The relationships between the Mössbauer parameters ΔEQ and δ, and molecular vibrations - a theoretical study

Abstract

This thesis considers the relationships between the Mössbauer parameters and molecular vibrations. In Part I a relationship between electric field gradient and molecular force constants is postulated. The force constants are calculated for seventeen tin species, using Normal Coordinate Analysis. The electric field gradients are calculated and it is shown that the magnitude of the quadrupole interactions in Mössbauer Spectra can be predicted provided a value of the Sternhiemer antishielding factor is known. Further, comparison of calculated and observed electric field gradients indicates that the antishielding factor not only depends on the tin nucleus but also to a minor extent on the type of ligands, and their distribution, around the nucleus. In Part II the relationship between isomer shift and molecular vibration frequencies is discussed. The Mössbauer event is represented by a pseudo chemical reaction and statistical mechanics is applied to derive a value for the electronic energy, ΔE° of the Mössbauer event. It is found that ΔE° depends only on the Mössbauer nucleus and the molecular vibration frequencies of the species under consideration. Comparison of ΔE° with the observed isomer shifts, for 10 tin species, shows that for chemically similar species ΔE° and δ are linearly related.