We have studied the influence of sodium ions bound near the ice–vacuum interface on the electron solvation dynamics in amorphous D2O ice layers by means of femtosecond time-resolved two photon photoelectron spectroscopy. Adsorption of sub-monolayer coverages of sodium on top of multilayers of amorphous ice leads to the formation of Na+ ions and to pronounced changes in the observed ultrafast dynamics compared to pure amorphous ice. We identify a Na-induced species of excess electrons which exhibits a much longer lifetime compared to solvated electrons in pure D2O ice and approximate the decay of the Na-induced contribution by two decay times t2 = 880 fs and t3 = 9.6 ps. In addition, a faster energetic stabilization of the excited electrons with a rate of S = 0.73 eV/ps is observed. The population of these electrons depends non-linearly on the sodium coverage. We attribute the Na-induced contribution to a transient electron/ion/water complex which is located at the ice/vacuum-interface. This interpretation is corroborated by coverage dependent measurements and by overlayer experiments.
The original publication is available by link DOI: 10.1021/jp107253g