Diffusion and Hot Radical Kinetics in the Photolysis of Liquid Ethyl Iodide¹

Abstract

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

Radiolysis of ethyl iodide and carbon tetrachloride mixtures at 77°K

“…In such a way, we assume that the small, but measurable, radiochemical yield of C,H,' radicals in the concentration range less than 0.9 of ethyl iodide ( Fig. 2) results from reaction [7] and accounts for a g,(C,H,') = 0.07 in pure C,H,I.…”

“…2) indicates that another mechanism must be invoked in order to explain the small, but measurable, yield in the concentration range less than 0.9. The homolytic dissociation of excited C2H,I molecules formed in reactions [la] and [7] might be the process responsible for this slow decrease of G(C2H,'). On the other hand, at high concentrations of ethyl iodide (> X = 0.6) the observed G(CC1,') decreases, notwithstanding that one might expect that the yield of CCl;, being the counterpart of Cl-by reaction [4], should not differ much from that measured at low and moderate concentrations.…”

Photolyse De l'IODURE De Vinyle en Solution Dans Le Tetrachlorure De Carbone

“…Les coilclusions que nous pouvons tirer de ce travail sont les suivantes: (1) le mCcanisine de la "dismutation contr61Ce par diffusion" explique bien les phCnom&nes observCs; (3) l'Cthyl&ne est principalenlent form6 par la rkaction de radicaux vinyliques therrnalisCs par H I ; (3) nous devons postuler une rCaction de tCloinCrisation pour expliquer la diminution de la production d'bthylhe et de l'iode avec l'augmentation de la concentration en iodure de vinyle; (4) llefficacitC d'amor~age des chaines polyinCriques par le radical C2H3' est faible coinparCe aux autres rkactions coinpCtitives de disparition de ce radical. For personal use only.…”

“…Par consCquent, le dkficit en H I par rapport B C2H2 doit avoir une autre origine: soit l'addition de H I A la double liaison du monom&re, soit l'absorption de H I sur les parois, soit, encore, une autre cause qui nous Cchappe actuellement. E n appliquant l'hypoth2se de stationnaritb e t en nkgligeant la rkaction [8] (dont la contribution est faible), les rkactions de terminaison des tClom6res [lo] e t [ l l ] (dont nous ne saurions tenir compte), ainsi que la rkaction [7] (qui n'est importante qu'au tout dkbut de l'irradiation), on trouve les expressions suivantes pour la production de l'kthyl2ne e t du chlorure de vinyle: oh + 3 est kgal au rendement quantique de la rkaction [3]. On voit que:…”

The Self-induced Exchange of Tritium Gas with Methane

“…Furthermore resonant or near resonant reactions have a higher cross section than those in which there is a large energy difference. 6 The heats of reaction, AHr, for the ion-molecule reactions used in the discussion have been evaluated from the heats of formation of the ions.7-9 The numbers to the right of the chemical equations in the discussion are the calculated Afifr values in units of kilocalories per mole with a negative sign indicating that the reaction is exothermic as written.…”