The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(α,n${)}^{16}$O and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(α,α${)}^{13}$C reactions are investigated through the generator-coordinate method. Two bands with marked α${+\mathrm{}}^{13}$C structure are found in the ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ spectrum. Experimental candidates are proposed. The microscopic ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(α,α${)}^{13}$C cross sections are in fair agreement with experimental data. We show that the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(α,n${)}^{16}$O cross section at stellar energies is strongly affected by the 1/2 ${}_2{}^{+}{}_{}{}^{}$ (6.36 MeV) weakly bound state. The astrophysical S factor below $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=0.3\mathrm{}}$ MeV is therefore significantly enhanced with respect to the extrapolations used for astrophysical purposes.

• Received 3 June 1987

DOI:https://doi.org/10.1103/PhysRevC.36.2206