Vacuum generator spectrometer

Characterization methods. The 100 kV Vacuum Generator HB-5 STEM was used to mlcroanalyze samples. The HB-5 has a KEVEX SI(LI) energy dispersive X-ray spectrometer (EDS) and micro area electron diffraction (MAED) capabilities In conjunction with simultaneous bright and dark field Imaging capabilities. A more detailed explanation of the Instrumental operation can be obtained In a publication by C. Lyman(12). 

The combined UPS and XPS facilities available in the Vacuum Generators ESCA-3 Spectrometer (the name by which the prototype became known) provided a powerful means (5, 3a) of exploring solids, their surfaces, and in turn the reasons for their inherent chemical reactivities. We shall see that XPS and UPS enable both qualitative and quantitative characterization of the solid surface at the atomic level, the chemical environment of a particular... 

General. NMR spectra were obtained on a Bruker WM-250 instrument with tetramethylsilane (TMS) as internal standard. UV-visible spectra were taken on a Varian Cary 219. Fast-atom bombardment (FAB) mass spectrometry (MS) analysis were completed on a Vacuum Generators ZAB-2F double-focusing or a Varian MAT CH5 mass spectrometer equipped with an Ion Tech FAB Gun. Solvents for FAB matrix were made up of thioglycerol, dithiothreitol, and dithioerythretol (2 1 1) addition of 0.1M trifluoroacetic acid to the matrix facilitated the ionization of the porphyrins during FAB analysis.(13)... 

Spectrometer type and manufacturer Vacuum Generators Micromass 7070 H ... 

Experimental data are obtained using a Vacuum Generators ESCA III spectrometer equipped with a dual Al/Ag X-ray source. The base pressure is 10 1 mbar in the spectrometer. A1 depositions are made in the attached preparation chamber with a residual pressure in the 10" mbar range, by thermal evaporation or sputtering as displayed in Figure 1. 

The microscope used in obtaining the results presented in this paper was a Vacuum Generators HB-5 STEM. A Kevex energy dispersive x-ray spectrometer, EDS, with 10mm2 Be window was used for the elemental microanalysis. 

The Hel PE spectra of DHEA, 1 and 2 were recorded on a Vacuum Generators UV -G3 spectrometer 11 at 180 oC and a resolution of about 30 meV. The compounds were of commercial origin (Steraloid Inc. and Sigma Chemical Company) and high purity. Some decompositon of DHEA under measurement conditions occurs because signals corresponding to H2O and CO can be traced in the PE spectrum. 

The experiment has been described in detail elsewhere (5), and only an outline is presented here. The instrument used is a modified Vacuum Generators ZAB IF tandem mass spectrometer (Fig 1). Molecular ions are produced in a conventional source by electron bombardment of hydrogen gas. A beam of these ions is produced by applying an accelerating potential to the source, which may... 

The C Is and O Is peaks of model polymers [poly (bisphenol A carbonate) and poly (ethylene terephtalate)] have been recorded with two different spectrometers for which the 0/C concentration ratio was determined in a different way (a) ESC A 3 Mkll spectrometer from Vacuum Generators, Mg, use of Wagner empirical sensitivity factors and (b) SSX KXV206 spectrometer, monochromatized AIku, sensitivity factors determined from cross seclions and considering IMFP... 

The main one is the incompatibility of HPLC, utilizing flow rates of ml min of a liquid, and the mass spectrometer, which operates under conditions of high vacuum. Even if this can be overcome, attention must then be focussed on the ionization of the analyte, bearing in mind the limitations of El and Cl discussed earlier in Chapter 3, and the generation of analytically useful mass spectra. 

Mass spectrometers, workhorse instmments described in Chapter 2, require a vacuum to function. A mass spectrometer generates a beam of ions that is sorted according to specifications of the particular instrument. Usually, the sorting depends on differences in speed, trajectory, and mass. For instance, one type of mass spectrometer measures how long it takes ions to travel from one end of a tube to another. Residual gas must be removed from the tube to eliminate collisions between gas molecules and the ions that are being analyzed. As the diagram shows, collisions with unwanted gas molecules deflect the ions from their paths and change the expected mass spectral pattern. 

In a separate set of experiments designed to follow the gas phase reactions of CHj-radicals with NO, CHj- radicals were generated by the thermal decomposition of azomethane, CHjN NCHj, at 980 °C. The CH3- radicals were subsequently allowed to react with themselves and with NO in a Knudsen cell that has been described previously [12]. Analysis of intermediates and products was again done by mass spectrometry, using the VIEMS. Calibration of the mass spectrometer with respect to CH,- radicals was carried out by introducing the products of azomethane decomposition directly into the high vacuum region of the instrument. 

Metal-modified silicas were exposed to excess BuOOH vapor in order to generate the supported feri-butylperoxide complexes, followed by evacuation to remove PrOH and unreacted BuOOH. Reaction kinetics were monitored as the uptake of cyclohexene from the gas phase, using a ThermoNicolet Nexus FTIR spectrometer to measure the intensity of the o(C=C) mode. In situ spectra were recorded in custom-made glass reactors under vacuum. Formation of cyclohexene oxide was confirmed by GC/MS on an HP 6890 equipped with a DBI capillary column (J W Scientific). 

Modem instrumentation has improved substantially in recent years, which has enabled the measurement of XPS spectra of superior resolution necessary to reveal the small BE shifts present in highly covalent compounds such as those studied here. In a laboratory-based photoelectron spectrometer, a radiation source generates photons that bombard the sample, ejecting photoelectrons from the surface that are transported within a vacuum chamber to a detector (Fig. 2). The vacuum chamber is required to minimize the loss of electrons by absorption in air and, if a very high quality vacuum environment is provided (as is the case with modem instruments), the surface contamination is minimized so that the properties of the bulk material are more readily determined. 

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