Lamp, 121 pressure

A recent example of laser flash-lamp photolysis is given by Hippier etal [ ], who investigated the temperature and pressure dependence of the thennal recombmation rate constant for the reaction... 

The experiments were perfonued in a static reaction cell in a large excess of N2 (2-200 bar). An UV laser pulse (193 mu, 20 ns) started the reaction by the photodissociation of N2O to fonu O atoms in the presence of NO. The reaction was monitored via the NO2 absorption at 405 mu using a Hg-Xe high-pressure arc lamp, together with direct time-dependent detection. With a 20-200-fold excess of NO, the fonuation of NO2 followed a pseudo-first-order rate law ... 

With short periods of irradiation (with high-pressure mercury lamps) under oxygen in chloroform containing methylene blue as a sensitizer, variously substituted 2-arylthiazoles are converted in the corresponding 2-aryloxazoles (823). 

Isothiazole itself (283), Rx = Rj = Rj - H, is converted to thiazole in 7% yield, in propylamine as solvent using a low-pressure mercury lamp (642). 

On the other hand, 2-arylthiazoles are easily isomerized to 3-aryliso-thiazoles in 407o yield upon irradiation with a high-pressure mercury lamp, in benzene solution in the presence of iodine (738). A valence bond isomerization was proposed among several alternatives to account for these results. 

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

In practice, o2one concentrations obtained by commercial uv devices ate low. This is because the low intensity, low pressure mercury lamps employed produce not only the 185-nm radiation responsible for o2one formation, but also the 254-nm radiation that destroys o2one, resulting in a quantum yield of - 0.5 compared to the theoretical yield of 2.0. Furthermore, the low efficiency (- 1%) of these lamps results in a low o2one production rate of 2 g/kWh (100). 

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to >1 MPa (<1 to >10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

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