Supersonic beam sources

Those fixed-angle measurements reported to date have all used either a heated effusive inlet, or heated gas cell for sample admission [55, 56, 61, 62, 65]. Probably the higher sample number densities these sources generate, compared to a supersonic beam source, provides some compensation for the reduced collection efficiency in the fixed-angle measurement. 

Figure 1 is a schematic of the laser vaporization source. This diagram depicts a pulsed valve on the left which supplies high pressure helium flow directly towards the right. Several workers have also chosen to use continuous helium f ows(2,6,9). In general these sources are modifications of conventional supersonic beam sources. 

Note The high-pressure, high-temperature supersonic beam source has been described in detail by B. Brutschy and H. Haberland, J. Phy. E13, 150 (1980).]... 

Figure 6. Typical carbon cluster distribution obtained in a laser vaporization supersonic beam source under relatively mild clustering conditions.

Fig. 2.18. Side elevation of the molecular beam machine s two-chamber setup. Chi vacuum chamber to generate the molecular beam by adiabatic expansion. A seeded supersonic beam source is placed here. Further details are shown in Fig. 2.19. Ch2 here, the molecules interact with the laser pulses. Detection is performed by a quadrupole mass spectrometer (QMS) with a 90° ion deflector between the mass filter and secondary electron multiplier (SEM) (Fig. 2.20) or the Langmuir-Taylor detector (Fig. 2.22)...

Valentin J J, Coggiola M J and Lee Y T 1977 Supersonic atomic and molecular halogen nozzle beam source Rev. Sc/. Instrum 48 58-63... 

The fonnation of clusters in the gas phase involves condensation of the vapour of the constituents, with the exception of the electrospray source [6], where ion-solvent clusters are produced directly from a liquid solution. For rare gas or molecular clusters, supersonic beams are used to initiate cluster fonnation. For nonvolatile materials, the vapours can be produced in one of several ways including laser vaporization, thennal evaporation and sputtering. 

The spectrometer is fitted with a skimmed c.w. supersonic molecular beam source. Many chiral species of interest are of low volatility, so a heated nozzle-reservoir assembly is used to generate, in a small chamber behind a 70-pm pinhole, a sample vapor pressure that is then seeded in a He carrier gas as it expands through the nozzle [103], Further details of this apparatus are given elsewhere [36, 102, 104],... 

There are several preparative methods for the production of bare metal clusters including the fast flow reactor (PER), the fast flow tube reactor (FTR), the SIDT (24), the GIB (23), and a supersonic cluster beam source (SCBS) (198). Essentially, all of these methods are similar. The first process is to vaporize the metal sample producing atoms, clusters, and ions. Laser vaporization is generally favored although FAB or FIB may be used. The sample is located in a chamber or a tube and so vaporization generally takes place in a confined environment. An inert gas such as helium may be present in the vaporization source or may be pulsed in after the ionization process. 

Many of the metal cluster anions have been produced by cathode discharge in He doped with Ar and studied in a flow tube reactor. A few clusters have been prepared by laser vaporization using a supersonic cluster beam source and the reac-... 

Neutral clusters from supersonic beam 157 Spectroscopy of neutral clusters 158 Sources of ionic clusters 167 Mass spectrometry of ionic clusters 170... 

Scattering studies with metastable atoms are in many cases easier (and less expensive) than experiments with ground-state atoms, The discussion that follows is mainly concerned with helium, as most of the information is available for this atom. Figure 2 shows a skeletal setup of the experiment. A helium beam from a supersonic nozzle source is excited by electron impact to its two metastable states. The singlet state can be quenched by the 2g radiation from a helium-gas discharge lamp ... 

Atoms may be produced both in thermal and supersonic beams using the techniques of thermal dissociation [33] and dissociation by micro-wave [34] and radio frequency [35] discharges and by plasma sources [36]. Comparatively few reactions involving radicals have been studied in molecular beams, but sources have been developed that produce radicals by pyrolysis [37], reaction [25, 38, 39] and photolysis [40]. 

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