Spectra and energy levels of ions in the zinc isoelectronic sequence from Rb viii to Mo xiii

Spectra of the zinclike ions Rb viii, Sr ix, Y x, Zr xi, Nb xii, and Mo xiii were excited with sparks and laser-produced plasmas and observed with normal- and grazing-incidence vacuum spectrographs. Almost all levels of the 4s², 4s4p, 4p², 4s4d, 4s5s, 4s5p, 4p5s, and 4s5d configurations were established in these ions. Several 4s4f ³F--4s5g ³G transitions of Nb xii and Mo xiii were also identified. The observed energy levels were interpreted by means of least-squares parametric fits and Hartree-Fock calculations. The ionization energies were determined as 132.79(25) eV for Rb viii, 158.33(25) eV for Sr ix, 185.77(37) eV for Y x, 214.86(37) eV for Zr xi, 246.11(37) eV for Nb xii, and 279.09(50) eV for Mo xiii.