Mercury sensitized emission

The mercury sensitized emission, (process (b)) from TI and Na vapour has been discussed in Section 6.6.6. The quenching to 63P0 (process (d)) by CO, N2 and N O, NH3 are presented in Section 6.2. In presence of H2, the possible photochemical reactions are... 

Emission (AmaT = 380 nm), assigned to that from the lowest triplet state of water, has been observed following either y-irradiation or mercury sensitization of crystalline H20 or D20.439 For the mercury sensitization a triplet energy-transfer mechanism appears to be operative, while for the y-irradiation the excited state is formed via reaction (88). Photolysis of water adsorbed on various organic materials is observed with short-wavelength u.v. light (A < 250 nm).440... 

A portion of a spectrum that includes emission lines of mercury and lead is shown in Figure 4 the insert is a calibration plot for lead in this sample set. In general, LIBS provides detection on the ppm level for most elements in this case on the order of 30 ppm for lead in glass based matrices. For higher sensitivity, LA-ICP-MS provide ppb detection. 

Figure 19 shows the ultraviolet absorption spectrum of a typical diazonaphthoquinone and a common novolac resin. The naphthoquinone sensitizer has a strong absorbance at the 365 nm., 405 nm., and to a lesser extent the 436 nm. mercury emission lines. There are two diazonaphthoquinone isomers that are used in commercial photoresist formulations that are available at this time. The 5-arylsulfonates are by far the most commonly used. A spectrum of a representative of this class of materials is depicted in Figure 20. The 5-arylsulfonate materials are characterized by an absorbance maximum at approximately 400 nm. and a second, slightly stronger maximum at approximately 340 nm.

Figure 19. Absorbance spectrum of a typical diazonaphthoquinone sensitizer (in solution) and a cresylic acid novolac (film). The wavelengths of principle mercury emission lines are labeled.

A dry, weighed polyethylene film (length 50 mm, breadth 25 mm, thickness 0.1-0.2 mm) is placed in a tube (about 70 ml capacity) fitted with a ground glass joint and stopcock. After addition of some crystals of benzophenone (as sensitizer) the sample is heated for 1 h on a water bath at 60 °C.The outside of the tube is dried, the stopcock closed, and the tube exposed to 15 min irradiation from a mercury lamp (maximum of emission in the region of A = 253-254 nm). 

A number of analytical methods were developed for determination of elemental mercury. The methods are reviewed in Refs. [1-4]. They include traditional analytical techniques, such as atomic adsorption spectroscopy (AAS), atomic fluorescence spectroscopy (AFS), and atomic emission spectroscopy (AES). The AAS is based on measurements of optical adsorption at 253.7 or 184.9 nm. Typical value of the detection limit without pre-concentration step is over 1 pg/l. The AEF is much more sensitive and allows one to detect less than 0.1ng/l of mercury... 

Mercury has been identified as a very dangerous environmental contaminant, largely by reason of the process of concentration in the food chain. Thus, the presence of mercury in coal is an extremely sensitive issue. The possible emission of mercury that may be found in coal is an environmental concern. 

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