Computational thermochemistry of oxygenated polycyclic aromatic hydrocarbons and relevant radicals

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) have attracted growing attention due to their toxicological harmfulness and significant role in soot formation. This study comprehensively investigates the thermochemistry of OPAH species and relevant radicals via quantum-chemical calculations. Temperaturedependent enthalpy of formation, entropy, and heat capacity for C 5 -C 18 OPAHs (59 molecules and 33 radicals) are consistently determined at the M06-2X/6-311 ++ G(d,p) level of theory. Considerable differences are found to be introduced by different methods when calculating electronic energies, and the G3 method outperforms the composite compound methods G3/G4/CBS-APNO. The calculated thermochemical properties from the G3 method show excellent agreement with literature data. An accurate thermochemistry database for OPAHs is thus developed. In addition, the existing group additivity (GA) method does not apply to OPAHs since the group additivity values (GAVs) derived from small hydrocarbons fail to predict large polycyclic species. Based on our dataset, GAVs are obtained from combinatorial considerations. The updated GAVs can be applied with enhanced confidence to estimate the thermochemical parameters at different tem peratures for larger OPAHs where such high-accuracy quantum chemistry calculations are intractable. These thermodynamic properties and GAVs are crucial for the development of accurate kinetic models for OPAH formation chemistry and for achieving emission control. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the thermochemistry of OPAH species and relevant radicals using quantum-chemical calculations. Thermochemical properties for C 5 -C 18 OPAHs were determined at different temperatures, and a accurate thermochemistry database for OPAHs was developed. The existing group additivity method does not apply to OPAHs, and new group additivity values were obtained for larger OPAHs. These thermodynamic properties and group additivity values are crucial for accurate kinetic models for OPAH formation chemistry and emission control.