were studied at T \ 298 K using a fast-Ñow discharge system with resonance-Ñuorescence detection of Cl atoms. The rate coefficients were found to be pressure-independent over the range 1.5È12 Torr, and were cm3 molecule~1 s~1, c m 3 molecule~1 s~1,c m 3 molecule~1 s~1 and k 4 \ (46.8 ^4.9) ] 10~12 cm3 molecule~1 s~1. The rates of reaction of these alkyl iodides with Cl atoms in k 5 \ (0.85 ^0.09) ] 10~12 the marine boundary layer were compared with the rates of their photolysis and their reaction with OH. For early morning conditions, it is shown that reaction with Cl atoms can compete with photolysis and dominate over reaction with OH, if Cl atom concentrations are about 1 ] 105 molecule cm~3. Atomic iodine may be released following reaction of Cl with the alkyl iodides ; this atomic I can participate in catalytic destruction of ozone in the marine boundary layer.

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The first measurements of electron impact vibrational excitation of ozone are presented as a function of both incident electron energy, 3 eV

The rate coefficients for the reaction of with pent-1-ene and hex-1-ene have been measured directly for a range of tem-NO 3 peratures between 298 and 433 K using the discharge-Ñow technique coupled to a laser-induced Ñuorescence (LIF) detection system to monitor the radical. The values obtained for the rate coefficients at room temperature are (6.19 ^0.38) ] 10~14 NO 3 and (9.32 ^0.71) ] 10~14 cm3 molecule~1 s~1, respectively. These results are in excellent agreement with the predictions based on the correlation between the rate constant at room temperature and the ionization potential used as an indicator of HOMO energy. The Arrhenius expressions : k(T ) \ (2.05 ^0.95) ] 10~11 exp[([1703 ^80)/T ] and k(T ) \ (1.24 ^0.40) ] 10~12 exp[([816 ^23)/T ] cm3 molecule~1 s~1 are proposed for the two reactions. The rate constants for the reactions of pent-1-ene and hex-1-ene with have been compared with the coefficients for the reactions of these compounds with OH and O(3P). The NO 3 observed trends in reactivity are explained in terms of the presence of electron-withdrawing substituents, which reduce the reactivity of alkenes. Tropospheric half-lives of these compounds, at night and during the day, have been estimated for typical tropospheric and OH concentrations, in order to assess the lifetimes of the compounds in the atmosphere. NO 3