The extremely neutron-rich nucleus ${}^{19}\mathrm{C}$ has been studied by Coulomb dissociation into ${}^{18}\mathrm{C}+n$ at $67A\mathrm{MeV}$. A large $E1\mathrm{}$ strength of $0.71\pm 0.07e^2\mathrm{fm}{}^2$ has been observed at low excitation energies. An analysis of the angular distribution of ${}^{18}\mathrm{C}+n$ center of mass has led to a determination of the neutron separation energy of ${}^{19}\mathrm{C}$ to be $530\pm 130\mathrm{keV}$. The $E1\mathrm{}$ strength distribution can be well reproduced for a ${}^{19}\mathrm{C}$ ground state structure with a dominant $s$-wave valence neutron, providing a consistent picture of the neutron halo structure of ${}^{19}\mathrm{C}$.

• Received 25 February 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.1112