Double-resonance fluorescence dip Rydberg spectroscopy completes the iron period ionization potential table

The high melting points and appreciable spin multiplicities of some iron-period elements have made spectra of their highly excited states difficult to obtain and interpret. The authors have studied the spectra with state selective spectroscopy, without using any oven. RF sputtering discharge produces enough atoms to furnish a strong stable laser-induced fluorescence signal, excited by a beam at a resonance transition (e.g., 248.3 nm for iron). The fluorescent upper state serves as a labeled lower state for a tunable beam sufficiently intense to saturate transitions to nonfluorescent Rydberg and autoionizing states, and a fluorescence dip spectrum is obtained. The spectra include 4p-nd and 4p-ns Rydberg series to n ~ 40 and some features due to autoionizing states.