Equivalent Orbital Bond Moments: Applications to Carbon Dioxide and Water

Abstract

Self-consistent field molecular orbitals for CO2, H2O and the B2H4 skeleton of diborane have been transformed into equivalent orbital representations, and bond moments have been defined as the dipole moments of the corresponding equivalent orbitals. If a maximum localization criterion is imposed and if hybrid moments (atomic dipole terms) on central atoms are omitted, one obtains moments of 2.6D(C+O—) in CO2, 1.4D(O—H+) in water, and 2.03D(B2+H—) in a line perpendicular to the B–B bond in diborane. The treatment of water does not seem to allow a separation of well-localized bond and lone-pair moments with the proper directional properties. The bond moment of C–H in methane, according to these criteria, is 0.6D(C—H+). It is concluded that the method is a valid approach to the problem of nonempirical calculation of bond moments in polyatomic molecules.