Computational investigation on the reaction of dimethyl ether with nitric dioxide. I. Underlying mechanism and accurate energetics

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The reaction of dimethyl ether (DME) with nitrogen dioxide (NO2), which plays a critical role in the low-temperature oxidation behavior of DME, is employed as prototype for reactions of heavier clean ether fuels to assess different hybrid density functionals and “double-hybrid” density functionals. The reaction energies and barrier heights for the reaction system were computed with CCSD(T) theory extrapolated to the complete basis set limit using augmented cc-pVDZ and cc-pVTZ basis sets. The involved energetics were also improved by the CCSD(T)/6-311+G(2df,2p), QCISD(T)/6-311+G(2df,2p), G3B3, G3MP2B3, CBS-QB3, G4, and G4MP2 calculations. It is shown that “double-hybrid” density functionals with the TZVP basis set can give accurate geometries and principal moments of inertia of reactants and products and the B2PLYP/TZVP level can achieve results for barrier heights comparable in accuracy to the high-level ab initio results, which is identified as an important potential theoretical level for direct kinetics studies on the rates of these and homologous reaction systems. The calculated results indicate that NO2 preferentially captures an out-of-plane hydrogen atom from the DME molecule by the O or the N end via three distinct channels to produce trans-HONO, cis-HONO, and HNO2, respectively, and each channel involves the formation of a van der Waals post-reaction adducts lying lower in energy than their separate products.