Singlet-correlated radical ion pairs in irradiated alkanes

SINGLET-CORRELATED RADICAL ION PAIRS IN IRRADIATED ALKANES 

The formation of singlet-correlated radical ion pairs in alkane (RH) solutions containing acceptors of electrons (A) and holes (D) can be represented by the scheme below 

Both the primary pair RH. ..e and the secondary pairs D. ..e, Rtf. ..A and D . ..A can undergo singlet-triplet evolution and yield an excited product whose multiplicity corresponds to the spin pair multiplicity upon recombination. From the prospects of recording the spin coherence effects, such pairs exhibit the 

1) The probability of their recombination is close to unity, because in hydrocarbons, for most pairs, the initial distances between the partners are well within the Onsager radius. 

2) The time of the diffusive approach of radical ions in the pairs D. ..A and RH. ..A is large enough and can exceed the typical time of singlet-triplet evolution. In organic radical ions, the latter is usually determined by the constants of hyperfine interactions (hfi) and varies from nanoseconds to tens of nanoseconds. 

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