I utilize the radiative-transfer code CMFGEN to investigate properties of supernova ejecta. Currently, I am working on adding molecular chemistry and emission (in particular, carbon monoxide) to CMFGEN. Especially at late times, once the ejecta has cooled, molecules can dominate the state of the gas. Unfortunately, molecules are also much more complicated than atoms, even simple ones like carbon monoxide. Including molecular features in CMFGEN will hopefully allow us to constrain a much better picture of the composition and evolution of core-collapse supernovae.