COMPLETELY L(2) INTEGRABLE METHOD FOR STRONG-COUPLING MULTICHANNEL PHOTOIONIZATION - PHOTOELECTRON EMISSION OF HE BETWEEN THE N=3 AND 4 THRESHOLDS

We present a completely L2 integrable method to evaluate continuum states in multichannel photoionization. The Feshbach theory is used to separate the resonant and nonresonant components of the wave function. The nonresonant continuum is built from discretized uncoupled channels, using a formal scattering theory. In practice, the coupling between channels is introduced in a purely algebraic way, by simply solving a system of linear equations. The advantage of the present approach is that it can be used irrespective of the interaction strength between the uncoupled states. We have applied the method to study photoionization of helium between the N=3 and 4 thresholds. The results are in good agreement with the existing experimental data.