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Non Adiabaticity and other aspects of Polarisation in Positron molecule scattering



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J Phys B At Mol Opt Phys 22 1989 113 130 Printed in the UK Non adiabaticity and other aspects of polarisation in positron molecule scattering Brian K Elzai Thomas L Gibson Michael A Morrisont and Bidhan C Sahat t Department of Physics and Astronomy University of Oklahoma Norman Oklahoma 73019 USA Department of Physics Texas Technical University Lubbock Texas 79409 USA Received 7 June 1988 in final form 26 August 1988 Abstract We have investigated various aspects of polarisation correlation effects at low energies for the prototypical positron N2 system First we have found that like positron Hi cross sections those for this system are highly sensitive to terms in the adiabatic polarisation potential that explicitly depend on the sign of the charge of the projectile Insight into the nature of these sign dependent distortions is afforded by three dimensional graphs of polarised N density functions Second we have explored and characterised nonadiabatic correlation effects in this system using a simple two parameter model We have found that the onset of these effects in the near target region in positron scattering is much more gradual than in electron scattering By including in scattering calculations adiabatic and non adiabatic effects we obtain theoretical positron N2 cross sections in good agreement with recent experimental data 1 Introduction The last few years have seen a dramatic increase in research on low energy positronmolecule scattering see for example the review by Armour 1988 This activity is in part due to new technology for producing improved positron beams Canter and Mills 1982 Nevertheless there remain considerable uncertainties in measured values of positron molecule cross sections at collision energies below a few eV cf Hoffman et a1 1982 Charlton et al 1983 Sueoka and Mori 1984 and fundamental questions plague the calculation of theoretical positron scattering cross sections at these energies Below the threshold for positronium formation the most



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