Spectrum and energy levels of eleven-times ionized zirconium (Zr xii)

The spectrum of Zr xii was observed with a low-inductance spark and a laser-produced plasma in the region from 70 to 630 Å on the 10.7-m grazing incidence spectrograph at NBS. From the identification of 36 lines, a system of 28 energy levels was determined. The level system (Cu i isoelectronic sequence, 3d10nl) includes the series np (n = 4–6), nd (n = 4–6), nf (n = 4–8), and ng (n = 5–7). The 4f2F term has an anomalously small fine-structure interval (1 ± 3 cm−1). The ionization energy is determined from the ng series (n = 5–7) to be 1 905 500 ± 200 cm−1 (236.25 ± 0.03 eV).