X-Ray Absorption Spectrum of the N2+ Molecular Ion

The X-ray absorption spectrum of N2+ in the K-edge region has been measured by irradiation of ions stored in a cryogenic radio frequency ion trap with synchrotron radiation. We interpret the experimental results with the help of restricted active space multiconfiguration theory. Spectroscopic constants of the 1?u-1 ?2u+ state, and the two 1?u-13?g-11?g ?2u states are determined from the measurements. The charge of the ground state together with spin coupling involving several open shells give rise to double excitations and configuration mixing, and a complete breakdown of the orbital picture for higher lying core-excited states.