Modern Raman Spectroscopy – a practical approach

Since the first edition of our book, there has been a huge expansion in the use of Raman spectroscopy. Advances in optics, electronics and data handling combined with improvements made by manufacturers and spectroscopists have made Raman scattering easier to record and more informative. Small, portable spectrometers are rugged, reliable and are becoming less expensive. Some can work powered by lowvoltage (1.5 V) batteries and give good performance in hostile environments. At the other end of the scale, advanced equipment is simpler, more sensitive, more flexible and more reliable. New methods with improved performance have been developed. As a result, a technique which was once labelled by some as lacking sensitivity can now, in the correct form, probe the electronic structure of a single molecule or be used to help in the diagnosis of cancer. This has attracted many more users into the field with a wide range of backgrounds. Our aim in writing this book is to provide the understanding necessary to enable new users to apply the technique effectively. In the early chapters we provide basic theory and practical advice to enable the measurement and interpretation of Raman spectra with the minimum barrier to getting started. However, for those with a deeper understanding of the effect, Raman scattering is a very rich technique capable of providing unique information and a unique insight into specific problems. In writing this book some difficult choices have had to be made around the presentation of the theory, particularly with the wide variety of backgrounds we expect readers to possess. We have used as few equations as possible to show how the theory is developed and those are deliberately placed after the chapters on basic understanding. We concentrate on molecular polarizability, the molecular property which controls intensity. The equations are explained, not derived, so that those with little knowledge of mathematics can understand the conclusions reached and those of a more mathematical bent can use the framework for further investigation. This enables selection rules, resonance Raman scattering and some of the language in modern literature to be understood. This is not the traditional approach but, although deriving scattering theory from first principles is good for understanding, it adds little to Raman interpretation. Classical theory which does not use quantum mechanics cannot deliver the information required by most Raman spectroscopists. For these reasons, references to these areas are given but the theory is not explained.