On the Electric Multipole Moments of Carbon Monoxide

Electric moments are relevant for many phenomena caused by intermolecular interactions [1-4]. Recent work [5-13] has provided evidence that models relying on the knowledge of the electric moments of the monomers can be used to predict molecular structures and properties of weakly bonded van der Waals systems. Not all electric moments are easily amenable to experiment [2]. Experimental determinations of electric moments beyond the quadrupole are extremely rare. Theory can contribute to the field by predicting these properties. The electric moments of carbon monoxide have been the object of numerous experimental or theoretical studies [14-27], Of particular interest to theory is the determination of Hartree-Fock values for the dipole (p), quadrupole (0), octopole (ß) and hexadecapole (<P) moments from fully numerical calculations (NHF) by Laaksonen, Pyykkö and Sundholm [22]. This makes possible the construction of Gaussiantype basis sets of near Hartree-Fock quality and the subsequent prediction of accurate electric moments via theoretical methods that take into account electron correlation. In this work we report self-consistent field (SCF) and finite-field Moeller-Plesset perturbation theory (MP) calculations of p, 0, (2, and <P. The higher moments are extracted from the energies of the molecule perturbed by strategically placed electric point charges. This approach has been followed successfully in previous work on N 2 [28], F2 [29], HCl [30] and HCCH [31]. Previous correlated values of (2 and