Mixing of [Formula Presented] configurations in terminating dipole series of [Formula Presented]

Resonant [Formula Presented] states of [Formula Presented] below the [Formula Presented] threshold are studied in a semiempirical coupled-channel calculation, in which fine structure and QED corrections are included exactly. This leads to the termination of the dipole series of Feshbach resonances and to increasing mixing between different [Formula Presented] states toward the end of the series. We predict a total of three resonances in the series dominantly of [Formula Presented] nature, and four resonances in the series dominantly of [Formula Presented] nature. The highest state of the latter series contains a 17% admixture of [Formula Presented] configurations, so one-photon excitation of this state from the [Formula Presented] ground state is far from forbidden.