Double and triple excitations near theK-shell ionization threshold ofN2revealed by symmetry-resolved spectroscopy

High-resolution photoion yield spectra of N 2 are measured near the K-shell ionization threshold. Previously unresolved multiple excitations are distinguished in the Σ- and Π-symmetry-resolved spectra, which were obtainedfrom the ion yield spectra recorded at 0° and 90° relative to the polarization direction. The three 1 Π u and two 1 Σ + u doubly excited states are clearly identified. Furthermore, a weak Π-symmetry feature just at the σ*-shape resonance position (∼419 eV) is definitely resolved and assigned to the lowest 1 Π u triple excitation with the help of quantum chemical calculations.