Contribution of the MetastableEΣg+3State to the Population of theCΠu3State ofN2Following Electron-Impact Excitation

Following low-energy electron-impact excitation of molecular nitrogen, the method of delayed coincidence is used to separate the prompt and delayed radiation of the $C{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}\to B{}_{}{}^3{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ transition. The emission function of the prompt radiation, due to direct $C$-state excitation, is seen to increase smoothly above threshold. The emission function of the delayed emission, due to collisional deactivation of metastable states, is composed of two sharp peaks at 12.0 and 12.7 eV as well as a broader peak at about 22 eV. The first of these peaks is recognized as the direct resonant excitation of the metastable $E{}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ state. Evidence is found indicating that the other peaks, which may be associated with the excitation of the $a^{\prime \prime }{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ state, lead to indirect excitation of the $E$ state.