Abstract:linear with a slope related to k,. By using eq VIII, a plot of should be linear with a slope of k3 and an intercept of k4, the rate coefficients for reactions 3 and 4, respectively. Figure 7 shows a plot of for data obtained in the temperature range 191-240 K. As can be seen, k, or the slope of the plot is independent of temperature. Values of (2.15 f 0.13) X and (1.7 f 3.6) X lo-" cm3 molecule-' s-I were obtained for k3 and k4, respectively. The reported errors are twice the standard deviation of the slope an… Show more
“…The predictions of the diffusion−kinetic model for the various product yields are shown as a function of iodine scavenger concentration in Figures −3 for cyclopentane, cyclohexane, and cyclooctane, respectively. Alsoshown in these figures are the measured yields of the cycloalkenes, bicycloalkyls, and cycloalkyl iodides obtained using γ-radiolysis. ,, The experiments showed that a very large fraction of the cycloalkyl radicals produced in the radiolysis survive to times well beyond the lifetime of the spur. That is, much of the chemistry of the cycloalkyl radicals occurs while they have a homogeneous spatial distribution.…”
Section: Resultsmentioning
confidence: 99%
“…Model predictions for complete conversion of H atoms to cyclopentyl radicals are denoted by the dashed line and for no iodine quenching of the excited singlet state by the dotted line. 2 Predictions of the model for the γ-radiolysis of cyclohexane, solid lines, as a function of iodine concentration. Experimental points, ref , are (▪) cyclohexene, (·) bicyclohexyl, (▴) cyclohexyl iodide, (▵) 1.1 × cyclohexyl iodide, (+) 2Δ(C 6 + C 12 ) (twice the net change in yields of cyclohexene and bicyclohexyl), (◆) cyclohexyl radical yields calculated from k d / k c and the change in yield of bicyclohexyl. Model predictions for complete conversion of H atoms to cyclohexyl radicals are denoted by the dashed line and for no iodine quenching of the excited singlet state by the dotted line. 3 Predictions of the model for the γ-radiolysis of cyclooctane, solid lines, as a function of iodine concentration.…”
Section: Resultsmentioning
confidence: 99%
“…The rate coefficients for the radical−radical reactions and radical−iodine scavenging reactions were as previously measured . Experimental values for cycloalkyl radical disproportionation/combination ratios were also used. ,, No experimental values for the rate coefficients for H atom−H atom combination or for H atom scavenging by iodine are available in hydrocarbon liquids. Since these reactions are nearly diffusion limited, the appropriate value in each of the cycloalkanes was obtained by a viscosity scaling of the rate coefficients in water .…”
Section: Methodsmentioning
confidence: 99%
“…Iodine is believed to quench the singlet excited states of both cyclopentane and cyclohexane. , No rate coefficient for this reaction is available. However, the quenching of the excited singlet state is quite noticeable in the different dependences of cycloalkenes and bicycloalkyls on iodine concentration.…”
A deterministic diffusion−kinetic model has been
successfully applied to the radiation chemistry occurring
in a typical spur produced in the γ-radiolysis of liquid
cyclopentane, cyclohexane, and cyclooctane. The
predictions of the yields of the cycloalkenes, bicycloalkyls, and the
cycloalkyl iodides in solutions of iodine
are in excellent agreement with experimental data. The major
adjustable parameters in the model are the
characteristic radii of the initial Gaussian spatial distributions of
the reactive species. Values for these radii
were found to be 0.5, 1.1, and 0.55 nm in cyclopentane, cyclohexane,
and cyclooctane, respectively. The
results suggest that the spurs of cyclopentane and cyclooctane are very
small, ca. one molecular diameter,
with resulting large local concentrations of reactants. With
cyclohexane, the spur size is twice as large and
the initial local concentrations are an order of magnitude smaller.
The experimentally observed temporal
invariance of the cyclohexyl radical can be explained by competing
effects in the spur evolution. Details and
implications of the spur model are discussed.
“…The predictions of the diffusion−kinetic model for the various product yields are shown as a function of iodine scavenger concentration in Figures −3 for cyclopentane, cyclohexane, and cyclooctane, respectively. Alsoshown in these figures are the measured yields of the cycloalkenes, bicycloalkyls, and cycloalkyl iodides obtained using γ-radiolysis. ,, The experiments showed that a very large fraction of the cycloalkyl radicals produced in the radiolysis survive to times well beyond the lifetime of the spur. That is, much of the chemistry of the cycloalkyl radicals occurs while they have a homogeneous spatial distribution.…”
Section: Resultsmentioning
confidence: 99%
“…Model predictions for complete conversion of H atoms to cyclopentyl radicals are denoted by the dashed line and for no iodine quenching of the excited singlet state by the dotted line. 2 Predictions of the model for the γ-radiolysis of cyclohexane, solid lines, as a function of iodine concentration. Experimental points, ref , are (▪) cyclohexene, (·) bicyclohexyl, (▴) cyclohexyl iodide, (▵) 1.1 × cyclohexyl iodide, (+) 2Δ(C 6 + C 12 ) (twice the net change in yields of cyclohexene and bicyclohexyl), (◆) cyclohexyl radical yields calculated from k d / k c and the change in yield of bicyclohexyl. Model predictions for complete conversion of H atoms to cyclohexyl radicals are denoted by the dashed line and for no iodine quenching of the excited singlet state by the dotted line. 3 Predictions of the model for the γ-radiolysis of cyclooctane, solid lines, as a function of iodine concentration.…”
Section: Resultsmentioning
confidence: 99%
“…The rate coefficients for the radical−radical reactions and radical−iodine scavenging reactions were as previously measured . Experimental values for cycloalkyl radical disproportionation/combination ratios were also used. ,, No experimental values for the rate coefficients for H atom−H atom combination or for H atom scavenging by iodine are available in hydrocarbon liquids. Since these reactions are nearly diffusion limited, the appropriate value in each of the cycloalkanes was obtained by a viscosity scaling of the rate coefficients in water .…”
Section: Methodsmentioning
confidence: 99%
“…Iodine is believed to quench the singlet excited states of both cyclopentane and cyclohexane. , No rate coefficient for this reaction is available. However, the quenching of the excited singlet state is quite noticeable in the different dependences of cycloalkenes and bicycloalkyls on iodine concentration.…”
A deterministic diffusion−kinetic model has been
successfully applied to the radiation chemistry occurring
in a typical spur produced in the γ-radiolysis of liquid
cyclopentane, cyclohexane, and cyclooctane. The
predictions of the yields of the cycloalkenes, bicycloalkyls, and the
cycloalkyl iodides in solutions of iodine
are in excellent agreement with experimental data. The major
adjustable parameters in the model are the
characteristic radii of the initial Gaussian spatial distributions of
the reactive species. Values for these radii
were found to be 0.5, 1.1, and 0.55 nm in cyclopentane, cyclohexane,
and cyclooctane, respectively. The
results suggest that the spurs of cyclopentane and cyclooctane are very
small, ca. one molecular diameter,
with resulting large local concentrations of reactants. With
cyclohexane, the spur size is twice as large and
the initial local concentrations are an order of magnitude smaller.
The experimentally observed temporal
invariance of the cyclohexyl radical can be explained by competing
effects in the spur evolution. Details and
implications of the spur model are discussed.
“…1 for cyclohexane (LaVerne et al, 1992;Schuler, 1957;Enomoto et al, 2006b) Figs. 1-3 are the major products formed in radiolysis and thereby represent the main decomposition scheme. A large decrease in overall product yield is observed from cyclohexane to benzene.…”
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