Study of low energy charge transfer collisions using a radio-frequency quadrupole ion trap

Abstract

This experiment has measured the spin independent total charge transfer cross section for helium ions interacting with cesium atoms for an energy range between 0.1 and 1.0 electron volt. The result of this measurement of the cross section σ[subscript Cs] shows the familiar energy dependent form of σ[superscript 1/2] = a⁻b [cursive l]n <E>, where we have determined a = 5.32 x 10⁻⁸ cm and b = 1.46 x 10⁻⁸ cm. This yields for σ[subscript Cs] (7.5 ± 0.9) x 10⁻¹⁵ at 0.1 eV and (2.8 ± 0.4) x 10⁻¹⁵ cm² at 1 eV. The experiment was performed in a radio-frequency quadrupole ion trap used to store helium ions which collided with an atomic beam of cesium atoms. In addition, a study of the process of ⁴He⁺ and H₂⁺ ion creation by electron beam bombardment, the temporal behavior of the ion cloud after ion creation and ion-atom interactions, and the creation of H₃⁺ in the trap has been made. It was shown that for a saturated trap ion-ion collisions constitute the major loss process and limit the maximum number of ions stored. On the other hand ion-atom and ion-molecule reactions can also be studied, when care is taken to only partly fill the ion trap. The radio-frequency quadrupole ion trap is, therefore, a valuable new tool for the study of ion-atom and ion-molecule reactions. Since the experiments are performed in ultrahigh vacuum, other competing side reactions, which sometimes hamper the measurements the other methods, are avoided from the beginning.