We examine whether single molecule sensitivity in surface-enhanced Raman scattering (SERS) can be explained in the framework of classical electromagnetic theory. The influence of colloid particle shape and size, composition (Ag or Au) and interparticle separation distance on the wavelength-dependent SERS enhancement factor is reported. Our calculations indicate that the maximum enhancement factor achievable through electromagnetics is of the order 10(11). This is obtained only under special circumstances, namely at interstitial sites between particles and at locations outside sharp surface protrusions. The comparative rarity of such sites, together with the extreme spatial localization of the enhancement they provide, can qualitatively explain why only very few surface sites seem to contribute to the measured signal in single-molecule SERS experiments. Enhancement factors of the order 10(14)-10(15), which have been reported in recent experiments, are likely to involve additional enhancement mechanisms such as chemisorption induced resonance Raman effects.

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We have developed an explicit model to explain the radiative recombination in noble metals, arising from transitions between electrons in the spconduction band and holes in the d-band generated by optical excitation. We find that the observed photon distribution has its shape from two competing factors. The first is due to the optics and the final density of states for the exiting photons. This is off-set by a d-band density of states factor increasing as the number of available d-states increase. We give a satisfactory account of the observed spectrum, using constant matrix elements, and find that luminescence can be used as a complementary tool to the ordinary elastic light scattering, giving detailed information about occupied and unoccupied states, provided the elastic optical constants are measured on the same sample.

We discuss the collective resonances of the C60 molecule described by a spherical shell. Detailed results are given for the π and π + σ plasmons of C60, the polarisability and the dielectric function. We present results in good quantitative agreement with recent experiments. Some new features in the spectrum, like a monopole mode of oscillation, are predicted for a doped C60 molecule.