  A new paradigm emerging in the description of magnetic-sensitive
radical-ion-pair recombination reactions is presented. This paradigm is founded
on the realization that the recombination process of radical-ion pairs is a
continuous quantum measurement. In the regime of low magnetic fields we
describe the appearance of purely quantum phenomena, that fade away as the
magnetic field increases. We will analyze the magnetic sensitivity of these
reactions under this perspective and bridge the new full quantum theory with
the existing classical reaction theory applicable at high magnetic fields.
Based on the quantum theory of recombination we will then explain experimental
observations incompatible with classical reaction theory, in particular the
effect of deuteration on the magnetic sensitivity of radical-ion pair
recombination yields.
