Ep. Dasilva et al., ANNIHILATION DYNAMICS OF POSITRONS IN MOLECULAR ENVIRONMENTS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 143(1-2), 1998, pp. 140-148
We present recent results for positron-molecule scattering obtained wi
th the Schwinger multichannel method. Our calculations include integra
l, differential and momentum transfer cross sections and the annihilat
ion parameter Z(eff) for C2H2 and C2H4 molecules. We discuss a mechani
sm for annihilation of positrons in low-energy positron-molecule scatt
ering. We interpret the annihilation process through virtual electroni
c excitation of the target combined with electronic cloud relaxation a
nd virtual positronium formation. We study the influence of the first
electronic state of the target on the cross section and on the annihil
ation parameter in e(+)-C2H2 scattering. (C) 1998 Elsevier Science B.V
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