  The levels in 26Na with single particle character have been observed for the
first time using the d(25Na,p gamma) reaction at 5 MeV/nucleon. The measured
excitation energies and the deduced spectroscopic factors are in good overall
agreement with (0+1) hbar-omega shell model calculations performed in a
complete spsdfp basis and incorporating a reduction in the N=20 gap. Notably,
the 1p3/2 neutron configuration was found to play an enhanced role in the
structure of the low-lying negative parity states in 26Na, compared to the
isotone 28Al. Thus, the lowering of the 1p3/2 orbital relative to the 0f7/2
occurring in the neighbouring Z=10 and 12 nuclei -- 25,27Ne and 27,29Mg -- is
seen also to occur at Z=11 and further strengthens the constraints on the
modelling of the transition into the island of inversion.
