Creation and structure study of vacuum isolated clusters of argon, krypton, and xenon

• Published in: Journal of colloid and interface science 1982-01, Vol.87 (1), p.180-203
• Main Authors: Kim, Sang Soo, Stein, Gilbert D
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(82)90381-2

Homogeneous clusters of Ar, Kr, or Xe are formed in adiabatic, high Mach number expansions through very small, diverging Laval nozzle sources. A He carrier gas is employed and the mole fraction of condensable species varied from 1.0 to 0.06 in an effort to control the cluster size distribution and temperature. The nozzle source is part of a multistage molecular beam apparatus. Electron diffraction, using a 40 keV beam, is used to study cluster structure. Cluster sizes are varied from g ̄ = 50 to 1500 atoms per cluster and temperatures range from 20 to 60°K. The structure for g ̄ > 1000 is bulk fcc and transforms gradually into a noncrystalline structure as size decreases. The smallest structures, for all three noble gases, are consistent with the icosahedral structures which are theoretically favored energetically in this regime. For a fixed mole fraction of 0.06, the cluster temperatures, T c , are systematically higher going from Ar to Xe with dimensionless temperatures, kT c / ϵ3, systematically lower. There is evidence that P 0D o/(kT 0 ϵ3) is the unifying parameter for predicting the onset of massive clustering for rare gases in these nozzle-type sources.