Upper Limit on the molecular resonance strengths in the

Carbon burning is a crucial process for a number of important astrophysical scenarios. The lowest measured energy is around Ec.m. =2.1 MeV, only partially overlapping with the energy range of astrophysical interest. The currently adopted reaction rates are based on an extrapolation which is highly uncertain because of potential resonances existing in the unmeasured energy range and the complication of the effective nuclear potential. By comparing the cross sections of the three carbon isotope fusion reactions, 12C+12C, 12C+13C and 13C+13C, we have established an upper limit on the molecular resonance strengths in 12C+12C fusion reaction. The preliminary results are presented and the impact on nuclear astrophysics is discussed