Ultraviolet Spectroscopy

a branch of spectroscopy dealing with the generation, investigation, and application of emission, absorption, and reflection spectra in the ultraviolet region of the spectrum from 400 nanometers to 10 nanometers (nm). Spectra in the region of 200 to 10 nm are studied by vacuum spectroscopy. Work in the 400-200 nm region of the spectrum requires apparatus built to conform to the same optical principles as those in the visible spectral range. The only difference is the use of quartz instead of glass in lenses, prisms, and other optical details. In measuring the intensity of ultraviolet radiation, scientists use as the standard source those that have a known distribution of spectral luminosity, such as tungsten-filament lamps, carbon arc lamps, or synchrotron radiation. Standard receivers for the ultraviolet region are thermocouples and calibrated photometric components.

Ultraviolet spectroscopy is used in investigations of atoms, ions, molecules, and solid bodies to determine their energy levels, the probabilities of transitions to a different state, and other characteristics. The ultraviolet region includes the resonance lines of the neutral and singly or doubly ionized atoms, as well as the spectral lines emitted by the excited configurations of highly ionized atoms. The electronic-vibrational-rotational bands of molecules also generally tend to be located in the near-ultraviolet region of the spectrum. Also located in this region are the absorption bands of most semiconductors, which arise whenever there is a direct transition from the valence zone to the conduction zone. Many chemical compounds yield a strong absorption band in the ultraviolet region, one of the advantages of using ultraviolet spectroscopy in spectral analysis. Ultraviolet spectroscopy is of major importance in space astrophysics and in the study of the sun, stars, nebulas, and other celestial objects.