Theoretical electronic and vibrational study of AlCO and Al(CO)2 using density functional theory

The AlCO molecule has been experimentally characterized as a strong complex with a large red-shift of the νCO stretching mode. Post Hartree-Fock ab initio methods including the treatment of correlation effects have predicted this molecule to be a weakly bound van der Waals complex, and were not able to reproduce its vibrational spectrum. Electronic and vibrational calculations at the harmonic approximation of this complex have been accomplished using density functional theory (DFT) and close agreement with experiment is now obtained. The credibility of the calculations is also assessed by the good agreement between the DFT-calculated and experimental vibrational frequencies of the Al(CO)2 molecule. It is to be noticed that for this species the MP2 method reverses the order of the symmetric and antisymmetric νCO stretching mode frequencies with respect to the experimental ones.