Large clusters of benzene were generated in supersonic flow through a Laval nozzle with carrier gases He, Ne, or Ar. Benzene concentration and carrier pressures were varied over wide ranges. Diffraction patterns recorded from s=0.8 to 12 Å−1 revealed strong intermolecular interference features indicative of supercooled bulk liquid at 100–200 K. Computer simulations of nucleation and cluster growth were carried out and agreed with the following observations. An initial benzene partial pressure of ∼0.1 bar expanded through a nozzle of our design requires a carrier pressure of 2–3 bar to give reasonably complete condensation. Cluster diameter and fraction condensed decrease if (1) benzene mole fraction is reduced at constant carrier pressure, (2) carrier pressure is reduced at constant benzene partial pressure, and (3) carrier molecular weight is decreased. The simulations identify the factors accounting for the trends. Cluster intensities are compared with those calculated for small clusters proposed by Williams, small crystal fragments, and bulk fluid according to the statistical mechanical algorithm RISM. None of the models reproduce observed results within experimental error but comparisons provide information about size, temperature, and structure. Intrinsic deficiencies of RISM are indicated by the present experiments.
Peer Reviewed
http://deepblue.lib.umich.edu/bitstream/2027.42/70115/2/JCPSA6-80-4-1451-1.pdf