Shock tube and modeling study of the pyrolysis of dimethyl carbonate and its reaction with D- and O-atoms

The shock tube technique was used to study the high temperature thermal decomposition of dimethyl carbonate, CH3OC(O)OCH3 (DMC). The formation of H-atoms was measured behind reflected shock waves by using atomic resonance absorption spectrometry (ARAS) over a temperature range of 1053–1157 K at pressures ~ 0.5 bar. The measured formation of H-atoms is sensitive to the rate constants for the energetically lowest-lying bond fission channel CH3OC(O)OCH3 → CH3 + CH3OC(O)O. H-atoms form instantaneously at high temperatures from the sequence of radical β-scissions, CH3OC(O)O → CH3O + CO2 → H + CH2O + CO2. A master equation analysis was performed using CCSD(T)/cc-pv∞z//M06-2X/cc-pvtz energetics and molecular properties for all thermal decomposition processes in DMC. The theoretical predictions were found to be in good agreement with the present experimentally derived rate constants for the bond fission channel. Since bimolecular reactions like H/O + DMC are important fuel destruction processes at high temperatures, rate constants for the reactions D and O + DMC were experimentally determined. D + DMC is a surrogate for H + DMC since the theoretically predicted kinetic isotope effect at high temperatures (1000 – 2000 K) is close to unity. Measurements of D-atom and O-atom profiles using Dand O-ARAS allowed rate constant measurements for the reactions D/O + CH3OC(O)OCH3 → HD/OH + CH3OC(O)OCH2 (1030 K ≤ T ≤ 1264 K; P ~ 0.5 bar for D-ARAS and 862 K ≤ T ≤ 1167 K; 0.15 bar ≤ P ≤ 0.33 bar for O-ARAS experiments). C2D5I and O3 were used as precursors for Dand O-atoms. Conventional transition state theory calculations employing CCSD(T)/cc-pv∞z//M06-2X/cc-pvtz energetics and molecular properties for the bimolecular reactions are in good agreement with the experimental rate constants. The thermal dissociation of O3 was initially characterized before its subsequent use as an O-atom precursor.