Novel evidence for the σ-bond linear-chain molecular structure in 14C

A multi-nucleon transfer and cluster decay experiment, Li-7(B-11, C-14* -> alpha+Be-10)alpha, is conducted at an incident beam energy of 55 MeV. This reaction channel has a significantly large Q-value, which favors populating the high lying resonant states in C-14. The decay paths, from these resonances to various states of the final nucleus Be-10, can be selected, owing to the experimentally achieved optimal resolution of the Q-value spectrum. A number of resonant states are reconstructed from the forward emitting Be-10 + alpha fragments, and their major molecular structures can be detected according to the selective decay paths and relative decay widths. A state at 22.4(2) MeV validates the previously measured and theoretically predicted band head of the positive-parity sigma-bond linear-chain molecular band. Two additional resonances at 22.9(2) and 24.2(2) MeV are identified and consistent with the predicted 2(+) and 4(+) members of the same molecular band, thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes. A few high energy resonances, which also indicate the presence of the sigma-bond molecular structure, are observed; however, further studies are still required to clarify their ascription in band systematics.