Gas-phase thermochemistry of polycyclic aromatic hydrocarbons: an approach integrating the quantum chemistry composite scheme and reaction generator?

Physical Chemistry Chemical Physics Pub Date: 2021-12-24 DOI: 10.1039/D1CP03702A

Abstract

We introduce a protocol aimed at predicting the accurate gas-phase enthalpies of formation of polycyclic aromatic hydrocarbons (PAHs). Automatic generation of a dataset of equilibrated chemical reactions preserving the number of carbon atoms in each hybridization state on each side of equations is at the core of our scheme. The performed tests suggest the recommended enthalpy of formation to be derived via a two-step scheme. First, we consider the reactions with a minimal sum of the total number of particles involved, N, and the absolute difference between the total number of products and reactants, |ΔN|. Second, among these reactions, we identify the one with the smallest absolute reaction enthalpy change, Image ID:d1cp03702a-t1.gif. This approach has been applied to predict the gas-phase enthalpies of formation of 113 PAHs via the Feller–Peterson–Dixon approach. Our calculated Image ID:d1cp03702a-t2.gif values provide the mean absolute deviations of 1.7, 1.9, 4.2, 8.1, and 18.5 kJ mol?1 with respect to the literature group-based error corrected (GBEC) G3MP2B3, ATOMIC (HC), group equivalent M06-2X, GBEC B3LYP, and G4MP2 values. Our predicted Image ID:d1cp03702a-t3.gif values give the mean signed and mean absolute errors of ?7.5 and 12.9 kJ mol?1 with respect to the experimental enthalpies of formation. The combination of our predicted Image ID:d1cp03702a-t4.gif and the experimental Image ID:d1cp03702a-t5.gif values provide the solid-state enthalpies of formation, Image ID:d1cp03702a-t6.gif, which are not available for a few species. Approaching these values Image ID:d1cp03702a-t7.gif as well as Image ID:d1cp03702a-t8.gif, producing large discrepancies from the experimental side, would be indispensable for testing and further tuning of computational chemistry approaches.

Graphical abstract: Gas-phase thermochemistry of polycyclic aromatic hydrocarbons: an approach integrating the quantum chemistry composite scheme and reaction generator
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