ELECTRON-POSITIVE-ION SCATTERING NEAR REACTION THRESHOLDS - EFFECT OFLONG-RANGE POLARIZATION FORCES

A multichannel version of effective-range theory is developed, applica ble to electron scattering by positive ions. The formalism allows for the inclusion of the effect of long-range inverse-power-law interactio ns arising from target distortion in the field of the projectile. A pe rturbation theory is described for the construction of asymptotic stat es accounting for the combined effect of Coulomb and polarization forc es. The explicit extraction of threshold branch-point singularities le aves modified reaction-matrix elements that vary slowly with energy, t hereby permitting the smooth extrapolation of scattering parameters th rough reaction thresholds. A systematic procedure is made available to determine the effect of long-range forces on quantum defects and reso nance level shifts; it is applied here, as an illustration, in first o rder. The theory provides an extension, to a wider class of scattering systems and long-range interactions, of an analysis of threshold beha vior in electron-ion reactions given some time ago [M. Gailitis, Sov. Phys. JETP 17, 1328 (1963)]. [S1050-2947(98)03010-8].