Deflection magnetic

Probably the simplest mass spectrometer is the time-of-fiight (TOP) instrument [36]. Aside from magnetic deflection instruments, these were among the first mass spectrometers developed. The mass range is theoretically infinite, though in practice there are upper limits that are governed by electronics and ion source considerations. In chemical physics and physical chemistry, TOP instniments often are operated at lower resolving power than analytical instniments. Because of their simplicity, they have been used in many spectroscopic apparatus as detectors for electrons and ions. Many of these teclmiques are included as chapters unto themselves in this book, and they will only be briefly described here. 

Mattauch-Herzog geometry. An arrangement for a double-focusing mass spectrometer in which a deflection of n/A radians in a radial electrostatic field is followed by a magnetic deflection of nil radians. 

Accelerating voltage (high voltage) scan. An alternative method of producing a momentum (mass) spectrum in magnetic-deflection instruments. This scan can also be used, in conjunction with a fixed radial electrical field, to produce an ion kinetic energy spectrum. 

Experimental. The mass spectra in Figures 1-8 are positive-ion spectra produced by electron impact and were obtained from a single-focusing, magnetic deflection Atlas CH4 Mass Spectrometer. The ionizing potential was 70 e.v. and the ionizing current 18/a a. An enamel reservoir heated to 120°C. was used from which the sample was leaked into the ion source. 

In the past few years this pulsing technique has been used by several groups, utilizing both magnetic deflection (16, 31, 37) and time-of-flight (12, 13) instruments, to study ion-molecule reactions at thermal energies. Here we review the results obtained and discuss the applications and limitations of the method, based on our observations and experiences over the past three years. 

Stiller et al. [824] have described the determination of cobalt, copper, and mercury in Dead Sea water by neutron activation analysis followed by X-ray spectrometry and magnetic deflection of /i-ray interference. 

Walter Kanfmarm also reported the determination of the charge-to-mass ratio of cathode rays (abont 10 emu g- ) in a paper he submitted in April 1897 (7). Kanfmarm also based his result on magnetic deflection measurements however, he concluded that the hypothesis of cathode rays as emitted particles could not explain his data. (One of the outstanding questions in the study of cathode rays in the late 1890s was whether they were particles or electromagnetic waves. Thomson and Kanfmarm were typical of their coimtrymen most British researchers leaned toward the particulate hypothesis and most Germans toward waves.) Today Kanfmarm is better known for his careful measurements of the velocity-dependent mass of the electron published over several years beginning in 1901 these results were later explained by special relativity. 

The key specifications of EL3 are shown in Table I. EL3 combines a high current variable shaped beam column with a dual deflection system (42). Maximum beam size is 4 jam x 4 jam and shapes smaller than this are available in 0.1 m increments. Spot edge definition is better than 0.2 jam. A highly accurate but relatively slow magnetic deflection coil deflects the beam in a raster sequence to the center of an array of 75 jim subfields. The variable... 

There are two important categories of magnetic-deflection mass spectrometers low (unit) resolution and high resolution. Low-resolution instruments can be defined arbitrarily as the instruments that separate unit masses up to m/z 2000[R = 2000/(2000 — 1999) = 2000]. A high-resolution instrument with R = 20,000 can distinguish between C16H2602 and C15H24N02 ... 

Limit of determination Magnetic deflection Mass analyzer... 

Example Problem A dipole magnet deflects charged particle beams through an angle of 22.5° with a radius of 2.0 m. For ease of construction the magnet has rectangular pole pieces 0.5 x 1.5 m long. The beam enters normally at the... 

The intramolecular isotope effect, IH //D, on metastable ion decomposition of benzene to lose a hydrogen atom has been reported as 1.9 [59]. A tandem magnetic deflection/ion cyclotron resonance (ICR) instrument has been used to study isotope effects on metastable ion decompositions of benzene, toluene and anisole in some detail [779]. 

In studies of metastable ions [388, 671], H- losses from (CH4)t, (CH3D)t, (CH2D2)t and (CHD3) have been compared and the abundances (corrected for the number of H atoms available) found to be in the respective ratios 1 2.2 5.9 17 [388] and 1 2.2 3.5 11 [671]. The corresponding figures obtained with a tandem magnetic deflection/ICR instrument in which the observation window extended to a few milliseconds (ti ps t2 ms) were 1 2.2 4.4 12 [777]. The isotope effects are... 

A mass spectrometer ionizes molecules in a high vacuum, sorts the ions according to their masses, and records the abundance of ions of each mass. A mass spectrum is the graph plotted by the mass spectrometer, with the masses plotted as the x axis and the relative number of ions of each mass on the y axis. Several methods are used to ionize samples and then to separate ions according to their masses. We will emphasize the most common techniques, electron impact ionization for forming the ions, and magnetic deflection for separating the ions. 

Separation of Ions of Different Masses Once ionization and fragmentation have formed a mixture of ions, these ions are separated and detected. The most common type of mass spectrometer, shown in Figure 12-15, separates ions by magnetic deflection. 

W. WIEN analyses anode rays by magnetic deflection and then establishes that these rays carried a positive charge [14], Nobel Prize in 1911. 

Using Taylor s technique, Lewis determined the equilibrium between atoms and molecules of lithium, sodium, and potassium by the magnetically deflected molecular beam. This was done for a... 

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