Mercury resonance line

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... 

The absorption maximum of ozone occurs at 254 nm, which is close to the wavelength of the mercury resonance line at 253.7 nm. The decrease of the UV intensity at X = 254 nm is proportional to the concentration of ozone based on the Lambert-Beer s law of absorption ... 

In mercury vapor irradiated by the 2537-A mercury resonance line, ionization was observed91 and later attributed92 to the AI process (IV.2). Since then AI was reported for a large number of systems.93 Especially the homonuclear AI, also called Hornbeck-Molnar process,94... 

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. 

It is convenient for photochemical studies in the near ultraviolet to use the mercury resonance line at 3130 A. from a medium pressure mercury arc as a light source. This particular wavelength can be separated in high intensity from the remainder of the spectrum by suitable filters. 

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. 

Mercury Detection Instrument Use any suitable atomic absorption spectrophotometer equipped with a fast-response recorder and capable of measuring the radiation absorbed by mercury vapors at the mercury resonance line of 253.6 nm. A simple mercury vapor meter or detector equipped with a variable span recorder also is satisfactory. 

The mercury resonance line at X 2537 A, corresponding to the transition 6(3Pi) 6(1 So), has been used in most studies and monoisotopic photosensitisation has been specifically employed to examine the possible isotopic enrichment of the mercury compounds produced in these reactions. Thus, in the Hg monoisotopic photosensitised decomposition of methyl chloride " - the main products are methane, ethane, dichloroethane and hydrogen chloride together with calomel enriched with the ° Hg isotope. The following mechanism has been proposed " for the decomposition... 

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... 

In principle, all elements may be determined on the basis of their ability to absorb light energy, but in practice this is not technically possible. There are several elements which have their strongest spectral lines in the vacuum UV region (A < 200 nm), and thus makes their determination by direct AAS methods impossible (Table 46). On the other hand, some of these elements may be determined by using less sensitive absorption lines. For example, the sensitivity of the mercury resonance line at 186.96 nm is about 50 times more sensitive than the line at 253.65 nm used for the determination of mercury. 

Die Anregungsfunktion der Quecksilberresonanzlinie 2537 (The excitation function of the mercury resonance line A2537 A), Z Phys. 54, 848-851 (1929). 

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]. 

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. 

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. 

Displacements of the Hyperfine Components of the 2537-A. Resonance Line of Mercury from the X200 Component in cm. 1 X 103 Hyperfine References... 

The absorption coefficient, of mercury vapor for a Doppler-broadened resonance line is given by the expression ... 

In the case of the other resonance line of mercury, the mechanism is ... 

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