Electromagnetic spectroscopy



Electromagnetic spectroscopy, also known as spectrophotometry is the electromagnetic radiation.

Electromagnetic spectroscopy involves the use of a spectrophotometer.

Types of electromagnetic radiation measured

This can be in any range of wavelengths:

Electromagnetic spectroscopy can be classified into narrower fields as discussed below, though in some spectroscopic techniques, several processes may be happening at the same time.

Types of electromagnetic spectroscopy

Emission spectroscopy

 

spontaneous emission.

Examples:

Absorption spectroscopy

molar absorptivity).

Examples of absorption spectroscopy:

  • Vibrational spectroscopy - absorption of infrared radiation, see infrared spectroscopy; often used as an analytical tool
  • Atomic absorption - often used as an analytical tool
  • ultraviolet and visible light; often used as an analytical tool
  • Mossbauer spectroscopy - Measures the absorption of gamma rays by atoms bound in a solid as a function of gamma-ray energy. This is not an analytical technique; it is a means to understand certain microscopic processes in matter.

Other techniques

Electromagnetic radiation can interact with matter in ways other than simple absorption and emission, such as in the following techniques:

  • Circular dichroism spectroscopy - measures effects of a sample on the polarization of light.
  • Magnetic circular dichroism
  • Absorption peaks correspond to transitions in the nuclear spin states of the sample molecule(s).
  • Electron spin resonance - similar to NMR, but looking at electrons.
  • Raman spectroscopy - A molecule can absorb a part of the energy of a photon, which results in a change in frequency (or wavelength) of the photon. The amount of absorbed energy corresponds to an infrared transition in the molecule, even though the photon might have a visible-light wavelength.
  • Stark spectroscopy - measures effects of electrical fields on the spectra.

Examples

The spectrum of sunlight

Matter reflects, absorbs or scatters regions of the electromagnetic radiation shown upon it. Depending on the Correlated Color Temperature of the light source, you will perceive the object to be of a differing color. Man has attempted to utilize Plank's Law to assign a specific Correlated Color temperature to each light source sold in your store. Each bulb measured, was assigned a Correlated Color Temperature CCT in black body radiator.

The higher the temperature, the shorter (and bluer) the average visible wavelength. The sun, which has a temperature around 6000 K, emits most strongly in the visible light. However, certain wavelengths are missing from the solar spectrum, which is the result of sun that have resonant transitions at those wavelengths. From the exact wavelengths of these missing parts of the spectrum, or absorption lines, we can deduce which elements are present in the sun. The fact that these elements have absorbed the radiation indicates that the chromosphere is cooler than the photosphere.

However absorption spectra can not give us information about the abundance of the various elements. This is because emission spectrum of elements in the chromosphere. It is only possible to assess this when the photosphoric radiation is totally obscured during an eclipse. At this time the emission spectrum of the chromosphere is highly dominated by hydrogen, which is the main constituent of the sun.

Absorption in the atmosphere

The material in Earth's atmosphere absorbs some of the sunlight passing through it. This has been measured at sea level and various altitudes. Estimates were made of the likely spectrum of sunlight above the atmosphere and the absorption within the atmosphere. Actual measurements above the atmosphere required spacecraft which were able to take such readings. These efforts are illustrated in the following images.

See also
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Electromagnetic_spectroscopy". A list of authors is available in Wikipedia.