The rates of reactions between OH radicals and CHClF2, CH2ClF, CH2ClCF3, and CH3CClF2 in the range 260–370 K as well as OH + CH3CHF2 at 293 K have been studied using stationary flash photolysis combined with OH UV‐resonance absorption detection.
The results are:
at 293 K. The implication of the rate data with respect to the tropospheric degradation of the halocarbons is discussed.
Formation of hydroxy‐cyclohexadienyl (HCHD), the product of the OH + benzene reaction, has been observed directly in the gas phase at 298 K using long‐path cw‐UV‐laser absorption at 308 nm. The absorption cross section at this wavelength is found to be (9.2 ± 2) · 10−18 cm2. The use of this technique to study directly the subsequent oxidation of HCHD by O2 is emphasized.
Rate constants for the recombination reaction (1) ClO + NO2 (+ N2) → ClONO2 (+ N2) have been measured in the pressure range 23 – 1040 mbar and at temperatures of 264, 298 and 343 K using flash photolysis to generate ClO radicals and time dependent UV absorption in the A‐X system as their monitor. k1, is found to show a strong pressure dependence with an onset to “fall‐off” at pressures above ∼ 50 mbar. The “fall‐off” behaviour is interpreted in terms of complete and symmetrical Kassel integrals and is found to be in agreement with the accepted low pressure limit as well as with a theoretical estimate of the high pressure limiting rate constant, k1∞ = 1.2 · 10−11 cm3/s.
The rate coefficient for reaction between ClO (2II) and O2 (1Δg) has been measured using a flow/flash photolysis technique. An upper limit of k1 ≤ 3·10−15 cm3/s at 298 K was found. The formation of symmetrical ClO3 (2A1) as a product is spin and orbital symmetry allowed but is probably prevented by an activation barrier and by equilibrium constraints. The rate coefficient for quenching of O2(1Δ) by Cl2 was found to be 2·10−17 cm3/s at 298 K.
The rate coefficient of the title reaction (which may be a potential pathway to the generation of "odd" oxygen (O, O3) in the stratosphere) has been measured using a flow/flash photolysis technique.
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