Impact of Sub–2.5 MeV 12 C+ 12 C Resonances on the Production of Elements from C to Pd in Core-collapse Supernovae

We explore the impact of a more efficient 12 C+ 12 C reaction on the structure and nucleosynthesis of massive stars. We calculate nonrotating stellar models with initial masses of 15, 16, 18, 20, 22, 25, and 40 M ⊙ and solar metallicity by means of the FRANEC code. Furthermore, we simulate the core-collapse supernova (SN) of these models with the thermal bomb technique, using two different approaches to inject the thermal energy into the pre-SN structure. Our results show that a more efficient 12 C+ 12 C rate extends the duration of the central carbon-burning phase, developing more massive convective cores and leading to a different and less compact pre-SN structure with respect to models calculated with a standard 12 C+ 12 C rate. These structural differences significantly impact nucleosynthesis. In particular, an increased rate enhances the production of elements heavier than Fe, produced by the s- process nucleosynthesis and driven by the more efficient activation of the 13 C( α , n) 16 O neutron source in the early carbon-burning shells. We find that the differences in the chemical composition of the core-collapse SN ejecta are primarily determined by these pre-SN structural changes, which dominate over the effects of different explosion prescriptions.