We study the coupling induced by retardation effects when two plasmon-reson
ant nanoparticles are interacting. This coupling leads to an additional res
onance, the strength of which depends on a subtle balance between particle
separation and size. The scattering cross section and the near field associ
ated with this coupled resonance are studied for cylindrical particles in a
ir and in water. Implications for surface-enhanced Raman scattering and nan
o-optics are discussed. (C) 2001 Optical Society of America.