Cluster and Solute Velocity Distributions in Free-Jet Expansions of Supercritical CO2

The free-jet expansions of high-pressure CO2 Supercritical solutions are probed by direct sampling mass spectrometry. Both cluster intensity measurements and velocity distribution measurements are reported for expansions which result in cluster formation by condensation and fragmentation of supersaturated vapors and superheated liquids. The resulting velocity distributions for these highly nonequilibrated expansions are characterized by up to three different peaks, depending on the source conditions: two primary peaks associated with very large clusters, the slower of which is associated with liquid fragmentation, and a smaller faster peak associated with monomers and small CO2 clusters. We have associated the slow peak, observed only for fragmentation of superheated liquid expansions, with a liquid or condensed phase fragment by measuring the velocity distribution of low vapor pressure solutes in the expansion of supercritical CO2 mixtures.