Homogeneous and light-induced nucleation of sulfur vapor - Diffusion cloudchamber investigations of constant rate supersaturation

Interesting results were obtained in the initial investigation of the nucle ation behavior of supersaturated sulfur vapor up to temperatures above the transition. This is a second-order phase transition in liquid sulfur charac terized 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 represent ed, it is surprising again how well classical nucleation theory describes e xperimental results even for such a complex substance. For homogeneous nucl eation, there are indications that the gimel transition influences the nucl eation behavior as a consequence of the changing thermophysical properties - density and surface tension - of the liquid sulfur. Photoinduced nucleati on shows a striking effect directly correlated with the transition. Below t he gimel temperature, the vapor is extremely sensitive to irradiation with light in the range 260-360 nm that decreases the constant rate supersaturat ion by about a factor of 10. At the transition temperature, the photo effec t vanishes sharply. The close correlation of the structure of liquid sulfur and the nucleation behavior is interpreted as a confirmation of the capill arity approximation that indeed the properties of the liquid determine nucl eation behavior.