Small polaron model for the absorption spectrum of solvated electrons in alcohols

Abstract

The absorption spectra of localized electrons in alcohol aggregates are studied in terms of the small-polaron model. The red and the visible spectra are ascribed to electrons in two different kinds of traps rather than to the “unrelaxed and relaxed” trapped electrons. The two trapping sites are hydrogen-bonded OH chains and the alkane part of the system. Each kind of trap is characterized by a finite activation energy for self-trapping, whose magnitude is related to the “stiffness”(or the frequency of the coupled normal mode) of the site. The OH chain has a higher frequency for the coupled vibrational mode than that of the alkane part, so that at 77 K electrons are initially trapped at the shallow alkane traps and then transferred to the deeper OH-chain traps. The proposed model is consistent with other experimental features: the effects of the size of the alkane part in normal alcohols and of the branched structure of the alkane part on the line-width and on the absorption peak of the visible spectrum, the chemical consequence of photo-bleaching the visible spectrum (i.e., production of H atoms), and the effect of scavengers on the growth of the visible spectra.