Editing Spectroscopy (section)

== History ==
{{Main|History of spectroscopy}}

The history of spectroscopy began with [[Isaac Newton]]'s optics experiments (1666–1672). According to [[Andrew Fraknoi]] and [[David Morrison (astrophysicist)|David Morrison]], "In 1672, in the first paper that he submitted to the [[Royal Society]], Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbow."<ref name="open-astro">{{cite web|author1=Andrew Fraknoi|author1-link=Andrew Fraknoi|author2=David Morrison|author2-link=David Morrison (astrophysicist)|date=October 13, 2016|title=OpenStax Astronomy|url=http://cnx.org/content/col11992/latest/}}</ref> Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism.

Fraknoi and Morrison state that "In 1802, [[William Hyde Wollaston]] built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the spectrum."<ref name="open-astro" /> During the early 1800s, [[Joseph von Fraunhofer]] made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics, and astronomy. Per Fraknoi and Morrison, "Later, in 1815, German physicist Joseph Fraunhofer also examined the solar spectrum, and found about 600 such dark lines (missing colors), are now known as Fraunhofer lines, or Absorption lines."<ref name="open-astro" />{{Better source needed|date=November 2020}}

In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical [[stationary state]]s of one system, such as an [[atom]], via an oscillatory source of energy such as a [[photon]]. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy {{mvar|E}} of a photon is related to its frequency {{mvar|ν}} by {{math|''E'' {{=}} ''hν''}} where {{mvar|h}} is the [[Planck constant]], and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as [[electron]]s and [[neutron]]s have a comparable relationship, the [[de Broglie relations]], between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.

Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The [[hydrogen spectral series]] in particular was first successfully explained by the [[Bohr model|Rutherford–Bohr quantum model]] of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the [[density of states|density of energy states]] is high enough. Named series of lines include the [[principal series (spectroscopy)|principal]], [[sharp series|sharp]], [[diffuse series|diffuse]] and [[fundamental series]].