  Unbound states in 17C were investigated via one-neutron removal from a 18C
beam at an energy of 245 MeV/nucleon on a carbon target. The energy spectrum of
17C, above the single-neutron decay threshold, was reconstructed using
invariant mass spectroscopy from the measured momenta of the 16C fragment and
neutron, and was found to exhibit resonances at Er=0.52(2), 0.77(2), 1.36(1),
1.91(1), 2.22(3) and 3.20(1) MeV. The resonance at Er=0.77(2) MeV [Ex=1.51(3)
MeV] was provisionally assigned as the second 5/2+ state. The two resonances at
Er=1.91(1) and 3.20(1) MeV [Ex=2.65(2) and 3.94(2) MeV] were identified,
through comparison of the energies, cross sections and momentum distributions
with shell-model and eikonal reaction calculations, as p-shell hole states with
spin-parities 1/2- and 3/2-, respectively. A detailed comparison was made with
the results obtained using a range of shell-model interactions. The YSOX
shell-model Hamiltonian, the cross-shell part of which is based on the
monopole-based universal interaction, was found to provide a very good
description of the present results and those for the neighbouring odd-A carbon
isotopes - in particular for the negative parity cross-shell states.
