Precise spectroscopy and lifetime measurement of electron-impact-excitedN2: Thec4’Σu+1(v=3) Rydberg level

An electron-optical double-resonance excitation scheme in a molecular beam has been used to observe the $c_4^{\mathcal{’}}$(3p) ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$(v=3) Rydberg level of ${\mathrm{N}}_2$ at a sub-Doppler limited resolution of about 90 MHz. The widths of rotational transitions in the $c_4^{\mathcal{’}}$ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$←a’ ’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$(3,0) band were measured to obtain the lifetime of the $c_4^{\mathcal{’}}$(3) level as a function of J. The average lifetime is 0.19 ns, which suggests that this level decays partially through predissociation. The J dependence of this lifetime reflects the configuration mixing between the $c_4^{\mathcal{’}}$ ${\Sigma }_u^{+}$(v=3) and b’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$(v=10) levels.