The energy associated with electromagnetic radiation covers a wide range of magnitude as do the
corresponding frequencies and wavelengths – the whole being termed the electromagnetic spectrum.
Figure 7.2 shows the range of energy and the corresponding frequencies, wavelengths and
wavenumbers. Atomic and molecular processes involving the emission or absorption of radiation are
shown opposite the appropriate energy ranges. The electromagnetic spectrum is divided into a number
of regions; these are artificial divisions in the sense that they have been defined solely as a result of
differences in the instrumentation required for producing and detecting radiation of a given frequency
range. It must be emphasized that the radiation itself is fundamentally the same over the entire
electromagnetic
Figure 7.2
The electromagnetic spectrum.