Collision dynamics for small helium cluster ions

Classical trajectories have been carried out for the collision of helium atoms with He2+ and He3+ using a potential energy which includes the effects of dispersion, polarisation and charge exchange. At a collision energy of 0.1 eV the cross-section for atom exchange in He + He2+ is calculated to be 21.5 إ, exchange occurring through both simple collisions and long-lived complexes. However, even for very long-lived complexes exchage never exceeds 50% so that complete permutation of atoms in the complex does not occur. The cross-section for exchange in He + He3+ at the same collision energy is found to be much smaller at 0.7 إ2 which is attributed to the much smaller dissociation energy of He4+. Rotational energy transfer for both collisions is similar, for impact parameters less than 3.5 إ only 50% of collisions transfer more than 10% of translational energy to rotation.