Kinetics of OH Radical Reactions with Methane in the Temperature Range 295−660 K and with Dimethyl Ether and Methyl-tert-butyl Ether in the Temperature Range 295−618 K

The pulse laser photolysis/laser induced fluorescence (PLP−LIF) technique has been used to measure the rate constants of the reactions of OH radicals with dimethyl ether and methyl- tert -butyl ether. OH radicals were produced by photolysis of H 2 O 2 at λ = 266 nm. The photolysis cell was heated by a small electric furnaces in order to obtain information on the temperature dependency of the rate constants in the domain of 295−660 K. A preliminary study of the reaction of OH with methane was carried out to control the experimental setup. The Arrhenius expression obtained in the temperature range of 295−668 K, k OH + CH 4 = (5.65 ± 0.49) × 10 -21 T 3.01 exp[−(959 ± 36)/ T ], is in very good agreement with previous determinations (bimolecular rate constant units: cm 3 molecule -1 s -1; error limits ± 2σ). For the reactions of OH with ethers, the Arrhenius expressions derived from our own results are k OH+DME (295−618 K) = (3.02 ± 0.10) × 10 -20 T 2.85 exp[(618 ± 13)/ T ] and k OH+MTBE (297−616 K) = (6.59 ± 0.43) × 10 -19 T 2.40 exp([(499 ± 22)/ T ]. Combining these data with those from previous experimental studies allows us to derive Arrhenius expressions in larger temperature domains: k OH+DME (230−650 K) = (4.59 ± 0.21) × 10 -19 T 2.46 exp[(476 ± 14)/ T ] and k OH+MTBE (230−750 K) = (1.58 ± 0.09) × 10 -20 T 2.93 exp([(716 ± 18)/ T ].