An ab initio Investigation of the dipole moment of the CO2…CO complex

The dipole moment of the CO2…CO van der Waals complex has been studied by highly correlated ab initio methods in the region of the experimental equilibrium geometry. Calculations at the CCSD(T) level of approximation combined with a basis of at least Pol(ANO)+f quality are needed to provide a reliable value of the dipole moment. The large amplitude motion in the van der Waals modes reduces the expectation value of the μz by ∼7%. The enhanced dipole is not primarily due to the field-induced bending of the CO2 partner, which increases the effective dipole by ∼20%, but to electronic polarization.