A Collinear Angle-Resolved Photoelectron Spectrometer - Instrumental Design and Photodetachment Measurements
For more than half a century, photoelectron spectroscopy has been used to investi- gate atoms, ions and molecules. Various techniques have been developed in order to measure electron energies and angular distributions using different radiation sources such as lasers and synchrotrons. In this work, a new spectrometer design for measurements of angular distributions of photoelectrons using synchrotron ra- diation is presented. The design takes advantage of a collinear interaction region, which is two orders of magnitude larger than obtainable with the crossed beams method. The number of events per time unit is thereby substantially increased compared to regular angle-resolved photoelectron spectrometers. This is of great value when the radiation source has a low photon flux and the background is large due to the high photon energy. The spectrometer has been tested on sys- tems where the angular distribution is well-known, in order to develop methods for compensation of the angular transformation between the ion rest frame and the lab frame. Further, a measurement of the angular distribution of a negative ion, P−, over a wide range of photon energies has been conducted. The results are in agreement with previous measurements and, more importantly, reveal new and valuable information about the theoretical modelling of angular distributions.
The experiments presented show that the spectrometer can be used to measure angular distributions of atomic and molecular ions, and that it can be a valuable asset at synchrotron beamline endstations. This work also includes a photoion- ization cross section measurement of Zn+, performed using the synchrotron at the Advanced Light Source (ALS), Berkeley, CA.