Observation of Direct Excitation of High-Orbital-Angular-Momentum High-Rydberg States by Threshold-Energy Electron Collisions

Threshold-energy peaks are observed for electron impact excitation of ${\mathrm{N}}_{2}$ and ${\mathrm{H}}_{2}$ to high-Rydberg states. These peaks are attributed to the direct excitation of high-$l$ states near threshold consistent with the prediction of Fano.