Light sources ultraviolet

Lasers (qv) and other high intensity or alternative light sources are usefiil in crime laboratories to visualize latent fingerprints, seminal fluid stains, obhterated writings, and erasures, and to aid in specialized photographic work. Infrared and ultraviolet light sources are also used to view items of evidence. 

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). 

Nitro-substituted indolino spiroben2opyrans or indolino spironaphthopyrans are photochromic when dissolved in organic solvents or polymer matrices (27). Absorption of uv radiation results in the colorless spiro compound [1498-88-0], C22H2gN202, being transformed into the colored, ring-opened species. This colored species is often called a photomerocyanine because of its stmctural similarity to the merocyanine dyes (see Cyanine dyes). Removal of the ultraviolet light source results in thermal reversion to the spiro compound. 

Besides the use of photochromic systems in light filters, their color development has also received considerable attention. For example, the introduction of photochromic components into product labels, tickets, credit cards, etc adds a mechanism for verification of authenticity (41,42). The active components are invisible until activated with an ultraviolet light source, after which they are easily detected. 

The chlorination of methyl chloroformate in sunlight was first reported by Hentschel, but without a detailed description of either the procedure or the results. The first step of the present procedure for the preparation of trichloromethyl chloroformate utilizes an ultraviolet light source and affords a simple and reproducible way to obtain this reagent. Although trichloromethyl chloroformate may also be synthesized by photochemical chlorination of methyl formate,the volatility of methyl formate causes losses during the reaction and increases the hazard of forming an explosive mixture of its vapor and chlorine gas. The preparation of trichloromethyl chloroformate by chlorination of methyl chloroformate in the dark with diacetyl peroxide as initiator has been reported. However, the procedure consists of several steps, and the overall yield is rather low. 

The nitrogen laser (X = 3200 A)supplies a high-power nanosecond ultraviolet light source which allows in many cases direct initiation of photochemical reactions. Sousa 169) excited a 10 ... 

Accelerated weathering tests are performed in special test chambers all of which are similar in that a coated specimen is exposed in a controlled environment containing a high intensity ultraviolet light source and a facility for spraying water onto the test surfaces. 

Photolysis is carried out in an 850-ml. Pyrex glass vessel equipped with a water-cooled quartz probe. The ultraviolet light source is a 450-watt lamp with a Vycor filterf. To reduce the dangers from a possible explosion or eye damage from ultraviolet radiation, the reaction vessel shown in Fig. 5 is contained in a wooden box. 

While there appears to be some discrepancy in the conclusions derived from these studies, the difference can be explained as being caused by the exposure conditions. To illustrate the effect of irradiation wavelength on the photooxidation, unstabilized polystyrene films were exposed to the following three ultraviolet light sources having different emission characteristics (Figure 16) ... 

Detection with an ultraviolet light source suitable for observations with short (254-nm) and long (360-nm) ultraviolet wavelengths may be called for in some cases. 

Care and precautions Precautions and strict management are necessary in the handling of perchloroethylene. It should not be used around an open flame, welding arc, intense ultraviolet light source, or smoke. Like most solvents containing chlorine, perchloroethylene also breaks down and releases very hazardous compounds such as phosgene, hydrochloric acid, and chlorine. 

However, it should be imderstood that many recently developed contact lens materials contain polymers that block the transmission of light in the ultraviolet region. Therefore when an ultraviolet light source, such as a... 

Ignoffo, C.M., Hostetter, D.L., Sikorowski, P.P., Sutter, G., and Brooks, W.M., 1977. Inactivation of representative species of entomopathogenic viruses, a bacterium, fungus, and protozoan by an ultraviolet light source. Eviron. Entomol., 6 411—415. 

Caution. Carbon monoxide is a toxic gas and should be used in an efficient fume hood. Avoid looking directly at the ultraviolet light source. Protective goggles should be worn. Carbon tetrachloride is a carcinogen and must be handled with care in a hood. 

In recent years this approach has been extensively employed and there is substantial evidence for the production of e aq. When steady state ultraviolet light sources were used, hydrated electrons were detected by competitive scavenging techniques (9, 21, 22, 51, 63, 71). When flash photolysis techniques were employed, e q was identified by its absorption spectrum and its reactivity followed spectrophotometrically (28, 38, 60). 

Intensive conventional ultraviolet light sources as well as various types of lasers are used in photon-assisted CVD [214-220]. 

Experimentally, a sample of the compound is irradiated in the gas phase by an ultraviolet light source. The emitted electrons are sorted by means of electric fields according to their kinetic energy and counted. The photoelectron spectrum is then obtained by plotting this count rate (intensity of the photoelectric current) against the energy difference /iv-JS kin (e) of equation 3. This is depicted schematically in Figure 1. 

Many of the photochemical advances that have occurred during the past two decades have followed from the development of microwave discharge vacuum ultraviolet light sources, emitting either intense monochromatic atomic resonance radiation at fixed wavelengths (determined by nature rather than for utility) or over broad continua produced by the fluorescent decay of rare gas excimers which provide tunable sources after passage through a vacuum monochromator (but at the cost of reduced intensity). 

An ultraviolet light source can be used to detect a blood stain that has been cleaned up. It s also possible to use a chemical substance like luminol or phenolphthalein to detect the presence of hemoglobin, revealing its presence even after the visible stain has been washed away. 

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