High pressure electron spectrometer

Fig. 3. Schematic drawing of the high pressure electron spectrometer. A, Argon ion gun D, differentially pumped region EL, electron lens G, gas cell HSEA, hemispherical electron analyzer LO, two-grid LEED optics LV, leak valve M, long travel rotatable manipulator P, pirani gauge S, sample TSP titanium sublimation pump W, window X, twin anode x-ray source.

Joyner RW, Roberts MW, Yates K (1979) A high-pressure electron spectrometer for surface studies. Surf Sci 87 501-509... 

Kebarle P 1988 Pulsed electron high pressure mass spectrometer Techniques for the Study of Ion-Molecule Reactions ed J M Farrar and W FI Saunders (New York Wiley-Interscience)... 

Method (b) corresponds to the usual method of investigating ion-molecule reactions in a high pressure mass spectrometer although charge exchange with slow ions is used instead of electron impact. After preliminary work (9, 23), the method was fully developed by Szabo 20, 21, 22). 

The important and stimulating contributions of Kebarle and co-workers 119 14 > provide most of the data on gas-phase solvation. Several kinds of high pressure mass spectrometers have been constructed, using a-particles 121>, proton- 123>, and electron beams 144> or thermionic sources 128> as primary high-pressure ion sources. Once the solute A has been produced in the reaction chamber in the presence of solvent vapor (in the torr region), it starts to react with the solvent molecules to yield clusters of different sizes. The equilibrium concentrations of the clusters are reached within a short time, depending on the kinetic data for the... 

Concerning the first field of application, the kinetics and equilibrium constants for several halide transfer reactions (equation 1) were measured in a pulsed electron high pressure mass spectrometer (HPMS)4 or in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR)5. From measurements of equilibrium constants performed at different temperatures, experimental values were obtained for the thermochemical quantities AG°, AH° and AS° for the reaction of equation 1. The heat of formation (AH°) of any carbocation of interest, R+, was then calculated from the AH0 of reaction and the AH° values of the other species (RC1, R Cl and R +) involved. 

The free energy for electron attachememt (AGa°) was determined for perfluorobenzenes C6F5X (X = F, Cl, Br, CF3, COMe, CHO, CN, N02, C6F5, COC6F5) by measuring the electron transfer equilibria with some reference anions A- (A was primarily S02) in a pulsed high pressure mass spectrometer (equation 29)273. 

The equilibrium constant for the case X = Cl and i = 1 agrees well with that obtained in a pulsed electron beam high pressure mass spectrometer, the other data have not been previously reported. 

The complementary techniques for determining rate constants for thermal electron attachment, detachment, and dissociation are the flowing afterglow, the microwave technique, the ion cyclotron resonance procedures, the swarm and beam procedures, the shock tube techniques, the detailed balancing procedures, the measurement of ion formation and decay, and the high-pressure mass spectrometer procedures. In all cases the measurement of an ion or electron concentration is made as a function of time so that kinetic information is obtained. In the determination of lifetimes for ions, a limiting value of the ion decay rate or k is obtained. 

Several high-pressure mass spectrometers were used at Alberta a high-pressure alpha-particle instrument capable of operating at pressures up to 200-300 Torr, " a 100-keV proton-beam mass spectrometer, and a 4-keV pulsed electron-beam instrument. 

McGrew DS, Knighton WB, Bognar JA and Grimsrud EP (1994) Concentration enrichment in the ion source of a pulsed electron beam high pressure mass spectrometer. International Journal of Mass Spectrometry and Ion Physics 139 47-58. 

High-pressure pumps operating at up to 6000 psi are required to force solvent through a tightly packed HPLC column, and electronic detectors are used to monitor the appearance of material eluting from the column. Alternatively, the column can be interfaced to a mass spectrometer to determine the mass spectrum of every substance as it elutes. Figure 12.18 shows the results of HPLC analysis of a mixture of 10 fat-soluble vitamins on 5 jam silica spheres with acetonitrile as solvent. 

In brief, the method consists of introducing small amounts (partial pressures of 10 3-10 4 torr) of the substance to be investigated into the ionization chamber of a mass spectrometer which contains a high pressure (1 torr) of methane, the reactant gas. Ionization is effected by electron impact, and because the methane is present in such an overwhelming preponderance, all but a negligibly small amount of the initial ionization occurs in the methane. The methane ions then undergo ion-molecule reactions to produce a set of ions which serve as reactant ions in the chemical ionization process. The important reactant ions formed from... 

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