This paper presents experimental evidence of sharp spectral features in the optical response of 2D arrays of gold nanorods. A simple coupled dipole model is used to describe the main features of the observed spectral line shape. The resonance involves an interplay between the excitation of plasmons localized on the particles and diffraction resulting from the scattering by the periodic arrangement of these particles. The authors investigate this interplay by varying the particle size, aspect ratio, and interparticle spacing, and observe the effect on the position, width, and intensity of the sharp spectral feature. Nanoparticles of noble metals have been the subject of many detailed studies due to their unique optical properties, in particular because they can support localized surface plasmon resonances (LSPR). The LSPR associated with metal nanoparticles exhibits a high degree of optical field confinement, together with a high sensitivity to their local environment. Where two or more metallic nanostructures are in close proximity, the possibility exists for interaction between the modes of the individual nanostructures to form new hybrid modes. For multiple nanostructures there is also the possibility of coherent interaction arising from multiple scattering. Light that is scattered so as to propagate in the plane of the particles will undergo multiple scattering by the regularly spaced particles. A geometric resonance arises when the wavelength of the scattered light is commensurate with the periodicity of the array, which, when it occurs in the same spectral range as the LSPR, may lead to a dramatic modification of the measured optical extinction. Experiments to confirm the existence of these sharp diffractive features in the optical response of metallic nanoparticle arrays have met with only limited success. The authors fabricated and characterized a number of gold nanorod arrays. The samples were produced by electron beam lithography on fused silica substrates. The optical characterization of the sample was undertaken using bright-field transmission spectroscopy at normal incidence. Two sets of transmission spectra are shown for varying particle separations. The results show that the periodic arrangement of nanorods introduces an interference feature close to the diffraction edge, and its position with respect to the localized plasmon resonance was varied by changing the particle separation. The authors show experimental evidence for the narrow spectral features in the optical response of periodic metal nanoparticle arrays that have been predicted in the literature for several years now.This paper presents experimental evidence of sharp spectral features in the optical response of 2D arrays of gold nanorods. A simple coupled dipole model is used to describe the main features of the observed spectral line shape. The resonance involves an interplay between the excitation of plasmons localized on the particles and diffraction resulting from the scattering by the periodic arrangement of these particles. The authors investigate this interplay by varying the particle size, aspect ratio, and interparticle spacing, and observe the effect on the position, width, and intensity of the sharp spectral feature. Nanoparticles of noble metals have been the subject of many detailed studies due to their unique optical properties, in particular because they can support localized surface plasmon resonances (LSPR). The LSPR associated with metal nanoparticles exhibits a high degree of optical field confinement, together with a high sensitivity to their local environment. Where two or more metallic nanostructures are in close proximity, the possibility exists for interaction between the modes of the individual nanostructures to form new hybrid modes. For multiple nanostructures there is also the possibility of coherent interaction arising from multiple scattering. Light that is scattered so as to propagate in the plane of the particles will undergo multiple scattering by the regularly spaced particles. A geometric resonance arises when the wavelength of the scattered light is commensurate with the periodicity of the array, which, when it occurs in the same spectral range as the LSPR, may lead to a dramatic modification of the measured optical extinction. Experiments to confirm the existence of these sharp diffractive features in the optical response of metallic nanoparticle arrays have met with only limited success. The authors fabricated and characterized a number of gold nanorod arrays. The samples were produced by electron beam lithography on fused silica substrates. The optical characterization of the sample was undertaken using bright-field transmission spectroscopy at normal incidence. Two sets of transmission spectra are shown for varying particle separations. The results show that the periodic arrangement of nanorods introduces an interference feature close to the diffraction edge, and its position with respect to the localized plasmon resonance was varied by changing the particle separation. The authors show experimental evidence for the narrow spectral features in the optical response of periodic metal nanoparticle arrays that have been predicted in the literature for several years now.