Pulse Radiolysis of Alcohol Glasses at 77°K: Mechanism of Electron Trapping

Abstract

Ethylene glycol/water (50/50), methanol/water (95/5), ethanol, 1‐propanol, 2‐propanol, and 2‐propanol/methyltetrahydrofuran (50/50) glasses were studied by pulse radiolysis at 77°K. In each glass a trapped electron spectrum is observed which shifts toward the blue on a microsecond timescale. This suggests a shift from shallow to deeper traps. The spectral shift appears to occur more rapidly in more polar matrices. This is the opposite of the direction expected based on relative matrix viscosities. When 10⁻²M biphenyl or benzyl chloride is added to 2‐propanol glass about 40% of the electrons are scavenged. The resulting biphenyl anion and benzyl radical spectra show no transient changes in intensity after the pulse while the residual trapped electron spectrum shows the same shift as before. Both the polarity and the solute effects indicate that molecular reorientation around the electron is responsible for the transient spectral shift. A short‐range electron—matrix interaction would presumably cause faster reorientation in more polar matrices. An alternative mechanism of a redistribution of electrons among shallow and deep preformed traps seems to be ruled out.