Clustering in molecular gases freely expanding into vacuum

Abstract

The actual enthalpies and entropies of clustering and the properties of clusters characterizing their catalytic effect on the rate of relaxation of vibrational degrees of freedom are used to compute (N2O)N and (CO2)N cluster formation and growth in gases expanding into a vacuum through a sonic nozzle. Relations are found between characteristics of gaseous N2O and CO2 in the nozzle source and in the jet flow containing clusters and those of the molecular cluster beam formed from the axial region of the jet. Calculated and measured values of the following cluster-beam characteristics are compared: intensity, flux density for molecules in the beam, scaling parameters for transition to well-developed condensation in the jet, cluster size distribution function, mean cluster size, and internal cluster temperature. Realistic characterization of cluster properties ensures good agreement between calculated and measured results and provides a basis for adequate description of the mechanisms of molecular cluster formation in supersonic jets issuing from sonic nozzles characterized by extremely rapid decrease in gas temperature and highly nonequilibrium distribution of energy over molecular degrees of freedom.