Witold M. Bartczak

Trapped electron in frozen ionic solutions— a theoretical model

The theoretical model of electron trapped in frozen solutions of ionic compounds is presented. The model is based on the lattice theory of concentrated electrolytes; water plays the role of dielectric continuum. Two possible ionic structures being the source of attractive potential—cation and anion vacancy—are considered. It appears that due to repulsive effects of the nearest neighbouring anions the cation site is very shallow electron trap or even has no bonding electron level. This structure is presumably responsible for IR absorption bands observed for LiCl or MgCl2 solutions. The F-centre like structure is rather deep trap characterized by electron energy level ca. -3 eV and optical transition ca. 2 eV. The numerical calculations were performed for Li+, Na+ and K+ solutions. The properties of e-vis and e-IR bands are discussed with respect to their explanation by the model.

Statistical approach to localized states A review of recent theoretical research institute of applied radiation chemistry

Abstract The paper reviews a series of recent theoretical papers worked out in the Institute of Applied Radiation Chemistry, Łodź, Poland. These papers are mainly devoted to the construction of the models of trapped or solvated electrons on a base of statistical formulation of the problem of the localized electron. The models reviewed in this paper concern: (1) statistical variety of electron traps in disordered polar matrices; (2) statistical model of the hydrated electron; (3) ionic traps capturing the electron in ionic solutions; (4) the Cl 2 - self-trapped hole in ionic solutions.

Model of electron capture in low-temperature glasses

Abstract The new model of electron capture by a statistical variety of traps in glassy matrices is proposed. The electron capture is interpreted as the radiationless transition (assisted by multiphonon emission) of the mobile electron to the localized state in the trap. The conception of “unfair” and “fair” traps is introduced. The “unfair” trap captures the mobile electron by the shallow excited state. In contrast, the “fair” trap captures the electron by the ground state. The model calculations of the statistical distributions of the occupied electron traps are presented and discussed with respect to experimental results.

Model for the self-trapped hole Cl2- in irradiated aqueous chloride solutions

Abstract Calculations on the self-trapped hole in the form of Cl2- in irradiated aqueous solutions are performed. The central molecule Cl2- and the first solvation shell composed of six water molecules arranged to form the octahedron are treated microscopically. Further molecules beyond the spheroidal cavity are treated by the continuous dielectric approximation. The hole self-trapping energy is found to be -0.525 eV. The energy of the optical transition 2Σ+u → 2Σ+g is calculated as a function of Na+ cation concentration. The energy effects for two possible mechanisms of self-trapped hole formation are discussed.

A model for relaxation of nonpolar glassy matrices—effect of relaxation on some of radiation chemistry processes

Abstract The model explaining semi-quantitatively the effect of the pre-irradiation annealing of the nonpolar glassy sample on decay of trapped electrons is presented. It is assumed that the changes proceeding in the stored amorphous sample tend towards increase of the local order. The force constant distribution and the vibrational spectrum of the stored sample is approximately calculated as a function of annealing time. The decay rate constant of the trapped electrons depends on the possibility of the dissipation of the excess energy after electron transfer and, in consequence, on the density of the matrix vibrational states in the high frequency part of the spectrum. The numerical calculations are performed for pre-irradiation annealing of the 3-MP matrix.

Trapped electron in frozen ionic solutions—II. Asymmetry and relaxation of electron traps

Abstract The theoretical model of the electron localized in frozen ionic solutions has been applied to investigate the influence of the trap distortion on the electron energy levels in the trap. It has been found that asymmetric traps are slightly more shallow than the symmetrical trap. The differences between electron absorption spectra obtained by pulse radiolysis and those by γ-radiolysis are then explained in terms of the relaxation of distorted ionic traps.

Stabilized hydrogen atom in frozen polar matrices—A theoretical model

Abstract A semicontinuum model for the stabilized H atom in frozen aqueous solutions is proposed. The directions of the dipoles are assumed to undergo statistical distributions and thus a statistical variety of traps is taken into account in the model. Numerical calculations are performed for 8 M HCl at 77 K and the results are discussed with respect to the experimental verification of the model.

Electron capture in alcohol alkane solutions

Abstract The mechanism of primary solvation of the excess electron in dilute solutions of alcohol in hydrocarbons is discussed. The considerations are based on the experimental results obtained by Baxendale et al. and on the recently constructed model of alcohol self-association in such mixtures. While solvation by dimers can not be entirely excluded, the provided arguments support the predominant solvation of the excess electron by larger clusters, particularly trimers and cyclic tetramers.

Relaxation processes connected with electron localization A review of recent theoretical research in institute of applied radiation chemistry

Abstract The paper reviews a series of recent theoretical papers worked out in the Institute of Applied Radiation Chemistry, Łodź, Poland. These papers are mainly devoted to various relaxation processes connected with electron localization in irradiated disordered media as well as to the construction of the models of trapped or solvated electron. The models reviewed in this paper (the first part of the review) concern: (1) electron trap relaxation via electron tunnelling followed by molecular reorientation; (2) molecular structure of alcohol-hydrocarbon mixtures and electron localization in these matrices; (3) the glass relaxation effect on trapped electron reactions.