Hydrogen-rich DNA dinucleotide cation radicals (dGG + 2H)(+center dot), (dCG + 2H)(+center dot), and (dGC + 2H)(+center dot) represent transient species comprising protonated and hydrogen atom adducted nucleobase rings that serve as models for proton and radical migrations in ionized DNA. These DNA cation radicals were generated in the gas phase by electron-transfer dissociation of dinucleotide dication-crown-ether complexes and characterized by UV-vis photodissociation action spectra, ab initio calculations of structures and relative energies, and time-dependent density functional theory calculations of UV-vis absorption spectra. Theoretical calculations indicate that (dGG + 2H)(+center dot) cation radicals formed by electron transfer underwent an exothermic conformational collapse that was accompanied by guanine ring stacking and facile internucleobase hydrogen atom transfer, forming 3'-guanine C-8-H radicals. In contrast, exothermic hydrogen transfer from the 5'-cytosine radical onto the guanine ring in (dCG + 2H)(+center dot) was kinetically hampered, resulting in the formation of a mixture of 5'-cytosine and 3'-guanine radicals. Conformational folding and nucleobase stacking were energetically unfavorable in (dGC + 2H)(+center dot) that retained its structure of a 3'-cytosine radical, as formed by one-electron reduction of the dication. Hydrogen-rich guanine (G + H)(center dot) and cytosine (C + H)(center dot) radicals were calculated to have vastly different basicities in water, as illustrated by the respective pK(a) values of 20.0 and 4.6, which is pertinent to their different abilities to undergo proton-transfer reactions in solution.