  New Molecular Dynamics simulations have been carried out in order to get an
insight on the physical mechanisms that determine the drift mobility of
negative Oxygen ions in very dense Neon gas in the supercritical phase close to
the critical point. Two ion-neutral interaction potentials have been used that
differ by their repulsive part. We have observed that the potential with a
harder repulsive part gives much better agreement with the experimental data.
The differences with the softer repulsive potential previously used are
discussed. We propose that the behavior of the ion mobility as a function of
the gas density is related to the number of neutral atoms loosely bound in the
first solvation shell around the ion.
