CLUSTER-SIZE DETERMINATION FROM DIFFRACTIVE HE ATOM SCATTERING

In a crossed molecular beam arrangement helium atoms are scattered fro m argon clusters which are produced in an averaged size range of (n) o ver bar = 6 to (n) over bar = 90 by adiabatic expansion through sonic and conical nozzles. The diffraction oscillations in the total differe ntial cross section are used to derive information on the size distrib ution of the clusters by comparison with quantum mechanical calculatio ns based on a model potential. In the size range covered by the measur ements, the average cluster size is given by (n) over bar = 38.4(Gamma /1000)(1.64), where Gamma* is the scaling parameter of the source con ditions introduced by Hagena [Z. Phys. D 4, 291 (1987)]. The results a re in agreement with recent measurements of corrected mass spectra but disagree with the results obtained from electron diffraction. General relations are recommended which connect the scaling parameter with th e averaged size. (C) 1996 American Institute of Physics.