Quantum nature of the sign preference in ion-induced nucleation.

Observed first in Wilson's pioneering experiments in the cloud chamber, the sign preference has remained a mystery for more than a century. We investigate the sign preference using a quantum approach and show that this puzzling phenomenon is essentially quantum in nature. It is shown that the effect of the chemical identity of the core ion is controlled by the electronic structure of the core ion through the influence on the intermolecular bonding energies during the initial steps of cluster formation. Our results demonstrate the superiority of the quantum approach and indicate fundamental problems of conventional ion-induced nucleation theories, in which the electronic structure of the core ion is either ignored or not treated rigorously.