Theory of long range interatomic forces

The theory of angular momentum suggests general methods for calculating the electrostatic interaction energies between atoms in ground and excited states. In developing these, the effects of spin-orbit coupling on the interaction energies have been included. The classical interaction energy between two atoms is written as a contraction of irreducible tensors which permits the calculation of the general term of any multipole order. The formalism is first applied to the interaction of noble gas and alkali atoms in their ground states. The theory is then extended to describe the interaction of alkali atoms in arbitary excited states. The use of a coupled representation is valid only as long as the electrostatic interaction is a true perturbation on the system. To investigate the transition from a representation in which spin effects are neglected to the one which includes the spin-orbit coupling correctly, a more general perturbation method has been formulated. Attention is also given to the interaction energies between an alkali atom in the first excited and another one in a higher excited state. Here a number of energy curves show maxima and minima in first order which are due to competition of different multipoles. Formulas of second order dispersion energies are given to any desired multipole order