FTIR Spectroscopy of UF6 Clustering in a Supersonic Laval Nozzle

The clustering of UF 6 seeded in Ar was observed in a continuous supersonic Laval nozzle flow. The onset conditions for UF 6 clustering were investigated by measuring the FTIR spectra of UF 6 monomer and clusters in the nozzle. The onset conditions for the clustering, temperature, density of UF 6 (or partial pressure), and cooling rate, were determined as {130 K, 0.009 mol m -3 (10 Pa), 0.6 × 10 6 K s -1 } and {155 K, 0.06 mol m -3 (80 Pa), 1.5 × 10 6 K s -1 }. The onset temperature determined here was higher by 40−50 K than that determined by a light-scattering method. The frequency shift of the main peak of the UF 6 clusters from the monomer peak was about −17 cm -1, which was smaller than the shift of the crystalline UF 6 by about 11 cm -1 . The increase in temperature caused by the heat of condensation and the change of the spectra of UF 6 clusters with the growth after the onset were also observed. It was shown that the clustering rate due to the collision between the monomer and cluster is much higher than that due to the collision between the monomers.