Trapped Electrons Produced in Ethanol Glass at 4°K

Abstract

Optical absorption and ESR measurements were carried out on et− produced in ethanol at 4°K. The same et− yield for γ radiolysis at 4 and 77°K indicates that electrons are stabilized in pre-existing traps at 4°K where molecular dipoles remain unrelaxed. et− prior to solvation can be classified into two groups. One with λmax = 1500 nm, W1/2= 4 × 103 cm−1 and Δ Hpp = 5.5 ± 0.5 G is easily photobleached by the infrared light. The other with broad absorption band in the visible and Δ Hpp = 13.5 ± 1.5 G is not photobleached by the infrared light. The successive shift of the absorption spectrum to the higher energy side on warming is interpreted by the molecular reorientation mechanism. et− decay is observed during the solvation process, depending on time required for the solvation. The blue shift of the absorption spectrum on reducing the temperature is attributed to contraction of electron traps.

Electron solvation in methanol revisited

“…3. Comparing the spectra in the present paper to those published by Turi et al (1997) for the mechanism with shorter indirect solvation, it can be observed that the spectra in (Hase et al, 1972).) The smoother spectra found here suggest that electron solvation in methanol might proceed via model (2), rather than according to the shorter indirect solvation channel considered in the paper of Turi et al (1997).…”

Alternative Mechanisms for Solvation Dynamics of Laser-Induced Electrons in Methanol

“…On the contrary, model 3 has to consider major molar absorption coefficients from these species in order to explain important signal attenuation from quite low visible wavelengths to the near-IR at early times. However, it may be argued that this spectral feature has also been observed in glassy ethanol at 4 K, where there is a big overlap of the spectra of the presolvated electron with the fully solvated one in the visible wavelength range and the IR-band of the presolvated species has a large visible tail stretching well below 400 nm. , …”

"Initial" spectra of trapped electrons in alcohol glasses from 12 to 115 K

“…They concluded that the evolution of the electron spectrum is due mostly to the selective decay of the IR-absorbing electrons such that, in glassy ethanol, only about 40% of the IR-absorbing electrons transform into visible-absorbing electrons during the spectral evolution to contribute about 20% of the steady spectrum at 77 K. This might appear to contradict a pulse radiolysis study from this laboratory,2 and later confirmed,18 which showed that the spectral shift in ethanol at 76 K which occurred between 200 ns and 35 ms was accompanied by very little change in the integrated area of Ge vs. cm-1 which suggested little change in the oscillator strength or the electron concentration during solvation. However, it seems reasonable to us that a sample held at 4 K for more than 1 h and subsequently warmed to 77 K should suffer more loss of shallowly trapped electrons by tunneling (a low activation energy process) leading to reaction than a sample pulsed at 76 K. Ogasawara et al17 were able to follow the spectral shift after warming from 4 to 77 K because the shift occurred very slowly (on the minutes time scale), the slowness being related in some way to the extent of the dose given the samples and perhaps to the length of time taken to irradiate the samples. The lack of any hint of structure in the spectrum for ethanol either at 4 K17 or at 200 ns, 76 K,2 even though both methods seem capable of showing small deviations from a smooth spectrum, does not lend support to the interpretation of Ogasawara et al The 4 K spectra of Ogasawara et al are clearly far from the initial spectra since Gtmax for ethanol and 1-propanol are about one-third of the values measured by pulse radiolysis at "6" K (ref 9 and Figure 1, this work).…”