A COMPARATIVE THEORETICAL STUDY OF PHOTOIONIZATION CROSS SECTIONS AND ANGULAR DISTRIBUTIONS

Photoionization cross sections and angular distributions are computed in the dipole length and dipole velocity approximations. The initial state is described by ab initio 4—31G molecular orbitals, and the final state by plane waves, Coulomb waves, one-center pseudopotential functions, or multicenter multiple-scattering functions for an effective muffin-tin model potential. HeI and HeII results for the molecules H2, N2, O2, CO, and CO2 are reported. The best agreement with experiment is obtained when using the dipole length approximation with multiple-scattering continuum functions. This approach is therefore employed to study the cross sections and angular distributions as a function of the photon energy, up to 50 eV. Considering the simplicity of the effective potential used, the spectral variations including several resonances are described reasonably well