We propose a realizable and efficient approach for exciting long-range ion-pair molecules, known as heavy Rydberg states, in an ultracold 85 Rb gas via Feshbach resonances. Heavy Rydberg states, the molecular analogs of electronic Rydberg states, with the electron replaced by an atomic anion, offer opportunities for novel physics, including the formation of ultracold anions and strongly coupled plasmas. We map the positions, lifetimes, and Franck-Condon factors of heavy Rydberg resonances across a wide range of excitation energies, and we calculate the rates of formation for the most promising transitions through long-lived intermediate interferometric resonances.

We report an upper bound to the ionization energy of 85 Rb2 of 31 348.0(6) cm −1 , which also provides a lower bound to the dissociation energy D0 of 85 Rb + 2 of 6 307.5(6) cm −1. These bounds were measured by the onset of autoionization of excited states of 85 Rb2 below the 5s+7p atomic limit. We form 85 Rb2 molecules via photoassociation of ultracold 85 Rb atoms, and subsequently excite the molecules by single-photon ultraviolet transitions to states above the ionization threshold.

We report on hyperfine-resolved spectroscopic measurements of the electric-dipole forbidden 5p 3/2 → 8p 1/2 transition in a sample of ultracold 87 Rb atoms. The hyperfine selection rules enable the weak magnetic-dipole (M1) contribution to the transition strength to be distinguished from the much stronger electric-quadrupole (E2) contribution. An upper limit on the M1 transition strength is determined that is about 50 times smaller than an earlier experimental determination. We also calculate the expected value of the M1 matrix element and find that it is less than the upper limit extracted from the experiment.

Abstract. We describe the design and realization of a scheme for uv laser spectroscopy of singly-ionized iron (Fe II) with very high resolution. A buffer-gas cooled laser ablation source is used to provide a plasma close to room temperature with a high density of Fe II. We combine this with a scheme for pulsed-laser saturation spectroscopy to yield sub-Doppler resolution. In a demonstration experiment, we have examined an Fe II transition near 260 nm, attaining a linewidth of about 250 MHz. The method is well-suited to measuring transition frequencies and hyperfine structure. It could also be used to measure small isotope shifts in isotope-enriched samples. ‡ Present address: