Search

We describe the calculation of singly differential (energy-sharing) cross sections for electron-impact ionization. First, using exterior complex scaling, we calculate the outgoing portion of the scattering wave function without explicit use of asymptotic boundary conditions. Once that wave function is known for a finite region of space, the outgoing flux can be calculated and extrapolated to large distances according to behavior that is specific to the ionization problem. The differential cross section is proportional to the outgoing flux in specific directions of a hyperspherical angle in the coordinates. Calculations on the singlet s-wave radial limit (Temkin-Poet and collinear) models of electron-hydrogen atom ionization are presented. {copyright} {ital 1997} {ital The American Physical Society}

An analysis of the close-coupling method as it is traditionally formulated for electron-scattering problems shows that it can give rise to spurious resonances at intermediate energies when multiconfiguration target states are used. These resonances are associated with excited states of the target that are not explicitly included in the close-coupling expansion. We develop a modification of the close-coupling technique that allows one to isolate and systematically eliminate terms from the total wave function which are responsible for the spurious behavior. We have applied this technique to the study of electron-impact dissociation of F{sub 2} through its two lowest excited states. The complex Kohn variational calculations we have performed on this system incorporate accurate, multiconfiguration descriptions of the target wave functions.

Time-dependent calculations of multiphoton processes in multielectron atoms can utilize effective potentials to reduce the calculation to one for a single electron. The time-dependent Schrodinger equation for the wavefunction of this electron is solved using a finite-difference, implicit integration scheme. From this time-dependent wave function we can extract cross-sections and/or rates for photoemission, excitation and ionization. The effective potentials are constructed from Hartree-Slater calculations on the ground state of the atoms. Illustrative results are presented.

We show how to extend close-coupling calculations into the intermediate energy region without explicitly including a large number of inelastic channels. By discretizing the target continuum in a suitably chosen set of complex functions, we can construct convergent representations of a Feshbach optical potential that represents open inelastic channels including the ionization continuum. The method can be implemented for electron scattering by atomic or molecular targets with minimal modifications to existing electronic structure codes. The method is illustrated by applying it to [ital e][sup [minus]]+Li[sub 2] elastic scattering.

It is shown that the Fredholm determinant for the Lippmann-Schwinger equation may be computed for complex energies using only ${L}^{2}$ basis functions. Analytic continuation to the real axis in the $E+i\ensuremath{\epsilon}$ limit gives elastic scattering phase shifts over a continuous range of energies, showing that it is not necessary to explicitly enforce asymptotic boundary conditions for numerical scattering computations, and suggesting that elastic electron-atom or -ion scattering information may be obtained using standard bound-state configuration-interaction methods.