  We present photodissociation of ultracold long-range Rydberg molecules as a
tool to characterize their electronic properties. We photoassociate K2 37P
molecules with highly entangled electronic and nuclear spins of the two bound
atoms and quantify the entanglement by projection of the molecular state onto
non-interacting atoms using radiofrequency photodissociation. By comparison of
experimental photodissociation rates with theoretical predictions we further
characterize the electronic and nuclear wavefunction of the photoassociated
molecules. Based on the complete characterization of the formed long-range
Rydberg molecules, we demonstrate a full hyperfine-spin flip of a free
ground-state atom through the interaction with a Rydberg atom.
