Cluster growth in binary N2–Kr supersonic jets: Effect of initial gas temperature and krypton gas concentration

Abstract

An electron diffraction diagnostics of substrate-free clusters formed in N2–Kr binary jets expanding through a supersonic nozzle into a vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol % krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30000 molecules per cluster. A change in the nucleation mechanism in the jet from homogeneous to heterogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 decreased from 120 to 100 K, which had a profound effect on the sizes, phase composition, and component composition of the clusters. The effect of cluster growth suppression by adding impurity with stronger intermolecular forces was revealed for the first time. It is shown that the effect is caused by the kinetics of gas condensation in a supersonic jet and is manifested at T0 = 120 K when the krypton gas content increases to 6 mol %. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase compared to the hcp.