Absorption and surface-enhanced Raman scattering (SERS) spectra of size-selected C8H2 adsorbed on Ag colloids were investigated. The Ag colloids after C8H2 adsorption are stable without precipitation of Ag nanoparticle aggregates. The spectra strongly depend on the C8H2 concentration. A good correlation between the concentration dependence of the absorption spectrum and that of SERS intensities supports the electromagnetic mechanism of SERS. The use of size-selected C8H2 made it possible to demonstrate also the chemical effects, which manifest themselves in the differences in the positions of SERS bands for different SERS enhancers, i.e., Ag colloid and Ag island film. (C) 2011 Elsevier B. V. All rights reserved.