Negative Ions Interacting with Photons and Electrons

Abstract: Negative ions are atoms or molecules where an extra electron is bound to neutral system. The nature of negative ions di?ers fundamentally from neutral and positive systems. The induced dipole potential responsible for the binding of the extra electron supports only a few bound states with relatively small binding energies. Since negative ions are so di?erent from their neutral equivalents the methods used to study them are also fundamentally di?erent. In this thesis the nature of negative ions is discussed and important properties of experimental investigations are presented. A general description of di?erent experimental techniques is given, including a number of ion sources, and ways of con?ning and controlling the ions. Di?erent reactions used to investigate the properties of the ions are discussed together with methods of detecting the reaction products. The focus is on photodetachment and electron collision experiments. A measurement of the absolute reaction cross sections for electron impact on Si2 ? is presented as an example of a collision experiment. Three photodetachment studies are included in the thesis, where one have previously been published. Fundamental studies have been performed on P? and W? and re?ned values for the electron a?nities are presented. WF5 ? and HfF5 ? have been investigated for the possibility of isobar selective photodetachment. With a laser based isobar ?lter the detection limit for 182 Hf in accelerator mass spectrometry measurements could be improved, but no suitable wavelength has so far been found. Experiments are presented in detail in the appended publications, with a summary of the experiments and the results in the main text. The results are compared with other types of measurements and results from other research groups.