Metastable states in NO²⁺ probed with Auger spectroscopy

High-resolution N 1s and O 1s photoelectron spectra (PES) of NO are presented together with spectra of the subsequent Auger decay. The PES are analyzed by taking spin-orbit splitting of the ²Π ground state into account providing detailed information on equilibrium distances, vibrational energies, and lifetime widths of the core-ionized states. In the Auger electron spectra (AES) transitions to five metastable dicationic final states are observed, with two of them previously unobserved. A Franck-Condon analysis of the vibrational progressions belonging to these transitions provides detailed information on the potential-energy curves of the dicationic final states as well as on the relative Auger rates. The present calculations of the potential-energy curves of NO²⁺ agree well with the experimental results and allow an assignment of the two hitherto unresolved Auger transitions to excited states of NO²⁺, C²Σ⁺and c⁴Π.