Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/157381

Title

Calculation of gamma spectra for positron annihilation on molecules

Author(s)

Green, D. G.;  Saha, S.;  Wang, Feng;  Gribakin, G. F.;  Surko, C. M.

Abstract

Calculations of gamma spectra for positron annihilation for a selection of molecules, including methane and its fluoro-substitutes, ethane, propane, butane and benzene are presented. The contribution to the gamma-spectra from individual molecular orbitals is obtained from electron momentum distributions calculated using the density functional theory (DFT) based B3LYP/TZVP model. For positrons thermalised to room temperature, the calculation, in its simplest form, effectively treats the positron as a plane wave and gives positron annihilation gamma spectra linewidths that are broader (30–40%) than experiment, although the main chemical trends are reproduced. The main physical reason for this is the neglect of positron repulsion from the nuclei. We show that this effect can be incorporated through momentum-dependent correction factors, determined from positron-atom calculations, e.g., many-body perturbation theory. Inclusion of these factors in the calculation gives linewidths that are in improved agreement with experiment.

Publication type

Journal article

Research centre

Swinburne University of Technology

Source

Materials Science Forum: Progress in positron annihilation: proceedings of the 39th Polish Seminar on Positron Annihilation (PSPA-10), Kazimierz Dolny, Poland, 20-25 June 2010 / Radoslaw Zaleski (ed.), Vol. 666, pp. 21-24

Publication year

2011

FOR Code(s)

0912 Materials Engineering;  1007 Nanotechnology

Keyword(s)

Electron momentum density;  Gamma spectra;  Molecules;  Positron annihilation

Publisher

Trans Tech Publications

ISSN

0255-5476 (series ISSN)

ISBN

9780878492084, 0878492089

Publisher URL

http://dx.doi.org/10.4028/www.scientific.net/MSF.666.21

Copyright

Copyright © (2011) Trans Tech Publications, Switzerland.

Peer reviewed