Subthreshold resonance in the6Li(d,α)4He reaction and its astrophysical implications

The total cross section of the ${}^6$Li$(d,\alpha {)}^4$He reaction has been measured for deuteron energies between 50 and 180 keV. From a detailed distorted-wave Born approximation analysis of the angular distributions and the excitation function up to 1 MeV it was possible to determine the strength of a subthreshold resonance that dominates the cross section at sub-Coulomb energies and contributes significantly to the increase of the astrophysical $S$ factor at low energies. Consequently the electron screening energy we have determined for the ${}^6$Li(d,$\alpha {)}^4$He reaction is considerably smaller than the value given in previous works which overestimate the theoretical predictions. In addition the stellar reaction rate has been calculated up to a temperature of $T_9$=3.