Spin correlation effects on reactions in spurs of radicals, radical ions and electrons after radiolysis
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 75, 123-140
- https://doi.org/10.1039/f29797500123
Abstract
Dissociation and ionisation in condensed phases produce pairs of radicals (and electrons) or radical ions. Recombination of such pairs into ground state molecules depends on their spin state: singlets can recombine, triplets separate; theoretical work on ions in hydrocarbons is extended here to other substances, especially aqueous solutions. Single pairs are usually singlet initially. Recombination in spurs containing two or more pairs gives a mixture of singlets (S) and triplets (T). The cross-reactions in spurs, which in water give H2 and H2O2, normally have S:T = 1:3. Generation of a pair in a large spur via a triplet intermediate and Heisenberg spin exchange both transfer singlet character from the back reactions to the cross reactions. In mobile liquids, two processes are fast enough to cause correlation decay before recombination in the spurs: coherent (oscillatory) decay due to the hyperfine interaction in free hydrogen atoms and spin relaxation in hydroxyl and other cylindrically symmetrical radicals. Calculations of the spin relaxation time of ·OH radicals are presented : the mechanism is shown to depend on viscosity. Correlation effects on recombination of solvated electrons in viscous and glasses are discussed. It is shown that studies of spur dynamics must include spin effects. A variety of effects of magnetic fields and of deuteration on reaction rates in pairs and on yields of radiolysis products are predicted. Quantitative predictions are not attempted for lack of information, but effects will be small in liquid water, larger in organic liquids.Keywords
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