Abstract
The reaction kinetics of dimethyl carbonate (DMC) and OH radicals were investigated behind reflected shock waves over the temperature range of 872–1295 K and at pressures near 1.5 atm. Reaction progress was monitored by detecting OH radicals at 306.69 nm using a UV laser absorption technique. The rate coefficients for the reaction of DMC with OH radicals were extracted using a detailed kinetic model developed by Glaude
et al.
(
Proc. Combust. Inst.
2005,
30
(1), 1111–1118). The experimental rate coefficients can be expressed in Arrhenius form as:
k
expt'l
= 5.15 × 10
13
exp(−2710.2/
T
) cm
3
mol
−1
s
−1
. To explore the detailed chemistry of the DMC + OH reaction system, theoretical kinetic analyses were performed using high-level
ab initio
and master equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) calculations. Geometry optimization and frequency calculations were carried out at the second-order Møller–Plesset (MP2) perturbation level of theory using Dunning's augmented correlation consistent-polarized valence double-ζ basis set (aug-cc-pVDZ). The energy was extrapolated to the complete basis set using single point calculations performed at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory. For comparison purposes, additional
ab initio
calculations were also carried out using composite methods such as CBS-QB3, CBS-APNO, G3 and G4. Our calculations revealed that the H-abstraction reaction of DMC by OH radicals proceeds
via
an addition elimination mechanism in an overall exothermic process, eventually forming dimethyl carbonate radicals and H
2
O. Theoretical rate coefficients were found to be in excellent agreement with those determined experimentally. Rate coefficients for the DMC + OH reaction were combined with literature rate coefficients of four straight chain methyl ester + OH reactions to extract site-specific rates of H-abstraction from methyl esters by OH radicals.