Resonance Raman studies have been carried out on length-sorted single walled carbon nanotubes (SWNTs). For nanotubes much shorter than the wavelength of light, a large increase in Raman intensity is observed for several features in the intermediate frequency mode (IFM) region. The changes in IFM intensities are found to be highly dependent on the laser excitation energies, the (n,m) indices, and the specific Raman features. A direct correlation is found between the amount of IFM intensity increase as a function of the average nanotube length, as well as the symmetry of the physical origin for the specific IFM feature. (c) 2007 Published by Elsevier B.V.