Theoretical Kinetic Study on Unimolecular Decomposition of tert -Amyl Methyl Ether

Abstract tert-Amyl methyl ether (TAME) is not only widely used as a gasoline additive but also demonstrates significant potential as an alternative fuel. Currently, the combustion reaction mechanism of TAME remains incompletely understood. A comprehensive theoretical investigation of the unimolecular decomposition of TAME is essential for developing its combustion model. Potential-energy surfaces for the unimolecular decomposition of TAME, including CH3OH elimination and C–O/C–C/C–H bond fission reaction channels, were constructed by the high-level ab initio calculations at the QCISD(T)/CBS//B2PLYP-D3/cc-pVTZ level of theory. Conventional transition state theory (CTST) was utilized for reactions with tight transition states, and variable reaction coordinate transition state theory (VRC-TST) was used for barrierless reaction channels. In VRC-TST calculations, the interaction energies between the two adducted radical fragments were determined at the CASPT2(2e,2o)/cc-pVDZ level of theory combined with geometry relaxation and basis set energy corrections. Temperature- and pressure-dependent rate constants were obtained by solving the Rice–Ramsperger–Kassel–Marcus/Master equation (RRKM/ME) at 500–2000 K and 0.01–100 atm. At 1 atm, the results demonstrate that, the elimination reaction channel of TAME ⇌ CH2═C(CH3)CH2CH3 + CH3OH is dominant at T < 1350 K, while the bond fission reaction channel TAME ⇌ ĊH3 + CH3OĊ(CH3)CH2CH3 dominates at T > 1350 K. Additionally, thermodynamic parameters (enthalpy ΔHf,298, entropy S298, and specific heat at constant pressure Cp) for all species in TAME decomposition reactions and cyclic ethers in TAME combustion models were calculated. Rate constants and thermochemical data calculated in this work are valuable for the model development of TAME combustion and greatly reduce the systematic bias of underpredicted ignition delays.