Experimental study of the 4dionization continuum in atomic iodine by photoelectron and photoion spectroscopy

Iodine atoms, produced by laser-induced dissociation of molecular iodine, have been photoionized with synchrotron radiation in the region of the 4d→εf shape resonance. By using photoelectron spectroscopy in conjunction with ionic spectroscopy, we have measured the 4d, 5p, 5s, and valence satellites’ absolute photoionization cross sections, as well as the relative oscillator strengths for the production of ${\mathrm{I}}^{+}$, ${\mathrm{I}}^{2+}$, and ${\mathrm{I}}^{3+}$. Some specific open-shell effects have been observed such as the strong 4d-5p hole electrostatic coupling, as revealed by the 4d photoelectron spectrum, and the weak enhancement of the outer-shell cross sections, especially the 5p one, in the region of the 4d→εf shape resonance, as compared with xenon. Multiple-electron processes associated with 4d photoemission have been studied and account for about 20% of the photoabsorption cross section. Moreover, as already pointed out in iodine compounds, the total oscillator strength of atomic iodine is found, in the studied spectral region, to be surprisingly weak.