Probing free electrons in non-polar liquids by time-domain terahertz spectroscopy

Summary form only given. Terahertz time-domain spectroscopy (THz TDS) and its extension to probing the transient properties of materials through pump-probe measurements have been shown to be powerful probes of the steady-state and dynamical properties of charge carriers. While the method has been applied extensively to solids such as semiconductors and superconductors, it has not yet been exploited to address one of the classic problems of condensed-phase chemistry: the nature of electrons solvated in liquids. In this paper, we demonstrate the unique capabilities of THz TDS to investigate the properties of such electrons in non-polar liquids. The solvated electrons in non-polar liquids are generally described with a two-state model in which the solvated electrons are in equilibrium between the quasi-free state probed in our measurements and a bound state formed by a favorable local configuration of the solvent. THz TDS also permits insight into this bound state to be gained. This is accomplished by measuring the temperature dependence of the quasi-free electron concentration. From these data, a binding energy of 150 meV was deduced for n-hexane, comparable to that inferred previously.