  UV-Vis absorption spectroscopy is frequently used to characterize the size
and shape of gold nanoparticles. We present a full-spectrum model that yields
reliable results for the commonly encountered case of mixtures of spheres and
rods in varying proportions. We determine the volume fractions of the two
populations, the aspect ratio distribution of the nanorods (average value and
variance) and the interface damping parameter. We validate the model by
checking the fit results against small-angle X-ray scattering and transmission
electron microscopy data and show that correctly accounting for the
polydispersity in aspect ratio is essential for a quantitative description of
the longitudinal plasmon peak.
