  We have measured the spontaneous and photo-induced decays of anionic gold
clusters, Au$_N^-$, with sizes ranging from $N = 2$ to 13, and 15. After
production in a sputter ion source, the size-selected clusters were stored in
the cryogenic electrostatic ion-beam storage ring DESIREE and their
neutralization decays were measured for storage times between 0.1 and 100 s.
The dimer was observed to decay by electron emission in parallel to neutral
atom emission at long times, analogously to the behavior of copper and silver
dimers, implying a breakdown of the Born-Oppenheimer approximation. Radiative
cooling is observed for all cluster sizes except for the dimer. The decay rates
of clusters $N=3,6,8-13,15$ show only a single radiative cooling time. For
$N=6-13$ the cooling times have a strong odd-even oscillation with an amplitude
that decrease with cluster size, and with the even $N$ having the fast cooling.
We compare our results with previous measurements of radiative cooling rates of
the corresponding cationic gold clusters, Au$_N^+$, which also show an odd-even
effect with a similar oscillation amplitude but at orders of magnitude shorter
time scales, and out of phase with the anions.
