  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.
