Cluster Growth in Supersonic Jets of CO_2 through a Slit Nozzle

摘要

The condensation produced in planar supersonic jets of CO_2 from a 0.13×3.0 mm slit nozzle is investigated quantitatively by means of Raman and Rayleigh scattering. The rotational and vibrational temperatures of the free-monomers bath, the cluster number density n_c, and the mean cluster size N are obtained for several jets with stagnation pressures P_0 from 1 to 3 bar and 295 K stagnation temperature. In a planar jet, the distance to a collision-free regime is larger than in an axisymmetric expansion through a circular nozzle, allowing more clusters to be formed through three- or two-body collisions. Data on the first stage of the nucleation and cluster growth processes in planar expansions are reported here, and are compared with previous data in axisymmetric jets [Ramos et al. Phys. Rev. A 72, 053204 (2005)]. On the basis of Raman spectra we investigate here the formation and evolution of the clusters, and the coexistence of liquid and solid CO_2. An inverse correlation between vibrational temperature of the free monomers and the mean cluster size N is also observed, suggesting some kind of cluster-mediated mechanism for the vibrational relaxation in CO_2.