POSITRON-MOLECULE SCATTERING EXPERIMENTS

We have extended our measurements of the relative elastic differential cross sections (DCSs) and positronium formation cross sections (Q(Ps) s) for positron scattering to include molecules of varying complexity and symmetry. Diffraction effects observed in our earlier e(+)-Ar and e(+)-CH4 DCS measurements [Phys. Rev. A 55 (1997) 4244] are shown to h ave disappeared for a linear tri-atomic molecule, CO2. In contrast to the structureless, bell-shaped Ps-formation curves of H and H-2 [Phys. Rev. A 55 (1997) 361], the Ps-formation cross section curves for CH4, CO2, and SF6 show structure which may be associated with electron tra nsfer of inner orbital electrons of the molecule. (C) 1998 Elsevier Sc ience B.V. All rights reserved.