Crossed beam experiments

The neutral beam is pulsed by a rotating chopper wheel (E) at a frequency of about 200 Hz to discriminate the product ions formed in the reaction zone from those produced outside the reaction zone. The source is operated at 55°C and is assumed to provide a corresponding Boltzmann distribution. The energy analyser (F) consists of a fine grid (90 lines per in.) at the potential of the last ion lens, followed by a finer screen (375 lines per in.) to which variable retarding potential is applied. 

In addition to these qualitative features, the results also provide a basis for quantitative discussion. From the Newton diagrams, the most probable CM velocities Ua r n the product ion ArD are obtained. Using these values one can calculate the translational exoergicity Q (see 

The angular distributions and the relation (78) for the translational exoergicity were two exciting experimental results which stimulated later theoretical development. Following this experiment, many investigators, 

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There are many experimental methods by which photodissociation of ions have been studied. The earliest were crossed-beams experiments on Hjbeginning in the late 1960s [24, 25 and 26] and experiments on a... 

In a crossed-beam experiment the angular and velocity distributions are measured in the laboratory coordinate system, while scattering events are most conveniently described in a reference frame moving with the velocity of the centre-of-mass of the system. It is thus necessary to transfonn the measured velocity flux contour maps into the center-of-mass coordmate (CM) system [13]. Figure B2.3.2 illustrates the reagent and product velocities in the laboratory and CM coordinate systems. The CM coordinate system is travelling at the velocity c of the centre of mass... 

Figure B2.3.2. Velocity vector diagram for a crossed-beam experiment, with a beam intersection angle of 90°. The laboratory velocities of the two reagent beams are and while the corresponding velocities in the centre-of-mass coordinate system are and U2, respectively. The laboratory and CM velocities for one of the products (assumed here to be in the plane of the reagent velocities) are denoted if and u, respectively.

Kaiser R I and Suits A G 1995 A high-intensity, pulsed supersonic carbon course with C( P ) kinetic energies of 0.08-0.7 eV for crossed beam experiments Rev. Sc/. Instrum. 66 5405-11... 

A mass spectrometer provides an example of a molecular beam, in this case a beam of molecular ions. Molecular beams are used in many studies of fundamental chemical interactions. In a high vacuum, a molecular beam allows chemists to study the reactions that take place through specifically designed types of collisions. For example, a crossed-beam experiment involves the intersection of two molecular beams of two different substances. The types of substances, molecular speeds, and orientations of the beams can be changed systematically to give detailed information about how chemical reactions occur at the molecular level. Chemists also have learned how to create molecular beams in which the molecules have very little energy of motion. These isolated, low-energy molecules are ideal for studies of fundamental molecular properties. 

Compared to the H-atom Rydberg tagging technique,65 the resolution of the present method is somewhat worse, by about a factor of two. This loss in resolution, however, is realized in general only for photodissociation studies. In a typical crossed beam experiment, the product translational energy resolution is usually limited by the energy spread of the initial collision energy rather than the detection scheme. On the other hand, the present... 

The setup used for crossed beam experiments is basically the same apparatus used in the H2O photodissociation studies but slightly modified. In the crossed beam study of the 0(1D) + H2 — OH + H reaction and the H + HD(D2) — H2(HD) + D reaction, two parallel molecular beams (H2 and O2) were generated with similar pulsed valves. The 0(1D) atom beam was produced by the 157 photodissociation of the O2 molecule through the Schumann-Runge band. The 0(1D) beam was then crossed at 90° with the... 

IV CROSSED-BEAM EXPERIMENTS WITH LASER-EXCITED... 

The technique for investigating scattering processes in crossed-beam experiments is well developed. For example, elastic scattering experiments with neutral particles at thermal energies are well understood,85 and the techniques for producing molecular and alkali atom beams and to detect them and interpret their kinematics has been reviewed on several occasions.86, 87. The new aspect of the present work is the technique for... 

IV. Crossed-Beam Experiments with Laser-Excited Sodium Atoms 359... 

One of the main goals of the crossed-beam experiment is to measure the internal energy AEvlh rol transferred to the molecule. In principle, this is possible in either of two ways. First, the scattered molecules could be detected and their product-state population analyzed. Infrared emission or absorption techniques may be considered, similar to those used in cell experiments.13 21 Although such studies would lead to the most detailed results (at least for polar molecules), under crossed-beam conditions they are impossible for intensity reasons, even if the possibility of measuring differential cross sections is renounced and the molecules in the scattering volume itself are detected. Detection via electronic molecular transitions may be invisaged. Unfortunately, the availability of tunable lasers limits this possibility to some exotic molecules such as alkali dimers. The future development of UV lasers could improve the situation. Hyper-Raman... 

Note added in proof-. Recently, Kwei and colloborators have investigated in a somewhat different crossed beam experiment Na + N2,C0,02 and NO. Their results differ in some details from ours, but agree in general trends.136... 

The problem of quenching alkali resonance radiation in E-VR energy-transfer collisions with simple molecules is important as a model case for basic processes in photochemistry and serves its own right for a variety of practical applications, such as in laser physics. It has been studied for many years in the past, but only recent progress has led to information of the final internal energy of the molecule. In particular, crossed-beam experiments with laser-excited atoms allow a detailed measurement of energy-transfer spectra. There can be no doubt that the curve-crossing... 

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