Photoionization and electron-impact ionization of Kr3+

Absolute photoionization cross sections for Kr3+ were measured in the energy range 39.05–143.2 eV for single ionization and 120.6–137.7 eV for double ionization. For comparison, an electron-impact singleionization measurement was made in the energy range 43.1–179.1 eV and normalized to previously published absolute measurements. The Flexible Atomic Code and Cowan atomic structure codes were used to calculate energy levels, excitation energies and oscillator strengths for 3d→np, 3d→nf, and 4s→np autoionizing transitions from the ground and metastable states. From the single-photoionization measurements, ionization thresholds of the 2Po3/2, 2Do5/2 metastable states and 4So3/2 ground state were measured to be 46.62±0.02, 48.59±0.01, and 50.70±0.02 eV, nearly 2 eV lower than National Institute of Standards and Technology tabulated values. Within the experimental uncertainty, oscillator strengths determined from the photoionization measurements are in agreement with both calculations. Excitation-autoionization and resonant-excitation double-autoionization features are evident in the electron-impact ionization cross section