Collision-induced ion-pair formation of CsCl and Cs2Cl2

Abstract
Absolute cross sections have been determined for collision‐induced ion‐pair formation of cesium chloride (monomers and dimers) from collisions with Ar, Kr, and Xe atoms. The rare gas atoms were aerodynamically accelerated in H2, with maximum energies of 6.8, 12.1, and 18.3 eV (in the laboratory frame), respectively. Time‐of‐flight mass spectrometry permitted the determination of partial cross sections for each ion channel resulting from the collision. For the monomer, the cross secions for the channel leading to Cs++Cl were similar in magnitude for the three rare gas atoms and were approximately 3×10−16 cm2 at 3 eV above threshold. The rearrangement ionization channel leading to CsM+ (M=Ar, Kr, and Xe) exhibited a step behavior at threshold followed by a very rapid fall off at higher collision energies. Collisions with the dimers produced both Cs2Cl++Cl and Cs++CsCl2 but no detectable ions containing the rare gas atoms. The magnitude of the cross sections for the Cs2Cl+ channel varied significantly with the rare gas although the corresponding thresholds were similar. In the case of CsCl2, however, the magnitudes of the cross sections were similar, but the thresholds varied. A possible explanation for this difference in behavior is given based on simple dynamical models. The cross sections for each product ion from both the monomer and dimer (except for CsM+) exhibited a power‐law rise with increasing energy σ=const× (EtotE0)n/Erel up to about 1–1.15 eV above threshold, where Etot is the total energy, E0 the threshold energy, and Erel the relative kinetic energy. Values of n and E0 were determined for each system. The threshold for each reaction M+CsCl→M+Cs++Cl was determined most accurately from the peak in the CsM++Cl excitation function, which occurs (after energy deconvolution) at the threshold for collision‐induced dissociation.