Editing Absorption spectroscopy (section)

===Atomic and molecular physics===
Theoretical models, principally [[quantum mechanics|quantum mechanical]] models, allow for the absorption spectra of atoms and molecules to be related to other physical properties such as [[electronic structure]], [[atomic mass|atomic]] or [[molecular mass]], and [[molecular geometry]]. Therefore, measurements of the absorption spectrum are used to determine these other properties. [[Microwave spectroscopy]], for example, allows for the determination of bond lengths and angles with high precision.

In addition, spectral measurements can be used to determine the accuracy of theoretical predictions. For example, the [[Lamb shift]] measured in the [[hydrogen atom|hydrogen]] atomic absorption spectrum was not expected to exist at the time it was measured. Its discovery spurred and guided the development of [[quantum electrodynamics]], and measurements of the Lamb shift are now used to determine the [[fine-structure constant]].