Knowledge Bank

An experimental technique has been developed for the study of large clusters (aerosols) whose sizes are in the micron regime. The method is a variant of the technique developed by De Lucia1 in which the gas of interest is injected into a helium-filled, liquid nitrogen cooled gas cell wherein rapid collisional cooling occurs. The diffusion time to the cell walls greatly exceeds the cooling time, such that the gas is ``diffusion trapped'' and may homogeneously condense to form clusters. The FTIR spectroscopy of the clusters reveals scattering and absorbance features. With the assumption of spherical clusters, Mie theory calculations have been performed using the bulk optical constants of the materials. From this analysis the size distribution has been determined. Results for $C2H2NH3$, and $H2O$ will be discussed, as well as applications of the technique to atmospheric studies.