Mercury photosensitization photochemistry

Mechanistic Organic Photochemistry, A New Approach to (Zimmerman) Mercury Photosensitization, Isotopic Effects and the Mechanism of... 

Little experimental data on the photochemistry of compounds with B—0 bonds have been reported. Boron-hydride/oxygen mixtures are explosive. These explosions can be initiated by photochemical processes. Grimm and Porter have studied the photochemical decomposition of H2B2O3 using a low pressure mercury lamp. The UV spectrum of this compound is illustrated in Fig. 13. The rate of the reaction was increased when mercury was present as a photosensitizer. 

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. 

Sensitization was another word requiring definition and correct application. Thus, a stable molecule could be made photosensitive by the additirai of a small amount of another molecule, but this might involve different phenomena, as illustrated by Berthoud [62]. These ranged from the photochemical formation of a reactive compound to that of a catalyst. Atoms could be generated and transfer their energy to other species, as demonstrated for atoms of mercury or of oxygen [63]. Noyes pointed out to the reaction of molecules, e.g., NO2, at an irradiated mercury surface, and on the differences and similarity between photochemistry and photo-ionization [64]. 

Photochemistry. Molecular hydrogen containing traces of mercury vapour (photosensitizer) is irradiated by UV radiation (A = 253.7nm). The gas can then bring about... 

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