Energy of Interaction between Two Excited Hydrogen Atoms in either 2s or 2p States

Abstract

A complete set of potential energy curves arising from the interaction between two excited hydrogen atoms in either 2s or 2p states is given for intermediate and large internuclear separations. These include first- and second-order perturbation energies. The first-order perturbation energies are obtained by using exact integrals and properly symmetrized wave functions with an effective nuclear charge of unity. The possibility of occurrence of ionic states, which become important at small internuclear separations, is ignored. The first-order energies are essentially Coulombic in the long-range region and can be described in terms of simple electrostatic dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions. Approximate values of the second-order perturbation energies are obtained by using nonsymmetrized wave functions and omitting in the expansion of the perturbation potential all terms beyond the leading one. For most states, the second-order perturbation energies are small compared to the first-order energies throughout the long-range region.