Lamps mercury resonance

Smith32 reported that the absorbance of frozen cytosine solutions (0.5 mg/ml) decreased only 3-5% when irradiated with light from a mercury resonance lamp, but that the rate of loss of cytosine doubled when the frozen solution contained both cytosine and uracil. In solutions containing cytosine and thymine, a mixed dimer was apparently formed. Dried films of cytosine were apparently stable to the resonance radiation under conditions where there was 9% conversion of uracil and 17% conversion of thymine. There is a report that uracil dimer was formed in low yield in the photolysis of frozen cytosine solutions.32,81... 

In low-pressure (fluorescent) lamps the phosphor is excited by energy-rich mercury resonance lines at 254 and 185 nm. For many years the most important phosphors were the halophosphates. In the search for more efficient phosphors with greater... 

Resonance Lamp.—Such lamps (sometimes called low pressure lamps) are often used as line sources in photochemical studies. These usually contain a small amount of a metal vapor (e.g., mercury, cadmium, zinc, etc.) and several mm pressure of a rare gas. They operate at relatively low current (ca. 100 ma.) and high voltages (several thousand volts). This is in contrast to a typical medium pressure lamp which may operate off a 110-220 v. power supply delivering ca. 3-5 amp. The most common example in photochemistry is the mercury resonance lamp which has strong emission of the unreversed resonance lines at 2537 A. and 1849 A. (ca. 90% or more of the total) along with other, much weaker lines ( resonance lines are those which appear both in absorption and emission). There is little continuum. Sources of this type are widely used for photosensitized reactions. 

Further information on this system is available from studies directed at photochemical isotope enrichment (16). In this work a mercury resonance lamp containing only Hg19S was used as a source. A flowing mixture of natural mercury and water vapor exposed to the Hg198 fine structure component of the mercury resonance radiation (2537 A.) was found to result in HgO considerably enriched in Hg198. It was concluded that this could only occur if Hg(3Pj) atoms reacted in a primary step to form either a compound which is removed from further contact with the reaction or which itself may react further but must not regenerate free Hg. Either reaction (55) or (56) would satisfy these conditions. If reaction (55) is the primary reaction, the further reaction... 

In some of the experimental work on this system a mercury resonance lamp made with isotope 202 has been used. Mercury with the usual isotopic distribution was mixed with the methyl chloride. Let X1 be the atomic fraction of isotope 202 in the HgCl formed and X1 be the atomic fraction of isotope 202 in ordinary mercury. Then... 

In spite of this very small range of absorption there is a preferential absorption by a single isotope when a mercury resonance line from a single isotope is used. The quantum yield of the isotopically specific step (50) with methyl chloride is 0.28 and of course part of the nonspecific step (49) will also be brought about by the isotope used to make the resonance lamp. 

The reaction vessel is a 550-ml. Pyrex cylindrical flask with a Hanovia internally sealed cold-cathode low-pressure mercury resonance coil lamp (2537 A.). The lamp is fitted to the reactor... 

Procedure Transfer 100 mL of Standard Solution to a 300-mL mercury analysis reaction vessel, add 2 drops of a 1 20 potassium permanganate solution, and mix (the solution should be purple add additional permanganate solution, drop-wise, if necessary). Add 5 mL of 11 A nitric acid, stir, and allow to stand for not less than 15 s. Add 5 mL of 18 A sulfuric acid, stir, and allow to stand for not less than 45 s. Add 5 mL of a 3 200 hydroxylamine hydrochloride solution, stir, and allow to stand until the solution turns light yellow or colorless. Add 5 mL of a 1 10 stannous chloride solution, immediately insert the aerator connected to an air pump, and determine the maximum absorbance of the treated Standard Solution at the mercury resonance line of 253.65 nm, with a suitable atomic absorption spectrophotometer equipped with a mercury hollow-cathode lamp and an absorption cell that permits the flameless detection of mercury. 

For example, many authors profess to use the 2537 A. line of mercury. In most lamps this line is reversed and the radiation comes from the wings broadened to an extent dependent on the pressure and temperature in the lamp. A mercury resonance lamp, on the other hand, gives a... 

Sheinker has studied the u.v. and i.r. spectra of azidoformates. The 285 nm band, seen in alkyl azides, was not found perhaps it disappears into the short wavelength band due to a blue shift. The u.v. spectrum of ethyl azidoformate extends to nearly 300 nm (see Table 2) but its photolysis is most conveniently carried out with the mercury resonance line near 254 nm, for which efficient lamps are available . Ethyl azidoformate shows i.r. absorption bands at 2185 and 2137 cm"i (Ng), 1759 and 1730 (C=0) and 1242 (0-0) cm i 235 -pjje y spectrum is given in Table 2. The i.r. and... 

It must be stressed that the co-adsorption of mercury (from the vacuum line) could lead to mercury photosensitization of the adsorbed gas and great care must be taken to distinguish sensitization by the surface or other substances on the surface with mercury sensitized decomposition. The use of low pressure mercury resonance lamps which produce the 253.7 nm mercury line... 

For toluene and o-xylene, where analyses are directly comparable, there are no significant products found in the vapor- which are not also produced in liquid-phase irradiation. Further, all of these products except ethylene, acetylene, and benzocyclobutene are also formed in vapor-phase photolyses (17) at 2537 A. even these exceptions have been detected in photolyses of o-xylene at shorter wavelengths. Benzocyclobutene was found (13) among the products of photolysis at 1600-2100 A. this product, as well as acetylene and ethylene, was observed (18) on irradiation with an unfiltered mercury resonance lamp. 

In contrast to the low-pressure lamps (1—130 Pa) which primarily emit at the resonance line at A = 254nm, high-pressure lamps (lO —10 Pa) also produce numerous bands in the UV and VIS regions (Fig. 16). Table 3 lists the emission lines and the relative spectral energies of the most important mercury lamps (see also [44]). The addition of cadmium to a mercury vapor lamp increases the numbei of emission lines particularly in the visible region of the spectrum [45] so that it i. also possible to work at A = 326, 468, 480, 509 and 644 nm [46]. 

Spectral interferences in AAS arise mainly from overlap between the frequencies of a selected resonance line with lines emitted by some other element this arises because in practice a chosen line has in fact a finite bandwidth . Since in fact the line width of an absorption line is about 0.005 nm, only a few cases of spectral overlap between the emitted lines of a hollow cathode lamp and the absorption lines of metal atoms in flames have been reported. Table 21.3 includes some typical examples of spectral interferences which have been observed.47-50 However, most of these data relate to relatively minor resonance lines and the only interferences which occur with preferred resonance lines are with copper where europium at a concentration of about 150mgL 1 would interfere, and mercury where concentrations of cobalt higher than 200 mg L 1 would cause interference. 

The standard astm test method (D-1149-64) for rubber damage includes a test chamber (volume, 0.11-0.14 m ) through which ozonized air flows at a rate greater than 0.6 m/s. Because the residence time of the ozonized air in the test chamber is about 1 s, the ozone may be expected to reach the material in about 0.1 s. A somewhat similar test procedure (aatcc test method 109-1972 ansi L14, 174-1973) is used in testing colorfastness. The ozone generator is usually (but not necessarily) a mercury-vapor resonance lamp with emission lines at 184.9 and 253.7 nm. The 184.9-nm line is absorbed, and two ground-state oxygen atoms are produced ... 

High intensity, microwave powered emission sources have recently been developed that are reported to provide substantially higher DUV output than classical electrode discharge mercury lamps 76). These sources suffer from self-absorption of the intense 254 nm emission but have a relatively high output in a band between 240 and 280 nm. They are extended sources of finite size rather than point sources, and they must also be an integral part of a tuned, resonant microwave cavity. Consequently, extensive condenser design work would be required in order to utilize the microwave powered sources in projection printers. 

The action of light on yellow arsenic has been described on p. 29 the rate of change is not affected by radium rays. When placed in the light from a mercury lamp, arsenic exhibits a photoelectric effect, emitting electrons the longest effective wavelength is A 2360. At 1100° to 1150° C. a resonance series is excited in the vapour of arsenic 1 by each of the mercury lines AA 2483, 2536, 2654 and 2804 the fundamental frequency is apparently 410 cm.-1, which gives as the distance As to As in the diatomic molecules 1-94 A., or 77 per cent, of the distance in crystalline arsenic (see p. 35). 

Reversed Radiation.—A pressure broadened resonance emission line with radiation in the middle of the line virtually absent because of self-absorption near the walls, (e.g., the 2537 A. line obtained from medium pressure mercury lamps). 

During recent years real progress has been made in understanding a few of the reactions of excited mercury. If the primary step is (9) the reactions of the radicals will be the same in a given system no matter how they are formed. Mercury has seven stable isotopes and when ordinary mercury vapor is irradiated by a resonance lamp made of ordinary mercury all seven will be excited at rates proportional to their abundances and to the relative intensities of the hyperiine components from the resonance lamp. Even though some isotopes are more abundant than others and the intensities from the resonance lamp will be higher for the abundant isotopes than for others, there is no specificity about (9) and no dependence on isotopic composition would be expected. 

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