Supersonic cluster beam source

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-... 

Smalley, Direct Injection Supersonic Cluster Beam Source for FT-ICR Studies of Clusters, Rev. Sci. Instrum. 61, 3686-3693 (1990). 

Another remarkable endohedral complex which, has recently been created is U C2s.[Gu92] This affords a counterexample to the observation that endohedral complexes are typically based on fullerenes larger than Ceo- Indeed, C28 appears to be the smallest fullerene produced in supersonic cluster beams from a laser-vaporization source. Photofragmentation experiments ve an additional sense of how strongly the internal U stabilizes C28- Larger, empty fullerenes can be blasted down to C32, but... 

Generation of the Molecular/Cluster Beam. In the first chamber the molecules and clusters are produced in a seeded supersonic nozzle source. It is perhaps the most intense molecular/cluster beam source available. In this source, alkali metal is vaporized in a hot oven as sketched in Fig. 2.19. The alkali... 

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

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

Figure 2.37 Carbon cluster distribution showing prominence of Ceo- Note that x 10 magnification is used for ions larger than Cso. Source Reprinted from Rohifing EA, Cox DM, Kaldor A, Production and characterization of supersonic carbon cluster beams, J Chem Phys, 81 3322, 1984.

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. 

In a seeded supersonic expansion source [35-37[, the material is heated in an oven and a mixture of gaseous material and a seed gas expands through a nozzle into the vacuum. This source produces a highly intense beam of small pure and mixed metal clusters, but it is limited to metals with a low boiling point (Li, Na, K, etc.). Laser vaporization sources [13,38[ are more widely used as they produce pure and mixed clusters of most elements and when operated at low frequency (1-10 Hz) they have been successfully used... 

Fig. 1.19. Scheme of the experimental setup for infrared multiphoton ionization or dissociation of clusters or of metal clusters-rare gas complexes. The charged and neutral clusters are directly emitted from the laser vaporization/supersonic expansion source. The beam passes a skimmer and is subsequently crossed by the tightly focused beam of the FELIX. At some time after the FELIX pulse is over, the time-of-flight mass spectrometer acceleration plates are pulsed to high voltage, and a mass spectrum is recorded in a standard reflectron setup. Also schematically depicted is the particular pulse structure of the FELIX light [126,127]... 

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