Observation of the pi(2)sigma(2)-bond linear-chain molecular structure in C-16

Measurements of the H-2(C-16,C-16* -> He-4 + Be-12 or He-6 + Be-10) H-2 inelastic excitation and cluster-decay reactions have been carried out at a beam energy of about 23.5 MeV/u. A specially designed detection system, including one multilayer silicon-strip telescope at around zero degrees, has allowed the high-efficiency threefold coincident detection and therefore the event-by-event determination of the energy of the unstable nucleus beam. The decay paths from the C-16 resonances to various states of the final Be-10 or Be-12 nucleus are recognized thanks to the well-resolved Q-value spectra. The reconstructed resonances at 16.5(1), 17.3(2), 19.4(1), and 21.6(2) MeV are assigned as the 0(+), 2(+), 4(+), and 6(+) members, respectively, of the positive-parity (3/2(pi)(-))(2)(1/2(sigma)(-))(2)-bond linear-chain molecular band in C-16, based on the angular-correlation analysis for the 16.5 MeV state and the excellent agreement of decay patterns between the measurements and theoretical predictions. Moreover, another intriguing high-lying state was observed at 27.2(1) MeV which decays almost exclusively to the approximate to 6 MeV states of Be-10, in line with the newly predicted pure sigma-bond linear-chain configuration.