Photoabsorption and photoionization cross sections are reported from 3d<sup>2</sup>4s4p<sup>3</sup>D<sup>0</sup><sub>2</sub>, 3d<sup>2</sup>4s4p<sup>3</sup>G<sup>0</sup><sub>3,4</sub>, and 3d<sup>3</sup>4p<sup>5</sup>F<sup>0</sup><sub>5</sub> initial states of titanium, reaching final-state energies from −500 to 8000 cm<sup>−1</sup> relative to the first ionization threshold 3d<sup>2</sup>4s<sup>4</sup>F<sub>3/2</sub>. The nearly ab initio calculations use the eigenchannel R-matrix method, the multichannel quantum-defect theory, and the LS → jj relativistic recoupling frame transformation. The last two steps use experimental energies of Ti<sup>+</sup> levels. Radial orbitals needed to calculate short-range interaction parameters are obtained in a multiconfiguration Hartree–Fock approximation that directly generates natural orbitals for the target states. This method bypasses an intermediate step followed in earlier eigenchannel R-matrix studies, in which a set of primitive orbitals was used. Theoretical cross sections are compared with experimental data, in particular near the two lowest ionization thresholds 3d<sup>2</sup>4s<sup>4</sup>F and 3d<sup>3</sup> <sup>4</sup>F. Our results, which at these energies are accurate to within errors of ˜0.03 in the quantum defects, account for most of the experimental features. Predictions are also made for the spectra at higher energies, where overlapping Rydberg series seriously complicate the photoabsorption pattern.
© 1996 Optical Society of AmericaPDF Article