Date of Original Version
We have measured the mass distribution of cluster ions formed from a supercritical expansion of helium gas. We find two distinct cluster groups which we identify as condensation and fragmentation clusters. The latter first appear when the expansion conditions approach the critical isentrope. The measurements also suggest that the neutral fragmentation cluster mass distribution is a universal function of the source entropy.
Jiang, T. & Northby, J. A. (1992). Fragmentation clusters formed in supercritical expansions of 4He. Physical Review Letters, 68(17), 2620-2623. doi: 10.1103/PhysRevLett.68.2620
Available at: http://dx.doi.org/10.1103/PhysRevLett.68.2620