Theory for the Nonlinear Ultrafast Dynamics of Small Clusters after Ionization

The ultrafast relaxation of small clusters immediately after ionization is studied. For small Hg$_n$ clusters we determine the fragmentation-time distributions induced by ionization. A dramatic change of the fragmentation behaviour occurs when the temperature before ionization reaches the melting point of the neutral clusters. The ultrafast dynamics depends nonlinearly on initial conditions regarding atomic positions and velocities. The resultant largest Lyapunov exponent increases strongly upon ionization.