Double-resonance spectroscopy of autoionizing states ofN2near the ionization threshold

Double-resonance spectroscopy of ${\mathrm{N}}_2$ via the ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$, v’=5 level has enabled the definitive assignment of a number of intense and heretofore unidentified bands observed in the single-photon spectrum in the region between the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ ${\mathit{v}}^{+}$=0 and 1 ionization thresholds. The results resolve several long-standing controversies concerning the assignment of Rydberg states of low principal quantum number that converge to the ${\mathit{A}}^2$ ${\mathrm{\Pi }}_{\mathit{u}}$ and ${\mathit{B}}^2$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$ states of the ion and indicate that significant revisions of previous assignments are necessary. The spectra are discussed in the context of the entire manifold of states in this region, which includes high vibrational levels of the b’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$ valence state as well as Rydberg states that converge to the ${\mathit{X}}^2$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$, and ${\mathit{B}}^2$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$ states of the ion.