Editing Spectroscopy (section)

==== Molecules ====
The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states ([[electron paramagnetic resonance]]), [[rotational spectroscopy|molecular rotations]], [[molecular vibration]], and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimetre-wave spectral regions. Rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and [[Raman spectroscopy]]. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as [[fluorescence spectroscopy]].<ref name="Crouch-Skoog-Holler2007" /><ref>{{Cite book |last=Kroto |first=H. W. |url=https://books.google.com/books?id=Nu8NAQAAIAAJ |title=Molecular Rotation Spectra |date=1975 |publisher=Wiley |isbn=9780471508533 |oclc=793428}}</ref><ref>Philip R. Bunker and Per Jensen (1998),''Molecular Symmetry and Spectroscopy'', 2nd ed.  NRC Research Press, Ottawa [https://volumesdirect.com/products/molecular-symmetry-and-spectroscopy?_pos=1&_sid=ed0cc0319&_ss=r] {{ISBN|9780660196282}}</ref><ref>{{Cite book |last1=Papoušek |first1=Dušan |last2=Aliev |first2=Mamed Ragimovich |url=https://books.google.com/books?id=fb7vAAAAMAAJ |title=Molecular Vibrational-rotational Spectra: Theory and Applications of High Resolution Infrared, Microwave, and Raman Spectroscopy of Polyatomic Molecules |date=1982 |publisher=Elsevier Scientific Publishing Company |isbn=9780444997371 |location=Amsterdam |oclc=7278301}}</ref><ref>{{Cite book |last1=Wilson |first1=Edgar B. |url=https://books.google.com/books?id=CPkvsDrPiv0C |title=Molecular Vibrations: The Theory of Infrared and Raman Vibrational Spectra |last2=Decius |first2=John C. |last3=Cross |first3=Paul C. |date=1980-03-01 |publisher=Courier Corporation |isbn=9780486639413 |oclc=1023249001}}</ref>

Studies in molecular spectroscopy led to the development of the first [[maser]] and contributed to the subsequent development of the [[laser]].