LAUSR

A new method is presented that can yield particle-size distribution parameters and aspect ratios for chain-like aggregates in a diffusion flame using dynamic light scattering (DLS). Measurements of polarized and depolarized correlation functions are carried out in a Fe(CO)5-seeded CO-O diffusion flame as function of position above the burner surface. The measurements are combined with the method of cumulants to yield, for the first time to our knowledge, both the translational and rotational diffusion coefficients of chain-like aggregates along the axis of symmetry of the flame in the temperature range 863-1087 K. The average primary particle diameters inferred from DLS are compared with the results of transmission electron microscopy analysis and the differences are less than 12%. Furthermore, the aspect ratios of the chain-like aggregates are combined with their residence time in the flame to yield aspect ratio growth rates of (5.33±0.30)/s. It is demonstrated that the laser beam Gaussian factor needs to be considered in the data analysis in order to obtain physically meaningful results. In addition, the limitations of the approach are discussed.