Observation of the $\ddot{I}{€}^2\ddot{I}{ƒ}^2$-bond linear-chain molecular structure in ${}^{16}$C

Abstract

Measurements of the ${}^2$H(${}^{16}$C,${}^{16}$C${}^{\ast }$${\to }^4$He+${}^{12}$Be or ${}^6$He+${}^{10}$Be)${}^2$H 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 multi-layer silicon-strip telescope at around zero degrees, has allowed the high-efficiency three-fold coincident detection and therefore the event-by-event determination of the energy of the unstable nucleus beam. The decay paths from the ${}^{16}$C resonances to various states of the final ${}^{10}$Be or ${}^{12}$Be 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 $(3/2_{\ddot{I}}{€}^{-}{)}^2(1/2_{\ddot{I}}{ƒ}^{-}{)}^2$-bond linear-chain molecular band in ${}^{16}$C, 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 $\sim$6 MeV states of ${}^{10}$Be, in line with the newly predicted pure $\ddot{I}ƒ$-bond linear-chain configuration.

13 pages, 10 figures