Closed-Shell Organic Compounds Might Form Dimers at the Surface of Molecular Clusters

Abstract

The role of covalently bound dimer formation is studied using high-level quantum chemical methods. Reaction free energy profiles for dimer formation between common oxygen-containing functional groups are calculated, and based on the Gibbs free energy differences between transition states and reactants, we show that none of the studied two-component gas-phase reactions are kinetically feasible at 298.15 K and 1 atm. Therefore, the catalyzing effect of water, base, or acid molecules is calculated, and sulfuric acid is identified to lower the activation free energies significantly. We find that the reactions yielding hemiacetal, peroxyhemiacetal, α-hydroxyester, and geminal diol products occur with activation free energies of less than 10 kcal/mol with sulfuric acid as a catalyst, indicating that these reactions could potentially take place on the surface of sulfuric acid clusters. Additionally, the formed dimer products bind stronger onto the pre-existing cluster than the corresponding reagent monomers do. This implies that covalent dimerization reactions stabilize the existing cluster thermodynamically and make it less likely to evaporate. However, the studied small organic compounds, which contain only one functional group, are not able to form dimer products that are stable against evaporation at atmospheric conditions. Calculations of dimer formation onto a cluster surface and the clustering ability of dimer products should be extended to large terpene oxidation products in order to estimate the real atmospheric significance.

Gas-to-Particle Partitioning of Cyclohexene- and α-Pinene-Derived Highly Oxygenated Dimers Evaluated Using COSMOtherm

“…These reactions are likely only occurring in the condensed phase because the reactions have high activation energies in the gas phase. 30 Recently, Kahnt et al 31 and Iyer et al 32 proposed a formation of a trioxide adduct from a peroxy radical and an alkoxy radical (RO) as a source of atmospheric dimers that have been detected in ambient and chamber measurements in high-loading conditions …”

Clustering mechanism of oxocarboxylic acids involving hydration reaction: Implications for the atmospheric models

“…Thus, NPF may be driven not only by clustering processes, but also by various other complex and condition-dependent atmospheric chemical reactions. [16][17][18][19][20][21][22][23] , which can influence the physical and chemical processes of NPF [24][25][26] . This makes the assessment of the role of organic compounds in the NPF process very complicated.…”

Unexpected quenching effect on new particle formation from the atmospheric reaction of methanol with SO 3

“…Many recent studies have suggested that atmospheric species generated from gas-phase chemical reactions can play an important role in the NPF process (15)(16)(17)(18)(19). Alcohols are active species in the atmosphere, and they can be involved in many chemical reactions (20)(21)(22).…”