Homogeneous nucleation and droplet growth in supersaturated argon vapor: the cryogenic nucleation pulse chamber.

We built a cryogenic nucleation pulse chamber for measuring homogeneous nucleation rates of argon. First measurements show that the growth rate of argon droplets at nucleation conditions is rather high so that nucleation and growth could not yet be decoupled. Nevertheless, the experiments permit an estimate of the onset of nucleation corresponding to a nucleation rate of J=10(7(+/-2)) cm(-3) s(-1) at temperatures 52<TK<59 and supersaturations around S approximately 10. Despite their preliminary nature these experiments indicate a severe failure of the classical nucleation theory, which predicts nucleation rates on the order of 10(-28)-10(-13) cm(-3) s(-1) for the quoted conditions. Recent calculations based on density functional theory can only partially explain the discrepancy. In addition to the first nucleation experiments, we obtained and analyzed growth curves for argon droplets from constant angle Mie-light scattering. The good agreement of the experimental growth curves with model calculations according to Fuchs and Sutugin [Highly Dispersed Aerosols (Ann Arbor Science, Ann Arbor, MI, 1970)] permits a near-quantitative description of the experimental light-scattering signal. The procedure provides an estimate for the number density of the droplets along with a measure of their polydispersity.