Atomic and Molecular Physics
There are currently two atomic and molecular physics projects at ISA both of which utilise the higher flux output from an undulator as compared to a bending magnet ( ~ 2 or 3 orders of magnitude).
Photoionisation of positive ions
The purpose of this experiment is to measure cross-section for the photoionisation of ions as a function of photon energy. Photoionisation of ions is a process active in many regions of space, ranging from dying stars to supernovae and quasars and data are of considerable interest in astronomy.
In this experiment, the output from the MIYAKE monochromator is merged over a distance of 60cm with a positive atomic or molecular ion beam of a few millimeters in diameter and of a kinetic energy which is variable between ~2 to 5 keV.
A magnetic deflector system located after the interaction region separates the parent and product ions into charge states of +1, +2, +3 or +4 for detection. A calibrated photodiode for the incident SR flux , together with a system of ion beam profile monitors allows absolute cross-sections for the various photoionisation processes which may occur to be measured. This project is a joint collaboration between IFA, ISA and Daresbury Laboratory.
Electron-molecule Interactions
In this project, which is a collaboration between ISA, Université Paul Sabatier, Toulouse, France, Observatoire de Meudon, Paris, France, The Open University and Queens University of Belfast, synchrotron radiation is used to generate a beam of very low energy electrons by photoionisation of argon at threshold which then subsequently interacts with a target molecular species in the gas phase, and in the near future, in the solid phase.
Processes of electron scattering take place in all plasmas, man made - for microcircuit fabrication and nano-technology applications - and in nature, in the atmosphere of Earth and in many contexts in outer space, for example in star-forming regions.
There are several processes which may occur when an electron encounters a molecule. Electrons may be scattered without changing the internal energy of the target (elastic scattering), a portion of the electron kinetic energy may be transferred into internal energy states in the target molecule (inelastic scattering) or it may attach forming a negative ion which could undergo subsequent dissociation into a product ion and a neutral fragment (dissociative attachment) or remain as the parent ion. All of these processes yield considerable insight into fundamental aspects of the strange world of cold quantum scattering.
The electron attachment apparatus located on the SGM II beamline, is capable of studying all of these processes over the electron kinetic energy range from 5 meV up to 20 eV.
More details of both of these projects can be found in the 1998 ISA activity report.
For further information about the Atomic and Molecular Physics research program at ISA, please contact,
Last Modified 18 October 2010
