The proton single-particle states have been investigated using the in-beam γ-ray spectroscopy technique via the following reactions: 4He(22O,23F); 4He( 23F,23F); 4He(24F,23F); and 4He(25Ne,23F). The characters of excited states in 23F were deduced by comparison of the population strengths in these reactions. We found that the 2268- and 4059-keV levels have strong proton single-particle nature of the s1/2 and d3/2 orbitals, respectively. These singleparticle states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which indicates that the centroid energy gaps for πd5/2-πs1/2 and πd 5/2-πd3/2 are wider than predicted.
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