Total and double differential cross sections of ion-pair formation in collisions of K atoms with SnCl4 and CCl4

Abstract

The reaction K+ACl4→K++(A−Cl4)−* with A=Sn and C was examined as a function of the collision energy from threshold up to about 40 eV in the c.m. system. Total cross sections of the mass-selected negative ions and doubly differential cross sections (energy and angle) of the K+ ions have been determined. Electron affinities, bond energies, and electronic excitation were calculated from the appearance potentials. In addition, the total cross sections for SnCl4 were measured and are contrasted with the earlier results of CCl4 from Dispert and Lacmann. Although both parent molecules have the same electron affinity within their error limits (2.2 eV for SnCl4 and 2.0 eV for CCl4) and the same dissociation energy for the negative ions of 1.4±0.2 eV, the product ion yields differ drastically. The main negative ion yield in K+SnCl4 results from SnCl−4 formation (over 80%). Its lowest dissociation channel leads to SnCl−3 formation, while Cl− ions are the main ions produced (90%) from CCl4, with only 7% leading to CCl−3+Cl formation at higher energies. These results support orbital energy considerations of electron addition to SnCl4 and CCl4 as applied to the results of reactive collisions of these molecules. The electron affinity and an electronically excited state of SnCl3 have been also determined. Morse potentials of CCl−4 and SnCl−4 were fitted to the experimental results of energy loss measurements from this work. The vertical electron affinities thus derived are 1.15 eV for SnCl4 and −1.0 eV for CCl4.