Temporal evolution of free neutral and ionized argon clusters

The evolution of free argon clusters, traveling in vacuum after formation and after ionization, was studied experimentally and theoretically. The average lifetime of the cluster ions was measured in the pulsed jet as a function of the stagnation pressure at different distances from the electron impact ionizer (12–26 μs). The changing of mass distribution of the cluster ions with the distance from the ionizer was studied and two fractions of cluster ions were observed. The decay of the heavy fraction is consistent with the considered model of the evaporative decomposition. The light fraction decomposes mainly due to ejection of the cluster ions. This process has a threshold character as a function of time elapsed after ionization.