Collision-induced dissociation of the cesium halides

Abstract

Total cross sections vs the relative collision energy are reported for collision-induced dissociation (CID) of CsF and CsBr to ion pairs on collision with beams of accelerated projectiles M, where M includes Ar, Kr, and Xe atoms as well as SF6 molecules. Measurements of the CID of CsCl with Ar and SF6 are also presented. Partial cross sections for both three body dissociation and for the formation of the weakly bound molecular ions CsM+ are determined. The cross sections for CID of CsF are found to be considerably smaller than those for the other halides for all projectiles but particularly for SF6. For Xe colliding with CsF the CID cross sections are determined to be only weakly dependent on the CsF internal energy, in contrast to earlier studies on CsI where a strong dependence was obtained. Two-dimensional in-plane trajectory calculations for Xe colliding with the four cesium halides are performed to identify the important dynamical effects governing the efficiency of CID. For CsCl, CsBr, and CsI the dissociation efficiency is found to depend mainly on the effects of relative mass, whereas for CsF, the relative size of the projectile vs the F− ion strongly affects the dissociation efficiency. A surprisingly strong influence of the weak attractive forces between the projectile and the cesium or halogen product ion is found which affects an increase in the energy transfer, and is related to the formation of either bound or transient molecular ions. A general discussion of the experimental results for the four cesium halides, as well as the dynamical effects involved in both three body dissociation and molecular ion formation, is presented.