Completing the iron period: double-resonance, fluorescence-dip Rydberg spectroscopy and ionization potentials of titanium, vanadium, iron, cobalt, and nickel

We have used the fluorescence-dip technique to obtain double-resonance spectra of transition-metal atoms produced in a rf glow-discharge sputtering machine. Rydberg spectra of the neutral elements Ti, V, Fe, Co, and Ni have been analyzed to yield ionization potentials accurate to 1 cm−1, completing the table of values for the iron period (K through Zn). The 63 737-cm−1 value obtained for Fe agrees with a recently reported result, and new ionization potentials for Ti, V, Co, and Ni are 55 073, 54 413, 63 565 and 61 619 cm−1, respectively. Quantum defects for nd and ns series were obtained. Series converging to some excited ion core levels do not show detectable s–d mixing, which would provide a direct ionization channel and lead to the asymmetric line shapes that are characteristic of autoionization. Fano q parameters were determined for states autoionizing without a change in core configuration. Resolved spectra of low-lying Rydberg states display a complicated level structure not observed in studies of alkali or rare-gas atoms.