Pseudopotential Method for Inelastic Processes in Atoms and Molecules. I. General Method and Photodetachment ofO−

With the ultimate goal of elucidating inelastic processes in molecules, we have developed a pseudopotential method by which one can compute the wave functions for electron scattering states around atoms, molecules, and their respective ions. The method depends upon knowledge of the phase shift, obtained from scattering experiments or from Quantum Defect calculations. A one-parameter model is chosen to fit the boundary conditions and an approximate pseudowave function derived from it. First-order perturbation theory is then carried out in the Green's function formalism, both to yield an improved wave function and to fit the parameter which optimizes our model. As a test of our model, we apply the theory to the calculation of the $s$-wave continuum wave function and cross section for the photodetachment of electrons from ${\mathrm{O}}^{-}$.