Optical absorption spectroscopy in geosciences: Part I: Basic concepts of crystal field theory
Manfred Wildner, Michael Andrut, Czesław Z. Rudowicz, 2004. "Optical absorption spectroscopy in geosciences: Part I: Basic concepts of crystal field theory", Spectroscopic methods in mineralogy, Anton Beran, Eugen Libowitzky
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Chapters Chapter 3 and Chapter 4 deal with optical absorption spectroscopy and comprise two interrelated parts. Part I, the present chapter, is intended as an introduction for the beginners, e.g. undergraduate students of geosciences, in order to help them acquire an understanding of the basic theoretical principles, focussing on the crystal field (CF) concept. After a short introductory section including some “technical” information, the reader is guided step by step through the development of the qualitative principles of the CF theory (CFT), referring to several aspects important for geosciences. The necessary concepts and tools are briefly outlined, whereas references to a selection of relevant textbooks and publications are given for further reading. Concise tables and figures help to illustrate and summarise important topics. Examples of the actual spectra are provided, mainly concerning the “many-electron systems” (of the first-row transition ions, i.e., 3d2,3,7,8), since they cover the full diversity of the crystal field based spectroscopic aspects.
Part II (Chapter 4 in this volume – Andrut et al., 2004) deals with the quantitative aspects of the crystal field theory and its applications. It highlights the power of semi-empirical methods for the calculation of energy levels of the transition metal complexes with arbitrary low symmetry.
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Spectroscopic methods provide information about the local structure of minerals. The methods do not depend on long-range periodicity or crystallinity. The geometric arrangement of atoms in a mineral phase is only one aspect of its constitution. Its vibrational characteristic, electronic structure and magnetic properties are of greatest importance when we consider the behaviour of minerals in dynamic processes. The characterisation of the structural and physico-chemical properties of a mineral requires the application of several complementary spectroscopic techniques. However, it is one of the main aims of this School to demonstrate that different spectroscopic methods work on the same basic principles. Spectroscopic techniques represent an extremely rapidly evolving area of mineralogy and many recent research efforts are similar to those in materials science, solid state physics and chemistry. Applications to different materials of geoscientific relevance have expanded by the development of microspectroscopic techniques and by in situ measurements at low- to high-temperature and high-pressure conditions.