INTRODUCTION

Properties of electromagnetic radiation

The interaction of electromagnetic radiation with matter is essentially a quantum phenomenon and is dependent upon both the properties of the radiation and the appropriate structural parts of the material involved. This is not surprising, as the origin of the radiation is due to energy changes within the matter itself. An understanding of the properties of electromagnetic radiation and its interaction with matter leads to a recognition of the variety of types of spectra and consequently spectroscopic techniques and their application to the solution of biological problems. Also the transitions which occur within matter (see e.g. Section 12.1.2) are quantum phenomena and the spectra which arise from such transitions are, at least in principle, predictable. Table 12.1 shows the various interactions, with parts of matter, of the electromagnetic spectrum and corresponding wavelengths. The various parts of matter both give rise to and are affected by the radiation in the corresponding region of the spectrum.

Electromagnetic radiation (Fig. 12.1) is composed of both an electric vector and magnetic vector (which gives rise to the name), which oscillate in planes at right angles (normal) to each other and mutually at right angles to the direction of propagation.

Interaction with matter

Electromagnetic phenomena exhibit energy, frequency, wavelength and intensity. All these are interrelated and can be explained either in terms of waveforms or particles termed photons or quanta.