Alkali Metal Beam

Bydin and Bukhteev and Bukhteev et al reported the earliest studies on collisional ionization of fast alkali metal beams with various... 

In the late 1960s several major advances were made in the study of thermal electron reactions. These were based on the ECD, the extension of the magnetron method of studying electron molecule reactions to determine equilibrium constants for electron molecule reactions, and the invention of high-pressure thermal electron negative-ion sources for mass spectrometry [5-7], Electron swarms were also used to determine rate constants for thermal electron reactions [8, 9]. The electron affinities of molecules were measured using electron and alkali metal beams [10, 11]. Relative electron affinities were obtained from the direction of the reaction of a negative ion with a molecule [12, 13], Other major advances were photodetachment and photoelectron spectroscopy [14—17],... 

Another method used alkali metal beams (AMB) to give a negative ion and a positive ion (equation 2.15). The threshold is the sum of the ionization potential of the alkali metal and the electron affinity of the molecule. A related procedure is the determination of the threshold for endothermic charge transfer (EnCT) from one anion to a neutral to form a second anion. The threshold is equal to the difference in the electron affinities of the species so that the electron affinity of the reactant must be known. These procedures yielded accurate electron affinities of the halogen molecules [18-19, 28, 29]. 

Recent reviews on alkali metal beam studies, theoretical and experimental determinations of electron affinities using photon methods, and atomic electron affinities and an Internet source for electron affinities all give compilations [113-117]. The evaluation of molecular electron affinities is a major objective of this book. 

ELECTRON AFFINITIES DETERMINED USING THE MAGNETRON, ALKALI METAL BEAM, PHOTON, AND COLLISIONAL IONIZATION METHODS... 

Since the demonstration by Schumacher et al ) of the use of alkali metal vapor inclusion into a supersonic beam to produce clusters, there have been a number of attempts to generalize the approach. It has recently been recognized that instead of high temperature ovens, with their concommitant set of complex experimental problems, an intense pulsed laser beam focused on a target could be effectively used to produce metal atoms in the throat of a supersonic expansion valve. ) If these atoms are injected into a high pressure inert gas, such as helium, nucleation to produce clusters occurs. This development has as its most important result that clusters of virtually any material now can be produced and studied with relative ease. 

The sample is dissolved in 1-5 % of the solvent and it is then placed in a solution cell consisting of transparent windows of alkali metal halides. A second cell containing pure solvent is then placed in the path of reference beam to cancel out solvent interferences. 

A parallel investigation on the binding of alkali metal cations to nucleobases, employing guided ion beam mass spectrometry, has recently been reported by Rodgers and Armentrout . ... 

HF.RSCHBACH. DUDLEY R. (1932-). Awarded the Nobel prize in chemistry in 19X6 for work reporting that the energies of reactions of crossed molecular beams of isolated alkali metal atoms and alkyl halide molecules appeared mostly as vibrational excited states of products. This method ol studying all types of chemical reactions led to a more detailed knowledge of reaction processes. Doctorate awarded from Harvard in 1958. 

Fig. 3.4 Apparatus for the study of Rydberg states of alkali metal atoms a, the atomic beam source b, the electric field plates c, the pulsed laser beams and d, the electron multiplier...

References for this section are mainly to review papers. The examples given here do not show all the alkali metal atom reaction studies. Luminescence (D-line or continuum) is produced by steps following those tabulated. Radiation from MX has not been identified in these studies. Molecular beam studies show internal excitation (vibration plus rotation). 

Crossed molecular beams have been used to study nearly as wide a range of alkali metal atom reactions as has been examined by diffusion flames. An excellent review has been provided by Herschbach2. The multi-step mechanism displayed for chemiluminescence studies does not apply to the scattering experiments. Only the initial bimolecular reaction is important at the low pressures used. 

Typical reactions with an early barrier studied by molecular beams include those of the alkali metals with halogens and other simple molecules. 

The pellet (pressed-disk) technique depends on the fact that dry, powdered potassium bromide (or other alkali metal halides) can be compacted under pressure to form transparent disks. The sample (0.5-1.0 mg) is intimately mixed with approximately 100 mg of dry, powdered KBr. Mixing can be effected by thorough grinding in a smooth agate mortar or, more efficiently, with a small vibrating ball mill, or by lyophilization. The mixture is pressed with special dies under a pressure of 10,000-15,000 psi into a transparent disk. The quality of the spectrum depends on the intimacy of mixing and the reduction of the suspended particles to 2 gm or less. Microdisks, 0.5-1.5 mm in diameter, can be used with a beam condenser. The microdisk technique permits examination of samples as small as 1 fxg. Bands near 3448 and 1639 cm-1, resulting from moisture, frequently appear in spectra obtained by the pressed-disk technique. 

Cation emitters The alkali metal zeolites, and other alkali metal aluminosilicates, are efficient emitters of alkali metal cations. The cation emitters have been known for a much longer time than the anion emitters, but the anion emitters are better understood from a chemical perspective hence they are discussed here. Both types of emitters, however, can be scaled up in intensity readily to be used for the primary ion guns in static SIMS instruments. Ion beams of 50 pA to 1 nA focused to a 1-mm spot size are routinely produced by using these emitters. These emitters are primarily used in SIMS guns, as opposed to being used for isotope ratio analyses. 

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