ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The 147 nm (8.4 eV) photolysis of gaseous C2H5I, n-C3H7I, and sec-C3H7I was investigated in the presence of and absence of HI. The main overall processes are: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcll} {{\rm C}_{\rm 2} {\rm H}_{\rm 5} {\rm I} + h\nu} &\to& {{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + H + I}} & {\phi = 0.75} \\{{\rm n{-} C}_{\rm 3} {\rm H}_{\rm 7} {\rm I} + h\nu }&\to& {{\rm C}_{\rm 3} {\rm H}_{\rm 6} {\rm + H + I}} & {\phi = 0.38} \\& \to&{ {\rm CH}_{\rm 3} +{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + I}} & {\phi = 0.47} \\ {\sec - \,{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm I}\, + h\nu} &\to &{{\rm C}_{\rm 3} {\rm H}_{\rm 6} {\rm + H + I}} & {\phi = 0.80} \\ &\to&{ {\rm CH}_{\rm 3} +{\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm + I}} & {\phi = 0.07} \\\end{array} $$\end{document} These dissociative processes occur mainly as a result of initial cleavage of the weak C—I bond, followed by decomposition of the internally excited alkyl radicals. In all cases, approximately 5-10% of the alkyl radicals thus formed do not undergo dissociation at pressures around 3-7 torr. There is also evidence for the elimination of HI as well as C—C cleavage in the primary dissociation. The former is indicated by deuterium labeling experiments and the formation of cyclopropane (Φ = 0.04) as a product in the photolysis of n-C3H7I. Because the processes listed above provide a constant source of H atoms whose quantum yield can be exactly determined, it was feasible to obtain accurate values for ka/kb: For thermally equilibrated H atoms (300 K), ka/kb is 0.44 ± 0.04, 0.57 ± 0.06, 0.95 ± 0.1, and 0.024 ± 0.01 for C2H5I, n-C3H7I, sec-C3H7I, and C2H5Br, respectively.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550050515
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