Optical Absorption Characteristics and Photobleaching Behavior of Trapped Electrons in γ-Irradiated Alkaline Ice

Abstract

Trapped electrons, et−, are produced by γ irradiation of alkaline ice (10M NaOH) at 77°K. The et− absorption band maximum at 590 nm shifts to shorter λ for bleaching at 700 nm and shifts to longer λ for bleaching at 400 nm. After partial bleaching, electrons can be shifted back and forth between traps characterized by long and short λ. Although this suggests at least two trap depths, there is probably a broad spectrum of trap depths. The quantum efficiency, φ, for photobleaching et− is 0.15 and independent of λ when the optical density is measured at 590 nm. For the optical density measured at the bleaching wavelength, φ increases to 0.52 at 400 nm and to 0.26 at 700 nm; φ also increases in the presence of electron scavengers. φ decreases as the fraction of et− bleached, F, increases and follows φ = 0.15 exp( − 3.7F) for F = 0–0.85. All of these changes are explained by retrapping and trap interconversion. φ is also independent of temperature between 4 and 77°K in agreement with photoconductivity measurements. ε(590 nm) = 1.94 × 104M−1·cm−1, and the oscillator strength is ≥ 0.86 for the et−band.