Tungsten, isotope ratio measurements

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

The ratio of the quadrupole moments in tungsten isotopes as measured by Mossbauer spectroscopy - collected from [222-228] - is... 

In 1923, Kingdom and Langmuir [1] first observed SI (Fig. 1). This phenomenon consisted of desorption of cesium (Cs) atoms in the form of positive ions from the surface of a heated tungsten (W) filament. Subsequently, numerous studies of positive-ion SI have been conducted, since this effect opens interesting possibilities for analysis of chemical species with low ionization energy (IE), for ion production, and for the detection of molecular and atomic beams. After the Saha-Langmuir equation [2] was established and well defined, further studies have [3,4] been directed to the atoms of virtually all elements, which have a low ionization energy. Especially, SI was studied for suitability as a source of ions for precise isotope-ratio measurements [5] and isotope-dilution techniques. It is apparent, however, that its use has, until recently, been restricted to metals. 

Precise measurement of isotope ratios can be obtained by comparing the yields of isotopic ions desorbing from a sample placed on a strongly heated filament that is generally made from platinum, tantalum, rhenium, or tungsten. 

In the latter, when equal amounts of deuterated and undeuterated 2,2 -divinylbiphenyls were combined with either molybdenum or tungsten catalysts, the ratios of undeuterated, dideuterated, and tetradeuterated molecules after about % reaction were found to be approximately 1 2 1 (24.3% isotope scrambling in the remaining divinylbiphenyls was measured as... 

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