The Importance of Thermodynamic Data for Pyrrole Pyrolysis and Combustion Chemistry

In this work, the CCSD(T)/Extrapolate(3/4,def2)//PBE0/def2-QZVP levels of theory were utilized in ORCA 6.1.1 to derive enthalpy and entropy of formation at 298.15 K for 32 species that include both radicals and stable molecules relevant to the pyrolysis and combustion of pyrrole. The comparison revealed major discrepancies in thermochemical data of species like allyloxy cyanide, cis-formimidoyl, cyanomethylidyne, cyano-propen-2yl radical, cyano-propen-4yl radical, carbonyl cyanide, and propionitrile primary radical. The effects of the thermochemical data computed in this work on the performance of Pelucchi et al. (Energy & Fuels, 2021) and Konnov et al. (Proceedings of the Combustion Institute, 2024) mechanisms were assessed. It was found that the updated thermochemical data improved the mole fraction predictions of certain species (e.g., hydrogen cyanide and acetylene) during the pyrolysis of pyrrole. However, an opposite trend of predictive performance deterioration was observed for species like acetonitrile during both pyrolysis and combustion ( $\phi$  = 0.5, 1, and 2) of pyrrole. In some cases, one model's performance improved, whereas the other's deteriorated. Therefore, this study reveals the significance of simultaneously improving the accuracy of both thermodynamic and reaction parameters of future pyrrole combustion chemistry models.