RMG can now generate isotopically labeled reaction mechanisms via a post-processing algorithm. After a normal RMG job is completed, the isotopes module can generate all combinations of isotopically labeled species and reactions (Figure ). To obtain consistent thermodynamics, RMG modifies species' entropy based on changes to molecular symmetry and modifies kinetic Arrhenius factors based on reaction path degeneracy. Classical, mass-dependent kinetic isotope effects (KIE) are also available.