The spectral lines observed in the absorption and emission spectra of atoms or molecules are the result of transitions occurring between different energy levels as electromagnetic radiation is absorbed or emitted. The frequency ()and wavelength (&lgr;) of this electromagnetic radiation are related through the following equation: = c/&lgr;, where c is the speed of light. Thus, UV light absorbed at 3,000 angstroms (Å) corresponds to a frequency of (2.96 x 10 10 cm/sec) / 3 x 10-5 cm = 1015 sec-1 = 1015 hertz (Hz).

The variable that can be most accurately measured is &lgr;. However, it is the frequency that is directly related to the energy, so spectroscopists usually locate the position of spectral lines using a unit called the wavenumber, which is inversely proportional to the wavelength and is represented by . Thus, if &lgr; is measured in cm, is then measured in cm-1 and is equal to the number of waves...