Threshold truncation of a  giant  dipole resonance in photoionization of Ti^<b>3+</b>

Abstract

Photoionization of triply charged titanium ions was investigated using the merged photon–ion beam technique at a synchrotron light source. The experimental photon energy range 42.6–49.4 eV encompasses the threshold for the photoionization of Ti3+(3p6 3d2 D3/2) ground-state ions at 43.267 eV. Prominent resonance features due to 3p → 3d and 3p → 4s excitations are observed with the strongest one being the 'giant' 3p5(3d23F)2F dipole resonance which has a width of 1.5 eV. Since it is located only 0.2 eV above the ionization threshold a cut-off of this resonance is observed in photoionization. By employing the principle of detailed balance the results are compared with an earlier experimental study of the time-reversed Ti4+ photorecombination. The comparison clarifies the giant resonance's role in photorecombination and yields state-selective photoionization and photorecombinaton cross sections on an absolute scale.