Eigenchannel quantum-defect theory of open-shell atoms. I. Autoionization resonances and eigenphase shifts of chlorine

A multichannel quantum-defect theory focused on the time-delay matrix is applied to the analysis of Rydberg levels and autoionization resonances of the chlorine atom. The analysis shows that recently observed photoionization cross sections above the 3$p^4$ ${(\mathrm{}}^3$P) threshold of the chlorine ion may be interpreted in terms of unresolved groups of resonances with three different total angular momenta J and approximately the same energy. Experimental data of Rydberg levels were used to determine the phase shift of the collisional eigenstate (quantum defect) and the time-delay matrix for the electron-ion scattering process. The LS coupling scheme is assumed for the electron + ion compound state. The channel interaction strengths and dipole matrix elements of even-parity states relevant to electron-ion collisional and recombination processes are obtained. The branching ratio of photoelectrons is calculated.