Collisional excitation and fragmentation of alkali-metal halide cluster ions

Abstract

Caesium iodide cluster ions have been formed by bombardment of the solid salt in vacuo with xenon atoms possessing kiloelectron volt (keV) kinetic energies, and the ions have been mass-selected on the basis of magnetic deflection. The mass-selected cluster ions with translational energies of ca. 10 keV have been allowed to collide with thermal inert and other gases, and the translational energy spectra of surviving cluster ions and of fragment ions have been measured using a cylindrical electric sector analyser. Cluster ions suffered large translational energy losses ΔE(e.g. 100 eV) in those collisions leading to fragmentation. Different fragment ions were associated with translational energy losses of different magnitudes. For a given fragment ion, the magnitude of the translational energy loss tended to be related to the mass of the collision gas, typically being larger for lighter gases. Translational energy losses tended to be greater in the case of larger incident cluster ions. The translational energy spectra are discussed in terms of direct momentum transfer in an impulsive collision.