Why the aspect ratio? Shape equivalence for the extinction spectra of gold nanoparticles.

We compare the light extinction spectra of elongated gold nanoparticles with different shapes (cylinder, spherocylinder and ellipsoid) and sizes of 10 to 100 nm. We argue that the equivalence of the various moments of mass distribution is the natural comparison criterion--rather than the length-to-diameter (aspect) ratio generally used in the literature--and that it leads to better spectral correspondence between the various shapes.