  We report the first experimental evidence of spontaneous electron emission
from a homonuclear dimer anion through direct measurements of $\rm{Ag}_2^-
\rightarrow \rm{Ag}_2 + \rm{e}^-$ decays on milliseconds and seconds time
scales. This observation is very surprising as there is no avoided crossing
between adiabatic energy curves to mediate such a process. The process is weak
but yet dominates the decay signal after 100 ms when ensembles of internally
hot Ag$_2^-$ ions are stored in the cryogenic ion-beam storage ring, DESIREE,
for 10 seconds. The electron emission process is associated with an
instantaneous, very large, reduction of the vibrational energy of the dimer
system. This represents a dramatic deviation from a Born-Oppenheimer
description of dimer dynamics.
