Photoabsorption spectra of I and its ions in the 4d region

We have studied the 4d photoabsorption process of I, I + , I 2 + , and I 3 + by using linear density-response theory together with density-functional theory to take into account the dynamic electron correlation, which is crucially important in reproducing the 4d giant resonance. The current approach, however, differs from previous approaches of this type in that we use an optimized effective potential and explicitly incorporate a self-interaction correction. We found that the 4d photoabsorption spectrum of the I + ion is almost the same as that of the neutral I atom, and that in moving from I to I 3 + the spectrum changes from one notably characterized by a giant resonance into one with multiple sharp peaks. Convoluting the spectra with the experimental energy resolution yielded spectra in excellent agreement with absolute experimental photoabsorption cross-section spectra. Moreover, our results showed better agreement with experiment than earlier theoretical studies. In addition, increasing the energy resolution revealed peaks not observed in the experimental spectra.