Ultraviolet region of spectrum

The word laser is an acronym derived from light amplification by the stimulated emission of radiation . If the light concerned is in the microwave region then the alternative acronym maser is often used. Although the first such device to be constructed was the ammonia maser in 1954 it is the lasers made subsequently which operate in the infrared, visible or ultraviolet regions of the spectrum which have made a greater impact. 

A distinction is normally made between the visible and ultraviolet regions of the spectrum when detecting absorbing substances. Detection in the visible part of the spectrum can be carried out with the eye or with a photomultiplier. 

A particularly important property of ozone is its strong absorption in the ultraviolet region of the spectrum between 220-290 nm ( max255.3nm) this protects the surface of the earth and its inhabitants from the intense ultraviolet radiation of the sun. Indeed, it is this absorption of energy, and the consequent rise in temperature, which is the main cause for the existence of the stratosphere in the first place. 

Excimer lasers use gases, but because of their special properties are usually considered as a class of their own. Excimer is short for excited dimer, which consists of two elements, such as argon and fluorine, that can be chemically combined in an excited state only. These lasers typically emit radiation with veiy small wavelengths, in the ultraviolet region of the electromagnetic spectrum. This shorter wavelength is an enormous advantage for many applications. 

Absorption spectrum (Section 12.5) A plot of wavelength of incident light versus amount of light absorbed. Organic molecules show absorption spectra in both the infrared and the ultraviolet regions of the electromagnetic spectrum. 

In spectrophotometric analysis a source of radiation is used that extends into the ultraviolet region of the spectrum. From this, definite wavelengths of radiation are chosen possessing a bandwidth of less than 1 nm. This process necessitates the use of a more complicated and consequently more expensive instrument. The instrument employed for this purpose is a spectrophotometer. 

Spectrophotometry proper is mainly concerned with the following regions of the spectrum ultraviolet, 185-400 nm visible 400-760 nm and infrared, 0.76-15 /tm. Colorimetry is concerned with the visible region of the spectrum. In this chapter attention will be confined largely to the visible and near ultraviolet region of the spectrum. 

Visual methods have been virtually displaced for most determinations by methods depending upon the use of photoelectric cells (filter photometers or absorptiometers, and spectrophotometers), thus leading to reduction of the experimental errors of colorimetric determinations. The so-called photoelectric colorimeter is a comparatively inexpensive instrument, and should be available in every laboratory. The use of spectrophotometers has enabled determinations to be extended into the ultraviolet region of the spectrum, whilst the use of chart recorders means that the analyst is not limited to working at a single fixed wavelength. 

The various porphyrinogens are colorless, whereas the various porphyrins are all colored. In the smdy of porphyrins or porphyrin derivatives, the characteristic absorption spectrum that each exhibits—in both the visible and the ultraviolet regions of the spectrum—is of great value. An example is the absorption curve for a solution of porphyrin in 5% hydrochloric acid (Figure 32-10). Note particularly the sharp absorption band near 400 nm. This is a distinguishing feamre of the porphin ring and is characteristic of all porphyrins regardless of the... 

All dyes absorb light. Fluorescent dyes re-emit the absorbed energy as light of longer wavelengths. An FBA is a fluorescent chemical that absorbs in the ultraviolet region of the spectrum and emits blue-violet light. A typical FBA shows maximum absorption at a... 

FIGURE 5.15 Molecular orbitals for ethylene. Promotion of an electron from the ground state to the excited state is known as a n - n transition and is usually accompanied by an absorption of radiation in the ultraviolet region of the spectrum. 

Emission of electromagnetic radiation in the visible and ultraviolet regions of the spectrum by atoms and ions after electronic excitation in a high temperature gas plasma. Laser excitation sometimes used. 

In the ultraviolet region of the spectrum quartz optical materials are required. There are some plastic materials that may also be used in the... 

Which atomic spectroscopic technique will benefit from the availability of a tunable laser that provides radiation in the visible and ultraviolet region of the electromagnetic spectrum ... 

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