Electronic Spectra of Radical Ions

Organic molecules may accept an extra electron to form radical anions, R+, or give up an electron by ionization to form radical cations, R+. Some of the radical ions are relatively stable in their ground states in solution phase and can be readily characterized by spectroscopic methods. Electron spin resonance spectroscopy provides an ideal tool for the study of the unshared electron in these radical ions. Most radical ions are intensely colored and give characteristic absorption bands in the electronic spectra. Further, electronic spectroscopy is one of the few tools available for the study of the dianions, which are generally diamagnetic. Electronic spectroscopy is used not merely for the characterization of the ionic species in solution but also for the study of the chemical equilibria involving various kinds of ionic species.