The excitation energy of the second excited state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been measured to be 7654.00 ± 0.20 keV. Combining this result with the recent precise measurement of the atomic mass of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ by Smith and Wapstra, the $Q$ value for the reaction $3\alpha \to {}_{}{}^{12}{}_{}{}^{}\mathrm{C}\mathrm{}\left(7654.00\right)\mathrm{}$ is determined to be 379.31 ± 0.21 keV. This result implies a change of +9%, at a stellar temperature of ${10}^8$ K, in the $3\alpha$ reaction rate quoted in the recent compilation of Fowler, Caughlan, and Zimmerman.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(p,p^{\prime })$, $E=34.75\mathrm{}$ MeV; magnetic spectrograph; measured excitation energies of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(7.65 MeV), ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(7.56 MeV), and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(6.13 MeV) states with 200 eV uncertainties. Measurement related to astrophysical helium burning ($3\alpha$) rate.

• Received 12 January 1976

DOI:https://doi.org/10.1103/PhysRevC.13.1773