Resonances in the Metastable Excitation of Molecular Nitrogen

The excitation function for metastable molecular nitrogen has been studied over the electron-impact energy range 7-14 eV with an energy resolution of 0.05 eV. No resonances were observed below 11.8 eV in the $A{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ and $a{}_{}{}^1{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ channels. There is a sharp resonance at the threshold of the metastable $E{}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ with a peak at 12.00 eV. Smaller structures were seen at 12.14 and 12.25 eV. A series of five resonances were observed at 12.59, 12.80, 13.03, 13.24, and 13.52 eV presumably in one or both of the $A{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ and $a{}_{}{}^1{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ channels. These confirm some of the structures observed in a recent transmission experiment. On the basis of the spacings and relative intensities of these resonances, a possible assignment for them is a temporary state of $N_2^{}{}_{}{}^{-}$ consisting of two Rydberg electrons around a core state $A{}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ of $N_2^{}{}_{}{}^{+}$.