Mercury/xenon lamps, spectrum

Figure 2. Fluorescence spectrum in a nitrogen matrix at 15 K (excited by a 2.5-kW mercury-xenon lamp) of an adsorption chromatography fraction from a coking plant water sample. Compounds BbF, benzo[b]fluorene C, chrysene BeP, ben-zo[e]pyrene P, pyrene BkF, benzo[k]fluoranthene BaP, benzo[a]pyrene U, unknown ( ).

The most intense sources of UV radiation are the high-pressure ( 100 bar) mercury arcs. The spectral lines are broadened due to the high pressure and temperature and they are superimposed on a continuous background of radiation (Figure 3.4). While common mercury xenon [Hg(Xe)] lamps still produce significant mercury emission bands, especially in the UV region, the smoother xenon lamp spectrum finds application in environmental photochemistry experiments because of its resemblance to solar radiation (Figure 1.1). 

The effect of irradiating the poly(carbon suboxide) film with the full spectrum of a 200 watt mercury-xenon lamp on the ESR spectrum is illustrated in Figure 6. There is a significant and rapid increase in the signal to a steady-state level intensity but no change in spectrum shape or line width. A scan of 500 to 5500 gauss showed no half field transition or absorptions at any other magnetic field. 

The optical train employed for photometric determinations of fluorescence depends on the problem involved. A spectral resolution of the emitted fluorescence is not necessary for quantitative determinations. The optical train sketched in Figure 22B can, therefore, be employed. If the fluorescence spectrum is to be determined the fluorescent light has to be analyzed into its component parts before reaching the detector (Fig. 28). A mercury or xenon lamp is used for excitation in such cases. 

The light source is commonly a tungsten filament lamp (covering the visible region of the spectrum, typically 340-8(X) nm) or a deuterium discharge lamp for the UV region (200-350 nm). For some applications, more intense sources such as a xenon or xenon/mercury arc lamp, or even lasers, may be required. 

Using matrix isolation techniques, we obtained the first spectroscopic evidence for the intermediacy of the hitherto unknown silacarbonyl and silathiocarbonyl yUdes in a low temperature matrix. Irradiation of the oxasUirane (75a) in an isopentane/3-methylpentane (Ip/3-Mp) matrix at 77 K with a low-pressure mercury lamp led to the appearance of a new band at 610 nm in the UV-vis spectrum and the matrix became interestingly blue in color. This absorption band was stable at 77 K on prolonged standing. However, it immediately disappeared on brief irradiation with a Xenon lamp (X >460 nm) or when the matrix was allowed to melt. This colored species was independently generated by the reaction of dimesitylsilylene with l,l,3,3-tetramethyl-2-indanone (76a). Furthermore, irradiation of 2,2-dimesitylhexamethyltrisUane in the presence of 76a in IP/3-MP at 77 K... 

Several lamps, especially xenon and mercury-xenon, have been used in laboratory studies to simulate the solar near UV spectrum. As Fig.7 suggests, these lamps may have a substantial 290-310 nm contribution vs. sea level solar, and the use of such lamps to... 

Figure 7 (A) Spectrum of a 1000 W tungsten-halogen lamp. Reproduced with permission from Oriel Corporation (1994) Oriel 1 4 Catalog, Volume II. (B) Spectrum of a 200 W mercury arc lamp. Reproduced with permission from Oriel Corporation (1994) Oriel 1994 Catalog, Volume II. (C) Spectrum of a 150 W xenon arc lamp. Reproduced with permission from Oriel Corporation (1994) Oriel 1994 Catalog, Volume II.

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