Generation of molecular clusters of controlled size

Abstract

A novel gasdynamic source capable of producing small clusters of controlled size is described. Two versions of this Multiple Expansion Cluster Source (MECS) are discussed: one which produces transition metal clusters of interest in catalysis and one which produces water clusters of atmospheric interest. The clusters are formed as an aerosol supported in an inert gas flow. They can be isolated from the carrier gas by impingment on a surface or by expansion through a sonic orifice into a vacuum region to form a molecular beam. A controlled mean size ranging from the dimer up to several thousand of the monomer species is possible. The full width at half maximum of the distribution of cluster sizes that is produced is as small as is theoretically possible with a condensation type process. For a mean size greater than ≈50, the FWHM has a constant value in diameter space of approximately twice the diameter of the monomer.