Identification of the core hole excited states of N2: A failure of the equivalent core approximation

Monochromatic soft x-rays were used to excite the nitrogen molecule at resonances near the K-ionization edge. The absorption anisotropy parameter β was determined from the simultaneous measurement of the photofragment flux emanating from the x-ray/molecular-beam interaction region along two axes, one parallel and the other perpendicular to the electric vector of the polarized synchrotron radiation. The value of the anisotropy parameter identifies the symmetry species of a resonance and allows the core-hole excited states to be assigned from experimental data. These data force a new assignment of Rydberg states and reveal a failure of the equivalent core approximation.