Dipole-quadrupole dispersion forces associated with some metastable atoms

An estimate is made of the coefficients C (6) and C (8) of the R -6 and R -8 terms in the interatomic potential between the metastable 3 P states of Hg and of He interacting with sodium. Limited Hartree-Fock wave functions are used for Hg* and Coulomb wave functions for He*. The one-electron wave functions used still show some deficiencies, but in both systems the dipole-quadrupole term is found to contribute roughly 8–10 per cent to the total cross section at thermal energies. The effect of the C (8) term on the phase shifts near the rainbow region is of similar magnitude. The R -8 term should be allowed for in the analysis of metastable scattering experiments.