  Associative electronic detachment (AED) between anions and neutral atoms
leads to the detachment of the anion's electron resulting in the formation of a
neutral molecule. It plays a key role in chemical reaction networks, like the
interstellar medium, the Earth's ionosphere and biochemical processes. Here, a
class of AED involving a closed-shell anion (OH^-) and alkali atoms (rubidium)
is investigated by precisely controlling the fraction of electronically excited
rubidium. Reaction with the ground state atom gives rise to a stable
intermediate complex with an electron solely bound via dipolar forces. The
stability of the complex is governed by the subtle interplay of diabatic and
adiabatic couplings into the autodetachment manifold. The measured rate
coefficients are in good agreement with ab initio calculations, revealing
pronounced steric effects. For excited state rubidium, however, a lower
reaction rate is observed, indicating dynamical stabilization processes
suppressing the coupling into the autodetachment region. Our work provides a
stringent test of ab initio calculations on anion-neutral collisions and
constitutes a generic, conceptual framework for understanding electronic state
dependent dynamics in AEDs.
