Heterogeneous cluster formation in a supersonic argon-krypton jet according to cathodoluminescence data in the vacuum ultraviolet

Abstract

Processes of cluster formation in a supersonic argon-krypton jet at low concentrations of the krypton impurity (down to 1×10−3%) are investigated by a luminescence method. VUV diagnostics of the picture of heterogeneous nucleation, including its earliest stages, is employed for the first time. Attention is focused mainly on the behavior of the emission bands belonging to the neutral excimers Ar2* and Kr2* and the charged homoatomic complexes (Ar4+)* and (Kr4+)* and the heteroatomic exciplexes (Ar∕Kr)*. In the first stage of heterogeneous nucleation the nuclei can be krypton atoms (dimers). Beginning at krypton concentrations in the gas mixture of 0.02% and higher a multiatomic krypton core is formed in the cluster. When such clusters are ionized the ion is located in the krypton core, and its electric field has a substantial influence on the parameters of the emission band of an Ar∕Kr molecule found at the argon/krypton boundary. The results of this study demonstrate the high efficiency of VUV spectroscopy for studying processes of heteroatomic cluster formation in supersonic jets.