Medium-resolution studies of extreme ultraviolet emission fromN2by electron impact: Vibrational perturbations and cross sections of thec4’Σu+1and b’Σu+1states

We have studied in a crossed-beam experiment the electron-impact-induced fluorescence spectrum of ${\mathrm{N}}_2$ in the extreme ultraviolet (euv) at a spectral resolution of up to 0.03 nm. The optically thin experiment allowed us to obtain the highest-resolution electron-impact emission spectrum of the Rydberg and valence states of ${\mathrm{N}}_2$. The spectral measurements provide the emission cross sections of each of the vibrational transitions of the $c_4^{\mathcal{’}}$ ${}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ Carroll-Yoshino band system and the b’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ Birge-Hopfield-II band system. The $c_4^{\mathcal{’}}$ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ and b’ ${}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ states strongly perturb one another by homogeneous configuration interactions. This perturbation leads to vibrational-excitation cross sections whose dependence on v’ is quite different from the variation of the unperturbed Franck-Condon factors.