The rates of reaction of OH with propyne, but-l-yne, but-2-yne, pent-l-yne and hex-l-yne have been measured directly by using a discharge-flow resonance-fluorescence technique over a range of temperatures from 253 to 343 K. The room-temperature rate coefficients-are compared with previous determinations; the new values for pent-l-yne and hex-l-yne fit into a general pattern of reactivity consistent with a mechanism involving initial electrophilic attack of OH at the triple bond. Similar trends are also presented for other series of reactions between radicals and unsaturated organic molecules. The temperature dependences of the rate constants for the OH-talkyne reactions are small or negative, suggesting that adduct formation is the initial step in the reaction mechanism.
A simplified combustion system was generated by reacting methane with decomposing ozone in the temperature range °C. Under most conditions an unusual and reproducible period of induction was observed followed by a rapid depletion of 03. With added 02 the reaction slowed. These effects were simulated by a 70-step mechanism which qualitatively accounted for the period of induction. A simpler 10-step mechanism which was more algebraically tractable was used to account quantitatively for the kinetics of inhibition with added oxygen. The main ozone-destroying chain is postulated to be the following: CH3 + 03 -CH30 + 02 (4), CH30 + 02 -CH20 + H02 (6), OH + CH4 -H20 + CH3 (7), and HOz + 03 -* OH + 202 (9). This gives the overall stoichiometry for ozone destruction as CH4 + 203 -CH20 + H20 + 202.No evidence was found for a molecular reaction between 03 and CH4. The reaction was chemiluminescent and the emission was identified as due to Meinel bands, presumably from + 03 -* OH* + 02 (35), where OH* = ( 2 , <9). No emission was found when the helium carrier gas was replaced by oxygen. The activation energy for light emission was measured as 28.7 ± 1.2 kcal/mol. This contrasts with the results of experiments where the methane was replaced by ethylene and where the light emission showed no temperature dependence.
The kinetics of the reaction between ozone and allene (A) were studied in the range of 226 to 325°K in the gas phase. Initial O3 pressures varied from 0.01 to 0.7 torr and allene pressures varied from 0.05 to 6 torr. At the higher initial 0 3 pressures the most important product was 0 2 followed by CO, H20, Cot, and CTH,. Oxygen balances averaging about llOyo were obtained, which implies that no important oxygenated products were missed. However, carbon balances were only about 5oy0 and hydrogen balances were even less, so that unidentified hydrocarbons were presumably formed. The
rate law found was --d[O3]/dt = kl[03][A] + k 2 a [ 0 3 ] 2 [ A ] / [ 0 3 ]~where log kl(M-'sec-') = 6.0 & 0.7 -(5500 =t 1000)/2.30RTand log kt,(M-lsec-l) = 6.9 f 0.7 -(6200 +800/ 2.30RT. A mechanism is proposed which accounts for the rate law and the observed stoichiometry of 0 2 formed-03 used. This involves a heterogeneous catalyzed decomposition of 0 3 . The rate constant k , is identified with the primary addition reaction A + 0 3 4 AO3, and this rate constant is compared with those from other 0 3 addition reactions.
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