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S J Gurman

Publications and source records attributed to S J Gurman.

10 recordsLinked to original sources
PubMed2003

Multiple-electron excitation in X-ray absorption: a screened model of the core-hole-photoelectron potential.

The probability of secondary electron shake-off in X-ray absorption is calculated using a model form for the time- and energy-dependent core-hole-photoelectron potential, screened by the single plasmon pole dielectric function of the surrounding material. The resultant excitation probabilities are related to the energy-dependent intrinsic loss function in EXAFS data analysis and compared with experiment. Reasonable agreement is obtained close to the absorption edge although the calculation is less accurate at higher photon energies. The theory described allows the losses to be calculated with little computational effort, making the method suitable for routine EXAFS data analysis.

Journal Article↗
PubMed2001

An investigation of the use of the Hedin-Lundqvist exchange and correlation potential in EXAFS data analysis.

In real systems, inelastic processes remove photoelectrons from the elastic scattering channel. This reduces the amplitude of the EXAFS. Traditionally the discrepancies between experimental and theoretical amplitudes were treated by including two semi-empirical reduction factors in the data analysis. Some inelastic effects may, however, be modelled more rigorously using a complex exchange and correlation potential, for example the Hedin-Lundqvist (HL) potential used in most EXAFS data-analysis programs. In this paper a systematic study of the effects of the HL potential on the calculated EXAFS amplitudes is presented. Expressions are derived whereby the EXAFS amplitudes may be examined in the presence of an arbitrary complex potential independently to the rest of the EXAFS signal. These results are used to study the effects of the HL potential on EXAFS data analysis in detail.

Journal Article↗
PubMed2001

Multiple-electron excitation in X-ray absorption: a simple generic model.

The probability of multiple-electron excitation in X-ray absorption is calculated using a simple generic model. The model permits calculations to be made for all atoms with little input data or computing effort. The high-energy limit of this probability, which gives the usual EXAFS amplitude reduction factor, is calculated in the 'sudden approximation' using Slater orbitals. Good agreement with experiment is found. The energy dependence of this probability is also calculated using a simple model form of perturbing potential and found to agree well with experiment for rare gas atoms. The effect on the X-ray absorption coefficient of including multiple-electron excitations is also determined and is found to be small, again in agreement with observation.

Journal Article↗
PubMed1995

Interpretation of EXAFS Data.

An outline of the theory of X-ray absorption as applied to X-ray absorption spectroscopy is given, concentrating on EXAFS, showing how structural parameters are contained within the theory. A full description of the scattering problem and of inelastic effects is also included, and a description is given of how structural information may be extracted from experimental data. The emphasis is on curve-fitting methods, including those techniques which allow the inclusion of external constraints.

Journal Article↗
PubMed1989

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