Formation and Characterization of Large (Ar) n , (N2) n , and Mixed (Ar) n (N2) m van der Waals Clusters Produced by Supersonic Expansion

Abstract

This paper reports the formation and characterization of large (Ar) n , (N2) n , and mixed binary (Ar) n (N2) m van der Waals clusters produced at room temperature in the process of supersonic expansion. The average cluster size is determined by the buffer gas induced beam-broadening technique. For both Ar and N2 clusters, power variations of the average cluster size $$ \ifmmode\expandafter\bar\else\expandafter\=\fi{n} $$ with the gas stagnation pressure P 0 give size scaling as $$ \ifmmode\expandafter\bar\else\expandafter\=\fi{n} \propto P^{{1.9}}_{0} $$ . The average cluster sizes of argon vary from 2950 to more than 30900 atoms per cluster with the argon gas stagnation pressures ranging from 4 to 14 bars, and of nitrogen vary from 600 to more than 10400 molecules per cluster with the nitrogen gas stagnation pressures ranging from 8 to 38 bars. The mixed binary (Ar) n (N2) m cluster is produced by supersonic expansion of an Ar–N2 mixture. The large mixed binary (Ar) n (N2) m clusters with the average sizes n + m between 1000 and 16000 are obtained. In coexpansion of Ar–N2 mixture, we find that the argon concentration becomes higher in the beam than before the expansion. This finding is discussed and may be helpful for further insight into the phenomenon of clustering.