The Nucleation of Ice in Supercooled D₂O and H₂O

Kurzfassung

The homogeneous nucleation rates of light and heavy water have been measured in supercooled levitated micro-droplets at different temperatures using a temperature jump experiment. Homogeneous nucleation times of ice in supercooled water follow the Poisson statistics. The nucleation rate has a negative temperature coefficient; it increases strongly with decreasing temperature. At the same degree of supercooling, the nucleation in heavy water is faster than in light water. The discussion of the experimental results is based on kinetic arguments in the frame of a two-state model of liquid water. The homogeneous nucleation rate J is tantamount to a volume-normalized apparent first-order rate constant J* which can be described by the product of the genuine rate constant j and an overall equilibrium constant K. K describes a large number of pre-equilibria, which are coupled to the rate-determining step of nucleation and influence the apparent nucleation rate J of formation of the critical germ.