Kinetic modeling for unimolecular β-scission of the methoxymethyl radical from quantum chemical and RRKM analyses

Time-Resolved Measurements and Master Equation Modelling of the Unimolecular Decomposition of CH3OCH2

“…The fit parameters from this MESMER analysis are given in Table 2, where it can be seen that the zero temperature barrier to dissociation, ΔE 0,1 , is defined with a small error (112.5 ± 0.6 kJ mol -1 ). This value is in good agreement with our ab initio calculation and the calculations by Gao et al [11], see Table 2. Figure 4 shows a plot of the experimental rate coefficients vs the calculated rate coefficients.…”

“…Additionally, methoxymethyl decomposition has been investigated using high level electronic structure calculations. Li et al [10] obtained 1 ∞ = 4.45x10 14 (T/K) -0.22 exp(-13700 K/T) s -1 which lies within a factor of ~ 2 of the results of Loucks and Laidler over the temperature range 400 -800 K. Gao et al [11] incorporated multiple structure effects into their calculations to account for torsional and anharmonic effects for the low frequency modes. They obtained 1 ∞ = 1.88x10 12 (T/300 K) 1.05 exp(-11062 K/T) s -1 , over the temperature range 450 -800 K, which is a factor of ~10 to ~3 greater than the expression of Loucks and Laidler.…”

“…[8] The ab initio potential energy surface of R1 was calculated by Li et al [10] and micro-canonical transition-state theory was then used to calculate 1 ∞ ( ), which is given in Table 2 and shown in Figure 3. Most recently, Gao et al [11] carried out further calculations on R1, where the calculations were at a higher level and attention was given to the low frequency torsions / anharmonic effects and to tunnelling. Multi-structural canonical variational transition-state calculations were carried out and their 1 ∞ ( ) is given in Table 2 and shown in Figure 3.…”

“…but this will not necessarily be true for lower pressures.While the current experiments on their own do not determine the heat of formation of CH 3 OCH 2 , it can be assigned by considering the study of Gao et al[11] From Table2, the two calculations for ΔE 0,1 from Gao et al are higher and lower than our value, but the associated reaction energy at 0 K from these calculations are 28.5 (G4) and 27.1 kJ mol -1 (QCISD(T)/augcc-pVTZ//MP2/TZVP); so the variation in reaction energy with level of calculation is significantly smaller than the variation in the barrier energies. If these two values for the heat of reaction are combined with the well-known zero K heats of formation of CH 3 (149.9 kJ mol -1 ) and CH 2 O (-105.38 kJ mol -1 ) (uncertainties less than 0.1 kJ mol -1[37,38]), then the heat of formation of CH 3 OCH 2 (∆ f H 0 (0 K)) is equal to 16.0 or 17.3 kJ mol-1 .…”

Experimental and numerical studies of the ignition of ammonia/additive mixtures and dimethyl ether burning velocities

“…For its use in the present work, a few modifications were made to improve its performance. The rate coefficients for thermal dissociation of CH3OCH2 to form CH2O + CH3 was drawn from the recent theoretical study by Gao et al [112], while for the dissociation of HO2CH2OCHO to OCH2OCHO + OH, the rate constant has been multiplied by a factor of two compared to the estimate of Burke et al [35]. There are no kinetic studies of DME/NH3 interactions reported in the literature and a kinetic subset was developed.…”