[en] In order to have access to fine phenomena such as ultrafast nuclear dynamics and electronic state - lifetime interferences (ELI) at high energies (few keV), one has to rely on great experimental resolution. The new experimental HAXPES endstation at the GALAXIES beamline of the French synchrotron SOLEIL provides photons in the 2-12 keV energy range along with a total instrumental resolution below 500 meV. In this work we show experimental evidences of ultrafast nuclear dynamics and ELI on HCl and CH_3Cl excited around the Cl 1s resonance. We show also simulations that allow to disentangle the contribution of nuclear dynamics and ELI in our experimental spectra. (paper)