The rates of redistribution of CCl3F clusters under subsaturation conditions

Pure CCl3F (Freon-11) vapor, initially below its room-temperature saturated vapor pressure, was compressed behind weak incident shock waves. The initi al pressure was varied from 26 to 747 min Hg, and the shock speed was varie d from 141 to 321 m/s. The equilibrium cluster-size distribution was thus p erturbed to varying degrees. Under the present experimental conditions clus ter-forming processes en route to homonuclear condensation were set into mo tion. The exothermic redistribution of cluster sizes at the new temperature and pressure was monitored using the laser-schlieren technique over a time period of 10-300 mus. A characteristic redistribution time scale was measu red as a function of temperature and pressure. The measured temperature and pressure dependence of the redistribution times are different than the cla ssical temperature and pressure dependence of lag times in supersaturated v apors. A negative activation energy is observed, indicative of a strong com petition between cluster formation, redissociation, and stabilization. A st ability analysis of the nonlinear kinetic mechanism leads to a criterion fo r the onset of oscillations, and provides a basis for extracting elementary rate constants from the observations. (C) 2001 American Institute of Physi cs.