ENDOR studies of the superhyperfine couplings of hydrogen bonded protons. II. Protonated radical anion in irradiated succinic acid single crystals

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Abstract
The carboxyl radical anion trapped at 77°K in an irradiated single crystal of succinic acid has been studied by ENDOR in order to determine if the anion is protonated. The ENDOR spectra showed that the anion exhibited hyperfine couplings to the two OH protons. The principal values of the two coupling tensors are nearly the same and the principal directions are accounted for by the structure of R–Ċ(OH)2, that is, the protonated form of the anion. The location of the extra proton suggests that the proton is transferred from the neighboring molecule across the hydrogen bridge.