Modified effective range analysis of low energy electron and positron scattering on CO2

Analytical solutions for the modified effective range problem have been applied to positron and electron scattering on carbon dioxide in the low (below 10 eV) energy range. For positrons, the solution with three partial waves reproduces very well experimental results up to the positronium formation threshold; the s-wave contribution rises in the limit of zero energy and the p-wave contribution reaches a very broad maximum at about 0.5 eV. For electron scattering, the present solution shows a sharp rise of the s-wave contribution in the limit of zero energy, explained by earlier calculations as a virtual negative ion state. The p-wave shows a resonant structure at about 5 eV corresponding to an experimentally well known 2IIu shape resonance. An additional maximum in the p-wave contribution is observed at about 1-2 eV. The latter feature would explain resonant-like scattering observed recently in high-resolution vibrational excitation measurements