Theoretical study about the hydrogen abstraction reactions on methyl acetate on combustion conditions

Methyl acetate is considered a prototype molecule to study biodiesel ignition and combustion and is seen as a possible fuel or fuel additive. For this reason, methyl acetate decomposition paths have been investigated in recent years. In the present study, hydrogen abstraction reactions on methyl acetate by OH(²Π), HO₂(²A'), H(²Σ_g), O(³P), and O₂(³Σ_g) were conducted, and the effect of methodology and anharmonic corrections on the rate coefficients were evaluated. The M06-2X and B3LYP-D3 functionals with the cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, and aug-cc-pVTZ basis set were used for methodology evaluation and the CCSD(T)/cc-pVTZ//M06-2X/aug-cc-pVTZ for the rate coefficients calculation and literature comparisons. The rate coefficients were calculated in the range of 250-3500 K, including tunneling corrections, methyl-hindered rotations, and anharmonic effects calculated by the VPT2 method. The methodology analysis showed that the B3LYP-D3 functional leads to lower activation energies for all elementary reactions studied, and the double-zeta basis is insufficient to calculate precise rate coefficients. The inclusion of anharmonic corrections consistently lowered the rate coefficients of all elementary reactions studied and changed the Arrhenius plot profile with the temperature. Significant anharmonic effects were observed at higher temperatures, being the reaction with O₂(³Σ_g) the most affected by this correction. Differences superior to 10⁵ cm³ molec^-1 s^-1 in the rate coefficients were observed in some cases.