Probing doubly excited ionic states of N₂⁺ via a triple excitation above the N 1s threshold in the N₂ molecule

Angle-resolved resonant Auger-electron spectroscopy has been carried out on the nitrogen molecule at selected photon energies around 419 eV, where a 1s core electron and two valence electrons are promoted into the lowest unoccupied molecular orbital 1π_g. Significant enhancement of a specific band, which cannot be disentangled in direct photoionization, is observed at a binding energy of 37.6 eV, with a value of the anisotropy parameter β much smaller than 2. We assign this new band to the transition to a doubly excited cationic state of N₂, in which two of the excited valence electrons remain in the 1π_g orbital, proposing a “double spectator” type decay mechanism. This observation shows how to preferentially probe multiply excited configurations of cations using multiple resonant excitation.