Surface modes of a pair of unequal spheres

The surface resonances of a pair of spheres of different radii are studied using a local dielectric function to describe the response of each particle. All modes are characterized by values of -{ε}({ω}) that diverge as the spheres approach touching. We show that to a good approximation these values depend only on the edge-to-edge separation measured in units of the smaller sphere, and not on the radius of the larger one.