MULTICHANNEL CONTINUUM STATES BY A LEAST-SQUARES APPROACH IN A SPLINEBASIS - APPLICATION TO HE-PHOTOIONIZATION AND H-PHOTOIONIZATION

A recently proposed algorithm for the determination of the continuum w avefunction employing a B-spline basis set expansion and a least-squar es approach is extended to a full multichannel formulation employing a general close coupling expansion of the continuum wavefunction. Photo ionization of the He atom up to the n=4 threshold and H- up to the n=3 threshold are described with a pure close coupling wavefunction (16 a nd 9 channels respectively), and an accurate full CI expansion for the ground state. Excellent agreement with previous accurate calculations is obtained for total and partial cross sections, resonance parameter s and angular distributions. For He a nine-channel wavefunction allows photoionization to be described up to 2 keV. Modification of the boun dary conditions to describe long Rydberg series is successfully tested . The proposed algorithm appears to be a general and flexible approach for the description of multichannel continuum wavefunctions by basis set expansion.