Rate constants for the reaction of atomic chlorine with methanol and dimethyl ether from 200 to 500 K

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Abstract
Absolute rate constants for the reaction of atomic chlorine with dimethyl ether and methanol, Cl+CH3OCH3→HCl+CH2OCH3 (1),Cl+CH3OH→HCl+CH2OH (2), have been measured over the temperature range 200–500 K, using the flash photolysis–resonance fluorescence technique. In both systems, the results were independent of substantial variations in reactant concentration, total pressure (Ar) and flash intensity (i.e., initial [Cl]). The rate constants were also shown to be invariant with temperature. The best representation for this temperature range was found to be k1= (1.76±0.15) ×10−10 cm3 molecule−1 s−1 and k2= (6.33±0.70) ×10−11 cm3 molecule−1 s−1, respectively, where the error is one standard deviation. These are the first determinations of the rate constants for Reactions (1) and (2). These reactions are theoretically discussed and compared to the related reactions of Cl with CH4, C2H6, and H2CO. Molecules of the type CH3OX (where X=H, OH, etc.) are likely to be formed in the stratosphere as products of the oxidation of methane. The molecules CH3OH and CH3OCH3 are considered as prototypes of molecules containing the methoxy group. The potential importance of the fast reactions Cl+CH3OX in stratospheric chemistry is discussed.