Band spectra is the name given to groups of lines so closely spaced that each group appears to be a band—e.g., nitrogen spectrum. Band spectra, or molecular spectra, are produced by molecules radiating their rotational or vibrational energies, or both simultaneously.

Although flames and discharges provide a convenient method of excitation, the environment can strongly perturb the sample being studied. Excitation based on broadband-light sources in which the generation of the light is separated from the sample to be investigated provides a less perturbing…

Molecular spectra result from either the absorption or the emission of electromagnetic radiation as molecules undergo changes from one quantized energy state to another. The mechanisms involved are similar to those observed for atoms but are more complicated. The additional complexities are due to interactions of…