Vol. 61 cm.3/molecule sec. that differs by less than the exposes (Westinghouse Type LV, Consolidated Electrodynamics Model 21-103 or -620) at pressures the order of 2-4 times normal operating pressure, it follows that the reaction cross section is of the order of 100 Á.2 Hence, at atmospheric pressure the half-life of the ion with respect to this reaction will be the order of 10-8 times its half-life with respect to recombination with an electron (for reasonable radiation dose rates). The characteristics of conventional analytical mass spectrometers are such that for such reactions to be easily observable the reaction cross section must be very large. Even an increase by a factor of 103 of the dynamic range of measurement by the mass spectrometer would result in the slowest secondary reaction observable with a mass spectrometer still being fast in comparison with the rate of recombination of ions.
Air-free ethyl iodide has been photolyzed both in the pure liquid state and in cyclohexane sulution, using light of 2537 A.The composition of the product mixture was independent of the extent of photolysis and in the case of pure ethyl iodide was ound to be: C?H4, 38.8; C2H6, 26.0; 12, 24.2; HI, 11.3; H1, 0.03 mole %. By the use of initially added H I and Iz it has been shown that the ratio CgH4/C2H6 is a linear function of Iz/HI. mole fraction, the ratio C2H4/C2Hs was depressed below the value predicted by the linear function, due to decrease in the C2H4 yield, which is constant a t lower H I concentrations. -4 tnechanism has been proposed and tested in which the primnry act is dissociation of the C-I bond. It is further proposed that diffusion-controlled reactions occur between the ethyl radicals and iodine atoms yielding for recombination & = 0.60, for ethylene and for hydrogen iodide & = 0.19, and for diffusion apart into the steady state 6 3 = 0.21. The effect of high concentrations i i f hydrogcn ioditlc i i t o diminiili c$, and 4. by intervention in the diffusioiicontrolled processes.IVhen H I exceeded 3 X
IntroductionThe quantum yield for production of iodine in photolysis of pure liquid ethyl iodide a t 2537 A. is 0.2G2 gram atom. Many previous investigations have considered iodine to be the only significant iodine-containing product, and have therefore taken this quantum yield to be equal to that for decomposition of ethyl iodide. Studies of the absorption spectrum3 have indicated that the primary process is the rupture of the C-I bond. By use of
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