Mercury arc source

Not aU chloroaromatic drugs appear to follow this type of reaction. For example, free chloride ion is not formed on irradiation of chlordiazepoxide for which an oxaziridine is the major photoproduct (33). There is variability among reports on other drugs with chlorine substituents. This can arise due to differences in the irradiation conditions. If an unfiltered xenon or mercury arc source is used, the sample will receive 250 to 300 nm irradiation and the C-Cl bond will certainly break, while under longer wavelength irradiation (300nm) the bond may be stable. 

One of the first uses of a 2-nitrobenzyl-based photocleavable protecting group was simply an 2-nitrobenzyl ester, reported in 1966 by Barltrop et al.f l 2-Nitrobenzyl benzoate was irradiated with ultraviolet light from a medium pressure mercury arc source, but the yield of benzoic acid was only 17%. The low yield was largely a result of the further reaction of the byproduct nitroso compound, which is converted into the light-filtering azo compound 1 (Scheme 2). 

Measurements made with mercury arc source and photomultiplier and filter ozone meter through 1450-foot distance (49)... 

A xenon-arc lamp is used as the source in most spectrofluorometers, since it emits continuously over the range 200-700 nm (see Fig. 9.4C) and hence can be used to obtain fluorescence excitation spectra as well as emission spectra. (Emission spectra for many substances could be obtained with a mercury-arc source, but excitation spectra could not, because the emission is discontinuous and the frequency range is so limited.) However, in uncorrected instruments using a xenon-arc lamp, no correction is made for the variation in intensity of the source with changing wavelength. 

Light sources can either be broadband, such as a Globar, a Nemst glower, an incandescent wire or mercury arc lamp or they can be tunable, such as a laser or optical parametric oscillator (OPO). In the fomier case, a monocln-omator is needed to achieve spectral resolution. In the case of a tunable light source, the spectral resolution is detemiined by the linewidth of the source itself In either case, the spectral coverage of the light source imposes limits on the vibrational frequencies that can be measured. Of course, limitations on the dispersing element and detector also affect the overall spectral response of the spectrometer. 

The use of vibrational Raman spectroscopy in qualitative analysis has increased greatly since the introduction of lasers, which have replaced mercury arcs as monochromatic sources. Although a laser Raman spectrometer is more expensive than a typical infrared spectrometer used for qualitative analysis, it does have the advantage that low- and high-wavenumber vibrations can be observed with equal ease whereas in the infrared a different, far-infrared, spectrometer may be required for observations below about 400 cm. ... 

Laser radiation is very much more intense, and the line width much smaller, than that from, for example, a mercury arc, which was commonly used as a Raman source before 1960. As a result, weaker Raman scattering can now be observed and higher resolution is obtainable. 

Chlorine free radicals used for the substitutioa reactioa are obtaiaed by either thermal, photochemical, or chemical means. The thermal method requites temperatures of at least 250°C to iaitiate decomposition of the diatomic chlorine molecules iato chlorine radicals. The large reaction exotherm demands close temperature control by cooling or dilution, although adiabatic reactors with an appropriate diluent are commonly used ia iadustrial processes. Thermal chlorination is iaexpeasive and less sensitive to inhibition than the photochemical process. Mercury arc lamps are the usual source of ultraviolet light for photochemical processes furnishing wavelengths from 300—500 nm. 

Radiation of a particular wavelength (monochromatic) is required to initiate a specific electronic transition, but most UV and visible light sources are polychromatic. For example, common mercury arc lamps emit around 50% of their energy in the 405 nm to 578 nm range. Hence, for most processes, well over half of the electrical energy... 

When the white light from a tungsten lamp was used for excitation, the fluorescence had the same intensity in the two tubes within the experimental error. But when a mercury arc burning at low pressure was used as source of excitation the fluorescence in the comparison tube was considerably stronger. The difference was not great, but quite definite. 

Modem light-scattering instmments use either a mercury arc or a laser as a source and detect the scattered light photoelectrically. 

Figure 5. Dependence of rate of dissolution of 5pM Y-FeOOH in pH 4.0, 0.01M NaCl on concentration of a) tartaric acid, and b) salicylic acid. Fitted parameters obtained for rectangular hyperbolic model are given. Light source mercury arc lamp with 365nm band-pass filtering.

Figure 7. Dissolution of 5ijM 6-Mn02 in pH 7.1, 0.01M NaCl/2mM NaHC03 solutions containing 10 mg/L Suwanee River fulvic acid under dark and light conditions in the presence and absence of oxygen. Light sources mercury arc lamp with 365nm band-pass filtering. (Reproduced from Ref. 45.).

Surface fluorescence of NADH/NADPH can be recorded continuously with a DC fluorimeter and correlated with changes in experimental conditions. A mercury arc lamp (with a 340-375 nm filter in front) is used as a hght source for fluorescence excitation. The fluorescence response of reduced NADH/NADPH was measured at 450-510 nm. The DC fluorimeter and the Hg arc lamp are connected to the kidney by a trifurcated fiber optics light guide. NADH/NADPH fluorescence emission can be corrected for changes in tissue opacity by a 1 1 subtraction of reflectance changes at 340-375 nm from the fluorescence. To determine NADH/NADPH redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The study demonstrated that the surface fluorescence method is simple and provides specific information about the mitochondrial oxidation-reduction state. 

Excimer and nitrogen lasers are sources of pulsed monochromatic UV radiation with a variety of interesting wavelengths and high output peak powers. However, they cannot compete with mercury arc lamps in large areas or fast-cure applications because of their low pulse repetition rates.9... 

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