Third Report of the Committee on Photochemistry Reprint and Circular Series of the National Research Council (1938) / Chapter Skim
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The Correlation of Photoprocesses in Gaseous and Liquid Systems
The Correlation of Photoprocesses in Gaseous and Liquid Systems
Pages 41-50
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From page 41... ...
In recent years theories of the liquid state and of various phenomena occurring in liquids have undergone active development; this may, for example, be seen in the general discussion of the liquid state published by the Faraday Society (43) as well as in other papers to which specific reference will be made.
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From page 42... ...
This arises partly from the relative simplicity of the phenomenon in the gaseous state, where the absorption is by fairly isolated molecules, and partly from the related fact that in condensed states the fine structure of absorption spectra is lost, together with the detailed information derivable from such structure. Aside from the smoothing out of fine structure into a continuum in solution, dissolved substances frequently show spectra differing from those of the same substances in the gaseous state, both as to magnitude of absorption coefficient and as to position of absorption maxima.
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From page 43... ...
For example, the absorption coefficients of the halogens in non-polar solvents such as carbon tetrachloride differ little from values for the gases. In cases where this close similarity exists, it is usual to presume that absorption is accompanied by the same electronic transition in both cases, and to draw inferences concerning the primary process in solution from a knowledge of that in the gas.
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From page 44... ...
If, in the gaseous state, an induced predissociation occurs in competition with fluorescence, then, in solution, the dissociation may evidently be favored. However, even if the molecule does dissociate, there exists a possibility that the dissociating partners, in view of the fact that they are closely hemmed in by solvent molecules, will frequently immediately recombine.
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From page 45... ...
Again if, in accord with ideas mentioned earlier, the total number of collisions between solute molecules is somewhat greater than the value given by the gas formula, say m times that value, then the calculated values of ~ become m/n times the values given above. Thus, while values of ~ of the order of magnitude of unity are compatible with the experimental results, more definite independent knowledge of the recombination rate is necessary in order to make a definite determination of ~ from the stationary concentrations.
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From page 46... ...
were found to stand in the ratios 1:0.87:0.75. Other halogen chain reactions in which yields somewhat smaller at longer wave lengths than at shorter have been reported are the following: the bromination of cinnamic acid in carbon tetrachloride solution (2~; the bromination of liquid benzene (32~; the bromination of maleic ester and its sensitized rearrangement to fumaric ester (15~; the iodination of various olefins in
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From page 47... ...
Considerable wave length effects in the same sense are often found in aqueous solution reactions, but caution must be exercised in attributing them to varying primary recombinations as opposed, for example, to reaction with solvent or to the occurrence of different electronic transitions on absorption. The situation can be somewhat different in the case of certain reaction mechanisms not involving a chain.
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From page 48... ...
With the aid of radioactive chlorine Rollefson and Libby (36) have shown that, when chlorine absorbs visible radiation in carbon tetrachloride solution, little if any reaction with the solvent occurs.
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From page 49... ...
of the decomposition of ethyl iodide, which occurs with a larger quantum yield in the liquid state than in the gaseous, and in a discussion (12) of the decomposition of ethylene iodide in carbon tetrachloride solution.
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From page 50... ...
D.: TranS. Faraday SOC.
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