Thermal collision rate constants for small nickel clusters of size 2--14 atoms
- Department of Nuclear Engineering, Texas A&M University, College Station, Texas 77843-3133 (United States)
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3133 (United States)
- National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321 (United States)
However in this case also, the observed trend suggests a better agreement for cluster sizes somewhat larger than the sizes considered in this study. The other significant reaction channel observed was monomer evaporation which becomes more frequent and persists for larger target cluster sizes as the size of the projectile cluster is increased. The cross section results in all three cases do not exhibit any dramatic dependence on cluster size, consistent with the experimental observation of smooth and featureless size distributions for nickel and other transition metal clusters. The cluster--monomer collision calculations were repeated by setting the internal temperature of the cluster to 0 K. For the 0 K case, the sticking cross section is underestimated by the hard sphere cross section even for the larger clusters. However, the observed trend indicates a better agreement between the two cross sections for cluster sizes outside the size regime considered. For all of the above cases considered, the hard sphere cross section appears to be easily parametrizable in terms of the cluster size. For a limited number of cluster sizes, the collision calculations were repeated using different integration times and from these calculations it appears that the collisionally formed clusters decay roughly in an exponential manner. This suggests that the cluster decay rates may be obtained using a simple statistical theory such as the RRK theory. Also, these calculations suggest that even the smallest of the collisionally formed clusters survives long enough to be cooled by collisions with background gas molecules. As a consequence, cluster growth may be determined by coagulation-type reactions, unless monomer is supplied continuously. The implications of the results of this study to cluster growth models are discussed. The results of this study may be improved by the inclusion of two factors, directional bonding and long range interactions in the potential.
- DOE Contract Number:
- FG05-91ER61207; FG03-94ER61952
- OSTI ID:
- 57915
- Journal Information:
- Journal of Chemical Physics, Vol. 102, Issue 19; Other Information: PBD: 15 May 1995
- Country of Publication:
- United States
- Language:
- English
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