The process of electron localization on a cluster of 32 water molecules at 20, 50, and 300 K is unraveled
using ab initio molecular dynamics simulations. In warm, liquid clusters, the excess electron relaxes from
an initial diffuse and weakly bound structure to an equilibrated, strongly bound species within 1.5 ps. In
contrast, in cold, glassy clusters the relaxation processes is not completed and the electron becomes
trapped in a metastable surface state with an intermediate binding energy. These results question the validity
of extrapolations of the properties of solvated electrons from cold clusters of increasing size to the
liquid bulk.