The Mercury Lamp

The mercury lamp has been the conventional light source used in photochemistry. The ground-state mercury atom, Hg, has two electrons in its highest occupied orbital, the 6s atomic orbital. Excited mercury 

Light emitted from a mercury lamp is caused by electronic transitions from higher-energy-level atomic orbitals to lower-energy-level atomic orbitals. The electronic transitions are subject to certain constraints known as selection rules  

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Use caution when handling the mercury lamp. Mercury is toxic. 

Plug in the mercury lamp and allow it to warm up for 10 minutes before taking data. 

Place the 404.7-nm filter over the phototube entrance. Position the mercury lamp so that it illuminates the phototube through the filter. The ammeter should register a current. 

Diisopropyl methylphosphonate does not undergo direct or indirect photolysis in aquatic systems, as demonstrated by the stability of the compound in distilled water or in a natural water sample after 232 hours of reaction time with the mercury lamp filtered to exclude all wavelengths below 290 nm (Spanggord et al. 1979). 

Rhodamine conjugates are less sensitive to pH and are less prone to photohleaching than are those of fluorescein. Their fluorescence intensity is generally lower than that of fluorescein conjugates under comparable conditions of excitation, but the intense 546-nm excitatory light provided by the mercury lamp of a fluorescence microscope may make rhodamine appear brighter (7). 

For comparison the output power of a high-pressure mercury lamp (Osram HBO 200) also is listed. The reader has to consider, however, that the mercury lamp radiates this power into the unit solid angle (= 60°) distributed over the spectral range from 2000 to 6000.A, whereas the laser intensity is concentrated at a single wavelength and collimated in a beam with a very small divergence between 10 and 10" sterad. 

Light source. The most suitable light system examined was a Chromato-Vue Model C-3 from Ultra Violet Products, Inc., San Gabriel, CA. The light source was a GE G15T8, 15-W, Germicidal, 2537 bulb. The mercury lamp emitted radiation maxima at 254, 265, 280, 302, 313, 365, 405, and 436 nm. Radiation from this source passed... 

Figure 52. Fluorescent-decay curves of the 4/9/2 >4fi5/2 transition of CaF2i(0.1 Er3+). In (a) the ion is excited with 2550-A monochromatic radiation emitted by a 50-/xsec xenon flash lamp. The curve is resolvable into the difference of two exponentials with r = 400 50 and r2 = 200 50 / sec. In (b) the ion is excited with 2537-A radiation from an electronically chopped low-pressure mercury lamp. The steady state of fluorescence was established each time before the mercury lamp was switched off electronically. The afterglow in the lamp was of the order of 10 / sec [from Ref. (762)].

Figure 5 shows the effect of thermal damage on polyethylene when utilizing a 2 keV, 1 microamp electron beam for charge neutralization. "Carbonization" of the surface begins to take place within the first few seconds of analysis when the electron beam is used whereas with the mercury-lamp-photoelectron method, a stable spectrum is obtained for periods of several minutes. 

The lamps are less stable than the mercury lamps and it was difficult at first to keep them from consuming too much power and... 

A good introduction to this topic can be found in an article by Rindone (24) who points out that one should be careful in interpreting solarization data because of the different test sources used. In this particular instance he is referring to the use of the mercury lamp versus a solar simulator. 

Experimental Procedure. As source of ultraviolet light the Author used sparks between zinc electrodes, the hydrogen lamp (which gives a continuous spectrum), or mercury lamps of differing model and power, fed by alternating or by direct current all the mercury lamps emit an arc spectrum. The spectra from these sources were determined by a spectrograph with quartz optics or a diffraction spectrograph with a fluorite window. ... 

An explanation of the differences in cure rate between DPI and TPS is less obvious, as the absorption spectra of these two compounds are -similar. Depending on the method of preparation, however, the TPS photoinitiator frequently shows some absorbance in the spectral region between 290 and 340 nm, overlapping the band at 310 in the mercury lamp emission spectrum. This may be the result of a fortuitous contaminant not completely removed in synthesis and purification of the TPS photoinitiator. 

As shown in Fig. 88, the amount of photodegraded nifedipine was proportional to the number of incident photons.403 Maximum photodegradation of nifedipine in tablets occurred at 420 nm (Fig. 89).404 On the other hand, the relationship between the discoloration rate of sulfisomidine in tablets irradiated by a mercury lamp versus ultraviolet light intensity was complex.405 The values of L, a, and b determined for the discoloration of the tablet depended on the energy of the mercury lamp.406 Photodegradation of menatetrenon yielded linear plots of log k versus the reciprocal of the illumination intensity, as shown in Fig. 90.407... 

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