Energy level structure and mobility of excess electrons in .gamma.-irradiated 5 M potassium carbonate aqueous glasses. Effect of ions on trapped and mobile electrons in aqueous glasses

Abstract

The energy level structure of trapped electrons (et") in -irradiated 5 M K2CO3 glassy ice at 77 K has been investigated via the wavelength dependence of the photocurrent. Scavenger effects demonstrate that the photogenerated charge carrier is an electron. The photocurrent wavelength response per unit incident photon does not coincide with the optical absorption band of the et~a nd can be phenomenologically resolved into two bands. The optical absorption band is a symmetrically bleached with monochromatic light and can also be resolved into at least two subbands. The photocurrent band at longer wavelength coincides with the longer wavelength absorption band. Thus the et~i n the shallower potential wells appear to have no bound excited state as is the case for et-in 10 M NaOH glassy ice. For et~i n the deeper potential wells, the shorter wavelength absorption and photocurrent bands do not coincide and indicate a bound excited state as is found for et" in crystalline ice. The difference between the energy level structure for et~i n different aqueous matrices can be understood in terms of a semicontinuum model of electron trapping and the modification of the polarization interactions by the ions present in the matrix. The analysis is supported by the photocurrent wavelength dependence in 4.5 M D-glucose glassy ice. The field and temperature dependence of the photocurrent and the electron drift mobility were also investigated. Superohmic photocurrents are observed in certain dose ranges at 77 K. The electron drift mobility is inversely proportional to field at high fields and exhibits a negative temperature dependence from 80 to 103 K. The dominant scattering mechanism near 77 K for photoexcited mobile electrons is lattice phonon scattering. In contrast to et" in 10 M NaOH ice, the mobility is independent of the hole (CO3") concentration and there appear to be no shallow traps relative to the conduction band associated with C03". These differences are explained in terms of the different degree of lattice polarization induced by CO3" and O" ions in aqueous matrices.

A photoconductivity study of trapped electrons in γ-irradiated hydrocarbon glasses at 77 K

“…If this assumption is accepted, the value of the right-hand side of eq. [4] gives the relative value of 4. The values of +p/k, for 3MP, 2MP, 3MHp, and 3MP-MCH systems are plotted as a function of photon energy in Fig.…”

“…Thus comparison of optical absorption and photoconductivity spectra is expected to provide information on the energy level structure of trapped electrons. For trapped electrons in polar glasses several photoconductivity studies have been made (2)(3)(4)(5)(6)(7)(8)(9) and theoretical approaches have been attempted to interpret these experimental results (10,11). On the other hand, only a few photoconductivity studies have been done for trapped electrons in nonpolar organic glasses (12,13).…”

Partial deconvolution of the absorption spectrum of trapped electrons in 15 M LiCl aqueous glasses at 77 K

“…Many of the conclusions reached so far rely solely upon the results of steady-state bleaching (2,9) and this has been shown to introduce ambiguities (10). In the hope of resolving these issues more conclusively, both steady-state and time-resolved photobleaching experiments have been conducted on the same system, and this is the topic of this paper.…”