A search for the neutron-unbound nucleus 21 C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with 20 C fragments. No evidence for a low-lying state was found, and the reconstructed 20 C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |a s | < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that 22 C is bound by less than 70 keV.

Proton removal reactions from a secondary 22 N beam were utilized to populate unbound states in neutronrich carbon isotopes. Neutrons were measured with the Modular Neutron Array (MoNA) in coincidence with carbon fragments. A resonance with a decay energy of 76 (14) keV was observed in the system 18 C +n corresponding to a state in 19 C at an excitation energy of 653 (95) keV. This resonance could correspond to the first 5/2 + state which was recently speculated to be unbound in order to describe 1n and 2n removal cross section measurements from 20 C.