theory at the second-order level (MP2) using Dunning's basis sets. The predicted structures are found to be rather similar compared with the calculations at the SCF/3-21G* level reported by Jamroz et al. (Jamroz, M. H.; Dobrowolski, J. C.; Bajdor, K.; Borowiak, M. A. J. Mol. Struct. 1995, 349, 9.). Nevertheless, the stabilization energies are found in our work to be 2 to 2.5 times lower including electron correlation. In addition, we have analyzed the vibrational spectra of these EDA complexes. In particular, we emphasized the splitting of the ν 2 bending mode of CO 2 and the ν S (OH) stretching mode of alcohols or the antisymmetric ν a (CCC) and symmetric ν s (CO) stretching modes of acetone. Finally, the shift and the IR and Raman intensity variations under the complex formation are discussed and compared with infrared absorption and Raman experimental measurements.