Mercury resonance line emission

The first observation of non-radiative excitation energy transfer was made by Cario and Franck [126]. They investigated Hg and Th vapor and illuminated with the resonance line of mercury and found emission spectra from both atoms although Thallium did not absorb the light from the mercury resonance line. Since radiation by re-absorption was not possible, only a non-radiative energy transfer could have been operative with the Hg atoms as donor (sensitizer) and the Th atoms as acceptors. 

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]. 

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. 

A Hanovla chromatollte lamp was used as the source of ultraviolet radiation. This Is a low-pressure mercury arc, the main emission comprising the resonance lines at 1849 and 253 R. The former Is completely absorbed by 1 cm of air, while the latter Is almost completely transmitted by air and 95% by silica. Thus virtually pure 253 X radiation Impinges on the polymer. The lamp was connected to an L.T.H. transistorized 1 kVA voltage regulator to ensure that fluctuations In mains output did not affect emission. 

EDLs are very intense, stable emission sources. They provide better detection limits than HCLs for those elements that are intensity-limited either because they are volatile or because their primary resonance lines are in the low-UV region. Some elements like As, Se, and Cd suffer from both problems. For these types of elements, the use of an EDL can result in a limit of detection that is two to three times lower than that obtained with an HCL. EDLs are available for many elements, including antimony, arsenic, bismuth, cadmium, germanium, lead, mercury, phosphorus, selenium, thallium, tin, and zinc. Older EDLs required a separate power supply to operate the lamp. Modern systems are self-contained. EDL lamps cost slightly more than the comparable HCL. 

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 ... 

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). 

Analytical uses of atomic fluorescence have been developed in recent years. Most of the methods utilize resonance fluorescence, but other types of fluorescence also are useful. For example, spectral emission lines of mercury have been used to produce fluorescence of elements such as iron, thallium, chromium, and magnesium. The instrumentation and techniques for analytical applications of atomic fluorescence are described in Chapter 11. 

Quimby et al examined the applicability of this type of detector to a range of elements including lead, silicon, phosphorus, mercury and manganese. The results they obtained for organolead compounds are discussed below and those for the other elements are discussed elsewhere. Quimby et al used a microwave emission detection system for gas chromatography which utilizes the TMq] q resonant cavity to sustain a plasma in helium at atmospheric pressure. The effluent from the gas chromatograph is split between a flame ionization detector and a heated transfer line directing it to a small... 

While some planets have deep atmospheres, others, such as Mercury and Mars, have relatively tenuous atmospheres. For these planets (and the Moon and satellites) the atmospheres are nearly transparent at radio wavelengths, except possibly in narrow wavelength ranges, where resonant absorption lines can produce strong absorption. Thermal emission from the surfaces of these planets is easily observed at radio wavelengths it is possible to interpret the measurements in terms of the physical properties of the near-surface materials. 

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