Abstract
The design and performance of a high-resolution momentum-imaging spectrometer for ions which is optimized for experiments using synchrotron radiation is presented. High collection efficiency is achieved by a focusing electrostatic lens; a long drift tube improves mass resolution and a position-sensitive detector enables measurement of the transverse momentum of ions. The optimisation of the lens for particle momentum measurement at the highest resolution is described. We discuss the overall performance of the spectrometer and present examples demonstrating the momentum resolution for both kinetics and for angular measurements in molecular fragmentation for carbon monoxide and fullerenes. Examples are presented that confirm that complete space-time focussing is possible for a two-field three-dimensional imaging spectrometer.
Highlights
Fundamental questions regarding photo induced chemical reactions, transient states in molecules, and dissociative states are of central importance to chemical physics
New scientific tools based upon spectroscopic imaging and multi coincidence experiments have emerged to address some of these issues, and have achieved great success in dynamic studies of ionised molecules and clusters using lasers, synchrotron radiation, and in collision experiments
In this paper we describe the design and performance of the instrument; we derive a semi-analytical expression from the space-time to momentum inversion, and present examples that illustrate how high kinetic-energy resolution illuminates details in the final dissociative states for carbon monoxide
Summary
Fundamental questions regarding photo induced chemical reactions, transient states in molecules, and dissociative states are of central importance to chemical physics. Synchrotron radiation is a unique light source providing the ability to selectively ionize particular electronic shells, excite localized core-electronic states, and to select the polarisation of the light. In this context, spectroscopic imaging instruments of various designs allow recording the velocity or momenta of several reaction products in coincidence with energy-analyzed electrons to reveal the details of dissociative states in molecules. While 2D imaging is advantageous for low repetition-rate measurements, three-dimensional imaging techniques using timing detectors do not require the Abel inversion and can be used for multi-coincidence measurements without constraints on the polarisation of the light.. Velocity imaging methods take advantage of efficient two-dimensional position-sensitive detectors to measure molecular photodissociation products. Implementation of a focusing lens to improve velocity resolution extended the imaging method significantly and several implementations of velocity imaging for synchrotron applications have been developed. While 2D imaging is advantageous for low repetition-rate measurements, three-dimensional imaging techniques using timing detectors do not require the Abel inversion and can be used for multi-coincidence measurements without constraints on the polarisation of the light. The space-time focussing condition is widely utilised in linear time-of-flight spectrometers, known as the WileyMcLaren condition, but so far a general solution for threea)Present address: MAX IV Laboratory, Lund University, Box 118, S-221 00 Lund, Sweden
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