PHASE-AMPLITUDE METHOD APPLIED TO DOUBLY-EXCITED STATES OF HE(S-1(E)

We present a phase-amplitude (PA) procedure, which emphasizes the evolution of the He** wave function from the origin of the hyper-radius R = square-root r1(2) + r2(2). This method, combined with quantum-defect theory, produces an R-dependent phase shift pitau(R) of the ionized channel, whose variation with R illustrates explicitly its coupling with the closed resonant channels. Previous calculations (e.g., of the R-matrix type) whose dynamical information remains hidden within a core region are thus complemented and extended by displaying the R dependence of phase shifts for several low doubly excited resonances of He(S-1(e)). The large R limit yields the familiar scattering phase shift, in fair agreement with experimental data. The results illustrate the dominant role of short-range channel coupling in the formation of resonances.