The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the 22O nucleus. We also measured the α inelastic scattering on 23F, the neutron knockout from 24F, and the two-nucleon knockout from 25Ne using a cocktail secondary beam. The excited states were identified by de-excitation γ-rays coincident with outgoing 23F, and we found the proton single-particle states at 2268 and 4059 keV by comparison of the population strengths among these reactions. These states were respectively assigned to have ℓ = 0 and ℓ = 2 by the angular distributions obtained in the transfer reaction, and therefore they were considered to have the configurations of π s1 / 2 and π d3 / 2. The excitation energies of these states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which may indicate that the centroid energy gaps between π d5 / 2 and π s1 / 2 are wider than predictions.
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