The color of coordination compounds of the transition elements is one of their characteristic properties. These colors are due to the absorption and subsequent emission of light in the visible part of the spectrum. Light in this region of the spectrum caused promotion of d–electrons from a lower to a higher energy level. The spectra which result are generally referred to as Electronic Spectra. Note that electronic transitions may also be effected by ultraviolet light. Because of the size of the quanta involved, electronic transitions in molecules are always accompanied by vibrational and rotational changes, and hence a band spectrum is observed. In general, the bands which arise are much broader than bands in an infrared spectrum and are little used for identification purposes.