High-pressure xenon arcs

From about 1970, but before the availability of suitable lasers, Parmenter and others obtained SVLF spectra, particularly of benzene, using radiation from an intense high-pressure xenon arc source (see Section 3.4.4) and passing it through a monochromator to select a narrow band ca 20 cm wide) of radiation to excite the sample within a particular absorption band. 

In flash photolysis, however, the absorption spectrum of CFj has been observed and Simons and Yarwood noted the presence of tetrafluoroethylene among the products of continuous photolysis of trifluoracetic acid with a high pressure xenon arc lamp, indicating the probable production of CFj radicals under these conditions. 

K15. Kldn, L., Measurements of spectral emission and absorption of a high pressure xenon arc in the stationary and the flashed modes. Appl. Opt. 7, 677-685 (1968),... 

Hydrogen and deuterium arcs, and high pressure xenon arcs are convenient, near-continuous, light sources for absorption studies. Kaufman and Del Greco have, however, used a rather special light source in experiments on hydroxyl radicals prep u ed in a low pressure flow system by the reaction... 

Figure 1. Energy distribution, as a function of wavelength, of a high pressure xenon arc lamp and noon summer sunlight (4)...

All results listed except where specifically noted were obtained with an apparatus composed of a 450-watt Osram high pressure xenon arc... 

Atomic fluorescence flame spectrometry is receiving increased attention as a potential tool for the trace analysis of inorganic ions. Studies to date have indicated that limits of detection comparable or superior to those currently obtainable with atomic absorption or flame emission methods are frequently possible for elements whose emission lines are in the ultraviolet. The use of a continuum source, such as the high-pressure xenon arc, has been successful, although the limits of detection obtainable are not usually as low as those obtained with intense line sources. However, the xenon source can be used for the analysis of several elements either individually or by scanning a portion of the spectruin. Only chemical interferences are of concern they appear to be qualitatively similar for both atomic absorption and atomic fluorescence. With the current development of better sources and investigations into devices other than flames for sample introduction, further improvements in atomic fluorescence spectroscopy are to be expected. 

Figure 9.7. Schematic diagram of an uncorrected spectrofluorometer. A high-pressure xenon arc is the usual source. The gratings can be adjusted manually, or driven by a motor for recording. The usual detector is the 1P21 photomultiplier tube. The response of the tube is displayed on a meter and is sometimes recorded. From G. H. Schenk, Absorption of Light and Ultraviolet Radiation, Boston Allyn and Bacon, 1973, p 278, by permission of the publisher.

It is also important that the light source in a multidimensional instrument be able to provide relatively continuous output over a range of wavelengths, since multiple excitation wavelengths are needed in the multidimensional measurement. In order to use multiple excitation wavelengths, a white light source, such as a high-pressure xenon arc lamp. 

If the incident radiation comes from a tungsten lamp or high-pressure xenon arc, 1( (0) will be essentially constant in the region of an absorption line. The transmitted intensity will then have a dip centred on and the spectral line is observed in absorption, as shown in Fig.10.3. The equivalent width, W, of the absorption line is defined as the width of a rectangular strip of height 1 (0) which has the same area as that of the absorption line. This equality is represented by the two shaded areas in Fig.10.3 and leads to the expression ... 

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