Photoionization from metastable (1s2s) 1Se and 3Se states of the He atom for energies between the N=2 and 3 thresholds of He+

Abstract

Photoionization cross sections from the metastable state (1s2s) $^{1}$${\mathit{S}}^{\mathit{e}}$ of the He atom for photon energies between the ${\mathrm{He}}^{+}$ (N=2) and (N=3) thresholds are calculated using the hyperspherical close-coupling method. The calculated spectra are convoluted with an energy resolution of 5.4 meV and are compared with the spectra for photoionization from the ground state. It is found that among the four possible outgoing channels, the 1s\ensuremath{\epsilon}p channel, which is the dominant channel for photoionization from the ground state, makes negligible contributions to the total cross sections for photoionization from the metastable state. As a result, the propensity rule derived from the ground-state photoionization no longer applies and more series of the doubly excited states are populated with significant spectral intensity in photoionization from the metastable state. Photoionization cross sections from the metastable (1s2s) $^{3}$${\mathit{S}}^{\mathit{e}}$ state are also calculated and analyzed.