Stark field control of nonadiabatic dynamics in triatomic hydrogen.

We show experimentally that an external electric field can be used to control the amplitudes of nonadiabatic paths taken by a dissociating molecule. In the example presented here, this control is achieved by Stark-field mixing in H(3) Rydberg states with different decay paths. The final state continuum is in each path formed by three-particle wave packets of slow neutral hydrogen atoms in their electronic ground state. Their momentum vector correlations show signs of interference, since the molecule can access the identical continuum via two distinctly different paths, involving different nonadiabatic coupling mechanisms. As an added feature a preferred alignment of the fragmentation plane in the laboratory frame emerges, corresponding to a selective dissociation of molecules oriented along the field direction.