  Traditionally, it has been assumed that the stopping of a swift ion
travelling through matter can be understood in terms of two essentially
independent components, i.e. electronic vs. nuclear. Performing extensive
Ehrenfest MD simulations of the process of proton irradiation of water ice that
accurately describe not only the non-adiabatic dynamics of the electrons but
also of the nuclei, we have found a stopping mechanism involving the interplay
of the electronic and nuclear subsystems. This effect, which consists in a
kinetic energy transfer from the projectile to the target nuclei thanks to the
perturbations of the electronic density caused by the irradiation, is
fundamentally different from the atomic displacements and collision cascades
characteristic of nuclear stopping. Moreover, it shows a marked isotopic effect
depending on the composition of the target, being relevant mostly for light
water as opposed to heavy water. This result is consistent with long-standing
experimental results which remained unexplained so far.
