The shapes and sizes of photochemically produced aerosol particles of polyacetylene, polyethylene, and polyhydrogen cyanide were studied experimentally. All of the single particles were found to be perfectly spherical and semiliquid. However, they aggregate readily, with a sticking coefficient near unity, to form nonspherical particles, which could give rise to the observed polarization from Titan's and Jupiter's upper haze layers. The absorbance of polyacetylene was remeasured and corrected, and it is now much closer to that of polyethylene. The measured real and imaginary indices of refraction of the two materials make them both suitable material for Titan's and Jupiter's upper haze layers. However, the larger abundance and higher rate of polymerization of acetylene would make it the dominant aerosol-forming material in both atmospheres. ¿ American Geophysical Union 1988