Multiple scattering theory for non-spherical potentials: application to photoelectron angular distributions from oriented diatomic molecules and the study of shape resonances

We use multiple scattering photoelectron diffraction theory to calculate th e angular distribution of electrons photoemitted from core levels of fixed- in-space molecules. Non-spherical scattering potentials, needed for low pho toelectron energies (E < 50 eV), are included in our formalism through non- diagonal scattering matrices; these fit directly into a new approach for mu ltiple scattering theory originally based on spherical potentials. When the kinetic energy of the photoelectron is low its scattering cannot be adequa tely represented by spherically-symmetric potentials. In addition, we have considered the effect of the final-state hole, and found this to be importa nt as well. As an example, we calculate the angular distribution of photoel ectrons emitted from the K shells of C in oriented gas-phase CO molecules, as recently measured by several groups. Particularly important are the ener gies for which shape resonances appear in the continuum, with the angular d istributions showing radical changes over such resonances. <(c)> 2001 Elsev ier Science B.V. All rights reserved.