Studies of State-Selective Electron Capture in Atomic Hydrogen by Translational Energy Spectroscopy

Abstract

This chapter reviews the translational energy spectroscopy (TES) approach together with a few representative results obtained with different partially ionized projectiles at keV energies. The use of a tungsten tube furnace to provide a highly dissociated target of hydrogen in the Belfast TES apparatus has proved to be an effective way of studying state-selective electron capture by slow multiply charged ions in collisions with atomic hydrogen. The chapter illustrates that in not all cases are the TES results in good accord with theoretical predictions, including those based on a fully quantal molecular approach. Such discrepancies illustrate the difficulty of carrying out accurate calculations. The TES measurements provide an unambiguous indication of the presence of metastable ions in the primary beam. However, a detailed quantitative analysis of the TES data is impossible unless the fraction of metastable ions present in the primary beam is known. For many reactions, this is a major complicating feature. The use of double translational energy spectroscopy (DTES) is an attractive possible solution to this problem that is planned for future work. DTES measurements require primary beam intensities between 103 and 104 times greater than a single TES experiment, but the yields available from an electron cyclotron resonance (ECR) ion source are expected to be adequate for studies of many reactions.