- Emission spectroscopy
Emission spectroscopy is a spectroscopic technique which examines the wavelengths of
photons emitted by atoms or molecules during their transition from an excited stateto a lower energy state. Each element emits a characteristic set of discrete wavelengths according to its electronic structure, by observing these wavelengths the elemental composition of the sample can be determined. Emission spectroscopy developed in the late 19th century and efforts in theoretical explanation of atomic emission spectra eventually lead to quantum mechanics.
There are many ways in which atoms can be brought to an excited state. Interaction with electromagnetic radiation is used in
fluorescence spectroscopy, protons or other heavier particles in Particle-Induced X-ray Emissionand electrons or X-ray photons in Energy-dispersive X-ray spectroscopyor X-ray fluorescence. The simplest method is to heat the sample to a high temperature, after which the excitations are produced by collisions between the sample atoms. This method is used in flame emission spectroscopy, and it was also the method used by Anders Jonas Ångströmwhen he discovered the phenomenon of discrete emission lines in 1850s.Fact|date=April 2007
Although the emission lines are caused by a transition between quantized energy states and may at first look very sharp, they do have a finite width, i.e. they are composed of more than one wavelength of light. This
spectral line broadeninghas many different causes.
Emission spectroscopy is often referred to as optical emission spectroscopy, due to the light nature of what is being emitted.
Emission lines from hot gases were first discoveredFact|date=April 2007 by Ångström, and the technique was further developed by
David Alter, Gustav Kirchhoffand Robert Bunsen.
spectrum analysisfor details.
Experimental technique in flame emission spectroscopy
The solution containing the relevant substance to be analysed is drawn into the burner and dispersed into the flame as a fine spray. The solvent evaporates first, leaving finely divided
solidparticles which move to hottest region of the flame where gaseous atomsand ionsare produced. Here electronsare excited as described above. It is common for a monochromatorto be used to allow for easy detection.
On a simple level, flame emission spectroscopy can be observed using just a
Bunsen burnerand samples of metals. For example, sodiummetal placed in the flame will glow yellow, whilst calciummetal particles will glow red, copperplaced into the flame will create a green flame.
Emission (electromagnetic radiation)
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