Oxygen with cesium

Many different types of photocathodes are used in photomultipliers. With a selection of various cathodes, it is possible to cover the range of response from the soft x-ray region (approximately 5 to 500 A) to the near infrared (approximately 12,000 A). Materials and combinations used include cesium-oxygen-silver cesium-antimony cesium-antimony-bismuth sodium-potassium antimony sodium-potassinm-cesinm-antimony copper-iodine and cesium-iodine. The thermal emission at 25°C of copper iodide and cesium iodide tends to run less than the other materials. 

Both oxygen and cesium ion beams are used. The former is more effective with the electropositive elements (i.e., B, Al, Cr, etc.), and the latter with the electronegative elements (i.e., C, O, As, etc.). Since the technique involves sputtering of the surface, depth profiling can be carried out readily. 

The following contribution is intended to continue our earlier review [6] dealing with the then known cesium assisted ractions only some very important earlier cesium assisted reactions are described here for the sake of completeness After a short description of the properties of some cesium compounds used in this respect in organic synthesis, those reactions are discussed that have been published more recently and which proceed under the intermediate formation of organic cesium salts at oxygen, nitrogen or sulphur functions. Only those cyclization reactions are considered which allow a direct comparison of the yields obtained with cesium compounds or cesium metal. The description starts with reactions leading to the formation of C—C bonds and proceeds to the syntheses of ethers, lactones, amines and sulfides. The discussion ends with a summary of the attempts to explain the cesium effect . 

Recently, two types of surfaces with coadsorbed cesium and oxygen have shown promise for low work function operation in thermionic converters. The first type of surface is made by codeposition of a "thick layer" ( 30 A) of cesium. As shown in Figure 13 ij), if the proportions of cesium and oxygen are properly controlled, a work function as low as 1.0 ev can be obtained. The substrate material does not affect the low obtained with a thick Cs - 0 layer. This type of surface could potentially be maintained in a thermionic converter by an equilibrium mixture of cesium, oxygen, and cesium oxide. Experiments to demonstrate this in operating diodes are underway ( ). 

The fluorination of adamantane and its derivatives can also be achieved with oxygen difluoride in the presence of sodium hydrogen carbonate as a hydrogen fluoride trap however, this reaction is complicated by competing oxidation.22 When the fluorination of adamantane is performed with cesium fluoroxysulfate, a mixture of monofluorinated products 4 and 5 arising from fluorination at tertiary and secondary sites, respectively, and difluorinated product 6 is obtained.23 The thermally initiated fluorination of adamantane using xenon difluoride gives a similar mixture but includes a small amount of trifluoride 7.24 25... 

Cesium is a soft metal with a low melting point. It is the most chemically reactive metal and, even more strongly than rubidium, combines readily with oxygen, with the halogens, and with water. Cesium will react with ice to a temperature as low as -177°F (-116°C). 

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