Experimental evidence for a virtual state in a cold collision: Electrons and carbon dioxide

Experimental data are presented for the scattering of cold electrons by CO₂, for both integral and backward scattering, down to energies of a few meV with an energy resolution of 0.95--1.5 meV (full width at half maximum) in the electron beam. The experimental data show evidence for the phenomenon of virtual-state scattering, a subject of extensive theoretical study. The measured scattering cross sections rise rapidly at low energy, to a limiting value in integral scattering in excess of 120 ². In addition, analysis shows that scattering is s-wave dominated and that the s-wave scattering length is negative. All features are characteristic of virtual state scattering.