K-shell photoabsorption of the ${\mathrm{N}}_2$ molecule

The K-shell photoabsorption spectrum of the ${\mathrm{N}}_2$ molecule, recorded with unprecedented energy resolution and statistical accuracy, reveals several new Rydberg transitions and double-excitation states. The nearly identical term values, vibrational frequencies and internuclear separations of the 1s-excited states of ${\mathrm{N}}_2$ and of the 2π-excited states of NO, allow for a complete peak assignment for the ${\mathrm{N}}_2$ Rydberg series and strongly support both the core-hole localization picture and equivalent-core model. Subtle differences are related to the final-state charge distribution in the vicinity of the nuclei and to the bonding character of the valence orbitals.