Structural Studies of Isolated Small Particles Using Molecular Beam Techniques
- David R. Schryer
Published Online: 21 MAR 2013
Copyright 1982 by the American Geophysical Union.
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
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1982
Print ISBN: 9780875900513
Online ISBN: 9781118663813
- Atmospheric chemistry—Addresses, essays, lectures
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.