Long-range potentials and (n-1) d+ns molecular resonances in an ultracold Rydberg gas

We have calculated long-range molecular potentials of the 0g+, 0u-, and 1u symmetries between highly excited rubidium atoms. Strong np+np potentials characterized by these symmetries are important in describing interaction-induced phenomena in the excitation spectra of high np Rydberg states. Long-range molecular resonances are one such phenomenon and they were first reported in S. M. Farooqi, Phys. Rev. Lett. 91, 183002 (2003). One class of these resonances occurs at energies corresponding to excited atom pairs (n-1) d+ns. Such resonances are attributed to l -mixing due to Rydberg-Rydberg interactions so that otherwise forbidden molecular transitions become allowed. We calculate molecular potentials in Hund's case (c), use them to find the resonance line shape, and compare to experimental results.