Interesting results were obtained in the initial investigation of the nucleation behavior of supersaturated sulfur vapor up to temperatures above the λ transition. This is a second-order phase transition in liquid sulfur characterized by a change in molecular structure from closed sulfur rings to open radical chains within a narrow temperature range. Although the temperature dependence of the constant rate supersaturation is not correctly represented, it is surprising again how well classical nucleation theory describes experimental results even for such a complex substance. For homogeneous nucleation, there are indications that the λ transition influences the nucleation behavior as a consequence of the changing thermophysical properties  density and surface tension  of the liquid sulfur. Photoinduced nucleation shows a striking effect directly correlated with the transition. Below the λ temperature, the vapor is extremely sensitive to irradiation with light in the range 260−360 nm that decreases the constant rate supersaturation by about a factor of 10. At the transition temperature, the photo effect vanishes sharply. The close correlation of the structure of liquid sulfur and the nucleation behavior is interpreted as a confirmation of the capillarity approximation that indeed the properties of the liquid determine nucleation behavior.

Evaluation of surface tension and Tolman length as a function of droplet radius from experimental nucleation rate and supersaturation ratio: Metal vapor homogeneous nucleationThe first experimental study of the spectral dependence of the nucleation of cesium vapor caused by light absorption is carried out in a diffusion cloud chamber. The spectral dependence of the nucleation rate is compared with the absorption and ionization spectra of cesium vapor. The results evidence that the observed structure in the nucleation spectrum at photon energies above the ionization threshold is correlated to the light-induced ionization of cesium dimers Cs 2 ϩ . At lower photon energies light-induced nucleation can be either due to generation of ions by direct ionization of cesium clusters, to various two-step ionization processes, or to optical excitation of cesium atoms. The spectral dependence of the nucleation rate provides a new and powerful tool to study ionization spectra of metal vapors. In addition to results obtained by conventional methods a more consolidated insight into energy levels of atoms and clusters under equilibrium conditions is possible.

No abstract