Fractional condensation in seeded supersonic free jets of SF6 has been
determined at different locations along the jet axis and at different
stagnation pressures using a diode laser absorption technique. Rotati
onal temperature and relative number densities of SF6 have been determ
ined from Q-branch absorption of the nu3 band. The fractional condensa
tion increases with increased stagnation pressure as well as with incr
eased dilution. The onset pressure for condensation of SF6 in pure SF6
jets is above 2000 torr, whereas in seeded jets, it is much lower (90
0-1200 torr). Calculated dimer mole fractions do not account for the o
bserved degree of condensation. Experimentally observed local onset nu
mber density can be reasonably correlated with the trimer critical mod
el of Fisher.