Hydrogen continued sources

A distinction must be made between continuous sources (hydrogen or deuterium lamps, incandescent tungsten lamps, high pressure xenon lamps) and spectral line sources (mercury lamps), which deliver spectrally purer light in the region of their emission lines. 

Continuous sources The sources of choice for measurements in the ultraviolet spectral region are hydrogen or deuterium lamps [1]. When the gas pressure is 30 to 60 X10 Pa they yield a continuous emission spectrum. The maxima of their radiation emission occur at different wavelengths (Hi A = 280 nm Di 2 = 220 nm). This means that the deuterium lamp is superior for measurements in the lower UV region (Fig. 15). 

The Rapid Recording of Absorption Spectra.—If the kinetics of the radical disappearance are to be studied the exposure time must be only a fraction of the radical lifetime which may mean io sec. or less. With continuous sources such as the hydrogen lamp the exposure time required is several seconds at least but three methods of high speed recording are available. 

A method of chemically synthesizing reduced products including methanol from carbon dioxide and hydrogen has been developed. The method utilizes a metal hydride foil membrane as a continuous source of reactive surface hydrogen atoms and an electrostatic field to enhance the adsorption of carbon dioxide and bicarbonate onto the hydrogen rich surface. The subsequent chemical(rather than electrochemical) reaction between the adsorbed carbon dioxide and surface hydrogen/metal hydride results in the formation of reduced products. 

Direct geometry instruments use choppers or crystal monochromators to fix the incident energy and they are found on both continuous and pulsed sources. To compensate for the low incident flux resulting from the monochromation process, direct geometry instruments have a large detector area. This makes the instruments expensive, they are generally twice the price of a crystal analyser instrument. At present, they are used infrequently for the study of hydrogenous materials, so we will limit our discussion to a chopper spectrometer at a pulsed source and a crystal monochromator at a continuous source. 

As we have already mentioned, atomic absorption lines are very narrow (about 0.002 nm). They are so narrow that if we were to use a continuous source of radiation, such as a hydrogen or deuterium lamp, it would be very difficult to detect any absorption of the incident radiation at all. Absorption of a narrow band from a continuum is illustrated in Fig. 6.4, which shows the absorption of energy from a deuterium lamp by zinc atoms absorbing at 213.9 nm. The width of the zinc absorption line is exaggerated for illustration purposes. The wavelength scale for the deuterium lamp in Fig. 6.4 is 50 nm wide, and is controlled by the monochromator bandpass. If the absorption line of Zn were 0.002 nm wide, its width would be 0.002 x 1/50= 1/25,000 of the scale shown. Such a narrow line would be detectable only under extremely high resolution (i.e., very narrow bandpass), which is not encountered in commercial AAS equipment. 

Processes or conditions involving wet hydrogen sulfide, that is, sour services, and the high incidence of sulfide-induced HlC may result in sulfide stress cracking (SSC), which has been a continuing source of trouble in the exploration and exploitation of oil and gas fields, and the subject of many international standards [22]. However, similar problems are encountered wherever wet hydrogen sulfide is encountered (e.g., acid gas scrubbing systems, heavy water plants, and waste water treatment). 

The upper limit of efficiency of the biophotolysis of water has been projected to be 3% for weU-controUed systems. This limits the capital cost of useful systems to low cost materials and designs. But the concept of water biophotolysis to afford a continuous, renewable source of hydrogen is quite attractive and may one day lead to practical hydrogen-generating systems. 

An early source of glycols was from hydrogenation of sugars obtained from formaldehyde condensation (18,19). Selectivities to ethylene glycol were low with a number of other glycols and polyols produced. Biomass continues to be evaluated as a feedstock for glycol production (20). 

A mixture of 50 g. (0.26 mole) of anhydrous stannous chloride and 225 ml. of dry ether is placed in a 1-1. three-necked round-bottomed flask fitted with a rubber-tube sealed stirrer, an inlet tube reaching nearly to the bottom of the flask, and a reflux condenser (Note 2) protected by a calcium chloride drying tube. The mixture is saturated with dry hydrogen chloride (Note 3) with continuous stirring. Within 3 hours all the stannous chloride dissolves, forming a clear viscous lower layer. The source of hydrogen chloride is then disconnected, and the freshly prepared imidyl chloride is transferred into the mixture with the aid of 25 ml. of dry ether (Note 4). Stirring is continued for 1 hour, and then the reactants are allowed to stand at room temperature for 12 hours. 

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