Ionization of π-stacked and H-bonded Uracil Dimers
Ionization energies (IE) of nuclear bases can be affected by the π-π and H-bonding interactions they experience in DNA.
Nucleic bases in DNA: π-stacking versus H-bonding
By using the EOM-IP method, we characterized the electronic states of the uracil dimer. We found that the interaction between bases lowers the dimer IE by 0.3 eV relative to the monomer.
Electronic states of the π-stacked dimer
Moreover, ionization changes bonding from van der Waals to covalent (see below), which has structural and spectroscopic implications. For example, the fragments move closer to each other and strong charge-resonance electronic transitions appear.