The transition strength for Coulomb breakup of ${}^6\mathrm{He}$ into ${}^4\mathrm{He}+n+n$ three-body unbound states is studied in the framework of the complex scaling method (CSM). We propose a method to analyze the three-body unbound states in which CSM is utilized to decompose the three-body transition strengths into resonance and continuum components. We calculate the contributions of $E1\mathrm{}$ and $E2\mathrm{}$ transitions, not only from three-body resonances, but also from two-body ${\mathrm{“}}^5\mathrm{He}+n\mathrm{”}$ and three-body ${\mathrm{“}}^4\mathrm{He}+n+n\mathrm{”}$ continuum states. From the calculated strength distributions, we discuss the characteristic structures of ${}^6\mathrm{He}$ in the positive energy region, and also the Coulomb breakup mechanism of ${}^6\mathrm{He}.$ We show that the two-body ${\mathrm{“}}^5\mathrm{He}+n\mathrm{”}$ component is dominant in the total Coulomb breakup cross section.

• Received 5 January 2001

DOI:https://doi.org/10.1103/PhysRevC.63.054313