Spectroscopy is the study of the interaction between matter and electromagnetic radiation (light). Spectroscopic data is often represented by a spectrum, which is a plot of the response of interest (most often intensity) as a function of wavelength or frequency. Most of what we know about the structure of atoms and molecules comes from studying their interaction with light. There are many types of spectroscopy. These include atomic absorption spectroscopy, infrared (absorption) spectroscopy, ultraviolet (absorption) spectroscopy, fluorescence spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, laser induced breakdown spectroscopy, and x-ray spectroscopy.
Spectroscopy is widely used to provide information on chemical structures and physical forms, to identify substances from their characteristic spectral patterns, and to determine quantitatively or semi-quantitatively the amount of a substance in a sample. Samples can be examined in a whole range of physical states; for example, as solids, liquids or vapours, in hot or cold states, in bulk, as microscopic particles, or as surface layers.1
The most common spectroscopic techniques employed to detect and characterise molecules are absorption spectroscopy (infrared, visible, or ultraviolet) and fluorescence spectroscopy, which are based on the processes of molecular absorption and emission respectively. Absorption spectroscopy in which a sample interacts with radiation in the infrared region (i.e. light with a longer wavelength and lower frequency than visible light), is called infrared absorption spectroscopy, and is the most useful spectroscopic technique for the analysis of organic compounds.
Another increasingly popular and very powerful spectroscopic technique for the detection and characterisation of molecules is Raman spectroscopy, which is based on the process of Raman scattering. Both Raman spectroscopy and infrared absorption spectroscopy are examples of vibrational spectroscopy, in which information about the chemical structure of a molecule is derived from its vibrations. They require not too dissimilar components and share some of the same features.
- Ewen Smith & Geoffrey Dent, Modern Raman Spectroscopy: A Practical Approach, John Wiley & Sons Ltd, 2005.