Electronic State Interferences in Resonant X-Ray Emission after K-Shell Excitation in HCl

We have measured a series of high-resolution x-ray spectra emitted upon resonant photoexcitation of HCl. The photon energy was tuned across the dissociative 1s -> 6 sigma* resonance and the Rydberg states converging to the Cl 1s(-1) threshold, and inelastic photon scattering was observed in the region of KL emission lines. Excellent agreement is found between fully ab initio calculated and measured spectra if interferences between different excitation-emission paths are taken into account. The effect of electronic state interferences is enhanced due to dynamical broadening of the 6 sigma* resonance in HCl.