Structural Studies of Isolated Small Particles Using Molecular Beam Techniques

  1. David R. Schryer
  1. Sang Soo Kim and
  2. Gilbert D. Stein

Published Online: 21 MAR 2013

DOI: 10.1029/GM026p0033

Heterogeneous Atmospheric Chemistry

Heterogeneous Atmospheric Chemistry

How to Cite

Kim, S. S. and Stein, G. D. (2013) Structural Studies of Isolated Small Particles Using Molecular Beam Techniques, in Heterogeneous Atmospheric Chemistry (ed D. R. Schryer), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM026p0033

Author Information

  1. Gasdynamics Laboratory, Department of Mechanical and Nuclear Engineering, Northwestern University, Evanston, Illinois 60201

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1982

ISBN Information

Print ISBN: 9780875900513

Online ISBN: 9781118663813

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Keywords:

  • Atmospheric chemistry—Addresses, essays, lectures

Summary

Small particles or clusters have been shown to be of importance in catalysis. Specially designed Laval nozzles are used as a continuous source of clusters of Ar, Kr, or Xe in a crossed molecular beam/40-keV electron beam experiment. Each of these noble gases is expanded adiabatically through the nozzle as a small mole fraction in He, thus permitting one to vary cluster concentration, mean size, and temperature. Because the clusters have random orientation, the electron diffraction patterns are of the Debye-Scherrer type. They reveal that the clusters are crystalline, with temperatures in the range 15 to 60 K and mean size from g = 50 to 1000 atoms per cluster. As g decreases below 500 a progressive change in structure from bulk face-centered cubic is observed. Theoretical diffraction patterns are calculated using a multishell icosahedral structure in addition to that of the bulk. Similar structure changes occur in all three species. Since particles in this size range can be present in the atmosphere, especially due to photochemical production, the possibility exists that they may possess nonbulk properties in general and enhanced catalytic activity in particular.