Wannier threshold law for two electron escape in the presence of an external electric field

摘要

We consider double ionization of atoms or ions by electron impact in thepresence of a static electric field. As in Wanniers analysis of the analogoussituation without external field the dynamics near threshold is dominated by asaddle. With a field the saddle lies in a subspace of symmetrically escapingelectrons. Near threshold the classical cross section scales with excess energyE like sigma=E^alpha, where the exponent alpha can be determined from thestability of the saddle and does not depend on the field strength. For example,if the remaining ion has charge Z=2, the exponent is 1.292, significantlydifferent from the 1.056 without the field.