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Phys" Rev. BJL4, 4808 (1976). 14 M 9 Cross, Phys. Rev. B jj5, 602 (1977). 15 ln Refo 5 there is an indication of the third peak but of a fractional intensity -2x 10" 3 0 The authors attribute it to possible pre-target molecular dissociation.We report the observation of doubly excited autoionizing Rydberg states of Sr, belonging to the configuration 5p 1 / 2 ,nh Gur procedure involves a three-step optical excitation process which incorporates Stark switching to reach higher I states not normally accessible because of dipole selection rules. Quantum defects are reported for several 5/> 1 / 2 , ns and 5pi/ 2 9 nd states. The lifetimes of the 5p 1^29 ns states are shown to scale as (n*) 3 , and the lifetimes of the 5p l / 2f 16/ states are shown to increase dramatically with increasing I

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We show that the dipole-dipole interaction between two Rydberg atoms can give rise to long range molecules. The binding potential arises from two states that converge to different separated atom asymptotes. These states interact weakly at large distances, but start to repel each other strongly as the van der Waals interaction turns into a resonant dipole-dipole interaction with decreasing separation between the atoms. This mechanism leads to the formation of an attractive well for one of the potentials. If the two separated atom asymptotes come from the small Stark splitting of an atomic Rydberg level, which lifts the Zeeman degeneracy, the depth of the well and the location of its minimum are controlled by the external electric field. We discuss two different geometries that result in a localized and a donut shaped potential, respectively.