Asymptotic three-particle approach to the Coulomb breakup process ⁶Li + ²⁰⁸Pb → ²⁰⁸Pb + α + d

On the basis of the distorted-wave method, experimental data on the triple-differential cross section for the Coulomb breakup reaction ²⁰⁸Pb(⁶Li, αd)²⁰⁸Pb are analyzed by employing a correct expression for the final-state ²⁰⁸Pb–α–d three-particle Coulomb wave function. It is shown that the effect of final-state three-particle Coulomb dynamics can be used to assess the kinematical condition of clean Coulomb breakup processes. New values of the astrophysical S factor for the direct-radiative-capture reaction d(α, γ)⁶Li at ultralow energies in the range of 70 ≤ E_dα ≤ 600 keV were extracted from experimental data. The value of S(0) = 1.60 ± 0.17 MeV nb was obtained.