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Production of $I^*(^2P_{1/2})$ in the ultraviolet photodissociation of \alpha-branched alkyl iodides

Uma, S and Das, Puspendu Kumar (1996) Production of $I^*(^2P_{1/2})$ in the ultraviolet photodissociation of \alpha-branched alkyl iodides. In: The Journal of Chemical Physics, 104 (12). pp. 4470-4474.

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Photodissociation dynamics of a series of \alpha-branched alkyl iodides at excitation wavelengths of 222, 266, and \sim 305 nm has been investigated by measuring the quantum yield $(\phi^*)$ of $I^*(^2P_{1/2})$ production. $I^*$ is found to be the major product at 222 nm and 266 nm from methyl and ethyl iodides but not from the higher \alpha-branched homologs. On the contrary, $I(2^P_{3/2})$ is the major product at ~305 nm for all the iodides. Assuming that $I^*$ originates from the $^3Q_0$ state over the entire A-band, production of both I and $I^*$ in methyl and ethyl iodides at 222 and 266 nm is explained by invoking the curve-crossing mechanism in the upper state. The crossing probability (P) between the $^3Q_0$ and $^1Q_1$ surfaces for these two molecules has been estimated. At ~305 nm, simultaneous excitation to the $^3Q_0$ and $^3Q_1$ states remains a distinct possibility. For higher branched (i.e., i-propyl and t-butyl) alkyl iodides, the mechanism for $I^*$ production is qualitatively different from that of unbranched iodides. Coupling of a-carbon bending vibrational modes with the C–I bond excitation as well as the actual time spent in the excited state surfaces in i-propyl and t-butyl iodides seem to be the reasons for altering the dynamics of dissociation drastically in comparison with that of methyl iodide.

Item Type: Journal Article
Publication: The Journal of Chemical Physics
Publisher: American Institute of Physics
Additional Information: Copyright of this article belongs to American Institute of Physics.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 05 Jan 2007
Last Modified: 19 Sep 2010 04:33
URI: http://eprints.iisc.ac.in/id/eprint/9328

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