View article

The inversion-symmetric oxygen molecule has been the showcase for demonstration of phenomena revealed by advances in the Resonant Inelastic X-ray Scattering (RIXS) technique [1], including mapping of the coupling dynamics at avoided potential-curve crossings [2], observation of spatial quantum beats [3], and interference between resonant and non-resonant scattering channels [4]. The early RIXS investigation [1] provided evidence that inversion symmetry remains unbroken in the core-excited states, as only transitions in compliance with the parity selection rules were observed. It has often been assumed that the observed parity selectivity constitutes a general rule in the sub-keV region.

In contrast, we observe violation of the parity selection rules in the RIXS spectra of the oxygen molecule excited on the p* resonance. We exploit the capabilities of the new Veritas beamline at MAX IV to measure high-quality …