CALCULATION OF SCATTERING-AMPLITUDES AS CONTINUOUS-FUNCTIONS OF ENERGY - R-MATRIX THEORY WITHOUT A BOX

An extension of the Kohn variational method for computing scattering a mplitudes is demonstrated that requires only matrix elements of the re solvent of the Hamiltonian between energy-independent test functions. Scattering boundary conditions are imposed by expanding the resolvent in a basis of square-integrable functions and outgoing-wave continuum functions. By employing several continuum basis functions with overlap s defined by suitable analytic continuation, the scattering amplitude can be expressed efficiently over a continuous range of energies. The method described here differs from previous approaches using time-inde pendent wave packets in that the wave packets which generate the initi al and final states in this approach can lie within the interaction re gion.