Analysis of the 8f, 9f, and 10f,v=1 Rydberg states ofN2

The autoionizing (${\mathit{X}}^2$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$) 8f, 9f, and 10f, v=1 states of ${\mathrm{N}}_2$ have been studied by using double-resonance ionization spectroscopy via numerous rotational levels of the ${\mathit{a}}^1$ ${\mathrm{\Pi }}_{\mathit{g}}$, v’=5 state. These nf states lie in a complex region of the spectrum that also contains transitions to high vibrational levels of the b’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$ valence state and Rydberg states that converge to the ${\mathit{X}}^2$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${\mathit{A}}^2$ ${\mathrm{\Pi }}_{\mathit{u}}$, and ${\mathit{B}}^2$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$ states of the ion. A long-range interaction model, which is based on the interaction of the Rydberg electron with the polarizability and quadrupole moment of the ${\mathrm{N}}_2^{+}$ ion core, has been used to intepret the f-state structure and to identify the extent of perturbations due to interactions with nearby states. A generalized least-squares fit of the model to the energies of the unperturbed 8f state yields an effective quadrupole moment of (3.2±0.1)${\mathit{ea}}_0^2$ and an isotropic polarizability of (16.1±0.4)${\mathit{a}}_0^3$ for the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$,${\mathit{v}}^{+}$=1 state of the ion. In addition, a new state that is observed to perturb the 9f, v=1 state is tentatively identified as the previously unobserved ( ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$)3dπ ${}_{}{}^1{}_{}{}^{}\mathrm{\Delta }_{\mathrm{u}}^{}{}_{}{}^{}$, v=2 state. The results presented here complete the interpretation of the single-photon absorption spectrum of ${\mathrm{N}}_2$ from the first ionization potential at ∼125 667 to ∼126 850 ${\mathrm{cm}}^{\mathrm{-}1}$.