Experimental detection of collective modes In a polar liquid: application to the case of the solvated electron in H2O and NH3

Abstract

We present experimental data that confirm the predicted existence of a collective mode in a liquid corresponding to the longitudinal optical mode in an ionic crystal. The experimental investigation was carried out in nitromethane, and the results bear out all the calculated properties of this collective mode: the dipolar plasmon. The calculated frequency of the dipolar plasmon, as well as the dielectric constant at high and low frequencies, are then used to calculate without adjustable parameters the polaron coupling constant of the solvated electron in NH3 and H2O. A comparison of the calculated and measured properties of the solvated electron indicates that in either case a polaron-like continuum theory can at most account for only a fraction of the energy of the observed optical absorption.