14C resonant states revisited

In neutron-rich nuclei clustering can form molecule-like structures, with neutrons acting like electrons in the covalent bonding to bind them. This can lead to predicted linear chains of α particles connected by neutron bonds analogous to π or σ atomic bonds. Here we present for the first time an experimental study of both the π - and σ -bond configurations in the neutron-rich 14C nucleus produced via the 10Be+4He reaction. We report elastic and inelastic scattering excitation functions measured over a broader energy range than previously available and, for the first time, provide the excitation function for the 4He(10Be,6He)8Be reaction. The previously identified positive-parity π -bond linear-chain band in 14C is revisited. Possible signatures of a negative-parity clustered configuration with similar rotational characteristics are also examined. Moreover, new evidence for a possible σ -bond configuration is discussed. Furthermore, the broad structures observed near 19 and 22.5 MeV are found to be consistent with reaction-dynamical surface resonances, indicating that not all structures observed in the excitation spectrum necessarily correspond to compound-nucleus states. Overall, the results provide an improved experimental basis for the study of clustering and molecular-like structures in 14C.