D. P. Lin

Energy Level Structure of Trapped Electrons in Methyltetrahydrofuran Glass from Photoconductivity and Optical Bleaching Studies

Electrons are trapped in γ irradiated methyltetrahydrofuran (MTHF) glass at 77°K. Monochromatic photoexcitation produces photoconductivity and optical bleaching with a threshold near 780 nm (1.6 eV) and a peak near 520 nm (2.4 eV). This transition is linear in light intensity and independent of temperature between 77 and 4.2°K, so it is interpreted as a one photon transition directly to the conduction band or to an autoionizing state. Effective double beam photoexcitation discloses a two photon transition which depends on the light intensity squared. The first photon corresponds to the well‐known optical absorption of trapped electrons in MTHF at 1.0 eV. This transition is interpreted as a 1s → 2 p type. The 2p state then presumably crosses to a 2s‐type state from which the second photon is absorbed. The wavelength dependence of the second photon transition shows a peak at 950 nm (1.3 eV) and a threshold near 1150 nm (1.1 eV). The temperature of both optical bleaching and photoconductivity under ir photoe...

Electron scavenging in ethylene glycol-water glass at 4 and 77K: Scavenging of trapped vs mobile electrons

Abstract Electron scavenging efficiencies have been measured at 77 and 4 K in ethylene glycol-water glass for the following scavengers which span a 250-fold range of scavenger efficiencies at 77 K: HCl, NaNO 3 and K 2 CrO 4 . The range of scavenging efficiencies decreases to 62 at 4 K with the largest relative change occurring for the less efficient scavengers. These results are suggested to be most consistent with a model in which scavenging occurs by tunneling from shallowly and deeply trapped electrons at 4 and 77 K, respectively.

Electron–electron double resonance study of magnetic energy transfer between trapped electrons and radicals in organic glasses: Relation between dipolar cross relaxation times and dipolar interaction distances

Electron–electron double resonance (ELDOR) has been used to measure cross‐relaxation times between trapped electrons and trapped radicals produced by γ irradiation of 2‐methyltetrahydrofuran and 3‐methylhexane organic glasses. The cross‐relaxation times are measured as a function of temperature, radiation dose, and the frequency difference Δf of the microwave frequencies used. The cross‐relaxation times are nearly temperature independent and depend on Δf2 at doses where the spin concentrations approach uniformity; these features indicate the dominance of single step over multistep cross‐relaxation processes. Equations have been derived to relate the dipolar cross‐relaxation distance to the measured cross‐relaxation times, and it is suggested that the cross‐relaxation line shape is Lorentzian in magnetically dilute systems. Typical electron–radical correlation distances in these organic glasses are 10 A.

Electron—proton distance changes during solvation of electrons in 3-methylhexane and other organic glasses by matrix ENDOR and second moment EPR lineshape analyses

Abstract Matrix proton ENDOR signals have been measured for stabilized electrons produced by irradiation at 4 K and at 77 K in 3-methylhexane glass. The matrix proton ENDOR linewidths are smaller when irradiation is carried out at 77 K. This difference is analyzed to show a 0.15 A change in the average electron—proton distance as the electron produced at 4 K is solvated by warming to 77 K. Similar distance changes have been deduced from a second moment EPR lineshape analysis for electrons in several organic glasses for which the proton hyperfine interaction is mainly dipolar.

Temperature dependence of the electron spin resonance linewidth of solvated electrons in aqueous alkaline glass: Determination of vibrational and torsional frequencies associated with the solvated electron complex

Abstract The electron spin resonance linewidth of solvated electrons produced by γ-irradiation of 10 M NaOH alkaline aqueous glass has been measured from 4.2 to 115 K at 9 GHz and from 12 to 115 K at 35 GHz. At both frequencies the linewidth reversibly decreases with increasing temperature. This is attributed to interaction with vibrational and rotational frequencies of the solvated electron complex. Analysis on this basis yields two frequencies which are associated with the solvated electron including its first solvation shell water molecules. The lower frequency, 1.5 cm−1, is tentatively assigned to torsional or twisting motions of the first solvation shell of water molecules and the higher frequency, 37 cm−1, is assigned to a solvated electron—nearest proton stretching motion. Model theoretical calculations partially support the latter assignment.