Dominant Nonadiabatic Contribution to the Long-Range Electron-Atom Interaction

In the scattering of low-energy electrons or positrons by spherically symmetric atoms, a significant role is played by the long-range interactions. These originate partially in the adiabatic polarization of the atom, which contributes 1q⁴, 1q⁶, and higher terms, where q is the electron-atom separation. There is also a non-adiabatic contribution, which behaves asymptotically as 3a₀β₁(e^')²q⁶, where e^' is the charge of the incident particle; this contribution was first studied by Mittleman and Watson in the case of hydrogen. We have obtained a useful if formally trivial extension of their results on β₁ to a wide class of atoms. We have also obtained rigorous if sometimes crude upper and lower bounds on β₁ which depend upon the availability of some information on the low-lying atomic energy levels and the associated oscillator strengths, and on the electric dipole polarizability. Bounds on β₁ have been obtained for He, Li, Ne, and Na. Statistical moment studies lead to estimates of β₁ for the rare-gas atoms.