Molecular beam collimation

Molecular beam Collimated stream of gaseous molecules produced by expansion of a gas through an orifice into an evacuated chamber. A supersonic molecular... 

Optothemial spectroscopy is a bolonietric method that monitors the energy in a stream of molecules rather than in the light beam. A well collimated molecular beam is directed toward a liquid helium cooled bolometer. There will be energy... 

Gopinath, C. S. and Zaera, F. (2000) Transient kinetics during the isothermal reduction of NO by CO on Rh(lll) as studied with effusive collimated molecular beams , J. Phys. Chem. B, 104, 3194. 

The molecular beam is formed by the supersonic expansion of gas through a pulsed nozzle. It is then collimated by two skimmers, and enters... 

Another apparatus that is very useful in studies of the mechanism of catalytic surface reactions is shown in Fig. 17. This is used in a molecular-beam surface scattering experiment (22b) in which a well-collimated beam of the reactant gas or gas mixture is scattered from a crystal surface and the products that are desorbed after a single scattering at a given solid angle... 

The experimental setup used by our group is shown in Figure 7-1. This apparatus consists of a molecular beam source coupled to a chamber housing the quadrupole mass spectrometer. The continuous beam source consists of a Campargue-type nozzle, an expansion chamber, and a collimation chamber. The nozzle assembly itself is mounted on a micrometer and is fitted with a gas handling line which... 

Figure 1 Schematic diagram of a molecular beam machine. A gas at elevated pressure emanates from an orifice. The gas stream is collimated in three differential pumping stages to reduce the gas load on the target chamber. Only the part of the gas stream that reaches the target though all collimators is indicated as shaded. In the UHV target chamber a crystal is positioned in the beam path. The pressure and the target chamber and particles reflected or desorbed from the sample surface are detected by particle detectors. Inert beam flags can be moved into the beam to determine the beam intensity and the sticking coefficient. From Kleyn [22],...

Figure 1 Schematic of the atomic beam dosing source used with REMPI detection by Murphy et al. to study the recombination of H [36, 37] and N [38] at metal single crystal surfaces. A single crystal surface is supported on a manipulator in the path of a collimated molecular beam. The beam supplies reactant molecules or atoms, produced using a microwave discharge in the glass nozzle, which react and recombine at the surface. The reaction products are ionised by the laser, which is focused in front of the surface (inset), and the resulting ions are timed into a microchannel plate detector.

Two methods of studying reactions under molecular beam conditions are commonly used the beam—gas and the beam—beam arrangements. The former method is used for studies of product vibrational, rotational and electronic energy distributions by absorption or emission spectroscopy. A well-collimated beam produced by one of the techniques described above, passes through a diffuse gas (<1 x 10 5 Torr) of the other reagent which either fills the entire detection chamber [78] or is... 

The ground electronic state of 139La160 is X2S+ audits electronic spectrum involving the excited B2Y,1 has been studied by Doppler-free laser-induced fluorescence by Bacis, Collomb and Bessis [85] and by Bernard and Sibai [86]. Both states have therefore been well characterised and the system is ideal for radiofrequency/optical double resonance, as described by Childs, Goodman, Goodman and Young [87]. They used a collimated molecular beam, with the laser pump/probe technique described elsewhere in this chapter. 

The problems associated with the formation and detection of molecular beams have already been referred to. They are interrelated and have largely determined which reactions have been studied with this technique. The simplest method to form a beam is to collimate the effusive flow occurring from a low-pressure source, conventionally called an oven, although its temperature may be subambient. Unfortunately, this yields low beam intensities, and the velocities in the beam are thermally distributed. As a result, even for the accurate assessment of the incident-beam intensity, a highly sensitive detector is required. Moreover, the relatively low beam temperature requires that the reaction has a small threshold energy so that an appreciable proportion of the scattering is reactive. 

In order to produce supported samples for STM or FEM study, clusters formed on the centerline of the condensation reactor are extracted through a 1 mm diameter capillary into a vacuum chamber typically kept at 10-5 Torr. The resulting supersonic free jet flow is collimated to form a molecular beam of metal clusters, uncondensed metal atoms and inert gas atoms. 

If molecules are allowed to escape from an enclosure into an evacuated space through a small hole under the conditions described for the effusion method in Section 3.3, they may be collimated into a molecular beam by the use of slits. If a pulse of this molecular beam is allowed to fall on a moving receiving plate, the condensed... 

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