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Methyl-Crotonate (MC, ( E )-methylbut-2-enoate, CH 3 CHCHC(O)OCH 3 ) is a potential component of surrogate fuels that aim to emulate the combustion of fatty acid methyl ester (FAME) biodiesels with significant unsaturated FAME content. MC has three allylic hydrogens that can be readily abstracted under autoignition and combustion conditions to form a resonantly-stabilized CH 2 CHCHC(O)OCH 3  radical. In this study we have utilized photoionization mass spectrometry to investigate the O 2  addition kinetics and thermal unimolecular decomposition of CH 2 CHCHC(O)OCH 3  radical. First we determined an upper limit for the bimolecular rate coefficient of CH 2 CHCHC(O)OCH 3  + O 2  reaction at 600 K ( k  ≤ 7.5 × 10 −17  cm 3  molecule −1  s −1 ). Such a small rate coefficient suggest this reaction is unlikely to be important under combustion conditions and subsequent efforts were directed towards measuring thermal unimolecular decomposition kinetics of CH 2 CHCHC(O)OCH 3  radical. These measurements were performed between 750 and 869 K temperatures at low pressures (&lt;9 Torr) using both helium and nitrogen bath gases. The potential energy surface of the unimolecular decomposition reaction was probed at density functional (MN15/cc-pVTZ) level of theory and the electronic energies of the stationary points obtained were then refined using the DLPNO-CCSD(T) method with the cc-pVTZ and cc-pVQZ basis sets. Master equation simulations were subsequently carried out using MESMER code along the kinetically important reaction pathway. The master equation model was first optimized by fitting the zero-point energy corrected reaction barriers and the collisional energy transfer parametersΔ   E   down  ,  ref$\Delta{E_{{\text{down}},\;{\text{ref}}}}$    and  n  to the measured rate coefficients data and then utilize the constrained model to extrapolate the decomposition kinetics to higher pressures and temperatures. Both the experimental results and the MESMER simulations show that the current experiments for the thermal unimolecular decomposition of CH 2 CHCHC(O)OCH 3  radical are in the fall-off region. The experiments did not provide definite evidence about the primary decomposition products.

zeitschrift für physikalische chemie

Direct Kinetic Measurements and Master Equation Modelling of the Unimolecular Decomposition of Resonantly-Stabilized CH 2 CHCHC(O)OCH 3  Radical and an Upper Limit Determination for CH 2 CHCHC(O)OCH 3  + O 2  Reaction