Abstract
We study isolated core excitation of ultra cold ytterbium Rydberg atoms of high orbital quantum number. Measurements were performed on the 6s_1/2 40l → 6p_1/2 40l transition with l=5-9. The extracted energy shifts and autoionization rates are in good agreement with a model based on independant electrons, taking into account interactions in a perturbative approach. We reveal a particularly long persistence of the autoionization rates with the orbital quantum number, explained by the strong coupling of the 6p_1/2nl autoionizing state with the 5d_3/2ε l' continua compared to previously studied divalent atoms.