Current nitromethane kinetic schemes do not fully capture the intermediate reaction states of deflagrating nitromethane, which is an explosive used in many combustion applications. There is a need for data on these transient species that can be used to validate and improve contemporary kinetic models. This work aims to analyze the evolution of identified transient species present in a nitromethane-air flame stabilized on a wick at ambient pressure. We detect several new emitters in excited electronic states, HNO*(A'), CN* (A(2)Sigma), NO2*, and in ground electronic states, CH, OH, NH, and H2O. We also confirm the presence of previously observed reaction species CH*(A(2)Delta). Formaldehyde and the characteristic C-2*(A(3)Pi(g)) swan bands are not observed. Results are reported as a function of flame position. Flame simulations for the nitromethane flame using reaction mechanisms by Brequigny et al. (Proc. Combust. Inst. 2014, 35, 703) and Mathieu et al. (Fuel 2016, 182, 597) yield good qualitative agreement to the experimental data for rich stoichiometries. While current mechanisms do not include excited state species, these results also provide insight into potential ground state precursors. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.