The onset of clustering and the size of clusters produced can be described by an empirical scaling parameter. Γ*, known as the Hegena parameter. [16 - TD69.pdf] page 311.
see formula (1) TD.69 page 311
where d is the nozzle diameter (in mm), α the expansion half-angle (α= 45° for sonic nozzles, α < 45° for supersonic), p0 the backing pressure (in mbar), T0 the pre-expansion temperature (in Kel- vin) and k, the condensation parameter, is a con- stant related to bond formation (kHe 1â„4 3:85 while kXe 1â„4 5500 17). Gas-jets with the same Cô° tend to form clusters of the same average size. Cluster formation is a statistical process and therefore there is usually a relatively broad distribution of cluster sizes 17–19. In the massive condensation regime, where nearly all the atoms have condensed into clusters of greater than ô°‚100 atoms, the av- erage number of atoms per cluster hNci scales ap- proximately as 17,20 hNc i ô°‚ Cô°2:0 : ð2Þ By varying T0 and p0, it is possible to control the value of Cô° to engineer a cluster medium of arbi- trary average density and cluster size. Optical Rayleigh scattering provides a convenient tech- nique for the in situ measurement of average cluster sizes 21–23,78.
See Also
Atomic Cluster X-Ray Emission Atomic Clusters Formation of Atomic Clusters Interaction of Intense Laser Pulses with Atomic Clusters - Measurements of Ion Emission Simulations and Applications TD69.pdf Laser Cluster Interactions