Hugh A. Gillis

Pulse radiolysis studies of time dependent spectral shifts of the solvated electron in ethanol and deuterated ethanol glasses at 76 K

The initial (?200 nsec) spectra of the trapped electron are similar in C2H5OH, C2H5OD, C2D5OH, and C2D5OD glasses at 76 K with λmax ∼1300 nm. The kinetics of the spectral shifts to the stable values of λmax near 540 nm are similar for C2H5OH and C2H5OD and resemble the kinetics of a series of first order processes or of tunneling reactions. Structure seems to be present in the partially relaxed spectra and may result from specific geoemetrical orientations of first solvation shell molecules.

Pulse radiolysis of aqueous solids at 76 K. An absorption band in the infrared

Abstract An IR absorption band with a maximum beyond 2400 nm has been found and assigned to the electron in the following systems irradiated at 76 K: crystalline D 2 O, and D 2 O glasses of ethylene glycol, MgCl 2 and LiCl. The band is tentatively attributed to an electron captured in a D-defect.

Optical Measurements on Solvated Electrons in Pulse-Irradiated Liquid Propane,

Abstract A broad absorption spectrum with λ max ⩾ 2000 nm has been observed in pulse-irradiated liquid propane at low temperatures, and assigned to the solvated electron. The electron decays by geminate recombination with an initial half-life of ⩽ 95 nsec at −185°C.

Evolution of the spectrum of the solvated electron in BeF2 aqueous glasses at 76 K

Evidence is presented for a spontaneous shift from infrared‐to‐ red‐to‐green in the overall spectrum of the electron trapped in an aqueous glass at 76 K following nanosecond pulse radiolysis. As with the alcohols, after the pulse the infrared absorption decays, there is a growth‐then‐decay of absorbance at intermediate wavelengths and net growth of absorption due to the equilibrated trapped electron state, e − vis. This progressive transition was not characterised by a single‐step process and was discernible in aqueous glasses containing 7.5 or 10.7M BeF2 in D2O. At higher BeF2 concentrations, or with LiBr as glass‐forming electrolyte, no growth of e − vis was observed, probably because of concurrent loss of e − vis in those glasses, as in LiCl and other glasses. BeF2 glasses of trapped electrons showed several other features of interest: (i) wavelength‐ selective bleaching of the e − vis band indicates that it is composed of a broad ’’green’’ band (λmax, 530–590 nm) which bleaches homogeneously, and a broad ’’red’’ region which bleaches inhomogeneously. (ii) λmax for e − vis changes with BeF2 concentration, being blue shifted with increasing concentration , with both green and red underlying structures shifting slightly. (iii) No absorption due to F− 2 was found following pulse radiolysis in these glasses at 76 K. (iv) Several recent findings with LiCl are mimicked by F− 2 glasses. For instance, G (e − vis) increases and G (e − ir) decreases as the electrolyte concentration is increased, while the combined yield remains constant at 1.8±0.1.

Luminescence and infrared absorption from laser excitation of trapped electrons in aqueous glasses

When samples of trapped electrons in 9.5M LiCl and 3.1M MgCl2 aqueous glasses at 77 K were bleached by single pulses of 694 nm light from a Q‐switched ruby laser, infrared absorption was produced, and luminescence observed in the near ultraviolet and visible. The luminescence had a spectrum centered at 400–420 nm and its intensity was measured over eight decades of time (100 ns to 10 s) following the laser pulse. Over much of this period the luminescence intensity was inversely proportional to the time. No such effects were found for trapped electrons in NaOH or K2CO3 glasses nor in γ‐irradiated LiCl or MgCl2 glasses when an electron scavenger was present. This suggests that optical excitation on the low energy side of the visible absorption band causes trapped electrons to be released from their traps, after which they may be temporarily caught in shallow traps from which they tunnel to radiation produced reaction partners, as has been observed during pulse radiolysis.

Solvated electrons in dimethylsulphoxide

The optical absorption spectrum obtained by pulse radiolysis of pure liquid dimethylsulphoxide includes a broad intense band in the near IR with λmax ⩾ 1500 nm. This band is assigned to solvated electrons with a half-life of 15 ± 2 nsec. The λmax of the solvated electron correlates better with dimethylsulphoxides inability to solvate negative ions than with its dielectric constant, which is 48.

Pulse radiolysis study of electron solvation in methanol2-methyltetrahydrofuran (MTHF) glasses of 109 K: solvation shell conversion from MTHF to methanol

Abstract Electrons produced by pulse radiolysis in glasses of 32 mole % methanol in MTHF at 109 K exhibit a spectral blue-shift from 0.1–14 μs indicating predominant initial solvation by the more abundant MTHF molecules converting to final solvation by the more polar methanol molecules. Although the kinetics are complex, conversion appears to occur by a diffusive process involving more than one step with methanol clusters.

Pulse radiolysis study of the reactions of hydrated electrons with naphthalene, phenanthrene, biphenyl and fluorene in aqueous micellar solutions

The reaction of hydrated electrons with naphthalene, phenanthrene, biphenyl and fluorene to form the respective aromatic radical anions has been studied in aqueous solutions (1 % methanol, pH 12.1) in the presence and absence of micellar hexadecyltrimethylammonium bromide (CTAB). The reaction rates are 3–9 times faster in the presence of micellar CTAB suggesting that CTAB will, in general, enhance this type of reaction. An absorption spectrum of the free fluorene radical anion was obtained. In the presence of CTAB the aromatic radical anions decay to second transients which are probably the hydrogen adducts of the aromatic molecules.

The effect of accumulated dose at 6 and 72 K on electron trapping in ethylene glycol-water glass

Abstract In the pulse radiolysis of ethylene glycol-D 2 O glass at 6 K, G (e - IR ) ⋍ 4.9 and G (e - vis )⋍0.3; by contrast pulse radiolysis of pure ethylene glycol glass at 6 K gives very little IR absorption. The effect of previous irradiation at 6 or 72 K on the ethylene glycol-D 2 O glass is to modestly reduce initial yields at 6 K. The results of the pulse experiments do not substantiate a previous report that shallow traps are efficiently consumed during irradiation at 77 K.

Two fast photodiodes for use in pulse radiolysis

Abstract In this paper we describe the characteristics of two photodiodes which make them very useful for pulse radiolysis studies. These detectors are the EG & G SHS-100 Si photodiode and the Barnes room temperature A-100 InAs photodiode. The former has a linear output up to at least 6·5 mA, has a 0–98% response time ≌ 15 ns and is distinguished from Si photodiodes previously described by having no detectable slow component to its response. The 0–98% response time of the A-100 photodiode and the circuit developed for it is about 60 ns, and it also shows no detectable slow response component. The output of the A-100 is linear up to at least 2 mA, and we have used it for absorption measurements between 450 and 3200 nm.