Relationship between the Charge Distribution and Dipole Moment Functions of CO and the Related Molecules CS, SiO, and SiS

The dipole moment functions of the titled molecules are written as the sum of a charge and induced atomic dipole contribution and the distance dependence interpreted in terms of these components. These two contributions have opposite signs over a large range of internuclear distances, and when they have equal magnitudes, the dipole moment vanishes. This happens with CO near the equilibrium bond length and is responsible for its small dipole moment. The dipole moment of CS is 0.770(ea0), rather large for a diatomic in which the two atoms have essentially the same electronegativities; this is because for CS, the two components of the dipole moment have the same sign at equilibrium and reinforce one another.