Photoabsorption and photoionization of titanium from excited states

Abstract

Photoabsorption and photoionization cross sections are reported from 3d24s4pD32o, 3d24s4pG33,4o and 3d34pF55o initial states of titanium, reaching final-state energies from −500 to 8000 cm−1 relative to the first ionization threshold 3d24s4F3/2. 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+ 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 3d24s4F and 3d3 4F. 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.