In this Rapid Communication we report on the autoionization dynamics of the 5d7d doubly excited state in barium in a static electric field. The different experiments and theory show Stark beatings in the autoionization process. Also it appears that the total spin of the two valence electrons plays a major role in the ionization dynamics. Absorption spectroscopy revealed the ionization dynamics near the core, while an atomic streak camera was used to record the time-dependent electron emission, probing the wave function when it is far from the core. Calculations based on multichannel quantum defect theory are compared to experimental data and we are able to predict the singlet-triplet mixing.