Maria Hilczer

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.

Preexisting traps for electrons in polar liquids. Statistical distributions of trap energy and structure

The statistical distributions of the electron energy level and the structural parameters of the preexisting traps in polar liquids have been investigated. The Monte Carlo calculations were performed for the TIPS intermolecular potentials with the parameters corresponding to the simple alcohols, methanol and ethanol, in liquid phase. The distributions of the trapping level obtained for the TIPS potential seem to be better correlated with the data provided by experiments than the distributions obtained for the point–dipole model of alcohol molecules.

Model of preexisting traps for electrons in polar liquids

The statistical distributions of structure parameters and the electron energy level of the preexisting traps in polar liquids have been investigated. The TIPS model of intermolecular interactions has been applied. The numerical computations were performed for methanol and are compared with the earlier Tachiya and Mozumder calculations.

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.

Electron solvation in liquid 1-propanol and 2-propanol. Effect of microscopic liquid structure

Abstract Difference in processes of electron solvation in primary and secondary alcohols is assumed usually as resulting from difference in microscopic structure of the two liquids. To check validity of this assumption for primary localization of an excess electron we analyse the pre-existing electron traps found in computer-generated structures of 1-propanol (1P) and 2-propanol (2P) at room temperature. Properties of these traps such as shape, volume or depth, are considered in relation to the local arrangement of molecules around the trap.

Electron localization in liquid alcohols. A statistical model

Abstract Statistical analysis of the electron trapping sites in polar liquids has been performed. The pre-existing electron traps defined as the attractive fluctuations of the random potential were analysed by the methods of stochastic geometry. These methods were applied to an ensemble of the molecular configurations obtained by the computer simulation of liquid methanol. The distribution functions of energy of the trapping sites were found and the statistical properties of the trap coordination number have been 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.

Electron localization in random potential fields. Statistics of potential in polar disordered media

Abstract A new method of statistical analysis of the preexisting traps for electrons in disordered media has been presented. The method is based on the mathematical theory of random fields. The potential energy surface produced by matrix molecules is considered as a random field and the preexisting electron traps are described as the extreme regions of the field. The distributions of concentration, size and maximum depth as well as some spatial relations for the traps are expressed in terms of the mean size and number density of excursions above a high level by an isotropic, gaussian random field. The preliminary calculations have been performed for the Coulomb random field in methanol at room temperature.

Statistical model of the localized electron in dilute ionic solutions

Abstract A theoretical model of the localized excess electron in dilute ionic solutions is presented. The model is based on the ion-pair theory of ionic solutions. The giant quasi-dipoles built of separated cation-anion pairs have been considered as electron traps. The statistical distribution of the depth of the electron traps and the optical absorption spectrum of the localized electron have been calculated. The trap distribution results from the statistical distribution of the distances separating two ionic partners of opposite charge and depends on the solvation degree of the ions. Numerical calculations of the electron absorption spectra have been performed for dilute NaX and LiX solutions (X stands for single-charged anion) in tetrahydrofuran at room temperature.