  In a recent experiment, carried out at RIBF/RIKEN, the
$^{25}$F$(p,2p)$$^{24}$O reaction was studied at 270 MeV/A in inverse
kinematics. Derived spectroscopic factors suggest that the effective core of
$^{25}$F significantly differs from a free $^{24}$O nucleus. We interpret these
results within the Particle-Rotor Model and show that the experimental level
scheme of $^{25}$F can be understood in the rotation-aligned coupling scheme,
with its $5/2^+_1$ ground state as the band-head of a decoupled band. The
excitation energies of the observed $1/2_1^+$ and $9/2_1^+$ states correlate
strongly with the rotational energy of the effective core, seen by the odd
proton, and allow us to estimate its $2^+$ energy at $\approx$ 3.2 MeV and a
moderate quadrupole deformation, $\epsilon_2 \approx 0.15$. The measured
fragmentation of the $\pi d_{5/2}$ single-particle strength is discussed and
some further experiments suggested.

Nuclear Theory;Nuclear Experiment