Abstract:
:High intensity two-photon picosecond excitation at 266 nm (effective energy 9.2 eV) has been shown to cause efficient photolysis of thymine in aqueous solution. Experimental results for the quantum yield of solvated electrons, phi (eaq-), and the net consumption of thymine, phi(-Thy) have been interpreted (Oraevsky and Nikogosyan, 1985) as indicating a stoichiometric excess of solvated electrons over thymine radical-cations. To account for this under conditions in which direct two-photon photolysis of water is negligible, it has been concluded that it is necessary to postulate the occurrence of extensive energy transfer from high-lying thymine states to dissociating/ionizing states of water. This Note demonstrates that: (i) the supposed excess of eaq- depends on an implicit assumption concerning the secondary radical reactions (dimerization) such that -delta Thy = delta Thy+; if secondary radicals dismutate then -Thy = 1/2 delta Thy+, leading a stoichiometric deficit of eaq-; and (ii) the experimental results can be accounted for by a mixed dimerization/dismutation mechanism, without invoking energy transfer. Thus there is no evidence unambiguously requiring the postulate of energy transfer. But if it occurs, stoichiometry places restrictions on the extent of transfer and the nature of the secondary radical reactions.
journal_name
Photochem Photobioljournal_title
Photochemistry and photobiologyauthors
Daniels Mdoi
10.1111/j.1751-1097.1991.tb01996.xsubject
Has Abstractpub_date
1991-07-01 00:00:00pages
133-6issue
1eissn
0031-8655issn
1751-1097journal_volume
54pub_type
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