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

The spin-independent total charge transfer cross section was measured 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 sigma/sub Cs/ shows the familiar energy-dependent form of sigma/sup 1/2/ = a - b ln , where a = 5.32 x 10-8 cm and b = 1.46 x 10-8 cm. This yields for sigma/sub Cs/ (7.5 +- 0.9) x 10-15 cm2 at 0.1 eV and (2.8 +- 0.3) x 10-15 cm2 at 1 eV. The experiment was performed in a radio-frequency quadrupole ion trap used to store helium ions that 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, ion-ion and ion-atom interactions, and the reaction of H3+ in the trap was 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 fill the ion trap only partly. The radio-frequency quadruple 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 with other methods, are avoided from the beginning