Abstract
The reactions of dimethyl ether (CH~3~OCH~3~, DME) with O(^3^P) and H atoms have been studied at high temperatures by using a shock tube apparatus coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients for the reactions CH~3~OCH~3~ + O(^3^P) → CH~3~OCH~2~ + OH (1) and CH~3~OCH~3~ + H → CH~3~OCH~2~ + H~2~ (2) were experimentally determined from the decay of O(^3^P) and H atoms as:
equation image
These results show that DME can react with O(^3^P) atoms more easily than with H atoms. By combining these results with the previous lower temperature data, we obtained the following modified Arrhenius expressions applied over the wide temperature range between 300 and 1500 K:
equation image
Both reactions of DME are faster than those of ethane, because the dissociation energy of the CH bond in DME is smaller. Furthermore, the rate coefficients for reactions (1) and (2) were calculated with the transition‐state theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6‐31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E^‡^~0~, was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E(1) = 23 kJ mol^−1^ and E(2) = 34 kJ mol^−1^ were in agreement with the G2 energy barriers, within the expected uncertainty, demonstrating that the experimentally determined rate coefficients were theoretically valid. © 2006 Wiley Periodicals, Inc. 39: 97–108, 2007