Study of the reaction chlorine monoxide + methyl peroxide .fwdarw. products at 300 K

Abstract

The first experimental study of the reaction CIO + CH302 -* products (1) is reported. The rate coefficient Aq and the product distributions were investigated in the modulated photolysis of Cl2/CH4/Cl20/02 mixtures. Reactants and products have been monitored by using UV-vis and Fourier-transform infrared gas-phase absorption spectroscopies. The value of A, was found to be equal to (3.1 ± 1.7) X 10"12 cm3 molecule"1 s'1 at 300 K and 240 Torr total pressure. The product channel forming ClOO and CH30 appears to be the dominant pathway at 300 K. The subsequent oxidation of CH30 to CH20 and its partial photolysis into Ff and HCO leads to enhanced production of odd hydrogen (OH, H02) radicals. Consequently, high concentrations of OH radicals can build up, leading to an additional source of active chlorine via the reaction HC1 + OH -Cl + H20, which destroys ozone by catalytic reactions. This strongly suggests that reaction 1 can play a substantial role in the photochemical processes that take place under stratospheric "ozone hole" conditions. 1986, 321, 755.

Environmental effects of large igneous province magmatism: a Siberian perspective

“…The recommended expressions for the overall rate constant is based on the results of Helleis et al [566]. It is consistent with the room temperature measurements of Simon et al [1190] and Kenner et al [699]. The results of Kukui et al [743] for the overall reaction are in agreement with the recommendation at room temperature, but these values show a slight negative temperature dependence in contrast with the slight positive temperature dependence recommended here.…”

“…This study, using a flash photolysis/long path ultraviolet absorption technique, is the most comprehensive study of this system, covering a wide range of temperature and pressure. These results are preferred over the results of earlier studies of the total bimolecular rate coefficient at low pressures by Clyne and Coxon [276], Clyne and White [302], and Clyne et al [289], and those of other studies reported by Hayman et al [560], Cox and Derwent [319], Simon et al [1191], Horowitz et al [599], and Horowitz et al [600]. The room temperature branching ratio are k 1 :k 2 :k 3 = 0.29:0.50:0.21.…”

“…There is general agreement that the only important reaction channels are the two channels resulting in the production of ClOO + CH 3 O (a) and CH 3 OCl + O 2 (b). However, there is severe disagreement on their relative importance; at room temperature reaction channel (a) is reported to be the major channel by Helleis et al [566], Simon et al [1190], Kukui et al and Helleis et al [567] but it is reported to be the minor channel by Biggs et al [140] and Daele and Poulet [340]. Because of this large discrepancy, no branching ratios are recommended.…”

The chain mechanism of ozone destruction by CFCl3 in the 214 nm photolysis of its mixtures with oxygen

“…Finally, according to recent findings in this laboratory [35], the reaction between CH302 and C10 radicals t 18) CH302 + c10 * CH30 + cloz is quite fast (k18 = 3.1 x lo-'' cm3 molecule-' s-') and can readily compete with the self reaction of CH302 radicals which proceeds with a rate constant of 3.6 x cm3 molecule-' s-l 1361. The self reaction of CFC1202 radicals might be considerably faster than the self reaction of CH30z radicals (~c c~~o~+ c c~~o z = 1.6 x lo-'' cm3 molecule-' s-l [37]).…”

Photodissociation of CH3OCl to CH3O + Cl at 248 nm

“…Though early experiments 8,9 were unable to detect the weakly absorbing, unstable CH 3 OCl products from reaction 3b, later work using a discharge flow/mass spectrometer apparatus showed that this channel accounts for ∼23% of the reaction at typical stratospheric temperatures of ∼200 K. 7 Helleis et al obtained a channel-specific rate constant of (4.1 ( 1) × 10 -13 cm 3 molecule -1 s -1 . 7 These measurements indicate that channel 3b may have a significant impact on stratospheric chlorine cycles.…”