He+-impact energy-loss spectrum of nitrogen

Electronic excitation of nitrogen molecules in collisions of 2.3-keV ${\mathrm{He}}^{+}$ ions has been investigated by means of ion-impact energy-loss spectroscopy. Vibrational band structures in the lowest five singlet and triplet excited states of ${\mathrm{N}}_2$ are resolved with a resolution of 0.13-eV full width at half maximum. The relative intensities of the vibrational band structures agree with the prediction from the Franck-Condon principle. Computer simulation of the observed spectrum suggests the participation of the optically forbidden $B^{\prime }{}_{}{}^3{}_{}{}^{}\Sigma _u^{-}{}_{}{}^{}{}_{\leftarrow }{}^{}{}_{}{}^{}X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ transition into excitation of ${\mathrm{N}}_2$ molecules by the ${\mathrm{He}}^{+}$-ion impact.