Clusters

The first step in the clustering process is the initiation. This involves a three body collision which the results in the formation of a dimer. The excess energy of the collision is carried away by either a carrier gas or the clustering species itself:

The next stage is the growth of the cluster. This proceeds by a three-body reaction, similar to the one shown above, until the cluster becomes large enough to absorb the collision energy within itself. Once this point is reached the dominant clustering process becomes:

Because of the nature of the growth process, large clusters have high internal energies. Clusters with high internal energies are known as 'hot', similarly those with low internal energies are known as 'cold' or 'ultracold' The main processes that lead to cooling of clusters are…

evaporation

sputtering

exchange