A Quantum Chemistry Insight into the Potential Role of the Singlet Oxygen-Acetone System as a Source for Production of Stable Secondary Organic Aerosols through a Multiwell Multipath Reaction.

The high abundance of acetone ((CH₃)₂C═O), which makes it a good candidate for oxygenated molecules, and the high reactivity of oxygen atoms in the first excited state O(¹D) are two well-known facts in the chemistry of the atmosphere. In this research, we prove that the singlet oxygen and acetone system is capable of proceeding through multiwell multipath reactions, leading to the production of several organic aerosols. Hence, the nature of species released by the (CH₃)₂C═O + O(¹D) reaction to air can be clarified by profound attention to the possible routes. To verify this, the singlet potential energy surface (PES) of the acetone + O(¹D) reaction is investigated by using various validated quantum chemistry approaches, especially the high-cost BD(TQ) method. By the carefully chosen theoretical methods, we forecast all possible multistep routes with high accuracy for the production of possible adducts in reliable conditions. Also, we use the kinetic results of the well-proven theories (TST and RRKM) to show the importance and atmospheric relevance of the simulated reactions. So, the rate constants of the (CH₃)₂C═O + O(¹D) reaction channels are computed at a large temperature range employing precise energetics and partition functions to show which products have a high percentage of yield. Moreover, the competitive canonical unified statistical (CCUS) model is utilized to show whether pressure influences the products generated by barrierless reactions. In addition, the thermodynamic functions of stationary points (at 298 K) and the rate constants of the found reaction routes demonstrate that the reaction adducts are very stable, so the reverse reactions have less importance compared to the forward reactions. In summary, this study illustrates how designed reaction routes could play a vital role in secondary aerosol formation in the atmosphere.