Ep. Dasilva et al., ANNIHILATION DYNAMICS OF POSITRONS IN MOLECULAR ENVIRONMENTS - THEORETICAL-STUDY OF LOW-ENERGY POSITRON-C2H4 SCATTERING, Physical review letters, 77(6), 1996, pp. 1028-1031
We present a theoretical study of low-energy positron-C2H4 scattering
using the Schwinger multichannel method. We calculated integral cross
sections and the annihilation parameter Z(eff) for positron impact ene
rgies from 0.001 to 6 eV. We have used up to 23 112 configurations in
a fully a initio calculation. Our results are in excellent agreement w
ith available experimental data. As seen experimentally, at low energi
es, our calculated Z(eff) and cross sections are very large. We attrib
ute this behavior to virtual positronium formation.