High temperature rate constants for H/D + methyl formate and methyl acetate

Abstract

The reactions of D/H with methyl formate (MF) and methyl acetate (MA) have been studied with both shock-tube experiments and ab initio transition state theoretical calculations. D-atom profiles were measured behind reflected shock waves using D-atom atomic resonance absorption spectrometry (ARAS) over the temperature range 1050–1270K, at pressures ≅0.5atm.The title reactions have been theoretically studied at the CCSD(T)/cc-pv∞z//MP2/aug-cc-pvtz and CCSD(T)/cc-pv∞z//B3LYP/6-311++G(d,p) levels of theory. Theoretical calculations suggest the dominance of the abstraction processes in comparison to addition processes in the 300–2000K T-range. Over the T-range of the present experiments, the theoretically predicted isotope effects, kD/kH, are near unity.D-atom depletion in the present experiments is sensitive only to the reactions,(A)D+CH3OC(O)H→products(B)D+CH3OC(O)CH3→productsSimulations of the measured D-atom profiles allow for determinations of total rate constants for the processes (A) and (B). In combination with results obtained from recent H-ARAS experiments from our laboratory on MF decomposition, total experimental rate constants kA can be described by the Arrhenius equation,kA=(4.47±1.54)×10-10exp(-5843±416K/T)cm3molecule-1s-1(1050–1270K)For H/D+MF, total experimental rate constants, kA, and branching ratios agree well with theoretical predictions.For D/H+MA, total rate constants predicted by theory are in reasonable agreement with the experimental data. The theoretical predictions are preferred for use, with kB represented by the modified Arrhenius equation,kB=3.078×10-19T2.78exp(-3261K/T)cm3molecule-1s-1(500–2000K)To our knowledge, the present experiments are the first direct measurements for the title reactions and the rate constants from this combined experimental/theoretical effort are recommended for use in combustion modeling.