Editing Spectroscopy (section)

=== Type of material ===
Spectroscopic studies are designed so that the [[radiant energy]] interacts with specific types of matter.

==== Atoms ====
[[File:Welsbach_Figure_IV_spektroskopische-lytischen-chemie-21.pdf|thumb|Atomic spectra comparison table, from "Spektroskopische Methoden der analytischen Chemie" (1922).]]
[[Atomic spectroscopy]] was the first application of spectroscopy. [[Atomic absorption spectroscopy]] and [[atomic emission spectroscopy]] involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to [[Atomic structure#Energy levels|electronic transitions]] of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states.

Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantitation of a sample's elemental composition. After inventing the spectroscope, [[Robert Bunsen]] and [[Gustav Kirchhoff]] discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to as [[Fraunhofer lines]] after their discoverer. A comprehensive explanation of the [[Hydrogen spectral series|hydrogen spectrum]] was an early success of quantum mechanics and explained the [[Lamb shift]] observed in the hydrogen spectrum, which further led to the development of [[quantum electrodynamics]].

Modern implementations of atomic spectroscopy for studying visible and ultraviolet transitions include [[flame emission spectroscopy]], [[inductively coupled plasma atomic emission spectroscopy]], [[Glow discharge#Use in analytical chemistry|glow discharge spectroscopy]], [[microwave induced plasma]] spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include [[X-ray spectroscopy]] and [[X-ray fluorescence]].

==== 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]].

==== Crystals and extended materials ====
The combination of atoms or molecules into crystals or other extended forms leads to the creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, i.e., broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well.
Pure crystals, though, can have distinct spectral transitions, and the crystal arrangement also has an effect on the observed molecular spectra. The regular [[lattice structure]] of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies.

==== Nuclei ====
Nuclei also have distinct energy states that are widely separated and lead to [[gamma ray]] spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for [[nuclear magnetic resonance spectroscopy]].