Multireference and Coupled-Cluster Study of Dimethyltetroxide (MeO₄Me) Formation and Decomposition

Area of Science:

• Atmospheric Chemistry
• Computational Chemistry
• Chemical Kinetics

Background:

• Peroxyl radicals (RO2) are key intermediates in atmospheric oxidation.
• Tetroxides (RO4R) form from RO2 + RO2 reactions, but their mechanisms are complex.
• Previous studies lacked a unified methodology for RO4R formation and decomposition.

Purpose of the Study:

• To develop and apply a unified computational methodology for RO4R reactions.
• To investigate the MeO2 + MeO2 reaction forming MeO4Me and its decomposition pathways.
• To model open-shell singlet electronic states involved in these reactions.

Main Methods:

• Utilized multireference (MR) computational methods.
• Benchmarked MR methods against high-level coupled-cluster (CCSD(T)/CBS, W2X, W3X-L) calculations.
• Employed CASPT2(22e,14o)-IPEA for detailed reaction pathway analysis.

Main Results:

• CASPT2(22e,14o)-IPEA accurately reproduced coupled-cluster relative energies.
• MeO2 + MeO2 → MeO4Me formation is exothermic; decomposition is endothermic.
• Concerted cleavage of MeO-O bonds in MeO4Me is energetically favored over sequential decomposition.

Conclusions:

• The CASPT2(22e,14o)-IPEA method provides a reliable approach for modeling RO4R chemistry.
• The study elucidates the preferred decomposition pathway of tetroxides.
• Findings contribute to a better understanding of atmospheric oxidation mechanisms.