Vacuum-UV sources

Continuous wave (CW) lasers such as Ar and He-Ne are employed in conmionplace Raman spectrometers. However laser sources for Raman spectroscopy now extend from the edge of the vacuum UV to the near infrared. Lasers serve as an energetic source which at the same hme can be highly monochromatic, thus effectively supplying the single excitation frequency, v. The beams have a small diameter which may be... 

CHARACTERISTIC LINES FOUND IN THE VACUUM UV OUTPUT OF HNU SOURCES... 

Excimer lasers are of great importance for UV and vacuum UV (VUV) spectroscopy and photochemistry. They are also found in a wide range of applications. For example, they are used in micromachine medical devices, including refractive surgery, in photo-lithography for the microelectronics industry, for material processing, as optical pump sources for other type of lasers (dyes), and so on. More details about excimer lasers can be found in Rodhes (1979). 

Monomer I (MAA) was dissolved in methanol and I moI% of crosslinking agent, tetraethyleneglycol dimethylacrylate (TEGDMA) (Polysciences, Inc., Warrington, PA), and I wt% of initiator, 2,2-dimethoxy-2-phenyI acetophenone (DMPA Aldrich, Milwaukee, WI) were added. The solution was cast on glass plates equipped with spacers and reacted under an UV source with an intensity of 1 mW/cm for 30 min. Polymer I (PMAA) was removed from the plates, washed in deionized water to remove all unreacted monomers, cut into discs, and dried in a vacuum oven. 

Isolation and Assays of Enzymes or Substances Resulting in Formation or Removal of Oxygen Radicals Biological sources of Of, 105, 59 overview of superoxygenase, 105, 61 methods for the study of superoxide chemistry in nonaqueous solutions, 105, 71 generation of superoxide radicals in aqueous and ethanolic solutions by vacuum-UV photolysis, 105, 81. 

For industrial applications of excimer UV sources, the dielectric barrier and the microwave discharge are simple, reliable, and efficient excitation modes. There are a large number of vacuum UV (VUV), UV, and visible light transitions available. This allows a selective photoexcitation for many systems. Some sources of monochromatic UV light for industrial applications and their characteristics are in Table 2.1. 

Reaction (20) has been observed experimentally18,61 by detection of the atmospheric band emission of 02(1E +) in the vacuum UV photolysis products of molecular oxygen, and this system provides a useful source of 02(129+) for kinetic studies.61... 

For some elements such as arsenic and selenium, which have their main atomic absorption wavelengths lying on the edge of the vacuum UV, the performance of hollow cathode lamps is often poor, the lamps displaying low intensity and poor stability. This, plus the search for more intense sources for AFS (see Chapter 1, section 10), resulted in the development of microwave-powered electrodeless discharge lamps (EDLs) as spectral line sources towards the end of the 1960s.3-5... 

Photoemission spectroscopy involves measurement of the energy distribution of electrons emitted from a solid under irradiation with mono-energetic photons. In-house experiments are usually performed with He gas discharge lamps which generate vacuum UV photons at 21.2 eV (He la radiation) or 40.8 eV (He Ila radiation ) or with Mg Ka (hv=1284.6 eV) or A1 Ka (hv=1486.6eV) soft X-ray sources. UV photoemission is restricted to the study of valence and conduction band states, but XPS allows in addition the study of core levels. Alternatively photoemission experiments may be performed at national synchrotron radiation facilities. With suitable choice of monochromators it is possible to cover the complete photon energy range from about 5 eV upward to in excess of 1000 eV. The surface sensitivity of photoemission derives from the relatively short inelastic mean free path of electrons in solids, which reaches a minimum of about 5A for electron energies of the order 50-100 eV. 

The wavelength range is divided into several sections which are shown in Table 4. As far as this discussion of sources is concerned, the range is divided into two the vacuum uv region is treated separately. 

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