Ordering of the $0d_{5/2}$ and $1s_{1/2}$ proton levels in light nuclei
  A survey of the available single-proton data in $A\leq17$ nuclei, along with calculations using a Woods-Saxon potential, show that the ordering of the $0d_{5/2}$ and $1s_{1/2}$ proton orbitals are determined primarily by the proximity of the $s$-state proton energy to the Coulomb barrier. This is analogous to the dependence of the corresponding neutron orbitals in proximity to the neutron threshold, that was previously discussed. 
C. R. Hoffman, B. P. Kay and J. P. Schiffer
nucl-ex nucl-th