Silicon isotope pattern

Cover Illustration Atomic force microscopy image of molybdenum oxide particles on flat, silicon dioxide substrate, which serves as a model system for a supported catalyst. The area shown corresponds to one square micrometer the maximum difference in height is approximately 10 nanometer. The superimposed curve is the secondary ion mass spectrum of the model catalyst, showing the caracteristic isotopic patterns of single molybdenum ions and of molybdenum oxide cluster ions. 

The isotopic patterns of sulfur and silicon are by far not as prominent as those of chlorine and bromine, but as pointed out, their contributions are sufficiently important (Fig. 3.5). 

Fig. 3.5. Calculated isotopic patterns for combinations of elemental silicon and sulfur. The peak shown at zero position corresponds to the monoisotopic ion at m/z X. The isotopic peaks are then located at m/z = X+1, 2, 3,...

Cosmic portraits of the isotopes are the main burden of this book. For each element there is an historical and chemical introduction, followed by a table of those isotopes of that element that have observed abundance in the natural world. Then a section on each isotope describes its nuclear characteristics, its abundance in the solar system relative to that of silicon, the means of nucleosynthesis of that isotope, astronomical observations ofit, and its participation in isotopic patterns differingfrom those known on Earth, primarily in presolar grains extracted from the meteorites. 

Most of the attention given to production of the exotic gas components (Table 2) has focused on their isotopic patterns, but except for the R-component, believed to be formed by in situ decay of Na, they also must be trapped components in their host phases, so models for their origin are incomplete without a trapping mechanism. There is significant evidence, including absence of fractionation from neighboring elements and comparison with laboratory simulation, that at least some of the components carried in diamonds and silicon carbide were trapped by ion implantation (e.g., Koscheev et al, 2001 ... 

The interpretation of SSMS data falls into two distinct areas — element Identification and estimates of quantity. The criteria used in our laboratory for positive elemental identification are the presence of the doubly ionized species and the Identification of the Isotopic pattern when possible. Quantitation will be discussed later. Last, the Instrument source must be cleaned regularly to avoid memory problems. Our approach to the memory problem is to have a complete set of source parts for each matrix. A set of parts are dedicated for silicon analyses, another for gallium arsenide, etc. These parts and the source Itself are cleaned on a regular and frequent basis. When these factors are under control, SSMS has proved to be a reliable, reproducible technique for the bulk analysis of trace impurities. 

The G and N components of noble gases are carried by presolar grains of silicon carbide. Diagnostic as far as their origins are concerned, are the isotopic patterns observed in the G component for Ne and Kr/Xe Ne-G [= Ne-E(H)] is dominated by Ne, with only small amounts of while Kr-G and Xe-G show large overabundances of... 

Fig. 6.46. El mass spectrum of l,2-bis(trimethylsiloxy)benzene. The isotopic pattern of silicon is clearly visible in the signals at m/z 13, 239, and 254 (Chap. 3.2.6). Spectrum used by permission of NIST. NIST 2002.

Is there an obvious isotope pattern, for example, for chlorine, bromine, silicon or sulfur The molecular ion shows all elements with stable isotopes in the compound. Is it possible to find out the maximum number of carbon atoms ... 

For organic mass spectrometry, only a few elements with noticeable isotope patterns are important, while in inorganic mass spectrometry there are many isotope patterns of metals, some of them very complex. From Table 3.7 it can be seen that the elements carbon, sulfur, chlorine, bromine and silicon consist of naturally occurring stable, nonradioactive isotopes. The elements fluorine, phosphorus and iodine are among the few monoisotopic elements in the periodic table (Rosman and Taylor, 1998). 

Silicon occurs very frequently in trace analysis. Silicones get into the analysis through derivatization (silylation), partly through clean-up (joint grease), but more frequently through bleeding from the septum or the column (septa of autosampler vials, silicone phases). The typical isotope pattern of all silicone masses can be recognized rapidly and excluded from further evaluation measures (Figure 3.42). 

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