Classical Chemical Dynamics Simulations of the Thermal Unimolecular Decomposition of Dimethyl Carbonate and Dimethyl Ether

Dimethyl carbonate (DMC) has been considered as a potential alternate fuel due to the absence of a C-C bond and the presence of high oxygen content. Experimental studies have shown that the dominant decomposition products of DMC are CO₂ and dimethyl ether (DME), among others. DME also undergoes decomposition under similar conditions, and a clear experimental distinction of DMC and DME dissociation products is difficult. In the present work, unimolecular decomposition of DMC and DME was investigated under the same reaction conditions using electronic structure theory, Born-Oppenheimer direct dynamics simulations, and Rice-Ramsperger-Kassel-Marcus (RRKM) theory rate constant calculations. The <i>on-the-fly</i> trajectory simulations were performed at the density functional B3LYP/cc-pVDZ level of electronic structure theory. DMC and DME were excited using the same average normal mode energies and subsequent atomic-level dissociation dynamics investigated. In agreement with previous studies, DME + CO₂ formation was dominant for the DMC molecule. In addition, another major pathway resulting in :CH₂ and carbonic acid monomethyl ester (CAME) was identified in the decomposition of DMC and this might be an important pathway at high temperatures. CAME underwent subsequent dissociation, resulting in other known products. For the DME decomposition, molecular H₂ elimination along with various byproducts was found to be dominant. The dissociation products of DMC and DME were separately quantified, and atomic-level dissociation mechanisms were presented.