On the origin of the competition between photofragmentation and photodetachment in hydrated electron clusters, (H2O)−n

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Abstract
Photoexcitation of size‐selected hydrated electron clusters, (H2O)−n , in the near IR results in a competition between photofragmentation and electron photodetachment. To investigate the origin of this competition, the decay probability into ionic fragments for the n=25 cluster was measured as a function of photon energy from 0.91≤hν≤3.49 eV. The photofragmentation probability increases rapidly with decreasing excitation energy in the general vicinity of the vertical detachment energy of this cluster (1.4 eV) determined via photoelectron spectroscopy. This result suggests that fragmentation accompanies photoexcitation of the excess electron with near zero kinetic energy. Thus, photofragmentation appears to proceed through an optically prepared intermediate similar to that reached in electron scattering from neutral clusters, which displays an enhanced dissociative attachment pathway with near zero kinetic energy electrons.