Study of Inelastic Collisions by Drifting Ions

Abstract

A series of experiments has been performed in which a mass-analyzed ion beam is injected into a drift tube containing gas. The ions drift through the tube under the action of a uniform electric field and they undergo inelastic processes. The product ions are mass analyzed upon exit. The drift velocity and the ratio of the primary and secondary ion currents are measured as a function of the electric field and the gas pressure in the drift tube. From these data the cross section of the process is calculated. The effect of the lateral diffusion in the drift tube is discussed theoretically. Cross sections are determined in the energy range from 0.06 to 10 eV for the processes, Ne++Ar→Ne+Ar+,Ar++Ne→Ar+Ne+,O++N2→O+N2+,O++O2→O+O2+.Because of the nature of the ion source used these processes are supposed to be conducted largely by the ions in their excited states. It is shown that the cross sections of the former two processes agree well with predictions based on the theory of Rapp and Francis if appropriate combinations of excited states are assumed. At the high-energy end, the cross sections of the latter two processes agree well with the results of the beam experiment of Stebbings et al. At the low-energy end, the cross section of the last process agrees well with experimental result of Fehsenfeld et al. at room temperature. A remarkable minimum is found in the last process.