Solvation dynamics of surface-trapped electrons at NH3 and D2O crystallites adsorbed on metals: from femtosecond to minute timescales

Abstract

The creation and stabilization of localized, low-energy electrons is investigated in polar molecular environments. We create such excess electrons in excited states in ice and ammonia crystallites adsorbed on metal surfaces and observe their relaxation in real time using time-resolved photoelectron spectroscopy. The observed dynamics proceed up to minute timescales and are therefore slowed down considerably compared to ultrafast excited state relaxation in front of metal surfaces, which proceeds typically on femto- or picosecond time scales. It is the highly efficient wave function constriction of the electrons from the metal that ultimately enables the investigation of the relaxation dynamics over a large range of timescales (up to 17 orders of magnitude). Therefore, it gives novel insight into the solvated electron ground state formation at interfaces. As these long-lived electrons are observed for both, D₂O and NH₃ crystallites, they appear to be of general character for polar molecule–metal interfaces. Their time- and temperature-dependent relaxation is analyzed for both, crystalline ice and ammonia, and compared using an empirical model that yields insight into the fundamental solvation processes of the respective solvent.