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We report lifetime measurements of the metastable 6d 2D5=2 and 6d 2D3=2 states of Raþ. The measured lifetimes, τ5 ¼ 303.8ð1.5Þ ms and τ3 ¼ 642ð9Þ ms, are important for optical frequency standards and for benchmarking high-precision relativistic atomic theory. Independent of the reported measurements, the D state lifetimes were calculated using the coupled-cluster single double triple method, in which the coupled- cluster equations for both core and valence triple excitations were solved iteratively. The method was designed for precise prediction of atomic properties, especially for heavy elements, where relativistic and correlation corrections become large, making their treatment more challenging. This Letter presents the first tests of the method for transition properties. Our prediction agrees with experimental values within the uncertainties. The ability to accurately predict the atomic properties of heavy elements is important for many applications, from tests of fundamental symmetries to the development of optical clocks. 

Molecules containing short-lived, radioactive nuclei are uniquely positioned to enable a wide range of scientific discoveries in the areas of fundamental symmetries, astrophysics, nuclear structure, and chemistry. Recent advances in the ability to create, cool, and control complex molecules down to the quantum level, along with recent and upcoming advances in radioactive species production at several facilities around the world, create a compelling opportunity to coordinate and combine these efforts to bring precision measurement and control to molecules containing extreme nuclei. In this manuscript, we review the scientific case for studying radioactive molecules, discuss recent atomic, molecular, nuclear, astrophysical, and chemical advances which provide the foundation for their study, describe the facilities where these species are and will be produced, and provide an outlook for the future of this nascent field.