Shock‐tube studies on the reactions of dimethyl ether with oxygen and hydrogen atoms

Abstract

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 CH 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