The impact of incorrect dissociation energies on inferred photospheric abundances

Spectral synthesis codes are essential for inferring stellar parameters and detailed chemical abundances. These codes require many physical inputs to predict an emergent spectrum. Developers adopt the best measurements of those inputs at the time they release their code, but those measurements usually improve over time faster than the software is updated. In general, the impact of using incorrect or uncertain dissociation energies are largely unknown. Here we evaluate how incorrect dissociation energies impact abundances measured from C2, CN, CH, TiO, and MgO features. For each molecule we synthesised optical spectra of FGKM-type main-sequence and giant stars using the literature dissociation energy, and an incorrect (perturbed) dissociation energy. We find that the uncertainties in the dissociation energies adopted by spectral synthesis codes for CN, CH, TiO, and MgO lead to negligible differences in flux or abundances. C2 is the only diatomic molecule where the uncertainty of the inputted dissociation energy translates to a significant difference in flux, and carbon abundance differences of up to 0.2 dex. For Solar-like stars, the impact on carbon abundance is up to 0.09 dex. These large abundance differences demonstrate the importance of updating the inputs adopted by spectral synthesis codes, as well as a consensus on appropriate values between different codes.