The Role of Molecular Properties on the Dimerization of Aromatic Compounds

TL;DR

This study investigates how molecular properties like oxygen content, shape, and bond type influence the dimerization of aromatic compounds, revealing key factors affecting particle inception in atmospheric chemistry.

Contribution

It provides a detailed analysis of molecular characteristics affecting aromatic compound dimerization using molecular dynamics, highlighting the relative importance of mass and bond flexibility.

Findings

Mass and rotatable bonds are key indicators of dimerization propensity.

Shape, oxygen content, and internal bonds influence dimerization differently with temperature.

Current models may overestimate the role of stabilomers in particle nucleation.

Abstract

Recent results have shown the presence and importance of oxygen chemistry during the growth of aromatic compounds, leading to the formation of oxygenated structures that have been identified in various environments. Since the formation of polycyclic aromatic compounds (PAC) bridge the formation of gas-phase species with particle inception, in this work we report a detailed analysis of the effects of molecular characteristics on physical growth of PAC via dimerization. We have included oxygen content, mass, type of bonds (rigid versus rotatable), and shape as main properties of the molecules and studied their effect on the propensity of these structures to form homo-molecular and hetero-molecular dimers. Using enhanced sampling molecular dynamics techniques, we have computed the free energy of dimerization in the temperature range $500-1680$~K. Initial structures used in this study were obtained from experimental data. The results show that although the effects of shape, presence of oxygen, mass, and internal bonds are tightly intertwined, and their relative importance changes with temperature. In general, mass and the presence of rotatable bonds are the best indicators. The results provide knowledge on the inception step and the role that particle characteristics play during inception. In addition, our study highlights the fact that current models that use stabilomers as monomers for physical aggregation are overestimating the importance of this process during particle nucleation.