Cross-beam technique

Recent measurements utilizing the crossed-beam technique have been performed as follows.37 A metastable helium beam is formed by electron-impact excitation of a thermal helium beam effusing from a multichannel array. The optical quenching method12 described earlier is applied to obtain results for He(2 5 ) and He(23S) separately. The target gas beam is... 

Montague, R.G., Harrison, M.F.A. and Smith, A.C.H. (1984). A measurement of the the cross section for ionisation of helium by electron impact using a fast crossed beam technique. J. Phys. B At. Mol. Phys. 17 3295-3310. 

Crossed-beam techniques must also be used when the targets are chemically unstable systems, such as hydrogen atoms. These techniques are now being used in many laboratories and have become indispensable in atomic collision physics. 

C.R. Blakley, M.J. McAdams, M.L. Vestal, A new LC-MS interface using crossed-beam techniques, Adv. Mass Spectrom., 7 (1978) 1616. 

In addition to product isomers, the crossed beam technique also provides information on the highly unstable reaction intermediates. The identified intermediates have been characterized by resorting to ah initio electronic structure calculations all the reaction intermediates are doublet radicals, internally excited, and hence highly reactive in planetary atmospheres. Although under the experimental single collision conditions the gas is too rarefied to allow three-body collisions, the collision induced stabilization of the intermediates is possible in Titan s dense atmosphere. Notably, these free radicals have unknown spectroscopic properties which could make them responsible for the orange color of the upper atmospheric layers. 

Photodetachment of alkali-metal negative ions by an argon-ion laser (4880 A) has been studied by the crossed-beam technique. Analysis of the energy of the photodetached electrons yields the electron affinities of the alkali-metals shown in Table 1. The values are relative to the independent measurement of the electron affinity of potassium.Included in the table for comparison are values from another investigation using a similar techniquethese are refined values of data reported in Vol. 3, Chapter 1. 

TJecent studies using a cross-beam technique have shown that free radicals produced in the vapor phase by irradiation with 100 e.v. electrons (18, 22, 23), 40 Kev. Ar+ ions (39), or 1 Mev. He+ ions (34), can be trapped at 77°K. and studied by ESR. Experiments on water vapor irradiated by 100 e.v. electrons (22), or by 1 Mev. He+ ions (34), showed the formation of trapped electrons, e t—a species thought to be the H02 radical—and provided indirect evidence for hydrogen atoms (34). Cyclohexane, cyclopentane, and benzene gave the same results from 1 Mev. He+ irradiation (40) as from 40 Kev. Ar+ irradiation (39)... 

Keil and co-workers (Dharmasena et al [16]) have combined the crossed-beam technique with a state-selective detection technique to measure the angular distribution of HF products, in specific vibration-rotation states, from the F + H2 reaction. Individual states are detected by vibrational excitation with an infrared laser and detection of the deposited energy with a bolometer [30]. 

Rates of Chemiionization. Rates of total chemiionization in reactive collisions of He(2 5) and He(2 5 ) with other species have been measured by Sholette and Muschlitz using a beam-gas apparatus and by Stebbings and co-workers by the crossed-beam technique. The latter workers have discussed the method of... 

Other new techniques include 3D-scanning, speckle reduction imaging and cross beam techniques. The gray-scale ultrasound is highly useful in the differential diagnosis of the most common benign lesions, namely simple cysts and hemangiomas. 

Phase analysis light scattering (PALS) is a technique that is very similar to laser Doppler electrophoresis (LDE) and is used to measure the electrophoretic mobilities of colloidal particles. This technique is particularly suited to measurements of charged particles suspended in nonpolar media and sensitivity of the method is far superior to that which could be obtained by LDE measurements. It makes use of a cross-beam technique and offsets one of the laser beams relative to the other by several kEIz. ... 

Of particular interest is the so-called crossed-beam method to study the dynamics of elementary reactions a field, in which D.R. Herschbach and Y.T. Lee were awarded the 1986 Nobel Prize in Chemistry for their fundamental development work. A key feature of the crossed-beam technique is to work under single collision conditions (see below). J.C. Polanyi shared the 1986 Nobel Prize in chemistry for his contribution in the study of the dynamics of elementary reactions using other methods, such as chemiluminescence and dynamical calculations. 

The crossed-beam technique is a very powerful tool to investigate the dynamics of chemical reactions in the gas phase, in clusters and at surfaces. In this chapter we will study bimolecular reactions with the reactant state being prepared, or the product being probed by lasers. 

Not only the product angular distribution can be determined, but also its recoil velocities. This type of measurement, i.e. both the angular and velocity distribution of the reaction products, is currently made using the universal crossed-beam technique in which a rotatable electron-impact mass spectrometer is used... 

A good example of the influence of electronic excitation of reagents on a chemical reaction is the reaction of an excited sodium atom with HCl that was investigated by the crossed-beam technique. Figure 22.3 shows the NaCl differential cross-sections observed for the reactions Na(3s S, 3p P, 5s S, 4d D) + HC1 NaCl -f H at 56 kcal mol collision energy. 

CROSSED-BEAM TECHNIQUES AND LASER SPECTROSCOPIC DETECHON... 

Crossed-beam techniques and laser spectroscopic detection towards the state-to-state differential reaction cross-section measurements... 

Muller,A., Huber, K.,Tinschert, K., Becker, R., Salzborn, E. (1985) An improved crossed-beam technique for the measurement of absolute cross-section for electron impact ionization of ions and its application to Ar ions. Journal of Physics B Atomic and Molecular Physics, 18, 2993-3009. 

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