Electron-impact excitation of the vibrational levels of thec4’Σu+1electronic state of the nitrogen molecule

Electron-impact excitation of the excited vibrational levels of the $c_4^{\mathcal{’}}$ ${}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ state of the nitrogen molecule has been studied. We measure the electron-impact optical emission cross sections of the (1,2), (4,0), and (4,1) vibration bands of the $c_4^{\mathcal{’}}$→a electronic transition of the nitrogen molecule and compare them with the direct electron-impact cross sections of the $c_4^{\mathcal{’}}$(v’) vibrational levels reported in the literature. The Franck-Condon factors between the ground vibrational level of the X ${}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ ground electronic state and the various vibrational levels of $c_4^{\mathcal{’}}$ have been calculated and compared with the electron-impact cross sections. The excitation cross sections of the v’=4 level of $c_4^{\mathcal{’}}$ are several orders of magnitude higher than predicted by the Franck-Condon picture. This discrepancy is due to the perturbations of the $c_4^{\mathcal{’}}$(v’=4) level by the b’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ state.