The interaction of normal and metastable helium atoms

Abstract

The energy of interaction of a normal helium atom and one excited to the first triplet or singlet metastable state is calculated over a range of nuclear separations from a$_{0}$ to 12a$_{0}$. The Heitler-London method is followed, with inclusion of all non-orthogonality integrals, and using analytic wave functions. Because of identity of the nuclei, g and u states of interaction occur, the energy of the u state having a minimum at about 2$\cdot $1a$_{0}$, and a positive maximum of 0$\cdot $29 and 0$\cdot $26 eV (for triplet and singlet states respectively) at about 4a$_{0}$; the g state is entirely repulsive. Comparison is made with experimental evidence for the binding energy of normal and metastable (triplet) atoms. An estimate is made of the second-order dipole-dipole interaction for large separations, and it seems certain that the first-order interaction dominates at least to 12a$_{0}$. Methods of calculating the necessary integrals are discussed in an appendix.