FDMR in Low-Temperature Solids. 2. Observation of Weakly Bound Electrons

Abstract

Time-resolved fluorescence-detected magnetic resonance (FDMR) was used to study radiolysis of organic solids at low temperatures (4-30 K). The mobility of charges generated in the primary events of solid-state radiolysis may be accounted for by two mechanisms: single-step tunneling and relatively slow (10[sup 6]-10[sup 7] s[sup [minus]1]) resonant charge transfer involving the solvent hole. Acting together, these mechanisms engender a variety of unusual and previously unknown spectral features. Although the tunneling satisfactorily explains FDMR behavior in general, quantitative agreement is poor, particularly for donor-acceptor systems. It appears that the origin of this discrepancy lies in an underestimation of the tunneling radii in reactions of negative charges. The latter is rationalized in terms of a selectivity of FDMR toward mobile weakly bound electrons and excited radical anions formed after electron scavenging. The possible nature of these weakly bound electronic states is discussed. 50 refs., 13 figs., 2 tabs.