The E1 capture cross section for the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(α,γ${)}^{16}$O to the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ground state has been measured for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=1.29\mathrm{}–}$3.00 MeV. A γ-ray–recoil-particle coincidence technique has been used to obtain essentially background-free reaction yields. A three-level R-matrix analysis of the E1 S factor leads to an allowed range for $S_{E1}$ at 300 keV of 0.00–0.14 MeV b. A model-dependent R-matrix analysis and a hybrid R-matrix analysis result in values of 0.14 and 0.08 MeV b, respectively, for $S_{E1}$(300).

• Received 14 December 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.1475